memcheck/mc_translate.c

/*--------------------------------------------------------------------*/
/*--- Instrument IR to perform memory checking operations.         ---*/
/*---                                               mc_translate.c ---*/
/*--------------------------------------------------------------------*/

/*
   This file is part of MemCheck, a heavyweight Valgrind tool for
   detecting memory errors.

   Copyright (C) 2000-2013 Julian Seward 
      jseward@acm.org

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307, USA.

   The GNU General Public License is contained in the file COPYING.
*/

#include "pub_tool_basics.h"
#include "pub_tool_poolalloc.h"     // For mc_include.h
#include "pub_tool_hashtable.h"     // For mc_include.h
#include "pub_tool_libcassert.h"
#include "pub_tool_libcprint.h"
#include "pub_tool_tooliface.h"
#include "pub_tool_machine.h"     // VG_(fnptr_to_fnentry)
#include "pub_tool_xarray.h"
#include "pub_tool_mallocfree.h"
#include "pub_tool_libcbase.h"

#include "mc_include.h"


/* FIXMEs JRS 2011-June-16.

   Check the interpretation for vector narrowing and widening ops,
   particularly the saturating ones.  I suspect they are either overly
   pessimistic and/or wrong.
*/

/* This file implements the Memcheck instrumentation, and in
   particular contains the core of its undefined value detection
   machinery.  For a comprehensive background of the terminology,
   algorithms and rationale used herein, read:

     Using Valgrind to detect undefined value errors with
     bit-precision

     Julian Seward and Nicholas Nethercote

     2005 USENIX Annual Technical Conference (General Track),
     Anaheim, CA, USA, April 10-15, 2005.

   ----

   Here is as good a place as any to record exactly when V bits are and
   should be checked, why, and what function is responsible.

   
   Memcheck complains when an undefined value is used:

   1. In the condition of a conditional branch.  Because it could cause
      incorrect control flow, and thus cause incorrect externally-visible
      behaviour.  [mc_translate.c:complainIfUndefined]

   2. As an argument to a system call, or as the value that specifies
      the system call number.  Because it could cause an incorrect
      externally-visible side effect.  [mc_translate.c:mc_pre_reg_read]

   3. As the address in a load or store.  Because it could cause an
      incorrect value to be used later, which could cause externally-visible
      behaviour (eg. via incorrect control flow or an incorrect system call
      argument)  [complainIfUndefined]

   4. As the target address of a branch.  Because it could cause incorrect
      control flow.  [complainIfUndefined]

   5. As an argument to setenv, unsetenv, or putenv.  Because it could put
      an incorrect value into the external environment.
      [mc_replace_strmem.c:VG_WRAP_FUNCTION_ZU(*, *env)]

   6. As the index in a GETI or PUTI operation.  I'm not sure why... (njn).
      [complainIfUndefined]

   7. As an argument to the VALGRIND_CHECK_MEM_IS_DEFINED and
      VALGRIND_CHECK_VALUE_IS_DEFINED client requests.  Because the user
      requested it.  [in memcheck.h]


   Memcheck also complains, but should not, when an undefined value is used:

   8. As the shift value in certain SIMD shift operations (but not in the
      standard integer shift operations).  This inconsistency is due to
      historical reasons.)  [complainIfUndefined]


   Memcheck does not complain, but should, when an undefined value is used:

   9. As an input to a client request.  Because the client request may
      affect the visible behaviour -- see bug #144362 for an example
      involving the malloc replacements in vg_replace_malloc.c and
      VALGRIND_NON_SIMD_CALL* requests, where an uninitialised argument
      isn't identified.  That bug report also has some info on how to solve
      the problem.  [valgrind.h:VALGRIND_DO_CLIENT_REQUEST]


   In practice, 1 and 2 account for the vast majority of cases.
*/

/* Generation of addr-definedness, addr-validity and
   guard-definedness checks pertaining to loads and stores (Iex_Load,
   Ist_Store, IRLoadG, IRStoreG, LLSC, CAS and Dirty memory
   loads/stores) was re-checked 11 May 2013. */

/*------------------------------------------------------------*/
/*--- Forward decls                                        ---*/
/*------------------------------------------------------------*/

struct _MCEnv;

static IRType  shadowTypeV ( IRType ty );
static IRExpr* expr2vbits ( struct _MCEnv* mce, IRExpr* e );
static IRTemp  findShadowTmpB ( struct _MCEnv* mce, IRTemp orig );

static IRExpr *i128_const_zero(void);

/*------------------------------------------------------------*/
/*--- Memcheck running state, and tmp management.          ---*/
/*------------------------------------------------------------*/

/* Carries info about a particular tmp.  The tmp's number is not
   recorded, as this is implied by (equal to) its index in the tmpMap
   in MCEnv.  The tmp's type is also not recorded, as this is present
   in MCEnv.sb->tyenv.

   When .kind is Orig, .shadowV and .shadowB may give the identities
   of the temps currently holding the associated definedness (shadowV)
   and origin (shadowB) values, or these may be IRTemp_INVALID if code
   to compute such values has not yet been emitted.

   When .kind is VSh or BSh then the tmp is holds a V- or B- value,
   and so .shadowV and .shadowB must be IRTemp_INVALID, since it is
   illogical for a shadow tmp itself to be shadowed.
*/
typedef
   enum { Orig=1, VSh=2, BSh=3 }
   TempKind;

typedef
   struct {
      TempKind kind;
      IRTemp   shadowV;
      IRTemp   shadowB;
   }
   TempMapEnt;


/* Carries around state during memcheck instrumentation. */
typedef
   struct _MCEnv {
      /* MODIFIED: the superblock being constructed.  IRStmts are
         added. */
      IRSB* sb;
      Bool  trace;

      /* MODIFIED: a table [0 .. #temps_in_sb-1] which gives the
         current kind and possibly shadow temps for each temp in the
         IRSB being constructed.  Note that it does not contain the
         type of each tmp.  If you want to know the type, look at the
         relevant entry in sb->tyenv.  It follows that at all times
         during the instrumentation process, the valid indices for
         tmpMap and sb->tyenv are identical, being 0 .. N-1 where N is
         total number of Orig, V- and B- temps allocated so far.

         The reason for this strange split (types in one place, all
         other info in another) is that we need the types to be
         attached to sb so as to make it possible to do
         "typeOfIRExpr(mce->bb->tyenv, ...)" at various places in the
         instrumentation process. */
      XArray* /* of TempMapEnt */ tmpMap;

      /* MODIFIED: indicates whether "bogus" literals have so far been
         found.  Starts off False, and may change to True. */
      Bool bogusLiterals;

      /* READONLY: indicates whether we should use expensive
         interpretations of integer adds, since unfortunately LLVM
         uses them to do ORs in some circumstances.  Defaulted to True
         on MacOS and False everywhere else. */
      Bool useLLVMworkarounds;

      /* READONLY: the guest layout.  This indicates which parts of
         the guest state should be regarded as 'always defined'. */
      VexGuestLayout* layout;

      /* READONLY: the host word type.  Needed for constructing
         arguments of type 'HWord' to be passed to helper functions.
         Ity_I32 or Ity_I64 only. */
      IRType hWordTy;
   }
   MCEnv;

/* SHADOW TMP MANAGEMENT.  Shadow tmps are allocated lazily (on
   demand), as they are encountered.  This is for two reasons.

   (1) (less important reason): Many original tmps are unused due to
   initial IR optimisation, and we do not want to spaces in tables
   tracking them.

   Shadow IRTemps are therefore allocated on demand.  mce.tmpMap is a
   table indexed [0 .. n_types-1], which gives the current shadow for
   each original tmp, or INVALID_IRTEMP if none is so far assigned.
   It is necessary to support making multiple assignments to a shadow
   -- specifically, after testing a shadow for definedness, it needs
   to be made defined.  But IR's SSA property disallows this.  

   (2) (more important reason): Therefore, when a shadow needs to get
   a new value, a new temporary is created, the value is assigned to
   that, and the tmpMap is updated to reflect the new binding.

   A corollary is that if the tmpMap maps a given tmp to
   IRTemp_INVALID and we are hoping to read that shadow tmp, it means
   there's a read-before-write error in the original tmps.  The IR
   sanity checker should catch all such anomalies, however.  
*/

/* Create a new IRTemp of type 'ty' and kind 'kind', and add it to
   both the table in mce->sb and to our auxiliary mapping.  Note that
   newTemp may cause mce->tmpMap to resize, hence previous results
   from VG_(indexXA)(mce->tmpMap) are invalidated. */
static IRTemp newTemp ( MCEnv* mce, IRType ty, TempKind kind )
{
   Word       newIx;
   TempMapEnt ent;
   IRTemp     tmp = newIRTemp(mce->sb->tyenv, ty);
   ent.kind    = kind;
   ent.shadowV = IRTemp_INVALID;
   ent.shadowB = IRTemp_INVALID;
   newIx = VG_(addToXA)( mce->tmpMap, &ent );
   tl_assert(newIx == (Word)tmp);
   return tmp;
}


/* Find the tmp currently shadowing the given original tmp.  If none
   so far exists, allocate one.  */
static IRTemp findShadowTmpV ( MCEnv* mce, IRTemp orig )
{
   TempMapEnt* ent;
   /* VG_(indexXA) range-checks 'orig', hence no need to check
      here. */
   ent = (TempMapEnt*)VG_(indexXA)( mce->tmpMap, (Word)orig );
   tl_assert(ent->kind == Orig);
   if (ent->shadowV == IRTemp_INVALID) {
      IRTemp tmpV
        = newTemp( mce, shadowTypeV(mce->sb->tyenv->types[orig]), VSh );
      /* newTemp may cause mce->tmpMap to resize, hence previous results
         from VG_(indexXA) are invalid. */
      ent = (TempMapEnt*)VG_(indexXA)( mce->tmpMap, (Word)orig );
      tl_assert(ent->kind == Orig);
      tl_assert(ent->shadowV == IRTemp_INVALID);
      ent->shadowV = tmpV;
   }
   return ent->shadowV;
}

/* Allocate a new shadow for the given original tmp.  This means any
   previous shadow is abandoned.  This is needed because it is
   necessary to give a new value to a shadow once it has been tested
   for undefinedness, but unfortunately IR's SSA property disallows
   this.  Instead we must abandon the old shadow, allocate a new one
   and use that instead.

   This is the same as findShadowTmpV, except we don't bother to see
   if a shadow temp already existed -- we simply allocate a new one
   regardless. */
static void newShadowTmpV ( MCEnv* mce, IRTemp orig )
{
   TempMapEnt* ent;
   /* VG_(indexXA) range-checks 'orig', hence no need to check
      here. */
   ent = (TempMapEnt*)VG_(indexXA)( mce->tmpMap, (Word)orig );
   tl_assert(ent->kind == Orig);
   if (1) {
      IRTemp tmpV
        = newTemp( mce, shadowTypeV(mce->sb->tyenv->types[orig]), VSh );
      /* newTemp may cause mce->tmpMap to resize, hence previous results
         from VG_(indexXA) are invalid. */
      ent = (TempMapEnt*)VG_(indexXA)( mce->tmpMap, (Word)orig );
      tl_assert(ent->kind == Orig);
      ent->shadowV = tmpV;
   }
}


/*------------------------------------------------------------*/
/*--- IRAtoms -- a subset of IRExprs                       ---*/
/*------------------------------------------------------------*/

/* An atom is either an IRExpr_Const or an IRExpr_Tmp, as defined by
   isIRAtom() in libvex_ir.h.  Because this instrumenter expects flat
   input, most of this code deals in atoms.  Usefully, a value atom
   always has a V-value which is also an atom: constants are shadowed
   by constants, and temps are shadowed by the corresponding shadow
   temporary. */

typedef  IRExpr  IRAtom;

/* (used for sanity checks only): is this an atom which looks
   like it's from original code? */
static Bool isOriginalAtom ( MCEnv* mce, IRAtom* a1 )
{
   if (a1->tag == Iex_Const)
      return True;
   if (a1->tag == Iex_RdTmp) {
      TempMapEnt* ent = VG_(indexXA)( mce->tmpMap, a1->Iex.RdTmp.tmp );
      return ent->kind == Orig;
   }
   return False;
}

/* (used for sanity checks only): is this an atom which looks
   like it's from shadow code? */
static Bool isShadowAtom ( MCEnv* mce, IRAtom* a1 )
{
   if (a1->tag == Iex_Const)
      return True;
   if (a1->tag == Iex_RdTmp) {
      TempMapEnt* ent = VG_(indexXA)( mce->tmpMap, a1->Iex.RdTmp.tmp );
      return ent->kind == VSh || ent->kind == BSh;
   }
   return False;
}

/* (used for sanity checks only): check that both args are atoms and
   are identically-kinded. */
static Bool sameKindedAtoms ( IRAtom* a1, IRAtom* a2 )
{
   if (a1->tag == Iex_RdTmp && a2->tag == Iex_RdTmp)
      return True;
   if (a1->tag == Iex_Const && a2->tag == Iex_Const)
      return True;
   return False;
}


/*------------------------------------------------------------*/
/*--- Type management                                      ---*/
/*------------------------------------------------------------*/

/* Shadow state is always accessed using integer types.  This returns
   an integer type with the same size (as per sizeofIRType) as the
   given type.  The only valid shadow types are Bit, I8, I16, I32,
   I64, I128, V128, V256. */

static IRType shadowTypeV ( IRType ty )
{
   switch (ty) {
      case Ity_I1:
      case Ity_I8:
      case Ity_I16:
      case Ity_I32: 
      case Ity_I64: 
      case Ity_I128: return ty;
      case Ity_F32:  return Ity_I32;
      case Ity_D32:  return Ity_I32;
      case Ity_F64:  return Ity_I64;
      case Ity_D64:  return Ity_I64;
      case Ity_F128: return Ity_I128;
      case Ity_D128: return Ity_I128;
      case Ity_V128: return Ity_V128;
      case Ity_V256: return Ity_V256;
      default: ppIRType(ty); 
               VG_(tool_panic)("memcheck:shadowTypeV");
   }
}

/* Produce a 'defined' value of the given shadow type.  Should only be
   supplied shadow types (Bit/I8/I16/I32/UI64). */
static IRExpr* definedOfType ( IRType ty ) {
   switch (ty) {
      case Ity_I1:   return IRExpr_Const(IRConst_U1(False));
      case Ity_I8:   return IRExpr_Const(IRConst_U8(0));
      case Ity_I16:  return IRExpr_Const(IRConst_U16(0));
      case Ity_I32:  return IRExpr_Const(IRConst_U32(0));
      case Ity_I64:  return IRExpr_Const(IRConst_U64(0));
      case Ity_I128: return i128_const_zero();
      case Ity_V128: return IRExpr_Const(IRConst_V128(0x0000));
      case Ity_V256: return IRExpr_Const(IRConst_V256(0x00000000));
      default:       VG_(tool_panic)("memcheck:definedOfType");
   }
}


/*------------------------------------------------------------*/
/*--- Constructing IR fragments                            ---*/
/*------------------------------------------------------------*/

/* add stmt to a bb */
static inline void stmt ( HChar cat, MCEnv* mce, IRStmt* st ) {
   if (mce->trace) {
      VG_(printf)("  %c: ", cat);
      ppIRStmt(st);
      VG_(printf)("\n");
   }
   addStmtToIRSB(mce->sb, st);
}

/* assign value to tmp */
static inline 
void assign ( HChar cat, MCEnv* mce, IRTemp tmp, IRExpr* expr ) {
   stmt(cat, mce, IRStmt_WrTmp(tmp,expr));
}

/* build various kinds of expressions */
#define triop(_op, _arg1, _arg2, _arg3) \
                                 IRExpr_Triop((_op),(_arg1),(_arg2),(_arg3))
#define binop(_op, _arg1, _arg2) IRExpr_Binop((_op),(_arg1),(_arg2))
#define unop(_op, _arg)          IRExpr_Unop((_op),(_arg))
#define mkU1(_n)                 IRExpr_Const(IRConst_U1(_n))
#define mkU8(_n)                 IRExpr_Const(IRConst_U8(_n))
#define mkU16(_n)                IRExpr_Const(IRConst_U16(_n))
#define mkU32(_n)                IRExpr_Const(IRConst_U32(_n))
#define mkU64(_n)                IRExpr_Const(IRConst_U64(_n))
#define mkV128(_n)               IRExpr_Const(IRConst_V128(_n))
#define mkexpr(_tmp)             IRExpr_RdTmp((_tmp))

/* Bind the given expression to a new temporary, and return the
   temporary.  This effectively converts an arbitrary expression into
   an atom.

   'ty' is the type of 'e' and hence the type that the new temporary
   needs to be.  But passing it in is redundant, since we can deduce
   the type merely by inspecting 'e'.  So at least use that fact to
   assert that the two types agree. */
static IRAtom* assignNew ( HChar cat, MCEnv* mce, IRType ty, IRExpr* e )
{
   TempKind k;
   IRTemp   t;
   IRType   tyE = typeOfIRExpr(mce->sb->tyenv, e);

   tl_assert(tyE == ty); /* so 'ty' is redundant (!) */
   switch (cat) {
      case 'V': k = VSh;  break;
      case 'B': k = BSh;  break;
      case 'C': k = Orig; break; 
                /* happens when we are making up new "orig"
                   expressions, for IRCAS handling */
      default: tl_assert(0);
   }
   t = newTemp(mce, ty, k);
   assign(cat, mce, t, e);
   return mkexpr(t);
}


/*------------------------------------------------------------*/
/*--- Helper functions for 128-bit ops                     ---*/
/*------------------------------------------------------------*/

static IRExpr *i128_const_zero(void)
{
   IRAtom* z64 = IRExpr_Const(IRConst_U64(0));
   return binop(Iop_64HLto128, z64, z64);
}

/* There are no I128-bit loads and/or stores [as generated by any
   current front ends].  So we do not need to worry about that in
   expr2vbits_Load */


/*------------------------------------------------------------*/
/*--- Constructing definedness primitive ops               ---*/
/*------------------------------------------------------------*/

/* --------- Defined-if-either-defined --------- */

static IRAtom* mkDifD8 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_I8, binop(Iop_And8, a1, a2));
}

static IRAtom* mkDifD16 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_I16, binop(Iop_And16, a1, a2));
}

static IRAtom* mkDifD32 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_I32, binop(Iop_And32, a1, a2));
}

static IRAtom* mkDifD64 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_I64, binop(Iop_And64, a1, a2));
}

static IRAtom* mkDifDV128 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_V128, binop(Iop_AndV128, a1, a2));
}

static IRAtom* mkDifDV256 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_V256, binop(Iop_AndV256, a1, a2));
}

/* --------- Undefined-if-either-undefined --------- */

static IRAtom* mkUifU8 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_I8, binop(Iop_Or8, a1, a2));
}

static IRAtom* mkUifU16 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_I16, binop(Iop_Or16, a1, a2));
}

static IRAtom* mkUifU32 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_I32, binop(Iop_Or32, a1, a2));
}

static IRAtom* mkUifU64 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_I64, binop(Iop_Or64, a1, a2));
}

static IRAtom* mkUifU128 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   IRAtom *tmp1, *tmp2, *tmp3, *tmp4, *tmp5, *tmp6;
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   tmp1 = assignNew('V', mce, Ity_I64, unop(Iop_128to64, a1));
   tmp2 = assignNew('V', mce, Ity_I64, unop(Iop_128HIto64, a1));
   tmp3 = assignNew('V', mce, Ity_I64, unop(Iop_128to64, a2));
   tmp4 = assignNew('V', mce, Ity_I64, unop(Iop_128HIto64, a2));
   tmp5 = assignNew('V', mce, Ity_I64, binop(Iop_Or64, tmp1, tmp3));
   tmp6 = assignNew('V', mce, Ity_I64, binop(Iop_Or64, tmp2, tmp4));

   return assignNew('V', mce, Ity_I128, binop(Iop_64HLto128, tmp6, tmp5));
}

static IRAtom* mkUifUV128 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_V128, binop(Iop_OrV128, a1, a2));
}

static IRAtom* mkUifUV256 ( MCEnv* mce, IRAtom* a1, IRAtom* a2 ) {
   tl_assert(isShadowAtom(mce,a1));
   tl_assert(isShadowAtom(mce,a2));
   return assignNew('V', mce, Ity_V256, binop(Iop_OrV256, a1, a2));
}

static IRAtom* mkUifU ( MCEnv* mce, IRType vty, IRAtom* a1, IRAtom* a2 ) {
   switch (vty) {
      case Ity_I8:   return mkUifU8(mce, a1, a2);
      case Ity_I16:  return mkUifU16(mce, a1, a2);
      case Ity_I32:  return mkUifU32(mce, a1, a2);
      case Ity_I64:  return mkUifU64(mce, a1, a2);
      case Ity_I128: return mkUifU128(mce, a1, a2);
      case Ity_V128: return mkUifUV128(mce, a1, a2);
      case Ity_V256: return mkUifUV256(mce, a1, a2);
      default:
         VG_(printf)("\n"); ppIRType(vty); VG_(printf)("\n");
         VG_(tool_panic)("memcheck:mkUifU");
   }
}

/* --------- The Left-family of operations. --------- */

static IRAtom* mkLeft8 ( MCEnv* mce, IRAtom* a1 ) {
   tl_assert(isShadowAtom(mce,a1));
   return assignNew('V', mce, Ity_I8, unop(Iop_Left8, a1));
}

static IRAtom* mkLeft16 ( MCEnv* mce, IRAtom* a1 ) {
   tl_assert(isShadowAtom(mce,a1));
   return assignNew('V', mce, Ity_I16, unop(Iop_Left16, a1));
}

static IRAtom* mkLeft32 ( MCEnv* mce, IRAtom* a1 ) {
   tl_assert(isShadowAtom(mce,a1));
   return assignNew('V', mce, Ity_I32, unop(Iop_Left32, a1));
}

static IRAtom* mkLeft64 ( MCEnv* mce, IRAtom* a1 ) {
   tl_assert(isShadowAtom(mce,a1));
   return assignNew('V', mce, Ity_I64, unop(Iop_Left64, a1));
}

/* --------- 'Improvement' functions for AND/OR. --------- */

/* ImproveAND(data, vbits) = data OR vbits.  Defined (0) data 0s give
   defined (0); all other -> undefined (1).
*/
static IRAtom* mkImproveAND8 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew('V', mce, Ity_I8, binop(Iop_Or8, data, vbits));
}

static IRAtom* mkImproveAND16 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew('V', mce, Ity_I16, binop(Iop_Or16, data, vbits));
}

static IRAtom* mkImproveAND32 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew('V', mce, Ity_I32, binop(Iop_Or32, data, vbits));
}

static IRAtom* mkImproveAND64 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew('V', mce, Ity_I64, binop(Iop_Or64, data, vbits));
}

static IRAtom* mkImproveANDV128 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew('V', mce, Ity_V128, binop(Iop_OrV128, data, vbits));
}

static IRAtom* mkImproveANDV256 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew('V', mce, Ity_V256, binop(Iop_OrV256, data, vbits));
}

/* ImproveOR(data, vbits) = ~data OR vbits.  Defined (0) data 1s give
   defined (0); all other -> undefined (1).
*/
static IRAtom* mkImproveOR8 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew(
             'V', mce, Ity_I8, 
             binop(Iop_Or8, 
                   assignNew('V', mce, Ity_I8, unop(Iop_Not8, data)), 
                   vbits) );
}

static IRAtom* mkImproveOR16 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew(
             'V', mce, Ity_I16, 
             binop(Iop_Or16, 
                   assignNew('V', mce, Ity_I16, unop(Iop_Not16, data)), 
                   vbits) );
}

static IRAtom* mkImproveOR32 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew(
             'V', mce, Ity_I32, 
             binop(Iop_Or32, 
                   assignNew('V', mce, Ity_I32, unop(Iop_Not32, data)), 
                   vbits) );
}

static IRAtom* mkImproveOR64 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew(
             'V', mce, Ity_I64, 
             binop(Iop_Or64, 
                   assignNew('V', mce, Ity_I64, unop(Iop_Not64, data)), 
                   vbits) );
}

static IRAtom* mkImproveORV128 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew(
             'V', mce, Ity_V128, 
             binop(Iop_OrV128, 
                   assignNew('V', mce, Ity_V128, unop(Iop_NotV128, data)), 
                   vbits) );
}

static IRAtom* mkImproveORV256 ( MCEnv* mce, IRAtom* data, IRAtom* vbits )
{
   tl_assert(isOriginalAtom(mce, data));
   tl_assert(isShadowAtom(mce, vbits));
   tl_assert(sameKindedAtoms(data, vbits));
   return assignNew(
             'V', mce, Ity_V256, 
             binop(Iop_OrV256, 
                   assignNew('V', mce, Ity_V256, unop(Iop_NotV256, data)), 
                   vbits) );
}

/* --------- Pessimising casts. --------- */

/* The function returns an expression of type DST_TY. If any of the VBITS
   is undefined (value == 1) the resulting expression has all bits set to
   1. Otherwise, all bits are 0. */

static IRAtom* mkPCastTo( MCEnv* mce, IRType dst_ty, IRAtom* vbits ) 
{
   IRType  src_ty;
   IRAtom* tmp1;

   /* Note, dst_ty is a shadow type, not an original type. */
   tl_assert(isShadowAtom(mce,vbits));
   src_ty = typeOfIRExpr(mce->sb->tyenv, vbits);

   /* Fast-track some common cases */
   if (src_ty == Ity_I32 && dst_ty == Ity_I32)
      return assignNew('V', mce, Ity_I32, unop(Iop_CmpwNEZ32, vbits));

   if (src_ty == Ity_I64 && dst_ty == Ity_I64)
      return assignNew('V', mce, Ity_I64, unop(Iop_CmpwNEZ64, vbits));

   if (src_ty == Ity_I32 && dst_ty == Ity_I64) {
      /* PCast the arg, then clone it. */
      IRAtom* tmp = assignNew('V', mce, Ity_I32, unop(Iop_CmpwNEZ32, vbits));
      return assignNew('V', mce, Ity_I64, binop(Iop_32HLto64, tmp, tmp));
   }

   if (src_ty == Ity_I32 && dst_ty == Ity_V128) {
      /* PCast the arg, then clone it 4 times. */
      IRAtom* tmp = assignNew('V', mce, Ity_I32, unop(Iop_CmpwNEZ32, vbits));
      tmp = assignNew('V', mce, Ity_I64, binop(Iop_32HLto64, tmp, tmp));
      return assignNew('V', mce, Ity_V128, binop(Iop_64HLtoV128, tmp, tmp));
   }

   if (src_ty == Ity_I32 && dst_ty == Ity_V256) {
      /* PCast the arg, then clone it 8 times. */
      IRAtom* tmp = assignNew('V', mce, Ity_I32, unop(Iop_CmpwNEZ32, vbits));
      tmp = assignNew('V', mce, Ity_I64, binop(Iop_32HLto64, tmp, tmp));
      tmp = assignNew('V', mce, Ity_V128, binop(Iop_64HLtoV128, tmp, tmp));
      return assignNew('V', mce, Ity_V256, binop(Iop_V128HLtoV256, tmp, tmp));
   }

   if (src_ty == Ity_I64 && dst_ty == Ity_I32) {
      /* PCast the arg.  This gives all 0s or all 1s.  Then throw away
         the top half. */
      IRAtom* tmp = assignNew('V', mce, Ity_I64, unop(Iop_CmpwNEZ64, vbits));
      return assignNew('V', mce, Ity_I32, unop(Iop_64to32, tmp));
   }

   /* Else do it the slow way .. */
   /* First of all, collapse vbits down to a single bit. */
   tmp1   = NULL;
   switch (src_ty) {
      case Ity_I1:
         tmp1 = vbits;
         break;
      case Ity_I8: 
         tmp1 = assignNew('V', mce, Ity_I1, unop(Iop_CmpNEZ8, vbits));
         break;
      case Ity_I16: 
         tmp1 = assignNew('V', mce, Ity_I1, unop(Iop_CmpNEZ16, vbits));
         break;
      case Ity_I32: 
         tmp1 = assignNew('V', mce, Ity_I1, unop(Iop_CmpNEZ32, vbits));
         break;
      case Ity_I64: 
         tmp1 = assignNew('V', mce, Ity_I1, unop(Iop_CmpNEZ64, vbits));
         break;
      case Ity_I128: {
         /* Gah.  Chop it in half, OR the halves together, and compare
            that with zero. */
         IRAtom* tmp2 = assignNew('V', mce, Ity_I64, unop(Iop_128HIto64, vbits));
         IRAtom* tmp3 = assignNew('V', mce, Ity_I64, unop(Iop_128to64, vbits));
         IRAtom* tmp4 = assignNew('V', mce, Ity_I64, binop(Iop_Or64, tmp2, tmp3));
         tmp1         = assignNew('V', mce, Ity_I1, 
                                       unop(Iop_CmpNEZ64, tmp4));
         break;
      }
      default:
         ppIRType(src_ty);
         VG_(tool_panic)("mkPCastTo(1)");
   }
   tl_assert(tmp1);
   /* Now widen up to the dst type. */
   switch (dst_ty) {
      case Ity_I1:
         return tmp1;
      case Ity_I8: 
         return assignNew('V', mce, Ity_I8, unop(Iop_1Sto8, tmp1));
      case Ity_I16: 
         return assignNew('V', mce, Ity_I16, unop(Iop_1Sto16, tmp1));
      case Ity_I32: 
         return assignNew('V', mce, Ity_I32, unop(Iop_1Sto32, tmp1));
      case Ity_I64: 
         return assignNew('V', mce, Ity_I64, unop(Iop_1Sto64, tmp1));
      case Ity_V128:
         tmp1 = assignNew('V', mce, Ity_I64,  unop(Iop_1Sto64, tmp1));
         tmp1 = assignNew('V', mce, Ity_V128, binop(Iop_64HLtoV128, tmp1, tmp1));
         return tmp1;
      case Ity_I128:
         tmp1 = assignNew('V', mce, Ity_I64,  unop(Iop_1Sto64, tmp1));
         tmp1 = assignNew('V', mce, Ity_I128, binop(Iop_64HLto128, tmp1, tmp1));
         return tmp1;
      case Ity_V256:
         tmp1 = assignNew('V', mce, Ity_I64,  unop(Iop_1Sto64, tmp1));
         tmp1 = assignNew('V', mce, Ity_V128, binop(Iop_64HLtoV128,
                                                    tmp1, tmp1));
         tmp1 = assignNew('V', mce, Ity_V256, binop(Iop_V128HLtoV256,
                                                    tmp1, tmp1));
         return tmp1;
      default: 
         ppIRType(dst_ty);
         VG_(tool_panic)("mkPCastTo(2)");
   }
}

/* --------- Accurate interpretation of CmpEQ/CmpNE. --------- */
/* 
   Normally, we can do CmpEQ/CmpNE by doing UifU on the arguments, and
   PCasting to Ity_U1.  However, sometimes it is necessary to be more
   accurate.  The insight is that the result is defined if two
   corresponding bits can be found, one from each argument, so that
   both bits are defined but are different -- that makes EQ say "No"
   and NE say "Yes".  Hence, we compute an improvement term and DifD
   it onto the "normal" (UifU) result.

   The result is:

   PCastTo<1> (
      -- naive version
      PCastTo<sz>( UifU<sz>(vxx, vyy) )

      `DifD<sz>`

      -- improvement term
      PCastTo<sz>( PCast<sz>( CmpEQ<sz> ( vec, 1...1 ) ) )
   )

   where
     vec contains 0 (defined) bits where the corresponding arg bits 
     are defined but different, and 1 bits otherwise.

     vec = Or<sz>( vxx,   // 0 iff bit defined
                   vyy,   // 0 iff bit defined
                   Not<sz>(Xor<sz>( xx, yy )) // 0 iff bits different
                 )
                    
     If any bit of vec is 0, the result is defined and so the 
     improvement term should produce 0...0, else it should produce
     1...1.

     Hence require for the improvement term:

        if vec == 1...1 then 1...1 else 0...0
     ->
        PCast<sz>( CmpEQ<sz> ( vec, 1...1 ) )

   This was extensively re-analysed and checked on 6 July 05.
*/
static IRAtom* expensiveCmpEQorNE ( MCEnv*  mce,
                                    IRType  ty,
                                    IRAtom* vxx, IRAtom* vyy, 
                                    IRAtom* xx,  IRAtom* yy )
{
   IRAtom *naive, *vec, *improvement_term;
   IRAtom *improved, *final_cast, *top;
   IROp   opDIFD, opUIFU, opXOR, opNOT, opCMP, opOR;

   tl_assert(isShadowAtom(mce,vxx));
   tl_assert(isShadowAtom(mce,vyy));
   tl_assert(isOriginalAtom(mce,xx));
   tl_assert(isOriginalAtom(mce,yy));
   tl_assert(sameKindedAtoms(vxx,xx));
   tl_assert(sameKindedAtoms(vyy,yy));
 
   switch (ty) {
      case Ity_I16:
         opOR   = Iop_Or16;
         opDIFD = Iop_And16;
         opUIFU = Iop_Or16;
         opNOT  = Iop_Not16;
         opXOR  = Iop_Xor16;
         opCMP  = Iop_CmpEQ16;
         top    = mkU16(0xFFFF);
         break;
      case Ity_I32:
         opOR   = Iop_Or32;
         opDIFD = Iop_And32;
         opUIFU = Iop_Or32;
         opNOT  = Iop_Not32;
         opXOR  = Iop_Xor32;
         opCMP  = Iop_CmpEQ32;
         top    = mkU32(0xFFFFFFFF);
         break;
      case Ity_I64:
         opOR   = Iop_Or64;
         opDIFD = Iop_And64;
         opUIFU = Iop_Or64;
         opNOT  = Iop_Not64;
         opXOR  = Iop_Xor64;
         opCMP  = Iop_CmpEQ64;
         top    = mkU64(0xFFFFFFFFFFFFFFFFULL);
         break;
      default:
         VG_(tool_panic)("expensiveCmpEQorNE");
   }

   naive 
      = mkPCastTo(mce,ty,
                  assignNew('V', mce, ty, binop(opUIFU, vxx, vyy)));

   vec 
      = assignNew(
           'V', mce,ty, 
           binop( opOR,
                  assignNew('V', mce,ty, binop(opOR, vxx, vyy)),
                  assignNew(
                     'V', mce,ty, 
                     unop( opNOT,
                           assignNew('V', mce,ty, binop(opXOR, xx, yy))))));

   improvement_term
      = mkPCastTo( mce,ty,
                   assignNew('V', mce,Ity_I1, binop(opCMP, vec, top)));

   improved
      = assignNew( 'V', mce,ty, binop(opDIFD, naive, improvement_term) );

   final_cast
      = mkPCastTo( mce, Ity_I1, improved );

   return final_cast;
}


/* --------- Semi-accurate interpretation of CmpORD. --------- */

/* CmpORD32{S,U} does PowerPC-style 3-way comparisons:

      CmpORD32S(x,y) = 1<<3   if  x <s y
                     = 1<<2   if  x >s y
                     = 1<<1   if  x == y

   and similarly the unsigned variant.  The default interpretation is:

      CmpORD32{S,U}#(x,y,x#,y#) = PCast(x# `UifU` y#)  
                                  & (7<<1)

   The "& (7<<1)" reflects the fact that all result bits except 3,2,1
   are zero and therefore defined (viz, zero).

   Also deal with a special case better:

      CmpORD32S(x,0)

   Here, bit 3 (LT) of the result is a copy of the top bit of x and
   will be defined even if the rest of x isn't.  In which case we do:

      CmpORD32S#(x,x#,0,{impliedly 0}#)
         = PCast(x#) & (3<<1)      -- standard interp for GT#,EQ#
           | (x# >>u 31) << 3      -- LT# = x#[31]

   Analogous handling for CmpORD64{S,U}.
*/
static Bool isZeroU32 ( IRAtom* e )
{
   return
      toBool( e->tag == Iex_Const
              && e->Iex.Const.con->tag == Ico_U32
              && e->Iex.Const.con->Ico.U32 == 0 );
}

static Bool isZeroU64 ( IRAtom* e )
{
   return
      toBool( e->tag == Iex_Const
              && e->Iex.Const.con->tag == Ico_U64
              && e->Iex.Const.con->Ico.U64 == 0 );
}

static IRAtom* doCmpORD ( MCEnv*  mce,
                          IROp    cmp_op,
                          IRAtom* xxhash, IRAtom* yyhash, 
                          IRAtom* xx,     IRAtom* yy )
{
   Bool   m64    = cmp_op == Iop_CmpORD64S || cmp_op == Iop_CmpORD64U;
   Bool   syned  = cmp_op == Iop_CmpORD64S || cmp_op == Iop_CmpORD32S;
   IROp   opOR   = m64 ? Iop_Or64  : Iop_Or32;
   IROp   opAND  = m64 ? Iop_And64 : Iop_And32;
   IROp   opSHL  = m64 ? Iop_Shl64 : Iop_Shl32;
   IROp   opSHR  = m64 ? Iop_Shr64 : Iop_Shr32;
   IRType ty     = m64 ? Ity_I64   : Ity_I32;
   Int    width  = m64 ? 64        : 32;

   Bool (*isZero)(IRAtom*) = m64 ? isZeroU64 : isZeroU32;

   IRAtom* threeLeft1 = NULL;
   IRAtom* sevenLeft1 = NULL;

   tl_assert(isShadowAtom(mce,xxhash));
   tl_assert(isShadowAtom(mce,yyhash));
   tl_assert(isOriginalAtom(mce,xx));
   tl_assert(isOriginalAtom(mce,yy));
   tl_assert(sameKindedAtoms(xxhash,xx));
   tl_assert(sameKindedAtoms(yyhash,yy));
   tl_assert(cmp_op == Iop_CmpORD32S || cmp_op == Iop_CmpORD32U
             || cmp_op == Iop_CmpORD64S || cmp_op == Iop_CmpORD64U);

   if (0) {
      ppIROp(cmp_op); VG_(printf)(" "); 
      ppIRExpr(xx); VG_(printf)(" "); ppIRExpr( yy ); VG_(printf)("\n");
   }

   if (syned && isZero(yy)) {
      /* fancy interpretation */
      /* if yy is zero, then it must be fully defined (zero#). */
      tl_assert(isZero(yyhash));
      threeLeft1 = m64 ? mkU64(3<<1) : mkU32(3<<1);
      return
         binop(
            opOR,
            assignNew(
               'V', mce,ty,
               binop(
                  opAND,
                  mkPCastTo(mce,ty, xxhash), 
                  threeLeft1
               )),
            assignNew(
               'V', mce,ty,
               binop(
                  opSHL,
                  assignNew(
                     'V', mce,ty,
                     binop(opSHR, xxhash, mkU8(width-1))),
                  mkU8(3)
               ))
	 );
   } else {
      /* standard interpretation */
      sevenLeft1 = m64 ? mkU64(7<<1) : mkU32(7<<1);
      return 
         binop( 
            opAND, 
            mkPCastTo( mce,ty,
                       mkUifU(mce,ty, xxhash,yyhash)),
            sevenLeft1
         );
   }
}


/*------------------------------------------------------------*/
/*--- Emit a test and complaint if something is undefined. ---*/
/*------------------------------------------------------------*/

static IRAtom* schemeE ( MCEnv* mce, IRExpr* e ); /* fwds */


/* Set the annotations on a dirty helper to indicate that the stack
   pointer and instruction pointers might be read.  This is the
   behaviour of all 'emit-a-complaint' style functions we might
   call. */

static void setHelperAnns ( MCEnv* mce, IRDirty* di ) {
   di->nFxState = 2;
   di->fxState[0].fx        = Ifx_Read;
   di->fxState[0].offset    = mce->layout->offset_SP;
   di->fxState[0].size      = mce->layout->sizeof_SP;
   di->fxState[0].nRepeats  = 0;
   di->fxState[0].repeatLen = 0;
   di->fxState[1].fx        = Ifx_Read;
   di->fxState[1].offset    = mce->layout->offset_IP;
   di->fxState[1].size      = mce->layout->sizeof_IP;
   di->fxState[1].nRepeats  = 0;
   di->fxState[1].repeatLen = 0;
}


/* Check the supplied *original* |atom| for undefinedness, and emit a
   complaint if so.  Once that happens, mark it as defined.  This is
   possible because the atom is either a tmp or literal.  If it's a
   tmp, it will be shadowed by a tmp, and so we can set the shadow to
   be defined.  In fact as mentioned above, we will have to allocate a
   new tmp to carry the new 'defined' shadow value, and update the
   original->tmp mapping accordingly; we cannot simply assign a new
   value to an existing shadow tmp as this breaks SSAness.

   The checks are performed, any resulting complaint emitted, and
   |atom|'s shadow temp set to 'defined', ONLY in the case that
   |guard| evaluates to True at run-time.  If it evaluates to False
   then no action is performed.  If |guard| is NULL (the usual case)
   then it is assumed to be always-true, and hence these actions are
   performed unconditionally.

   This routine does not generate code to check the definedness of
   |guard|.  The caller is assumed to have taken care of that already.
*/
static void complainIfUndefined ( MCEnv* mce, IRAtom* atom, IRExpr *guard )
{
   IRAtom*  vatom;
   IRType   ty;
   Int      sz;
   IRDirty* di;
   IRAtom*  cond;
   IRAtom*  origin;
   void*    fn;
   const HChar* nm;
   IRExpr** args;
   Int      nargs;

   // Don't do V bit tests if we're not reporting undefined value errors.
   if (MC_(clo_mc_level) == 1)
      return;

   if (guard)
      tl_assert(isOriginalAtom(mce, guard));

   /* Since the original expression is atomic, there's no duplicated
      work generated by making multiple V-expressions for it.  So we
      don't really care about the possibility that someone else may
      also create a V-interpretion for it. */
   tl_assert(isOriginalAtom(mce, atom));
   vatom = expr2vbits( mce, atom );
   tl_assert(isShadowAtom(mce, vatom));
   tl_assert(sameKindedAtoms(atom, vatom));

   ty = typeOfIRExpr(mce->sb->tyenv, vatom);

   /* sz is only used for constructing the error message */
   sz = ty==Ity_I1 ? 0 : sizeofIRType(ty);

   cond = mkPCastTo( mce, Ity_I1, vatom );
   /* cond will be 0 if all defined, and 1 if any not defined. */

   /* Get the origin info for the value we are about to check.  At
      least, if we are doing origin tracking.  If not, use a dummy
      zero origin. */
   if (MC_(clo_mc_level) == 3) {
      origin = schemeE( mce, atom );
      if (mce->hWordTy == Ity_I64) {
         origin = assignNew( 'B', mce, Ity_I64, unop(Iop_32Uto64, origin) );
      }
   } else {
      origin = NULL;
   }

   fn    = NULL;
   nm    = NULL;
   args  = NULL;
   nargs = -1;

   switch (sz) {
      case 0:
         if (origin) {
            fn    = &MC_(helperc_value_check0_fail_w_o);
            nm    = "MC_(helperc_value_check0_fail_w_o)";
            args  = mkIRExprVec_1(origin);
            nargs = 1;
         } else {
            fn    = &MC_(helperc_value_check0_fail_no_o);
            nm    = "MC_(helperc_value_check0_fail_no_o)";
            args  = mkIRExprVec_0();
            nargs = 0;
         }
         break;
      case 1:
         if (origin) {
            fn    = &MC_(helperc_value_check1_fail_w_o);
            nm    = "MC_(helperc_value_check1_fail_w_o)";
            args  = mkIRExprVec_1(origin);
            nargs = 1;
         } else {
            fn    = &MC_(helperc_value_check1_fail_no_o);
            nm    = "MC_(helperc_value_check1_fail_no_o)";
            args  = mkIRExprVec_0();
            nargs = 0;
         }
         break;
      case 4:
         if (origin) {
            fn    = &MC_(helperc_value_check4_fail_w_o);
            nm    = "MC_(helperc_value_check4_fail_w_o)";
            args  = mkIRExprVec_1(origin);
            nargs = 1;
         } else {
            fn    = &MC_(helperc_value_check4_fail_no_o);
            nm    = "MC_(helperc_value_check4_fail_no_o)";
            args  = mkIRExprVec_0();
            nargs = 0;
         }
         break;
      case 8:
         if (origin) {
            fn    = &MC_(helperc_value_check8_fail_w_o);
            nm    = "MC_(helperc_value_check8_fail_w_o)";
            args  = mkIRExprVec_1(origin);
            nargs = 1;
         } else {
            fn    = &MC_(helperc_value_check8_fail_no_o);
            nm    = "MC_(helperc_value_check8_fail_no_o)";
            args  = mkIRExprVec_0();
            nargs = 0;
         }
         break;
      case 2:
      case 16:
         if (origin) {
            fn    = &MC_(helperc_value_checkN_fail_w_o);
            nm    = "MC_(helperc_value_checkN_fail_w_o)";
            args  = mkIRExprVec_2( mkIRExpr_HWord( sz ), origin);
            nargs = 2;
         } else {
            fn    = &MC_(helperc_value_checkN_fail_no_o);
            nm    = "MC_(helperc_value_checkN_fail_no_o)";
            args  = mkIRExprVec_1( mkIRExpr_HWord( sz ) );
            nargs = 1;
         }
         break;
      default:
         VG_(tool_panic)("unexpected szB");
   }

   tl_assert(fn);
   tl_assert(nm);
   tl_assert(args);
   tl_assert(nargs >= 0 && nargs <= 2);
   tl_assert( (MC_(clo_mc_level) == 3 && origin != NULL)
              || (MC_(clo_mc_level) == 2 && origin == NULL) );

   di = unsafeIRDirty_0_N( nargs/*regparms*/, nm, 
                           VG_(fnptr_to_fnentry)( fn ), args );
   di->guard = cond; // and cond is PCast-to-1(atom#)

   /* If the complaint is to be issued under a guard condition, AND
      that into the guard condition for the helper call. */
   if (guard) {
      IRAtom *g1 = assignNew('V', mce, Ity_I32, unop(Iop_1Uto32, di->guard));
      IRAtom *g2 = assignNew('V', mce, Ity_I32, unop(Iop_1Uto32, guard));
      IRAtom *e  = assignNew('V', mce, Ity_I32, binop(Iop_And32, g1, g2));
      di->guard  = assignNew('V', mce, Ity_I1,  unop(Iop_32to1, e));
   }

   setHelperAnns( mce, di );
   stmt( 'V', mce, IRStmt_Dirty(di));

   /* If |atom| is shadowed by an IRTemp, set the shadow tmp to be
      defined -- but only in the case where the guard evaluates to
      True at run-time.  Do the update by setting the orig->shadow
      mapping for tmp to reflect the fact that this shadow is getting
      a new value. */
   tl_assert(isIRAtom(vatom));
   /* sameKindedAtoms ... */
   if (vatom->tag == Iex_RdTmp) {
      tl_assert(atom->tag == Iex_RdTmp);
      if (guard == NULL) {
         // guard is 'always True', hence update unconditionally
         newShadowTmpV(mce, atom->Iex.RdTmp.tmp);
         assign('V', mce, findShadowTmpV(mce, atom->Iex.RdTmp.tmp), 
                          definedOfType(ty));
      } else {
         // update the temp only conditionally.  Do this by copying
         // its old value when the guard is False.
         // The old value ..
         IRTemp old_tmpV = findShadowTmpV(mce, atom->Iex.RdTmp.tmp);
         newShadowTmpV(mce, atom->Iex.RdTmp.tmp);
         IRAtom* new_tmpV
            = assignNew('V', mce, shadowTypeV(ty),
                        IRExpr_ITE(guard, definedOfType(ty),
                                          mkexpr(old_tmpV)));
         assign('V', mce, findShadowTmpV(mce, atom->Iex.RdTmp.tmp), new_tmpV);
      }
   }
}


/*------------------------------------------------------------*/
/*--- Shadowing PUTs/GETs, and indexed variants thereof    ---*/
/*------------------------------------------------------------*/

/* Examine the always-defined sections declared in layout to see if
   the (offset,size) section is within one.  Note, is is an error to
   partially fall into such a region: (offset,size) should either be
   completely in such a region or completely not-in such a region.  
*/
static Bool isAlwaysDefd ( MCEnv* mce, Int offset, Int size )
{
   Int minoffD, maxoffD, i;
   Int minoff = offset;
   Int maxoff = minoff + size - 1;
   tl_assert((minoff & ~0xFFFF) == 0);
   tl_assert((maxoff & ~0xFFFF) == 0);

   for (i = 0; i < mce->layout->n_alwaysDefd; i++) {
      minoffD = mce->layout->alwaysDefd[i].offset;
      maxoffD = minoffD + mce->layout->alwaysDefd[i].size - 1;
      tl_assert((minoffD & ~0xFFFF) == 0);
      tl_assert((maxoffD & ~0xFFFF) == 0);

      if (maxoff < minoffD || maxoffD < minoff)
         continue; /* no overlap */
      if (minoff >= minoffD && maxoff <= maxoffD)
         return True; /* completely contained in an always-defd section */

      VG_(tool_panic)("memcheck:isAlwaysDefd:partial overlap");
   }
   return False; /* could not find any containing section */
}


/* Generate into bb suitable actions to shadow this Put.  If the state
   slice is marked 'always defined', do nothing.  Otherwise, write the
   supplied V bits to the shadow state.  We can pass in either an
   original atom or a V-atom, but not both.  In the former case the
   relevant V-bits are then generated from the original.
   We assume here, that the definedness of GUARD has already been checked.
*/
static
void do_shadow_PUT ( MCEnv* mce,  Int offset, 
                     IRAtom* atom, IRAtom* vatom, IRExpr *guard )
{
   IRType ty;

   // Don't do shadow PUTs if we're not doing undefined value checking.
   // Their absence lets Vex's optimiser remove all the shadow computation
   // that they depend on, which includes GETs of the shadow registers.
   if (MC_(clo_mc_level) == 1)
      return;
   
   if (atom) {
      tl_assert(!vatom);
      tl_assert(isOriginalAtom(mce, atom));
      vatom = expr2vbits( mce, atom );
   } else {
      tl_assert(vatom);
      tl_assert(isShadowAtom(mce, vatom));
   }

   ty = typeOfIRExpr(mce->sb->tyenv, vatom);
   tl_assert(ty != Ity_I1);
   tl_assert(ty != Ity_I128);
   if (isAlwaysDefd(mce, offset, sizeofIRType(ty))) {
      /* later: no ... */
      /* emit code to emit a complaint if any of the vbits are 1. */
      /* complainIfUndefined(mce, atom); */
   } else {
      /* Do a plain shadow Put. */
      if (guard) {
         /* If the guard expression evaluates to false we simply Put the value
            that is already stored in the guest state slot */
         IRAtom *cond, *iffalse;

         cond    = assignNew('V', mce, Ity_I1, guard);
         iffalse = assignNew('V', mce, ty,
                             IRExpr_Get(offset + mce->layout->total_sizeB, ty));
         vatom   = assignNew('V', mce, ty, IRExpr_ITE(cond, vatom, iffalse));
      }
      stmt( 'V', mce, IRStmt_Put( offset + mce->layout->total_sizeB, vatom ));
   }
}


/* Return an expression which contains the V bits corresponding to the
   given GETI (passed in in pieces). 
*/
static
void do_shadow_PUTI ( MCEnv* mce, IRPutI *puti)
{
   IRAtom* vatom;
   IRType  ty, tyS;
   Int     arrSize;;
   IRRegArray* descr = puti->descr;
   IRAtom*     ix    = puti->ix;
   Int         bias  = puti->bias;
   IRAtom*     atom  = puti->data;

   // Don't do shadow PUTIs if we're not doing undefined value checking.
   // Their absence lets Vex's optimiser remove all the shadow computation
   // that they depend on, which includes GETIs of the shadow registers.
   if (MC_(clo_mc_level) == 1)
      return;
   
   tl_assert(isOriginalAtom(mce,atom));
   vatom = expr2vbits( mce, atom );
   tl_assert(sameKindedAtoms(atom, vatom));
   ty   = descr->elemTy;
   tyS  = shadowTypeV(ty);
   arrSize = descr->nElems * sizeofIRType(ty);
   tl_assert(ty != Ity_I1);
   tl_assert(isOriginalAtom(mce,ix));
   complainIfUndefined(mce, ix, NULL);
   if (isAlwaysDefd(mce, descr->base, arrSize)) {
      /* later: no ... */
      /* emit code to emit a complaint if any of the vbits are 1. */
      /* complainIfUndefined(mce, atom); */
   } else {
      /* Do a cloned version of the Put that refers to the shadow
         area. */
      IRRegArray* new_descr 
         = mkIRRegArray( descr->base + mce->layout->total_sizeB, 
                         tyS, descr->nElems);
      stmt( 'V', mce, IRStmt_PutI( mkIRPutI(new_descr, ix, bias, vatom) ));
   }
}


/* Return an expression which contains the V bits corresponding to the
   given GET (passed in in pieces). 
*/
static 
IRExpr* shadow_GET ( MCEnv* mce, Int offset, IRType ty )
{
   IRType tyS = shadowTypeV(ty);
   tl_assert(ty != Ity_I1);
   tl_assert(ty != Ity_I128);
   if (isAlwaysDefd(mce, offset, sizeofIRType(ty))) {
      /* Always defined, return all zeroes of the relevant type */
      return definedOfType(tyS);
   } else {
      /* return a cloned version of the Get that refers to the shadow
         area. */
      /* FIXME: this isn't an atom! */
      return IRExpr_Get( offset + mce->layout->total_sizeB, tyS );
   }
}


/* Return an expression which contains the V bits corresponding to the
   given GETI (passed in in pieces). 
*/
static
IRExpr* shadow_GETI ( MCEnv* mce, 
                      IRRegArray* descr, IRAtom* ix, Int bias )
{
   IRType ty   = descr->elemTy;
   IRType tyS  = shadowTypeV(ty);
   Int arrSize = descr->nElems * sizeofIRType(ty);
   tl_assert(ty != Ity_I1);
   tl_assert(isOriginalAtom(mce,ix));
   complainIfUndefined(mce, ix, NULL);
   if (isAlwaysDefd(mce, descr->base, arrSize)) {
      /* Always defined, return all zeroes of the relevant type */
      return definedOfType(tyS);
   } else {
      /* return a cloned version of the Get that refers to the shadow
         area. */
      IRRegArray* new_descr 
         = mkIRRegArray( descr->base + mce->layout->total_sizeB, 
                         tyS, descr->nElems);
      return IRExpr_GetI( new_descr, ix, bias );
   }
}


/*------------------------------------------------------------*/
/*--- Generating approximations for unknown operations,    ---*/
/*--- using lazy-propagate semantics                       ---*/
/*------------------------------------------------------------*/

/* Lazy propagation of undefinedness from two values, resulting in the
   specified shadow type. 
*/
static
IRAtom* mkLazy2 ( MCEnv* mce, IRType finalVty, IRAtom* va1, IRAtom* va2 )
{
   IRAtom* at;
   IRType t1 = typeOfIRExpr(mce->sb->tyenv, va1);
   IRType t2 = typeOfIRExpr(mce->sb->tyenv, va2);
   tl_assert(isShadowAtom(mce,va1));
   tl_assert(isShadowAtom(mce,va2));

   /* The general case is inefficient because PCast is an expensive
      operation.  Here are some special cases which use PCast only
      once rather than twice. */

   /* I64 x I64 -> I64 */
   if (t1 == Ity_I64 && t2 == Ity_I64 && finalVty == Ity_I64) {
      if (0) VG_(printf)("mkLazy2: I64 x I64 -> I64\n");
      at = mkUifU(mce, Ity_I64, va1, va2);
      at = mkPCastTo(mce, Ity_I64, at);
      return at;
   }

   /* I64 x I64 -> I32 */
   if (t1 == Ity_I64 && t2 == Ity_I64 && finalVty == Ity_I32) {
      if (0) VG_(printf)("mkLazy2: I64 x I64 -> I32\n");
      at = mkUifU(mce, Ity_I64, va1, va2);
      at = mkPCastTo(mce, Ity_I32, at);
      return at;
   }

   if (0) {
      VG_(printf)("mkLazy2 ");
      ppIRType(t1);
      VG_(printf)("_");
      ppIRType(t2);
      VG_(printf)("_");
      ppIRType(finalVty);
      VG_(printf)("\n");
   }

   /* General case: force everything via 32-bit intermediaries. */
   at = mkPCastTo(mce, Ity_I32, va1);
   at = mkUifU(mce, Ity_I32, at, mkPCastTo(mce, Ity_I32, va2));
   at = mkPCastTo(mce, finalVty, at);
   return at;
}


/* 3-arg version of the above. */
static
IRAtom* mkLazy3 ( MCEnv* mce, IRType finalVty, 
                  IRAtom* va1, IRAtom* va2, IRAtom* va3 )
{
   IRAtom* at;
   IRType t1 = typeOfIRExpr(mce->sb->tyenv, va1);
   IRType t2 = typeOfIRExpr(mce->sb->tyenv, va2);
   IRType t3 = typeOfIRExpr(mce->sb->tyenv, va3);
   tl_assert(isShadowAtom(mce,va1));
   tl_assert(isShadowAtom(mce,va2));
   tl_assert(isShadowAtom(mce,va3));

   /* The general case is inefficient because PCast is an expensive
      operation.  Here are some special cases which use PCast only
      twice rather than three times. */

   /* I32 x I64 x I64 -> I64 */
   /* Standard FP idiom: rm x FParg1 x FParg2 -> FPresult */
   if (t1 == Ity_I32 && t2 == Ity_I64 && t3 == Ity_I64 
       && finalVty == Ity_I64) {
      if (0) VG_(printf)("mkLazy3: I32 x I64 x I64 -> I64\n");
      /* Widen 1st arg to I64.  Since 1st arg is typically a rounding
         mode indication which is fully defined, this should get
         folded out later. */
      at = mkPCastTo(mce, Ity_I64, va1);
      /* Now fold in 2nd and 3rd args. */
      at = mkUifU(mce, Ity_I64, at, va2);
      at = mkUifU(mce, Ity_I64, at, va3);
      /* and PCast once again. */
      at = mkPCastTo(mce, Ity_I64, at);
      return at;
   }

   /* I32 x I8 x I64 -> I64 */
   if (t1 == Ity_I32 && t2 == Ity_I8 && t3 == Ity_I64
       && finalVty == Ity_I64) {
      if (0) VG_(printf)("mkLazy3: I32 x I8 x I64 -> I64\n");
      /* Widen 1st and 2nd args to I64.  Since 1st arg is typically a
       * rounding mode indication which is fully defined, this should
       * get folded out later.
      */
      IRAtom* at1 = mkPCastTo(mce, Ity_I64, va1);
      IRAtom* at2 = mkPCastTo(mce, Ity_I64, va2);
      at = mkUifU(mce, Ity_I64, at1, at2);  // UifU(PCast(va1), PCast(va2))
      at = mkUifU(mce, Ity_I64, at, va3);
      /* and PCast once again. */
      at = mkPCastTo(mce, Ity_I64, at);
      return at;
   }

   /* I32 x I64 x I64 -> I32 */
   if (t1 == Ity_I32 && t2 == Ity_I64 && t3 == Ity_I64 
       && finalVty == Ity_I32) {
      if (0) VG_(printf)("mkLazy3: I32 x I64 x I64 -> I32\n");
      at = mkPCastTo(mce, Ity_I64, va1);
      at = mkUifU(mce, Ity_I64, at, va2);
      at = mkUifU(mce, Ity_I64, at, va3);
      at = mkPCastTo(mce, Ity_I32, at);
      return at;
   }

   /* I32 x I32 x I32 -> I32 */
   /* 32-bit FP idiom, as (eg) happens on ARM */
   if (t1 == Ity_I32 && t2 == Ity_I32 && t3 == Ity_I32 
       && finalVty == Ity_I32) {
      if (0) VG_(printf)("mkLazy3: I32 x I32 x I32 -> I32\n");
      at = va1;
      at = mkUifU(mce, Ity_I32, at, va2);
      at = mkUifU(mce, Ity_I32, at, va3);
      at = mkPCastTo(mce, Ity_I32, at);
      return at;
   }

   /* I32 x I128 x I128 -> I128 */
   /* Standard FP idiom: rm x FParg1 x FParg2 -> FPresult */
   if (t1 == Ity_I32 && t2 == Ity_I128 && t3 == Ity_I128
       && finalVty == Ity_I128) {
      if (0) VG_(printf)("mkLazy3: I32 x I128 x I128 -> I128\n");
      /* Widen 1st arg to I128.  Since 1st arg is typically a rounding
         mode indication which is fully defined, this should get
         folded out later. */
      at = mkPCastTo(mce, Ity_I128, va1);
      /* Now fold in 2nd and 3rd args. */
      at = mkUifU(mce, Ity_I128, at, va2);
      at = mkUifU(mce, Ity_I128, at, va3);
      /* and PCast once again. */
      at = mkPCastTo(mce, Ity_I128, at);
      return at;
   }

   /* I32 x I8 x I128 -> I128 */
   /* Standard FP idiom: rm x FParg1 x FParg2 -> FPresult */
   if (t1 == Ity_I32 && t2 == Ity_I8 && t3 == Ity_I128
       && finalVty == Ity_I128) {
      if (0) VG_(printf)("mkLazy3: I32 x I8 x I128 -> I128\n");
      /* Use I64 as an intermediate type, which means PCasting all 3
         args to I64 to start with. 1st arg is typically a rounding
         mode indication which is fully defined, so we hope that it
         will get folded out later. */
      IRAtom* at1 = mkPCastTo(mce, Ity_I64, va1);
      IRAtom* at2 = mkPCastTo(mce, Ity_I64, va2);
      IRAtom* at3 = mkPCastTo(mce, Ity_I64, va3);
      /* Now UifU all three together. */
      at = mkUifU(mce, Ity_I64, at1, at2);  // UifU(PCast(va1), PCast(va2))
      at = mkUifU(mce, Ity_I64, at, at3);   // ... `UifU` PCast(va3)
      /* and PCast once again. */
      at = mkPCastTo(mce, Ity_I128, at);
      return at;
   }
   if (1) {
      VG_(printf)("mkLazy3: ");
      ppIRType(t1);
      VG_(printf)(" x ");
      ppIRType(t2);
      VG_(printf)(" x ");
      ppIRType(t3);
      VG_(printf)(" -> ");
      ppIRType(finalVty);
      VG_(printf)("\n");
   }

   tl_assert(0);
   /* General case: force everything via 32-bit intermediaries. */
   /*
   at = mkPCastTo(mce, Ity_I32, va1);
   at = mkUifU(mce, Ity_I32, at, mkPCastTo(mce, Ity_I32, va2));
   at = mkUifU(mce, Ity_I32, at, mkPCastTo(mce, Ity_I32, va3));
   at = mkPCastTo(mce, finalVty, at);
   return at;
   */
}


/* 4-arg version of the above. */
static
IRAtom* mkLazy4 ( MCEnv* mce, IRType finalVty, 
                  IRAtom* va1, IRAtom* va2, IRAtom* va3, IRAtom* va4 )
{
   IRAtom* at;
   IRType t1 = typeOfIRExpr(mce->sb->tyenv, va1);
   IRType t2 = typeOfIRExpr(mce->sb->tyenv, va2);
   IRType t3 = typeOfIRExpr(mce->sb->tyenv, va3);
   IRType t4 = typeOfIRExpr(mce->sb->tyenv, va4);
   tl_assert(isShadowAtom(mce,va1));
   tl_assert(isShadowAtom(mce,va2));
   tl_assert(isShadowAtom(mce,va3));
   tl_assert(isShadowAtom(mce,va4));

   /* The general case is inefficient because PCast is an expensive
      operation.  Here are some special cases which use PCast only
      twice rather than three times. */

   /* I32 x I64 x I64 x I64 -> I64 */
   /* Standard FP idiom: rm x FParg1 x FParg2 x FParg3 -> FPresult */
   if (t1 == Ity_I32 && t2 == Ity_I64 && t3 == Ity_I64 && t4 == Ity_I64
       && finalVty == Ity_I64) {
      if (0) VG_(printf)("mkLazy4: I32 x I64 x I64 x I64 -> I64\n");
      /* Widen 1st arg to I64.  Since 1st arg is typically a rounding
         mode indication which is fully defined, this should get
         folded out later. */
      at = mkPCastTo(mce, Ity_I64, va1);
      /* Now fold in 2nd, 3rd, 4th args. */
      at = mkUifU(mce, Ity_I64, at, va2);
      at = mkUifU(mce, Ity_I64, at, va3);
      at = mkUifU(mce, Ity_I64, at, va4);
      /* and PCast once again. */
      at = mkPCastTo(mce, Ity_I64, at);
      return at;
   }
   /* I32 x I32 x I32 x I32 -> I32 */
   /* Standard FP idiom: rm x FParg1 x FParg2 x FParg3 -> FPresult */
   if (t1 == Ity_I32 && t2 == Ity_I32 && t3 == Ity_I32 && t4 == Ity_I32
       && finalVty == Ity_I32) {
      if (0) VG_(printf)("mkLazy4: I32 x I32 x I32 x I32 -> I32\n");
      at = va1;
      /* Now fold in 2nd, 3rd, 4th args. */
      at = mkUifU(mce, Ity_I32, at, va2);
      at = mkUifU(mce, Ity_I32, at, va3);
      at = mkUifU(mce, Ity_I32, at, va4);
      at = mkPCastTo(mce, Ity_I32, at);
      return at;
   }

   if (1) {
      VG_(printf)("mkLazy4: ");
      ppIRType(t1);
      VG_(printf)(" x ");
      ppIRType(t2);
      VG_(printf)(" x ");
      ppIRType(t3);
      VG_(printf)(" x ");
      ppIRType(t4);
      VG_(printf)(" -> ");
      ppIRType(finalVty);
      VG_(printf)("\n");
   }

   tl_assert(0);
}


/* Do the lazy propagation game from a null-terminated vector of
   atoms.  This is presumably the arguments to a helper call, so the
   IRCallee info is also supplied in order that we can know which
   arguments should be ignored (via the .mcx_mask field). 
*/
static
IRAtom* mkLazyN ( MCEnv* mce, 
                  IRAtom** exprvec, IRType finalVtype, IRCallee* cee )
{
   Int     i;
   IRAtom* here;
   IRAtom* curr;
   IRType  mergeTy;
   Bool    mergeTy64 = True;

   /* Decide on the type of the merge intermediary.  If all relevant
      args are I64, then it's I64.  In all other circumstances, use
      I32. */
   for (i = 0; exprvec[i]; i++) {
      tl_assert(i < 32);
      tl_assert(isOriginalAtom(mce, exprvec[i]));
      if (cee->mcx_mask & (1<<i))
         continue;
      if (typeOfIRExpr(mce->sb->tyenv, exprvec[i]) != Ity_I64)
         mergeTy64 = False;
   }

   mergeTy = mergeTy64  ? Ity_I64  : Ity_I32;
   curr    = definedOfType(mergeTy);

   for (i = 0; exprvec[i]; i++) {
      tl_assert(i < 32);
      tl_assert(isOriginalAtom(mce, exprvec[i]));
      /* Only take notice of this arg if the callee's mc-exclusion
         mask does not say it is to be excluded. */
      if (cee->mcx_mask & (1<<i)) {
         /* the arg is to be excluded from definedness checking.  Do
            nothing. */
         if (0) VG_(printf)("excluding %s(%d)\n", cee->name, i);
      } else {
         /* calculate the arg's definedness, and pessimistically merge
            it in. */
         here = mkPCastTo( mce, mergeTy, expr2vbits(mce, exprvec[i]) );
         curr = mergeTy64 
                   ? mkUifU64(mce, here, curr)
                   : mkUifU32(mce, here, curr);
      }
   }
   return mkPCastTo(mce, finalVtype, curr );
}


/*------------------------------------------------------------*/
/*--- Generating expensive sequences for exact carry-chain ---*/
/*--- propagation in add/sub and related operations.       ---*/
/*------------------------------------------------------------*/

static
IRAtom* expensiveAddSub ( MCEnv*  mce,
                          Bool    add,
                          IRType  ty,
                          IRAtom* qaa, IRAtom* qbb, 
                          IRAtom* aa,  IRAtom* bb )
{
   IRAtom *a_min, *b_min, *a_max, *b_max;
   IROp   opAND, opOR, opXOR, opNOT, opADD, opSUB;

   tl_assert(isShadowAtom(mce,qaa));
   tl_assert(isShadowAtom(mce,qbb));
   tl_assert(isOriginalAtom(mce,aa));
   tl_assert(isOriginalAtom(mce,bb));
   tl_assert(sameKindedAtoms(qaa,aa));
   tl_assert(sameKindedAtoms(qbb,bb));

   switch (ty) {
      case Ity_I32:
         opAND = Iop_And32;
         opOR  = Iop_Or32;
         opXOR = Iop_Xor32;
         opNOT = Iop_Not32;
         opADD = Iop_Add32;
         opSUB = Iop_Sub32;
         break;
      case Ity_I64:
         opAND = Iop_And64;
         opOR  = Iop_Or64;
         opXOR = Iop_Xor64;
         opNOT = Iop_Not64;
         opADD = Iop_Add64;
         opSUB = Iop_Sub64;
         break;
      default:
         VG_(tool_panic)("expensiveAddSub");
   }

   // a_min = aa & ~qaa
   a_min = assignNew('V', mce,ty, 
                     binop(opAND, aa,
                                  assignNew('V', mce,ty, unop(opNOT, qaa))));

   // b_min = bb & ~qbb
   b_min = assignNew('V', mce,ty, 
                     binop(opAND, bb,
                                  assignNew('V', mce,ty, unop(opNOT, qbb))));

   // a_max = aa | qaa
   a_max = assignNew('V', mce,ty, binop(opOR, aa, qaa));

   // b_max = bb | qbb
   b_max = assignNew('V', mce,ty, binop(opOR, bb, qbb));

   if (add) {
      // result = (qaa | qbb) | ((a_min + b_min) ^ (a_max + b_max))
      return
      assignNew('V', mce,ty,
         binop( opOR,
                assignNew('V', mce,ty, binop(opOR, qaa, qbb)),
                assignNew('V', mce,ty, 
                   binop( opXOR, 
                          assignNew('V', mce,ty, binop(opADD, a_min, b_min)),
                          assignNew('V', mce,ty, binop(opADD, a_max, b_max))
                   )
                )
         )
      );
   } else {
      // result = (qaa | qbb) | ((a_min - b_max) ^ (a_max + b_min))
      return
      assignNew('V', mce,ty,
         binop( opOR,
                assignNew('V', mce,ty, binop(opOR, qaa, qbb)),
                assignNew('V', mce,ty, 
                   binop( opXOR, 
                          assignNew('V', mce,ty, binop(opSUB, a_min, b_max)),
                          assignNew('V', mce,ty, binop(opSUB, a_max, b_min))
                   )
                )
         )
      );
   }

}


static
IRAtom* expensiveCountTrailingZeroes ( MCEnv* mce, IROp czop,
                                       IRAtom* atom, IRAtom* vatom )
{
   IRType ty;
   IROp xorOp, subOp, andOp;
   IRExpr *one;
   IRAtom *improver, *improved;
   tl_assert(isShadowAtom(mce,vatom));
   tl_assert(isOriginalAtom(mce,atom));
   tl_assert(sameKindedAtoms(atom,vatom));

   switch (czop) {
      case Iop_Ctz32:
         ty = Ity_I32;
         xorOp = Iop_Xor32;
         subOp = Iop_Sub32;
         andOp = Iop_And32;
         one = mkU32(1);
         break;
      case Iop_Ctz64:
         ty = Ity_I64;
         xorOp = Iop_Xor64;
         subOp = Iop_Sub64;
         andOp = Iop_And64;
         one = mkU64(1);
         break;
      default:
         ppIROp(czop);
         VG_(tool_panic)("memcheck:expensiveCountTrailingZeroes");
   }

   // improver = atom ^ (atom - 1)
   //
   // That is, improver has its low ctz(atom) bits equal to one;
   // higher bits (if any) equal to zero.
   improver = assignNew('V', mce,ty,
                        binop(xorOp,
                              atom,
                              assignNew('V', mce, ty,
                                        binop(subOp, atom, one))));

   // improved = vatom & improver
   //
   // That is, treat any V bits above the first ctz(atom) bits as
   // "defined".
   improved = assignNew('V', mce, ty,
                        binop(andOp, vatom, improver));

   // Return pessimizing cast of improved.
   return mkPCastTo(mce, ty, improved);
}


/*------------------------------------------------------------*/
/*--- Scalar shifts.                                       ---*/
/*------------------------------------------------------------*/

/* Produce an interpretation for (aa << bb) (or >>s, >>u).  The basic
   idea is to shift the definedness bits by the original shift amount.
   This introduces 0s ("defined") in new positions for left shifts and
   unsigned right shifts, and copies the top definedness bit for
   signed right shifts.  So, conveniently, applying the original shift
   operator to the definedness bits for the left arg is exactly the
   right thing to do:

      (qaa << bb)

   However if the shift amount is undefined then the whole result
   is undefined.  Hence need:

      (qaa << bb) `UifU` PCast(qbb)

   If the shift amount bb is a literal than qbb will say 'all defined'
   and the UifU and PCast will get folded out by post-instrumentation
   optimisation.
*/
static IRAtom* scalarShift ( MCEnv*  mce,
                             IRType  ty,
                             IROp    original_op,
                             IRAtom* qaa, IRAtom* qbb, 
                             IRAtom* aa,  IRAtom* bb )
{
   tl_assert(isShadowAtom(mce,qaa));
   tl_assert(isShadowAtom(mce,qbb));
   tl_assert(isOriginalAtom(mce,aa));
   tl_assert(isOriginalAtom(mce,bb));
   tl_assert(sameKindedAtoms(qaa,aa));
   tl_assert(sameKindedAtoms(qbb,bb));
   return 
      assignNew(
         'V', mce, ty,
         mkUifU( mce, ty,
                 assignNew('V', mce, ty, binop(original_op, qaa, bb)),
                 mkPCastTo(mce, ty, qbb)
         )
   );
}


/*------------------------------------------------------------*/
/*--- Helpers for dealing with vector primops.             ---*/
/*------------------------------------------------------------*/

/* Vector pessimisation -- pessimise within each lane individually. */

static IRAtom* mkPCast8x16 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_V128, unop(Iop_CmpNEZ8x16, at));
}

static IRAtom* mkPCast16x8 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_V128, unop(Iop_CmpNEZ16x8, at));
}

static IRAtom* mkPCast32x4 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_V128, unop(Iop_CmpNEZ32x4, at));
}

static IRAtom* mkPCast64x2 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_V128, unop(Iop_CmpNEZ64x2, at));
}

static IRAtom* mkPCast64x4 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_V256, unop(Iop_CmpNEZ64x4, at));
}

static IRAtom* mkPCast32x8 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_V256, unop(Iop_CmpNEZ32x8, at));
}

static IRAtom* mkPCast32x2 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_I64, unop(Iop_CmpNEZ32x2, at));
}

static IRAtom* mkPCast16x16 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_V256, unop(Iop_CmpNEZ16x16, at));
}

static IRAtom* mkPCast16x4 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_I64, unop(Iop_CmpNEZ16x4, at));
}

static IRAtom* mkPCast8x32 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_V256, unop(Iop_CmpNEZ8x32, at));
}

static IRAtom* mkPCast8x8 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_I64, unop(Iop_CmpNEZ8x8, at));
}

static IRAtom* mkPCast16x2 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_I32, unop(Iop_CmpNEZ16x2, at));
}

static IRAtom* mkPCast8x4 ( MCEnv* mce, IRAtom* at )
{
   return assignNew('V', mce, Ity_I32, unop(Iop_CmpNEZ8x4, at));
}


/* Here's a simple scheme capable of handling ops derived from SSE1
   code and while only generating ops that can be efficiently
   implemented in SSE1. */

/* All-lanes versions are straightforward:

   binary32Fx4(x,y)   ==> PCast32x4(UifUV128(x#,y#))

   unary32Fx4(x,y)    ==> PCast32x4(x#)

   Lowest-lane-only versions are more complex:

   binary32F0x4(x,y)  ==> SetV128lo32(
                             x#, 
                             PCast32(V128to32(UifUV128(x#,y#))) 
                          )

   This is perhaps not so obvious.  In particular, it's faster to
   do a V128-bit UifU and then take the bottom 32 bits than the more
   obvious scheme of taking the bottom 32 bits of each operand
   and doing a 32-bit UifU.  Basically since UifU is fast and 
   chopping lanes off vector values is slow.

   Finally:

   unary32F0x4(x)     ==> SetV128lo32(
                             x#, 
                             PCast32(V128to32(x#)) 
                          )

   Where:

   PCast32(v#)   = 1Sto32(CmpNE32(v#,0))
   PCast32x4(v#) = CmpNEZ32x4(v#)
*/

static
IRAtom* binary32Fx4 ( MCEnv* mce, IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   tl_assert(isShadowAtom(mce, vatomY));
   at = mkUifUV128(mce, vatomX, vatomY);
   at = assignNew('V', mce, Ity_V128, mkPCast32x4(mce, at));
   return at;
}

static
IRAtom* unary32Fx4 ( MCEnv* mce, IRAtom* vatomX )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   at = assignNew('V', mce, Ity_V128, mkPCast32x4(mce, vatomX));
   return at;
}

static
IRAtom* binary32F0x4 ( MCEnv* mce, IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   tl_assert(isShadowAtom(mce, vatomY));
   at = mkUifUV128(mce, vatomX, vatomY);
   at = assignNew('V', mce, Ity_I32, unop(Iop_V128to32, at));
   at = mkPCastTo(mce, Ity_I32, at);
   at = assignNew('V', mce, Ity_V128, binop(Iop_SetV128lo32, vatomX, at));
   return at;
}

static
IRAtom* unary32F0x4 ( MCEnv* mce, IRAtom* vatomX )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   at = assignNew('V', mce, Ity_I32, unop(Iop_V128to32, vatomX));
   at = mkPCastTo(mce, Ity_I32, at);
   at = assignNew('V', mce, Ity_V128, binop(Iop_SetV128lo32, vatomX, at));
   return at;
}

/* --- ... and ... 64Fx2 versions of the same ... --- */

static
IRAtom* binary64Fx2 ( MCEnv* mce, IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   tl_assert(isShadowAtom(mce, vatomY));
   at = mkUifUV128(mce, vatomX, vatomY);
   at = assignNew('V', mce, Ity_V128, mkPCast64x2(mce, at));
   return at;
}

static
IRAtom* unary64Fx2 ( MCEnv* mce, IRAtom* vatomX )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   at = assignNew('V', mce, Ity_V128, mkPCast64x2(mce, vatomX));
   return at;
}

static
IRAtom* binary64F0x2 ( MCEnv* mce, IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   tl_assert(isShadowAtom(mce, vatomY));
   at = mkUifUV128(mce, vatomX, vatomY);
   at = assignNew('V', mce, Ity_I64, unop(Iop_V128to64, at));
   at = mkPCastTo(mce, Ity_I64, at);
   at = assignNew('V', mce, Ity_V128, binop(Iop_SetV128lo64, vatomX, at));
   return at;
}

static
IRAtom* unary64F0x2 ( MCEnv* mce, IRAtom* vatomX )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   at = assignNew('V', mce, Ity_I64, unop(Iop_V128to64, vatomX));
   at = mkPCastTo(mce, Ity_I64, at);
   at = assignNew('V', mce, Ity_V128, binop(Iop_SetV128lo64, vatomX, at));
   return at;
}

/* --- --- ... and ... 32Fx2 versions of the same --- --- */

static
IRAtom* binary32Fx2 ( MCEnv* mce, IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   tl_assert(isShadowAtom(mce, vatomY));
   at = mkUifU64(mce, vatomX, vatomY);
   at = assignNew('V', mce, Ity_I64, mkPCast32x2(mce, at));
   return at;
}

static
IRAtom* unary32Fx2 ( MCEnv* mce, IRAtom* vatomX )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   at = assignNew('V', mce, Ity_I64, mkPCast32x2(mce, vatomX));
   return at;
}

/* --- ... and ... 64Fx4 versions of the same ... --- */

static
IRAtom* binary64Fx4 ( MCEnv* mce, IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   tl_assert(isShadowAtom(mce, vatomY));
   at = mkUifUV256(mce, vatomX, vatomY);
   at = assignNew('V', mce, Ity_V256, mkPCast64x4(mce, at));
   return at;
}

static
IRAtom* unary64Fx4 ( MCEnv* mce, IRAtom* vatomX )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   at = assignNew('V', mce, Ity_V256, mkPCast64x4(mce, vatomX));
   return at;
}

/* --- ... and ... 32Fx8 versions of the same ... --- */

static
IRAtom* binary32Fx8 ( MCEnv* mce, IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   tl_assert(isShadowAtom(mce, vatomY));
   at = mkUifUV256(mce, vatomX, vatomY);
   at = assignNew('V', mce, Ity_V256, mkPCast32x8(mce, at));
   return at;
}

static
IRAtom* unary32Fx8 ( MCEnv* mce, IRAtom* vatomX )
{
   IRAtom* at;
   tl_assert(isShadowAtom(mce, vatomX));
   at = assignNew('V', mce, Ity_V256, mkPCast32x8(mce, vatomX));
   return at;
}

/* --- 64Fx2 binary FP ops, with rounding mode --- */

static
IRAtom* binary64Fx2_w_rm ( MCEnv* mce, IRAtom* vRM,
                                       IRAtom* vatomX, IRAtom* vatomY )
{
   /* This is the same as binary64Fx2, except that we subsequently
      pessimise vRM (definedness of the rounding mode), widen to 128
      bits and UifU it into the result.  As with the scalar cases, if
      the RM is a constant then it is defined and so this extra bit
      will get constant-folded out later. */
   // "do" the vector args
   IRAtom* t1 = binary64Fx2(mce, vatomX, vatomY);
   // PCast the RM, and widen it to 128 bits
   IRAtom* t2 = mkPCastTo(mce, Ity_V128, vRM);
   // Roll it into the result
   t1 = mkUifUV128(mce, t1, t2);
   return t1;
}

/* --- ... and ... 32Fx4 versions of the same --- */

static
IRAtom* binary32Fx4_w_rm ( MCEnv* mce, IRAtom* vRM,
                                       IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* t1 = binary32Fx4(mce, vatomX, vatomY);
   // PCast the RM, and widen it to 128 bits
   IRAtom* t2 = mkPCastTo(mce, Ity_V128, vRM);
   // Roll it into the result
   t1 = mkUifUV128(mce, t1, t2);
   return t1;
}

/* --- ... and ... 64Fx4 versions of the same --- */

static
IRAtom* binary64Fx4_w_rm ( MCEnv* mce, IRAtom* vRM,
                                       IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* t1 = binary64Fx4(mce, vatomX, vatomY);
   // PCast the RM, and widen it to 256 bits
   IRAtom* t2 = mkPCastTo(mce, Ity_V256, vRM);
   // Roll it into the result
   t1 = mkUifUV256(mce, t1, t2);
   return t1;
}

/* --- ... and ... 32Fx8 versions of the same --- */

static
IRAtom* binary32Fx8_w_rm ( MCEnv* mce, IRAtom* vRM,
                                       IRAtom* vatomX, IRAtom* vatomY )
{
   IRAtom* t1 = binary32Fx8(mce, vatomX, vatomY);
   // PCast the RM, and widen it to 256 bits
   IRAtom* t2 = mkPCastTo(mce, Ity_V256, vRM);
   // Roll it into the result
   t1 = mkUifUV256(mce, t1, t2);
   return t1;
}


/* --- --- Vector saturated narrowing --- --- */

/* We used to do something very clever here, but on closer inspection
   (2011-Jun-15), and in particular bug #279698, it turns out to be
   wrong.  Part of the problem came from the fact that for a long
   time, the IR primops to do with saturated narrowing were
   underspecified and managed to confuse multiple cases which needed
   to be separate: the op names had a signedness qualifier, but in
   fact the source and destination signednesses needed to be specified
   independently, so the op names really need two independent
   signedness specifiers.

   As of 2011-Jun-15 (ish) the underspecification was sorted out
   properly.  The incorrect instrumentation remained, though.  That
   has now (2011-Oct-22) been fixed.

   What we now do is simple:

   Let the original narrowing op be QNarrowBinXtoYxZ, where Z is a
   number of lanes, X is the source lane width and signedness, and Y
   is the destination lane width and signedness.  In all cases the
   destination lane width is half the source lane width, so the names
   have a bit of redundancy, but are at least easy to read.

   For example, Iop_QNarrowBin32Sto16Ux8 narrows 8 lanes of signed 32s
   to unsigned 16s.

   Let Vanilla(OP) be a function that takes OP, one of these
   saturating narrowing ops, and produces the same "shaped" narrowing
   op which is not saturating, but merely dumps the most significant
   bits.  "same shape" means that the lane numbers and widths are the
   same as with OP.

   For example, Vanilla(Iop_QNarrowBin32Sto16Ux8) 
                  = Iop_NarrowBin32to16x8,
   that is, narrow 8 lanes of 32 bits to 8 lanes of 16 bits, by
   dumping the top half of each lane.

   So, with that in place, the scheme is simple, and it is simple to
   pessimise each lane individually and then apply Vanilla(OP) so as
   to get the result in the right "shape".  If the original OP is
   QNarrowBinXtoYxZ then we produce

   Vanilla(OP)( PCast-X-to-X-x-Z(vatom1), PCast-X-to-X-x-Z(vatom2) )

   or for the case when OP is unary (Iop_QNarrowUn*)

   Vanilla(OP)( PCast-X-to-X-x-Z(vatom) )
*/
static
IROp vanillaNarrowingOpOfShape ( IROp qnarrowOp )
{
   switch (qnarrowOp) {
      /* Binary: (128, 128) -> 128 */
      case Iop_QNarrowBin16Sto8Ux16:
      case Iop_QNarrowBin16Sto8Sx16:
      case Iop_QNarrowBin16Uto8Ux16:
      case Iop_QNarrowBin64Sto32Sx4:
      case Iop_QNarrowBin64Uto32Ux4:
         return Iop_NarrowBin16to8x16;
      case Iop_QNarrowBin32Sto16Ux8:
      case Iop_QNarrowBin32Sto16Sx8:
      case Iop_QNarrowBin32Uto16Ux8:
         return Iop_NarrowBin32to16x8;
      /* Binary: (64, 64) -> 64 */
      case Iop_QNarrowBin32Sto16Sx4:
         return Iop_NarrowBin32to16x4;
      case Iop_QNarrowBin16Sto8Ux8:
      case Iop_QNarrowBin16Sto8Sx8:
         return Iop_NarrowBin16to8x8;
      /* Unary: 128 -> 64 */
      case Iop_QNarrowUn64Uto32Ux2:
      case Iop_QNarrowUn64Sto32Sx2:
      case Iop_QNarrowUn64Sto32Ux2:
         return Iop_NarrowUn64to32x2;
      case Iop_QNarrowUn32Uto16Ux4:
      case Iop_QNarrowUn32Sto16Sx4:
      case Iop_QNarrowUn32Sto16Ux4:
         return Iop_NarrowUn32to16x4;
      case Iop_QNarrowUn16Uto8Ux8:
      case Iop_QNarrowUn16Sto8Sx8:
      case Iop_QNarrowUn16Sto8Ux8:
         return Iop_NarrowUn16to8x8;
      default: 
         ppIROp(qnarrowOp);
         VG_(tool_panic)("vanillaNarrowOpOfShape");
   }
}

static
IRAtom* vectorNarrowBinV128 ( MCEnv* mce, IROp narrow_op, 
                              IRAtom* vatom1, IRAtom* vatom2)
{
   IRAtom *at1, *at2, *at3;
   IRAtom* (*pcast)( MCEnv*, IRAtom* );
   switch (narrow_op) {
      case Iop_QNarrowBin64Sto32Sx4: pcast = mkPCast32x4; break;
      case Iop_QNarrowBin64Uto32Ux4: pcast = mkPCast32x4; break;
      case Iop_QNarrowBin32Sto16Sx8: pcast = mkPCast32x4; break;
      case Iop_QNarrowBin32Uto16Ux8: pcast = mkPCast32x4; break;
      case Iop_QNarrowBin32Sto16Ux8: pcast = mkPCast32x4; break;
      case Iop_QNarrowBin16Sto8Sx16: pcast = mkPCast16x8; break;
      case Iop_QNarrowBin16Uto8Ux16: pcast = mkPCast16x8; break;
      case Iop_QNarrowBin16Sto8Ux16: pcast = mkPCast16x8; break;
      default: VG_(tool_panic)("vectorNarrowBinV128");
   }
   IROp vanilla_narrow = vanillaNarrowingOpOfShape(narrow_op);
   tl_assert(isShadowAtom(mce,vatom1));
   tl_assert(isShadowAtom(mce,vatom2));
   at1 = assignNew('V', mce, Ity_V128, pcast(mce, vatom1));
   at2 = assignNew('V', mce, Ity_V128, pcast(mce, vatom2));
   at3 = assignNew('V', mce, Ity_V128, binop(vanilla_narrow, at1, at2));
   return at3;
}

static
IRAtom* vectorNarrowBin64 ( MCEnv* mce, IROp narrow_op, 
                            IRAtom* vatom1, IRAtom* vatom2)
{
   IRAtom *at1, *at2, *at3;
   IRAtom* (*pcast)( MCEnv*, IRAtom* );
   switch (narrow_op) {
      case Iop_QNarrowBin32Sto16Sx4: pcast = mkPCast32x2; break;
      case Iop_QNarrowBin16Sto8Sx8:  pcast = mkPCast16x4; break;
      case Iop_QNarrowBin16Sto8Ux8:  pcast = mkPCast16x4; break;
      default: VG_(tool_panic)("vectorNarrowBin64");
   }
   IROp vanilla_narrow = vanillaNarrowingOpOfShape(narrow_op);
   tl_assert(isShadowAtom(mce,vatom1));
   tl_assert(isShadowAtom(mce,vatom2));
   at1 = assignNew('V', mce, Ity_I64, pcast(mce, vatom1));
   at2 = assignNew('V', mce, Ity_I64, pcast(mce, vatom2));
   at3 = assignNew('V', mce, Ity_I64, binop(vanilla_narrow, at1, at2));
   return at3;
}

static
IRAtom* vectorNarrowUnV128 ( MCEnv* mce, IROp narrow_op,
                             IRAtom* vatom1)
{
   IRAtom *at1, *at2;
   IRAtom* (*pcast)( MCEnv*, IRAtom* );
   tl_assert(isShadowAtom(mce,vatom1));
   /* For vanilla narrowing (non-saturating), we can just apply
      the op directly to the V bits. */
   switch (narrow_op) {
      case Iop_NarrowUn16to8x8:
      case Iop_NarrowUn32to16x4:
      case Iop_NarrowUn64to32x2:
         at1 = assignNew('V', mce, Ity_I64, unop(narrow_op, vatom1));
         return at1;
      default:
         break; /* Do Plan B */
   }
   /* Plan B: for ops that involve a saturation operation on the args,
      we must PCast before the vanilla narrow. */
   switch (narrow_op) {
      case Iop_QNarrowUn16Sto8Sx8:  pcast = mkPCast16x8; break;
      case Iop_QNarrowUn16Sto8Ux8:  pcast = mkPCast16x8; break;
      case Iop_QNarrowUn16Uto8Ux8:  pcast = mkPCast16x8; break;
      case Iop_QNarrowUn32Sto16Sx4: pcast = mkPCast32x4; break;
      case Iop_QNarrowUn32Sto16Ux4: pcast = mkPCast32x4; break;
      case Iop_QNarrowUn32Uto16Ux4: pcast = mkPCast32x4; break;
      case Iop_QNarrowUn64Sto32Sx2: pcast = mkPCast64x2; break;
      case Iop_QNarrowUn64Sto32Ux2: pcast = mkPCast64x2; break;
      case Iop_QNarrowUn64Uto32Ux2: pcast = mkPCast64x2; break;
      default: VG_(tool_panic)("vectorNarrowUnV128");
   }
   IROp vanilla_narrow = vanillaNarrowingOpOfShape(narrow_op);
   at1 = assignNew('V', mce, Ity_V128, pcast(mce, vatom1));
   at2 = assignNew('V', mce, Ity_I64, unop(vanilla_narrow, at1));
   return at2;
}

static
IRAtom* vectorWidenI64 ( MCEnv* mce, IROp longen_op,
                         IRAtom* vatom1)
{
   IRAtom *at1, *at2;
   IRAtom* (*pcast)( MCEnv*, IRAtom* );
   switch (longen_op) {
      case Iop_Widen8Uto16x8:  pcast = mkPCast16x8; break;
      case Iop_Widen8Sto16x8:  pcast = mkPCast16x8; break;
      case Iop_Widen16Uto32x4: pcast = mkPCast32x4; break;
      case Iop_Widen16Sto32x4: pcast = mkPCast32x4; break;
      case Iop_Widen32Uto64x2: pcast = mkPCast64x2; break;
      case Iop_Widen32Sto64x2: pcast = mkPCast64x2; break;
      default: VG_(tool_panic)("vectorWidenI64");
   }
   tl_assert(isShadowAtom(mce,vatom1));
   at1 = assignNew('V', mce, Ity_V128, unop(longen_op, vatom1));
   at2 = assignNew('V', mce, Ity_V128, pcast(mce, at1));
   return at2;
}


/* --- --- Vector integer arithmetic --- --- */

/* Simple ... UifU the args and per-lane pessimise the results. */

/* --- V256-bit versions --- */

static
IRAtom* binary8Ix32 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifUV256(mce, vatom1, vatom2);
   at = mkPCast8x32(mce, at);
   return at;   
}

static
IRAtom* binary16Ix16 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifUV256(mce, vatom1, vatom2);
   at = mkPCast16x16(mce, at);
   return at;   
}

static
IRAtom* binary32Ix8 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifUV256(mce, vatom1, vatom2);
   at = mkPCast32x8(mce, at);
   return at;   
}

static
IRAtom* binary64Ix4 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifUV256(mce, vatom1, vatom2);
   at = mkPCast64x4(mce, at);
   return at;   
}

/* --- V128-bit versions --- */

static
IRAtom* binary8Ix16 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifUV128(mce, vatom1, vatom2);
   at = mkPCast8x16(mce, at);
   return at;   
}

static
IRAtom* binary16Ix8 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifUV128(mce, vatom1, vatom2);
   at = mkPCast16x8(mce, at);
   return at;   
}

static
IRAtom* binary32Ix4 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifUV128(mce, vatom1, vatom2);
   at = mkPCast32x4(mce, at);
   return at;   
}

static
IRAtom* binary64Ix2 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifUV128(mce, vatom1, vatom2);
   at = mkPCast64x2(mce, at);
   return at;   
}

/* --- 64-bit versions --- */

static
IRAtom* binary8Ix8 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifU64(mce, vatom1, vatom2);
   at = mkPCast8x8(mce, at);
   return at;   
}

static
IRAtom* binary16Ix4 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifU64(mce, vatom1, vatom2);
   at = mkPCast16x4(mce, at);
   return at;   
}

static
IRAtom* binary32Ix2 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifU64(mce, vatom1, vatom2);
   at = mkPCast32x2(mce, at);
   return at;   
}

static
IRAtom* binary64Ix1 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifU64(mce, vatom1, vatom2);
   at = mkPCastTo(mce, Ity_I64, at);
   return at;
}

/* --- 32-bit versions --- */

static
IRAtom* binary8Ix4 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifU32(mce, vatom1, vatom2);
   at = mkPCast8x4(mce, at);
   return at;   
}

static
IRAtom* binary16Ix2 ( MCEnv* mce, IRAtom* vatom1, IRAtom* vatom2 )
{
   IRAtom* at;
   at = mkUifU32(mce, vatom1, vatom2);
   at = mkPCast16x2(mce, at);
   return at;   
}


/*------------------------------------------------------------*/
/*--- Generate shadow values from all kinds of IRExprs.    ---*/
/*------------------------------------------------------------*/

static 
IRAtom* expr2vbits_Qop ( MCEnv* mce,
                         IROp op,
                         IRAtom* atom1, IRAtom* atom2, 
                         IRAtom* atom3, IRAtom* atom4 )
{
   IRAtom* vatom1 = expr2vbits( mce, atom1 );
   IRAtom* vatom2 = expr2vbits( mce, atom2 );
   IRAtom* vatom3 = expr2vbits( mce, atom3 );
   IRAtom* vatom4 = expr2vbits( mce, atom4 );

   tl_assert(isOriginalAtom(mce,atom1));
   tl_assert(isOriginalAtom(mce,atom2));
   tl_assert(isOriginalAtom(mce,atom3));
   tl_assert(isOriginalAtom(mce,atom4));
   tl_assert(isShadowAtom(mce,vatom1));
   tl_assert(isShadowAtom(mce,vatom2));
   tl_assert(isShadowAtom(mce,vatom3));
   tl_assert(isShadowAtom(mce,vatom4));
   tl_assert(sameKindedAtoms(atom1,vatom1));
   tl_assert(sameKindedAtoms(atom2,vatom2));
   tl_assert(sameKindedAtoms(atom3,vatom3));
   tl_assert(sameKindedAtoms(atom4,vatom4));
   switch (op) {
      case Iop_MAddF64:
      case Iop_MAddF64r32:
      case Iop_MSubF64:
      case Iop_MSubF64r32:
         /* I32(rm) x F64 x F64 x F64 -> F64 */
         return mkLazy4(mce, Ity_I64, vatom1, vatom2, vatom3, vatom4);

      case Iop_MAddF32:
      case Iop_MSubF32:
         /* I32(rm) x F32 x F32 x F32 -> F32 */
         return mkLazy4(mce, Ity_I32, vatom1, vatom2, vatom3, vatom4);

      /* V256-bit data-steering */
      case Iop_64x4toV256:
         return assignNew('V', mce, Ity_V256,
                          IRExpr_Qop(op, vatom1, vatom2, vatom3, vatom4));

      default:
         ppIROp(op);
         VG_(tool_panic)("memcheck:expr2vbits_Qop");
   }
}


static 
IRAtom* expr2vbits_Triop ( MCEnv* mce,
                           IROp op,
                           IRAtom* atom1, IRAtom* atom2, IRAtom* atom3 )
{
   IRAtom* vatom1 = expr2vbits( mce, atom1 );
   IRAtom* vatom2 = expr2vbits( mce, atom2 );
   IRAtom* vatom3 = expr2vbits( mce, atom3 );

   tl_assert(isOriginalAtom(mce,atom1));
   tl_assert(isOriginalAtom(mce,atom2));
   tl_assert(isOriginalAtom(mce,atom3));
   tl_assert(isShadowAtom(mce,vatom1));
   tl_assert(isShadowAtom(mce,vatom2));
   tl_assert(isShadowAtom(mce,vatom3));
   tl_assert(sameKindedAtoms(atom1,vatom1));
   tl_assert(sameKindedAtoms(atom2,vatom2));
   tl_assert(sameKindedAtoms(atom3,vatom3));
   switch (op) {
      case Iop_AddF128:
      case Iop_AddD128:
      case Iop_SubF128:
      case Iop_SubD128:
      case Iop_MulF128:
      case Iop_MulD128:
      case Iop_DivF128:
      case Iop_DivD128:
      case Iop_QuantizeD128:
         /* I32(rm) x F128/D128 x F128/D128 -> F128/D128 */
         return mkLazy3(mce, Ity_I128, vatom1, vatom2, vatom3);
      case Iop_AddF64:
      case Iop_AddD64:
      case Iop_AddF64r32:
      case Iop_SubF64:
      case Iop_SubD64:
      case Iop_SubF64r32:
      case Iop_MulF64:
      case Iop_MulD64:
      case Iop_MulF64r32:
      case Iop_DivF64:
      case Iop_DivD64:
      case Iop_DivF64r32:
      case Iop_ScaleF64:
      case Iop_Yl2xF64:
      case Iop_Yl2xp1F64:
      case Iop_AtanF64:
      case Iop_PRemF64:
      case Iop_PRem1F64:
      case Iop_QuantizeD64:
         /* I32(rm) x F64/D64 x F64/D64 -> F64/D64 */
         return mkLazy3(mce, Ity_I64, vatom1, vatom2, vatom3);
      case Iop_PRemC3210F64:
      case Iop_PRem1C3210F64:
         /* I32(rm) x F64 x F64 -> I32 */
         return mkLazy3(mce, Ity_I32, vatom1, vatom2, vatom3);
      case Iop_AddF32:
      case Iop_SubF32:
      case Iop_MulF32:
      case Iop_DivF32:
         /* I32(rm) x F32 x F32 -> I32 */
         return mkLazy3(mce, Ity_I32, vatom1, vatom2, vatom3);
      case Iop_SignificanceRoundD64:
         /* IRRoundingMode(I32) x I8 x D64 -> D64 */
         return mkLazy3(mce, Ity_I64, vatom1, vatom2, vatom3);
      case Iop_SignificanceRoundD128:
         /* IRRoundingMode(I32) x I8 x D128 -> D128 */
         return mkLazy3(mce, Ity_I128, vatom1, vatom2, vatom3);
      case Iop_ExtractV128:
         complainIfUndefined(mce, atom3, NULL);
         return assignNew('V', mce, Ity_V128, triop(op, vatom1, vatom2, atom3));
      case Iop_Extract64:
         complainIfUndefined(mce, atom3, NULL);
         return assignNew('V', mce, Ity_I64, triop(op, vatom1, vatom2, atom3));
      case Iop_SetElem8x8:
      case Iop_SetElem16x4:
      case Iop_SetElem32x2:
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_I64, triop(op, vatom1, atom2, vatom3));
      /* BCDIops */
      case Iop_BCDAdd:
      case Iop_BCDSub:
         complainIfUndefined(mce, atom3, NULL);
         return assignNew('V', mce, Ity_V128, triop(op, vatom1, vatom2, atom3));

      /* Vector FP with rounding mode as the first arg */
      case Iop_Add64Fx2:
      case Iop_Sub64Fx2:
      case Iop_Mul64Fx2:
      case Iop_Div64Fx2:
         return binary64Fx2_w_rm(mce, vatom1, vatom2, vatom3);

      case Iop_Add32Fx4:
      case Iop_Sub32Fx4:
      case Iop_Mul32Fx4:
      case Iop_Div32Fx4:
        return binary32Fx4_w_rm(mce, vatom1, vatom2, vatom3);

      case Iop_Add64Fx4:
      case Iop_Sub64Fx4:
      case Iop_Mul64Fx4:
      case Iop_Div64Fx4:
         return binary64Fx4_w_rm(mce, vatom1, vatom2, vatom3);

      case Iop_Add32Fx8:
      case Iop_Sub32Fx8:
      case Iop_Mul32Fx8:
      case Iop_Div32Fx8:
         return binary32Fx8_w_rm(mce, vatom1, vatom2, vatom3);

      default:
         ppIROp(op);
         VG_(tool_panic)("memcheck:expr2vbits_Triop");
   }
}


static 
IRAtom* expr2vbits_Binop ( MCEnv* mce,
                           IROp op,
                           IRAtom* atom1, IRAtom* atom2 )
{
   IRType  and_or_ty;
   IRAtom* (*uifu)    (MCEnv*, IRAtom*, IRAtom*);
   IRAtom* (*difd)    (MCEnv*, IRAtom*, IRAtom*);
   IRAtom* (*improve) (MCEnv*, IRAtom*, IRAtom*);

   IRAtom* vatom1 = expr2vbits( mce, atom1 );
   IRAtom* vatom2 = expr2vbits( mce, atom2 );

   tl_assert(isOriginalAtom(mce,atom1));
   tl_assert(isOriginalAtom(mce,atom2));
   tl_assert(isShadowAtom(mce,vatom1));
   tl_assert(isShadowAtom(mce,vatom2));
   tl_assert(sameKindedAtoms(atom1,vatom1));
   tl_assert(sameKindedAtoms(atom2,vatom2));
   switch (op) {

      /* 32-bit SIMD */

      case Iop_Add16x2:
      case Iop_HAdd16Ux2:
      case Iop_HAdd16Sx2:
      case Iop_Sub16x2:
      case Iop_HSub16Ux2:
      case Iop_HSub16Sx2:
      case Iop_QAdd16Sx2:
      case Iop_QSub16Sx2:
      case Iop_QSub16Ux2:
      case Iop_QAdd16Ux2:
         return binary16Ix2(mce, vatom1, vatom2);

      case Iop_Add8x4:
      case Iop_HAdd8Ux4:
      case Iop_HAdd8Sx4:
      case Iop_Sub8x4:
      case Iop_HSub8Ux4:
      case Iop_HSub8Sx4:
      case Iop_QSub8Ux4:
      case Iop_QAdd8Ux4:
      case Iop_QSub8Sx4:
      case Iop_QAdd8Sx4:
         return binary8Ix4(mce, vatom1, vatom2);

      /* 64-bit SIMD */

      case Iop_ShrN8x8:
      case Iop_ShrN16x4:
      case Iop_ShrN32x2:
      case Iop_SarN8x8:
      case Iop_SarN16x4:
      case Iop_SarN32x2:
      case Iop_ShlN16x4:
      case Iop_ShlN32x2:
      case Iop_ShlN8x8:
         /* Same scheme as with all other shifts. */
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_I64, binop(op, vatom1, atom2));

      case Iop_QNarrowBin32Sto16Sx4:
      case Iop_QNarrowBin16Sto8Sx8:
      case Iop_QNarrowBin16Sto8Ux8:
         return vectorNarrowBin64(mce, op, vatom1, vatom2);

      case Iop_Min8Ux8:
      case Iop_Min8Sx8:
      case Iop_Max8Ux8:
      case Iop_Max8Sx8:
      case Iop_Avg8Ux8:
      case Iop_QSub8Sx8:
      case Iop_QSub8Ux8:
      case Iop_Sub8x8:
      case Iop_CmpGT8Sx8:
      case Iop_CmpGT8Ux8:
      case Iop_CmpEQ8x8:
      case Iop_QAdd8Sx8:
      case Iop_QAdd8Ux8:
      case Iop_QSal8x8:
      case Iop_QShl8x8:
      case Iop_Add8x8:
      case Iop_Mul8x8:
      case Iop_PolynomialMul8x8:
         return binary8Ix8(mce, vatom1, vatom2);

      case Iop_Min16Sx4:
      case Iop_Min16Ux4:
      case Iop_Max16Sx4:
      case Iop_Max16Ux4:
      case Iop_Avg16Ux4:
      case Iop_QSub16Ux4:
      case Iop_QSub16Sx4:
      case Iop_Sub16x4:
      case Iop_Mul16x4:
      case Iop_MulHi16Sx4:
      case Iop_MulHi16Ux4:
      case Iop_CmpGT16Sx4:
      case Iop_CmpGT16Ux4:
      case Iop_CmpEQ16x4:
      case Iop_QAdd16Sx4:
      case Iop_QAdd16Ux4:
      case Iop_QSal16x4:
      case Iop_QShl16x4:
      case Iop_Add16x4:
      case Iop_QDMulHi16Sx4:
      case Iop_QRDMulHi16Sx4:
         return binary16Ix4(mce, vatom1, vatom2);

      case Iop_Sub32x2:
      case Iop_Mul32x2:
      case Iop_Max32Sx2:
      case Iop_Max32Ux2:
      case Iop_Min32Sx2:
      case Iop_Min32Ux2:
      case Iop_CmpGT32Sx2:
      case Iop_CmpGT32Ux2:
      case Iop_CmpEQ32x2:
      case Iop_Add32x2:
      case Iop_QAdd32Ux2:
      case Iop_QAdd32Sx2:
      case Iop_QSub32Ux2:
      case Iop_QSub32Sx2:
      case Iop_QSal32x2:
      case Iop_QShl32x2:
      case Iop_QDMulHi32Sx2:
      case Iop_QRDMulHi32Sx2:
         return binary32Ix2(mce, vatom1, vatom2);

      case Iop_QSub64Ux1:
      case Iop_QSub64Sx1:
      case Iop_QAdd64Ux1:
      case Iop_QAdd64Sx1:
      case Iop_QSal64x1:
      case Iop_QShl64x1:
      case Iop_Sal64x1:
         return binary64Ix1(mce, vatom1, vatom2);

      case Iop_QShlN8Sx8:
      case Iop_QShlN8x8:
      case Iop_QSalN8x8:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast8x8(mce, vatom1);

      case Iop_QShlN16Sx4:
      case Iop_QShlN16x4:
      case Iop_QSalN16x4:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast16x4(mce, vatom1);

      case Iop_QShlN32Sx2:
      case Iop_QShlN32x2:
      case Iop_QSalN32x2:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast32x2(mce, vatom1);

      case Iop_QShlN64Sx1:
      case Iop_QShlN64x1:
      case Iop_QSalN64x1:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast32x2(mce, vatom1);

      case Iop_PwMax32Sx2:
      case Iop_PwMax32Ux2:
      case Iop_PwMin32Sx2:
      case Iop_PwMin32Ux2:
      case Iop_PwMax32Fx2:
      case Iop_PwMin32Fx2:
         return assignNew('V', mce, Ity_I64,
                          binop(Iop_PwMax32Ux2, 
                                mkPCast32x2(mce, vatom1),
                                mkPCast32x2(mce, vatom2)));

      case Iop_PwMax16Sx4:
      case Iop_PwMax16Ux4:
      case Iop_PwMin16Sx4:
      case Iop_PwMin16Ux4:
         return assignNew('V', mce, Ity_I64,
                          binop(Iop_PwMax16Ux4,
                                mkPCast16x4(mce, vatom1),
                                mkPCast16x4(mce, vatom2)));

      case Iop_PwMax8Sx8:
      case Iop_PwMax8Ux8:
      case Iop_PwMin8Sx8:
      case Iop_PwMin8Ux8:
         return assignNew('V', mce, Ity_I64,
                          binop(Iop_PwMax8Ux8,
                                mkPCast8x8(mce, vatom1),
                                mkPCast8x8(mce, vatom2)));

      case Iop_PwAdd32x2:
      case Iop_PwAdd32Fx2:
         return mkPCast32x2(mce,
               assignNew('V', mce, Ity_I64,
                         binop(Iop_PwAdd32x2,
                               mkPCast32x2(mce, vatom1),
                               mkPCast32x2(mce, vatom2))));

      case Iop_PwAdd16x4:
         return mkPCast16x4(mce,
               assignNew('V', mce, Ity_I64,
                         binop(op, mkPCast16x4(mce, vatom1),
                                   mkPCast16x4(mce, vatom2))));

      case Iop_PwAdd8x8:
         return mkPCast8x8(mce,
               assignNew('V', mce, Ity_I64,
                         binop(op, mkPCast8x8(mce, vatom1),
                                   mkPCast8x8(mce, vatom2))));

      case Iop_Shl8x8:
      case Iop_Shr8x8:
      case Iop_Sar8x8:
      case Iop_Sal8x8:
         return mkUifU64(mce,
                   assignNew('V', mce, Ity_I64, binop(op, vatom1, atom2)),
                   mkPCast8x8(mce,vatom2)
                );

      case Iop_Shl16x4:
      case Iop_Shr16x4:
      case Iop_Sar16x4:
      case Iop_Sal16x4:
         return mkUifU64(mce,
                   assignNew('V', mce, Ity_I64, binop(op, vatom1, atom2)),
                   mkPCast16x4(mce,vatom2)
                );

      case Iop_Shl32x2:
      case Iop_Shr32x2:
      case Iop_Sar32x2:
      case Iop_Sal32x2:
         return mkUifU64(mce,
                   assignNew('V', mce, Ity_I64, binop(op, vatom1, atom2)),
                   mkPCast32x2(mce,vatom2)
                );

      /* 64-bit data-steering */
      case Iop_InterleaveLO32x2:
      case Iop_InterleaveLO16x4:
      case Iop_InterleaveLO8x8:
      case Iop_InterleaveHI32x2:
      case Iop_InterleaveHI16x4:
      case Iop_InterleaveHI8x8:
      case Iop_CatOddLanes8x8:
      case Iop_CatEvenLanes8x8:
      case Iop_CatOddLanes16x4:
      case Iop_CatEvenLanes16x4:
      case Iop_InterleaveOddLanes8x8:
      case Iop_InterleaveEvenLanes8x8:
      case Iop_InterleaveOddLanes16x4:
      case Iop_InterleaveEvenLanes16x4:
         return assignNew('V', mce, Ity_I64, binop(op, vatom1, vatom2));

      case Iop_GetElem8x8:
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_I8, binop(op, vatom1, atom2));
      case Iop_GetElem16x4:
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_I16, binop(op, vatom1, atom2));
      case Iop_GetElem32x2:
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_I32, binop(op, vatom1, atom2));

      /* Perm8x8: rearrange values in left arg using steering values
        from right arg.  So rearrange the vbits in the same way but
        pessimise wrt steering values. */
      case Iop_Perm8x8:
         return mkUifU64(
                   mce,
                   assignNew('V', mce, Ity_I64, binop(op, vatom1, atom2)),
                   mkPCast8x8(mce, vatom2)
                );

      /* V128-bit SIMD */

      case Iop_ShrN8x16:
      case Iop_ShrN16x8:
      case Iop_ShrN32x4:
      case Iop_ShrN64x2:
      case Iop_SarN8x16:
      case Iop_SarN16x8:
      case Iop_SarN32x4:
      case Iop_SarN64x2:
      case Iop_ShlN8x16:
      case Iop_ShlN16x8:
      case Iop_ShlN32x4:
      case Iop_ShlN64x2:
         /* Same scheme as with all other shifts.  Note: 22 Oct 05:
            this is wrong now, scalar shifts are done properly lazily.
            Vector shifts should be fixed too. */
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_V128, binop(op, vatom1, atom2));

      /* V x V shifts/rotates are done using the standard lazy scheme. */
      case Iop_Shl8x16:
      case Iop_Shr8x16:
      case Iop_Sar8x16:
      case Iop_Sal8x16:
      case Iop_Rol8x16:
         return mkUifUV128(mce,
                   assignNew('V', mce, Ity_V128, binop(op, vatom1, atom2)),
                   mkPCast8x16(mce,vatom2)
                );

      case Iop_Shl16x8:
      case Iop_Shr16x8:
      case Iop_Sar16x8:
      case Iop_Sal16x8:
      case Iop_Rol16x8:
         return mkUifUV128(mce,
                   assignNew('V', mce, Ity_V128, binop(op, vatom1, atom2)),
                   mkPCast16x8(mce,vatom2)
                );

      case Iop_Shl32x4:
      case Iop_Shr32x4:
      case Iop_Sar32x4:
      case Iop_Sal32x4:
      case Iop_Rol32x4:
      case Iop_Rol64x2:
         return mkUifUV128(mce,
                   assignNew('V', mce, Ity_V128, binop(op, vatom1, atom2)),
                   mkPCast32x4(mce,vatom2)
                );

      case Iop_Shl64x2:
      case Iop_Shr64x2:
      case Iop_Sar64x2:
      case Iop_Sal64x2:
         return mkUifUV128(mce,
                   assignNew('V', mce, Ity_V128, binop(op, vatom1, atom2)),
                   mkPCast64x2(mce,vatom2)
                );

      case Iop_F32ToFixed32Ux4_RZ:
      case Iop_F32ToFixed32Sx4_RZ:
      case Iop_Fixed32UToF32x4_RN:
      case Iop_Fixed32SToF32x4_RN:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast32x4(mce, vatom1);

      case Iop_F32ToFixed32Ux2_RZ:
      case Iop_F32ToFixed32Sx2_RZ:
      case Iop_Fixed32UToF32x2_RN:
      case Iop_Fixed32SToF32x2_RN:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast32x2(mce, vatom1);

      case Iop_QSub8Ux16:
      case Iop_QSub8Sx16:
      case Iop_Sub8x16:
      case Iop_Min8Ux16:
      case Iop_Min8Sx16:
      case Iop_Max8Ux16:
      case Iop_Max8Sx16:
      case Iop_CmpGT8Sx16:
      case Iop_CmpGT8Ux16:
      case Iop_CmpEQ8x16:
      case Iop_Avg8Ux16:
      case Iop_Avg8Sx16:
      case Iop_QAdd8Ux16:
      case Iop_QAdd8Sx16:
      case Iop_QSal8x16:
      case Iop_QShl8x16:
      case Iop_Add8x16:
      case Iop_Mul8x16:
      case Iop_PolynomialMul8x16:
      case Iop_PolynomialMulAdd8x16:
         return binary8Ix16(mce, vatom1, vatom2);

      case Iop_QSub16Ux8:
      case Iop_QSub16Sx8:
      case Iop_Sub16x8:
      case Iop_Mul16x8:
      case Iop_MulHi16Sx8:
      case Iop_MulHi16Ux8:
      case Iop_Min16Sx8:
      case Iop_Min16Ux8:
      case Iop_Max16Sx8:
      case Iop_Max16Ux8:
      case Iop_CmpGT16Sx8:
      case Iop_CmpGT16Ux8:
      case Iop_CmpEQ16x8:
      case Iop_Avg16Ux8:
      case Iop_Avg16Sx8:
      case Iop_QAdd16Ux8:
      case Iop_QAdd16Sx8:
      case Iop_QSal16x8:
      case Iop_QShl16x8:
      case Iop_Add16x8:
      case Iop_QDMulHi16Sx8:
      case Iop_QRDMulHi16Sx8:
      case Iop_PolynomialMulAdd16x8:
         return binary16Ix8(mce, vatom1, vatom2);

      case Iop_Sub32x4:
      case Iop_CmpGT32Sx4:
      case Iop_CmpGT32Ux4:
      case Iop_CmpEQ32x4:
      case Iop_QAdd32Sx4:
      case Iop_QAdd32Ux4:
      case Iop_QSub32Sx4:
      case Iop_QSub32Ux4:
      case Iop_QSal32x4:
      case Iop_QShl32x4:
      case Iop_Avg32Ux4:
      case Iop_Avg32Sx4:
      case Iop_Add32x4:
      case Iop_Max32Ux4:
      case Iop_Max32Sx4:
      case Iop_Min32Ux4:
      case Iop_Min32Sx4:
      case Iop_Mul32x4:
      case Iop_QDMulHi32Sx4:
      case Iop_QRDMulHi32Sx4:
      case Iop_PolynomialMulAdd32x4:
         return binary32Ix4(mce, vatom1, vatom2);

      case Iop_Sub64x2:
      case Iop_Add64x2:
      case Iop_Max64Sx2:
      case Iop_Max64Ux2:
      case Iop_Min64Sx2:
      case Iop_Min64Ux2:
      case Iop_CmpEQ64x2:
      case Iop_CmpGT64Sx2:
      case Iop_CmpGT64Ux2:
      case Iop_QSal64x2:
      case Iop_QShl64x2:
      case Iop_QAdd64Ux2:
      case Iop_QAdd64Sx2:
      case Iop_QSub64Ux2:
      case Iop_QSub64Sx2:
      case Iop_PolynomialMulAdd64x2:
      case Iop_CipherV128:
      case Iop_CipherLV128:
      case Iop_NCipherV128:
      case Iop_NCipherLV128:
        return binary64Ix2(mce, vatom1, vatom2);

      case Iop_QNarrowBin64Sto32Sx4:
      case Iop_QNarrowBin64Uto32Ux4:
      case Iop_QNarrowBin32Sto16Sx8:
      case Iop_QNarrowBin32Uto16Ux8:
      case Iop_QNarrowBin32Sto16Ux8:
      case Iop_QNarrowBin16Sto8Sx16:
      case Iop_QNarrowBin16Uto8Ux16:
      case Iop_QNarrowBin16Sto8Ux16:
         return vectorNarrowBinV128(mce, op, vatom1, vatom2);

      case Iop_Min64Fx2:
      case Iop_Max64Fx2:
      case Iop_CmpLT64Fx2:
      case Iop_CmpLE64Fx2:
      case Iop_CmpEQ64Fx2:
      case Iop_CmpUN64Fx2:
         return binary64Fx2(mce, vatom1, vatom2);      

      case Iop_Sub64F0x2:
      case Iop_Mul64F0x2:
      case Iop_Min64F0x2:
      case Iop_Max64F0x2:
      case Iop_Div64F0x2:
      case Iop_CmpLT64F0x2:
      case Iop_CmpLE64F0x2:
      case Iop_CmpEQ64F0x2:
      case Iop_CmpUN64F0x2:
      case Iop_Add64F0x2:
         return binary64F0x2(mce, vatom1, vatom2);      

      case Iop_Min32Fx4:
      case Iop_Max32Fx4:
      case Iop_CmpLT32Fx4:
      case Iop_CmpLE32Fx4:
      case Iop_CmpEQ32Fx4:
      case Iop_CmpUN32Fx4:
      case Iop_CmpGT32Fx4:
      case Iop_CmpGE32Fx4:
      case Iop_Recps32Fx4:
      case Iop_Rsqrts32Fx4:
         return binary32Fx4(mce, vatom1, vatom2);      

      case Iop_Sub32Fx2:
      case Iop_Mul32Fx2:
      case Iop_Min32Fx2:
      case Iop_Max32Fx2:
      case Iop_CmpEQ32Fx2:
      case Iop_CmpGT32Fx2:
      case Iop_CmpGE32Fx2:
      case Iop_Add32Fx2:
      case Iop_Recps32Fx2:
      case Iop_Rsqrts32Fx2:
         return binary32Fx2(mce, vatom1, vatom2);      

      case Iop_Sub32F0x4:
      case Iop_Mul32F0x4:
      case Iop_Min32F0x4:
      case Iop_Max32F0x4:
      case Iop_Div32F0x4:
      case Iop_CmpLT32F0x4:
      case Iop_CmpLE32F0x4:
      case Iop_CmpEQ32F0x4:
      case Iop_CmpUN32F0x4:
      case Iop_Add32F0x4:
         return binary32F0x4(mce, vatom1, vatom2);      

      case Iop_QShlN8Sx16:
      case Iop_QShlN8x16:
      case Iop_QSalN8x16:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast8x16(mce, vatom1);

      case Iop_QShlN16Sx8:
      case Iop_QShlN16x8:
      case Iop_QSalN16x8:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast16x8(mce, vatom1);

      case Iop_QShlN32Sx4:
      case Iop_QShlN32x4:
      case Iop_QSalN32x4:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast32x4(mce, vatom1);

      case Iop_QShlN64Sx2:
      case Iop_QShlN64x2:
      case Iop_QSalN64x2:
         complainIfUndefined(mce, atom2, NULL);
         return mkPCast32x4(mce, vatom1);

      case Iop_Mull32Sx2:
      case Iop_Mull32Ux2:
      case Iop_QDMulLong32Sx2:
         return vectorWidenI64(mce, Iop_Widen32Sto64x2,
                                    mkUifU64(mce, vatom1, vatom2));

      case Iop_Mull16Sx4:
      case Iop_Mull16Ux4:
      case Iop_QDMulLong16Sx4:
         return vectorWidenI64(mce, Iop_Widen16Sto32x4,
                                    mkUifU64(mce, vatom1, vatom2));

      case Iop_Mull8Sx8:
      case Iop_Mull8Ux8:
      case Iop_PolynomialMull8x8:
         return vectorWidenI64(mce, Iop_Widen8Sto16x8,
                                    mkUifU64(mce, vatom1, vatom2));

      case Iop_PwAdd32x4:
         return mkPCast32x4(mce,
               assignNew('V', mce, Ity_V128, binop(op, mkPCast32x4(mce, vatom1),
                     mkPCast32x4(mce, vatom2))));

      case Iop_PwAdd16x8:
         return mkPCast16x8(mce,
               assignNew('V', mce, Ity_V128, binop(op, mkPCast16x8(mce, vatom1),
                     mkPCast16x8(mce, vatom2))));

      case Iop_PwAdd8x16:
         return mkPCast8x16(mce,
               assignNew('V', mce, Ity_V128, binop(op, mkPCast8x16(mce, vatom1),
                     mkPCast8x16(mce, vatom2))));

      /* V128-bit data-steering */
      case Iop_SetV128lo32:
      case Iop_SetV128lo64:
      case Iop_64HLtoV128:
      case Iop_InterleaveLO64x2:
      case Iop_InterleaveLO32x4:
      case Iop_InterleaveLO16x8:
      case Iop_InterleaveLO8x16:
      case Iop_InterleaveHI64x2:
      case Iop_InterleaveHI32x4:
      case Iop_InterleaveHI16x8:
      case Iop_InterleaveHI8x16:
      case Iop_CatOddLanes8x16:
      case Iop_CatOddLanes16x8:
      case Iop_CatOddLanes32x4:
      case Iop_CatEvenLanes8x16:
      case Iop_CatEvenLanes16x8:
      case Iop_CatEvenLanes32x4:
      case Iop_InterleaveOddLanes8x16:
      case Iop_InterleaveOddLanes16x8:
      case Iop_InterleaveOddLanes32x4:
      case Iop_InterleaveEvenLanes8x16:
      case Iop_InterleaveEvenLanes16x8:
      case Iop_InterleaveEvenLanes32x4:
         return assignNew('V', mce, Ity_V128, binop(op, vatom1, vatom2));

      case Iop_GetElem8x16:
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_I8, binop(op, vatom1, atom2));
      case Iop_GetElem16x8:
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_I16, binop(op, vatom1, atom2));
      case Iop_GetElem32x4:
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_I32, binop(op, vatom1, atom2));
      case Iop_GetElem64x2:
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_I64, binop(op, vatom1, atom2));

     /* Perm8x16: rearrange values in left arg using steering values
        from right arg.  So rearrange the vbits in the same way but
        pessimise wrt steering values.  Perm32x4 ditto. */
      case Iop_Perm8x16:
         return mkUifUV128(
                   mce,
                   assignNew('V', mce, Ity_V128, binop(op, vatom1, atom2)),
                   mkPCast8x16(mce, vatom2)
                );
      case Iop_Perm32x4:
         return mkUifUV128(
                   mce,
                   assignNew('V', mce, Ity_V128, binop(op, vatom1, atom2)),
                   mkPCast32x4(mce, vatom2)
                );

     /* These two take the lower half of each 16-bit lane, sign/zero
        extend it to 32, and multiply together, producing a 32x4
        result (and implicitly ignoring half the operand bits).  So
        treat it as a bunch of independent 16x8 operations, but then
        do 32-bit shifts left-right to copy the lower half results
        (which are all 0s or all 1s due to PCasting in binary16Ix8)
        into the upper half of each result lane. */
      case Iop_MullEven16Ux8:
      case Iop_MullEven16Sx8: {
         IRAtom* at;
         at = binary16Ix8(mce,vatom1,vatom2);
         at = assignNew('V', mce, Ity_V128, binop(Iop_ShlN32x4, at, mkU8(16)));
         at = assignNew('V', mce, Ity_V128, binop(Iop_SarN32x4, at, mkU8(16)));
	 return at;
      }

      /* Same deal as Iop_MullEven16{S,U}x8 */
      case Iop_MullEven8Ux16:
      case Iop_MullEven8Sx16: {
         IRAtom* at;
         at = binary8Ix16(mce,vatom1,vatom2);
         at = assignNew('V', mce, Ity_V128, binop(Iop_ShlN16x8, at, mkU8(8)));
         at = assignNew('V', mce, Ity_V128, binop(Iop_SarN16x8, at, mkU8(8)));
	 return at;
      }

      /* Same deal as Iop_MullEven16{S,U}x8 */
      case Iop_MullEven32Ux4:
      case Iop_MullEven32Sx4: {
         IRAtom* at;
         at = binary32Ix4(mce,vatom1,vatom2);
         at = assignNew('V', mce, Ity_V128, binop(Iop_ShlN64x2, at, mkU8(32)));
         at = assignNew('V', mce, Ity_V128, binop(Iop_SarN64x2, at, mkU8(32)));
         return at;
      }

      /* narrow 2xV128 into 1xV128, hi half from left arg, in a 2 x
         32x4 -> 16x8 laneage, discarding the upper half of each lane.
         Simply apply same op to the V bits, since this really no more
         than a data steering operation. */
      case Iop_NarrowBin32to16x8: 
      case Iop_NarrowBin16to8x16: 
      case Iop_NarrowBin64to32x4:
         return assignNew('V', mce, Ity_V128, 
                                    binop(op, vatom1, vatom2));

      case Iop_ShrV128:
      case Iop_ShlV128:
         /* Same scheme as with all other shifts.  Note: 10 Nov 05:
            this is wrong now, scalar shifts are done properly lazily.
            Vector shifts should be fixed too. */
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_V128, binop(op, vatom1, atom2));

      /* SHA Iops */
      case Iop_SHA256:
      case Iop_SHA512:
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_V128, binop(op, vatom1, atom2));

      /* I128-bit data-steering */
      case Iop_64HLto128:
         return assignNew('V', mce, Ity_I128, binop(op, vatom1, vatom2));

      /* V256-bit SIMD */

      case Iop_Max64Fx4:
      case Iop_Min64Fx4:
         return binary64Fx4(mce, vatom1, vatom2);

      case Iop_Max32Fx8:
      case Iop_Min32Fx8:
         return binary32Fx8(mce, vatom1, vatom2);

      /* V256-bit data-steering */
      case Iop_V128HLtoV256:
         return assignNew('V', mce, Ity_V256, binop(op, vatom1, vatom2));

      /* Scalar floating point */

      case Iop_F32toI64S:
      case Iop_F32toI64U:
         /* I32(rm) x F32 -> I64 */
         return mkLazy2(mce, Ity_I64, vatom1, vatom2);

      case Iop_I64StoF32:
         /* I32(rm) x I64 -> F32 */
         return mkLazy2(mce, Ity_I32, vatom1, vatom2);

      case Iop_RoundF64toInt:
      case Iop_RoundF64toF32:
      case Iop_F64toI64S:
      case Iop_F64toI64U:
      case Iop_I64StoF64:
      case Iop_I64UtoF64:
      case Iop_SinF64:
      case Iop_CosF64:
      case Iop_TanF64:
      case Iop_2xm1F64:
      case Iop_SqrtF64:
         /* I32(rm) x I64/F64 -> I64/F64 */
         return mkLazy2(mce, Ity_I64, vatom1, vatom2);

      case Iop_ShlD64:
      case Iop_ShrD64:
      case Iop_RoundD64toInt:
         /* I32(rm) x D64 -> D64 */
         return mkLazy2(mce, Ity_I64, vatom1, vatom2);

      case Iop_ShlD128:
      case Iop_ShrD128:
      case Iop_RoundD128toInt:
         /* I32(rm) x D128 -> D128 */
         return mkLazy2(mce, Ity_I128, vatom1, vatom2);

      case Iop_D64toI64S:
      case Iop_D64toI64U:
      case Iop_I64StoD64:
      case Iop_I64UtoD64:
         /* I32(rm) x I64/D64 -> D64/I64 */
         return mkLazy2(mce, Ity_I64, vatom1, vatom2);

      case Iop_F32toD32:
      case Iop_F64toD32:
      case Iop_F128toD32:
      case Iop_D32toF32:
      case Iop_D64toF32:
      case Iop_D128toF32:
         /* I32(rm) x F32/F64/F128/D32/D64/D128 -> D32/F32 */
         return mkLazy2(mce, Ity_I32, vatom1, vatom2);

      case Iop_F32toD64:
      case Iop_F64toD64:
      case Iop_F128toD64:
      case Iop_D32toF64:
      case Iop_D64toF64:
      case Iop_D128toF64:
         /* I32(rm) x F32/F64/F128/D32/D64/D128 -> D64/F64 */
         return mkLazy2(mce, Ity_I64, vatom1, vatom2);

      case Iop_F32toD128:
      case Iop_F64toD128:
      case Iop_F128toD128:
      case Iop_D32toF128:
      case Iop_D64toF128:
      case Iop_D128toF128:
         /* I32(rm) x F32/F64/F128/D32/D64/D128 -> D128/F128 */
         return mkLazy2(mce, Ity_I128, vatom1, vatom2);

      case Iop_RoundF32toInt:
      case Iop_SqrtF32:
         /* I32(rm) x I32/F32 -> I32/F32 */
         return mkLazy2(mce, Ity_I32, vatom1, vatom2);

      case Iop_SqrtF128:
         /* I32(rm) x F128 -> F128 */
         return mkLazy2(mce, Ity_I128, vatom1, vatom2);

      case Iop_I32StoF32:
      case Iop_I32UtoF32:
      case Iop_F32toI32S:
      case Iop_F32toI32U:
         /* First arg is I32 (rounding mode), second is F32/I32 (data). */
         return mkLazy2(mce, Ity_I32, vatom1, vatom2);

      case Iop_F128toI32S: /* IRRoundingMode(I32) x F128 -> signed I32  */
      case Iop_F128toI32U: /* IRRoundingMode(I32) x F128 -> unsigned I32  */
      case Iop_F128toF32:  /* IRRoundingMode(I32) x F128 -> F32         */
      case Iop_D128toI32S: /* IRRoundingMode(I32) x D128 -> signed I32  */
      case Iop_D128toI32U: /* IRRoundingMode(I32) x D128 -> unsigned I32  */
         return mkLazy2(mce, Ity_I32, vatom1, vatom2);

      case Iop_F128toI64S: /* IRRoundingMode(I32) x F128 -> signed I64  */
      case Iop_F128toI64U: /* IRRoundingMode(I32) x F128 -> unsigned I64  */
      case Iop_F128toF64:  /* IRRoundingMode(I32) x F128 -> F64         */
      case Iop_D128toD64:  /* IRRoundingMode(I64) x D128 -> D64 */
      case Iop_D128toI64S: /* IRRoundingMode(I64) x D128 -> signed I64  */
      case Iop_D128toI64U: /* IRRoundingMode(I32) x D128 -> unsigned I64  */
         return mkLazy2(mce, Ity_I64, vatom1, vatom2);

      case Iop_F64HLtoF128:
      case Iop_D64HLtoD128:
         return assignNew('V', mce, Ity_I128,
                          binop(Iop_64HLto128, vatom1, vatom2));

      case Iop_F64toI32U:
      case Iop_F64toI32S:
      case Iop_F64toF32:
      case Iop_I64UtoF32:
      case Iop_D64toI32U:
      case Iop_D64toI32S:
         /* First arg is I32 (rounding mode), second is F64/D64 (data). */
         return mkLazy2(mce, Ity_I32, vatom1, vatom2);

      case Iop_D64toD32:
         /* First arg is I32 (rounding mode), second is D64 (data). */
         return mkLazy2(mce, Ity_I32, vatom1, vatom2);

      case Iop_F64toI16S:
         /* First arg is I32 (rounding mode), second is F64 (data). */
         return mkLazy2(mce, Ity_I16, vatom1, vatom2);

      case Iop_InsertExpD64:
         /*  I64 x I64 -> D64 */
         return mkLazy2(mce, Ity_I64, vatom1, vatom2);

      case Iop_InsertExpD128:
         /*  I64 x I128 -> D128 */
         return mkLazy2(mce, Ity_I128, vatom1, vatom2);

      case Iop_CmpF32:
      case Iop_CmpF64:
      case Iop_CmpF128:
      case Iop_CmpD64:
      case Iop_CmpD128:
      case Iop_CmpExpD64:
      case Iop_CmpExpD128:
         return mkLazy2(mce, Ity_I32, vatom1, vatom2);

      /* non-FP after here */

      case Iop_DivModU64to32:
      case Iop_DivModS64to32:
         return mkLazy2(mce, Ity_I64, vatom1, vatom2);

      case Iop_DivModU128to64:
      case Iop_DivModS128to64:
         return mkLazy2(mce, Ity_I128, vatom1, vatom2);

      case Iop_8HLto16:
         return assignNew('V', mce, Ity_I16, binop(op, vatom1, vatom2));
      case Iop_16HLto32:
         return assignNew('V', mce, Ity_I32, binop(op, vatom1, vatom2));
      case Iop_32HLto64:
         return assignNew('V', mce, Ity_I64, binop(op, vatom1, vatom2));

      case Iop_DivModS64to64:
      case Iop_MullS64:
      case Iop_MullU64: {
         IRAtom* vLo64 = mkLeft64(mce, mkUifU64(mce, vatom1,vatom2));
         IRAtom* vHi64 = mkPCastTo(mce, Ity_I64, vLo64);
         return assignNew('V', mce, Ity_I128,
                          binop(Iop_64HLto128, vHi64, vLo64));
      }

      case Iop_MullS32:
      case Iop_MullU32: {
         IRAtom* vLo32 = mkLeft32(mce, mkUifU32(mce, vatom1,vatom2));
         IRAtom* vHi32 = mkPCastTo(mce, Ity_I32, vLo32);
         return assignNew('V', mce, Ity_I64,
                          binop(Iop_32HLto64, vHi32, vLo32));
      }

      case Iop_MullS16:
      case Iop_MullU16: {
         IRAtom* vLo16 = mkLeft16(mce, mkUifU16(mce, vatom1,vatom2));
         IRAtom* vHi16 = mkPCastTo(mce, Ity_I16, vLo16);
         return assignNew('V', mce, Ity_I32,
                          binop(Iop_16HLto32, vHi16, vLo16));
      }

      case Iop_MullS8:
      case Iop_MullU8: {
         IRAtom* vLo8 = mkLeft8(mce, mkUifU8(mce, vatom1,vatom2));
         IRAtom* vHi8 = mkPCastTo(mce, Ity_I8, vLo8);
         return assignNew('V', mce, Ity_I16, binop(Iop_8HLto16, vHi8, vLo8));
      }

      case Iop_Sad8Ux4: /* maybe we could do better?  ftm, do mkLazy2. */
      case Iop_DivS32:
      case Iop_DivU32:
      case Iop_DivU32E:
      case Iop_DivS32E:
      case Iop_QAdd32S: /* could probably do better */
      case Iop_QSub32S: /* could probably do better */
         return mkLazy2(mce, Ity_I32, vatom1, vatom2);

      case Iop_DivS64:
      case Iop_DivU64:
      case Iop_DivS64E:
      case Iop_DivU64E:
         return mkLazy2(mce, Ity_I64, vatom1, vatom2);

      case Iop_Add32:
         if (mce->bogusLiterals || mce->useLLVMworkarounds)
            return expensiveAddSub(mce,True,Ity_I32, 
                                   vatom1,vatom2, atom1,atom2);
         else
            goto cheap_AddSub32;
      case Iop_Sub32:
         if (mce->bogusLiterals)
            return expensiveAddSub(mce,False,Ity_I32, 
                                   vatom1,vatom2, atom1,atom2);
         else
            goto cheap_AddSub32;

      cheap_AddSub32:
      case Iop_Mul32:
         return mkLeft32(mce, mkUifU32(mce, vatom1,vatom2));

      case Iop_CmpORD32S:
      case Iop_CmpORD32U:
      case Iop_CmpORD64S:
      case Iop_CmpORD64U:
         return doCmpORD(mce, op, vatom1,vatom2, atom1,atom2);

      case Iop_Add64:
         if (mce->bogusLiterals || mce->useLLVMworkarounds)
            return expensiveAddSub(mce,True,Ity_I64, 
                                   vatom1,vatom2, atom1,atom2);
         else
            goto cheap_AddSub64;
      case Iop_Sub64:
         if (mce->bogusLiterals)
            return expensiveAddSub(mce,False,Ity_I64, 
                                   vatom1,vatom2, atom1,atom2);
         else
            goto cheap_AddSub64;

      cheap_AddSub64:
      case Iop_Mul64:
         return mkLeft64(mce, mkUifU64(mce, vatom1,vatom2));

      case Iop_Mul16:
      case Iop_Add16:
      case Iop_Sub16:
         return mkLeft16(mce, mkUifU16(mce, vatom1,vatom2));

      case Iop_Mul8:
      case Iop_Sub8:
      case Iop_Add8:
         return mkLeft8(mce, mkUifU8(mce, vatom1,vatom2));

      case Iop_CmpEQ64: 
      case Iop_CmpNE64:
         if (mce->bogusLiterals)
            goto expensive_cmp64;
         else
            goto cheap_cmp64;

      expensive_cmp64:
      case Iop_ExpCmpNE64:
         return expensiveCmpEQorNE(mce,Ity_I64, vatom1,vatom2, atom1,atom2 );

      cheap_cmp64:
      case Iop_CmpLE64S: case Iop_CmpLE64U: 
      case Iop_CmpLT64U: case Iop_CmpLT64S:
         return mkPCastTo(mce, Ity_I1, mkUifU64(mce, vatom1,vatom2));

      case Iop_CmpEQ32: 
      case Iop_CmpNE32:
         if (mce->bogusLiterals)
            goto expensive_cmp32;
         else
            goto cheap_cmp32;

      expensive_cmp32:
      case Iop_ExpCmpNE32:
         return expensiveCmpEQorNE(mce,Ity_I32, vatom1,vatom2, atom1,atom2 );

      cheap_cmp32:
      case Iop_CmpLE32S: case Iop_CmpLE32U: 
      case Iop_CmpLT32U: case Iop_CmpLT32S:
         return mkPCastTo(mce, Ity_I1, mkUifU32(mce, vatom1,vatom2));

      case Iop_CmpEQ16: case Iop_CmpNE16:
         return mkPCastTo(mce, Ity_I1, mkUifU16(mce, vatom1,vatom2));

      case Iop_ExpCmpNE16:
         return expensiveCmpEQorNE(mce,Ity_I16, vatom1,vatom2, atom1,atom2 );

      case Iop_CmpEQ8: case Iop_CmpNE8:
         return mkPCastTo(mce, Ity_I1, mkUifU8(mce, vatom1,vatom2));

      case Iop_CasCmpEQ8:  case Iop_CasCmpNE8:
      case Iop_CasCmpEQ16: case Iop_CasCmpNE16:
      case Iop_CasCmpEQ32: case Iop_CasCmpNE32:
      case Iop_CasCmpEQ64: case Iop_CasCmpNE64:
         /* Just say these all produce a defined result, regardless
            of their arguments.  See COMMENT_ON_CasCmpEQ in this file. */
         return assignNew('V', mce, Ity_I1, definedOfType(Ity_I1));

      case Iop_Shl64: case Iop_Shr64: case Iop_Sar64:
         return scalarShift( mce, Ity_I64, op, vatom1,vatom2, atom1,atom2 );

      case Iop_Shl32: case Iop_Shr32: case Iop_Sar32:
         return scalarShift( mce, Ity_I32, op, vatom1,vatom2, atom1,atom2 );

      case Iop_Shl16: case Iop_Shr16: case Iop_Sar16:
         return scalarShift( mce, Ity_I16, op, vatom1,vatom2, atom1,atom2 );

      case Iop_Shl8: case Iop_Shr8: case Iop_Sar8:
         return scalarShift( mce, Ity_I8, op, vatom1,vatom2, atom1,atom2 );

      case Iop_AndV256:
         uifu = mkUifUV256; difd = mkDifDV256; 
         and_or_ty = Ity_V256; improve = mkImproveANDV256; goto do_And_Or;
      case Iop_AndV128:
         uifu = mkUifUV128; difd = mkDifDV128; 
         and_or_ty = Ity_V128; improve = mkImproveANDV128; goto do_And_Or;
      case Iop_And64:
         uifu = mkUifU64; difd = mkDifD64; 
         and_or_ty = Ity_I64; improve = mkImproveAND64; goto do_And_Or;
      case Iop_And32:
         uifu = mkUifU32; difd = mkDifD32; 
         and_or_ty = Ity_I32; improve = mkImproveAND32; goto do_And_Or;
      case Iop_And16:
         uifu = mkUifU16; difd = mkDifD16; 
         and_or_ty = Ity_I16; improve = mkImproveAND16; goto do_And_Or;
      case Iop_And8:
         uifu = mkUifU8; difd = mkDifD8; 
         and_or_ty = Ity_I8; improve = mkImproveAND8; goto do_And_Or;

      case Iop_OrV256:
         uifu = mkUifUV256; difd = mkDifDV256; 
         and_or_ty = Ity_V256; improve = mkImproveORV256; goto do_And_Or;
      case Iop_OrV128:
         uifu = mkUifUV128; difd = mkDifDV128; 
         and_or_ty = Ity_V128; improve = mkImproveORV128; goto do_And_Or;
      case Iop_Or64:
         uifu = mkUifU64; difd = mkDifD64; 
         and_or_ty = Ity_I64; improve = mkImproveOR64; goto do_And_Or;
      case Iop_Or32:
         uifu = mkUifU32; difd = mkDifD32; 
         and_or_ty = Ity_I32; improve = mkImproveOR32; goto do_And_Or;
      case Iop_Or16:
         uifu = mkUifU16; difd = mkDifD16; 
         and_or_ty = Ity_I16; improve = mkImproveOR16; goto do_And_Or;
      case Iop_Or8:
         uifu = mkUifU8; difd = mkDifD8; 
         and_or_ty = Ity_I8; improve = mkImproveOR8; goto do_And_Or;

      do_And_Or:
         return
         assignNew(
            'V', mce, 
            and_or_ty,
            difd(mce, uifu(mce, vatom1, vatom2),
                      difd(mce, improve(mce, atom1, vatom1),
                                improve(mce, atom2, vatom2) ) ) );

      case Iop_Xor8:
         return mkUifU8(mce, vatom1, vatom2);
      case Iop_Xor16:
         return mkUifU16(mce, vatom1, vatom2);
      case Iop_Xor32:
         return mkUifU32(mce, vatom1, vatom2);
      case Iop_Xor64:
         return mkUifU64(mce, vatom1, vatom2);
      case Iop_XorV128:
         return mkUifUV128(mce, vatom1, vatom2);
      case Iop_XorV256:
         return mkUifUV256(mce, vatom1, vatom2);

      /* V256-bit SIMD */

      case Iop_ShrN16x16:
      case Iop_ShrN32x8:
      case Iop_ShrN64x4:
      case Iop_SarN16x16:
      case Iop_SarN32x8:
      case Iop_ShlN16x16:
      case Iop_ShlN32x8:
      case Iop_ShlN64x4:
         /* Same scheme as with all other shifts.  Note: 22 Oct 05:
            this is wrong now, scalar shifts are done properly lazily.
            Vector shifts should be fixed too. */
         complainIfUndefined(mce, atom2, NULL);
         return assignNew('V', mce, Ity_V256, binop(op, vatom1, atom2));

      case Iop_QSub8Ux32:
      case Iop_QSub8Sx32:
      case Iop_Sub8x32:
      case Iop_Min8Ux32:
      case Iop_Min8Sx32:
      case Iop_Max8Ux32:
      case Iop_Max8Sx32:
      case Iop_CmpGT8Sx32:
      case Iop_CmpEQ8x32:
      case Iop_Avg8Ux32:
      case Iop_QAdd8Ux32:
      case Iop_QAdd8Sx32:
      case Iop_Add8x32:
         return binary8Ix32(mce, vatom1, vatom2);

      case Iop_QSub16Ux16:
      case Iop_QSub16Sx16:
      case Iop_Sub16x16:
      case Iop_Mul16x16:
      case Iop_MulHi16Sx16:
      case Iop_MulHi16Ux16:
      case Iop_Min16Sx16:
      case Iop_Min16Ux16:
      case Iop_Max16Sx16:
      case Iop_Max16Ux16:
      case Iop_CmpGT16Sx16:
      case Iop_CmpEQ16x16:
      case Iop_Avg16Ux16:
      case Iop_QAdd16Ux16:
      case Iop_QAdd16Sx16:
      case Iop_Add16x16:
         return binary16Ix16(mce, vatom1, vatom2);

      case Iop_Sub32x8:
      case Iop_CmpGT32Sx8:
      case Iop_CmpEQ32x8:
      case Iop_Add32x8:
      case Iop_Max32Ux8:
      case Iop_Max32Sx8:
      case Iop_Min32Ux8:
      case Iop_Min32Sx8:
      case Iop_Mul32x8:
         return binary32Ix8(mce, vatom1, vatom2);

      case Iop_Sub64x4:
      case Iop_Add64x4:
      case Iop_CmpEQ64x4:
      case Iop_CmpGT64Sx4:
         return binary64Ix4(mce, vatom1, vatom2);

     /* Perm32x8: rearrange values in left arg using steering values
        from right arg.  So rearrange the vbits in the same way but
        pessimise wrt steering values. */
      case Iop_Perm32x8:
         return mkUifUV256(
                   mce,
                   assignNew('V', mce, Ity_V256, binop(op, vatom1, atom2)),
                   mkPCast32x8(mce, vatom2)
                );

      default:
         ppIROp(op);
         VG_(tool_panic)("memcheck:expr2vbits_Binop");
   }
}


static 
IRExpr* expr2vbits_Unop ( MCEnv* mce, IROp op, IRAtom* atom )
{
   /* For the widening operations {8,16,32}{U,S}to{16,32,64}, the
      selection of shadow operation implicitly duplicates the logic in
      do_shadow_LoadG and should be kept in sync (in the very unlikely
      event that the interpretation of such widening ops changes in
      future).  See comment in do_shadow_LoadG. */
   IRAtom* vatom = expr2vbits( mce, atom );
   tl_assert(isOriginalAtom(mce,atom));
   switch (op) {

      case Iop_Sqrt64Fx2:
         return unary64Fx2(mce, vatom);

      case Iop_Sqrt64F0x2:
         return unary64F0x2(mce, vatom);

      case Iop_Sqrt32Fx8:
      case Iop_RSqrt32Fx8:
      case Iop_Recip32Fx8:
         return unary32Fx8(mce, vatom);

      case Iop_Sqrt64Fx4:
         return unary64Fx4(mce, vatom);

      case Iop_Sqrt32Fx4:
      case Iop_RSqrt32Fx4:
      case Iop_Recip32Fx4:
      case Iop_I32UtoFx4:
      case Iop_I32StoFx4:
      case Iop_QFtoI32Ux4_RZ:
      case Iop_QFtoI32Sx4_RZ:
      case Iop_RoundF32x4_RM:
      case Iop_RoundF32x4_RP:
      case Iop_RoundF32x4_RN:
      case Iop_RoundF32x4_RZ:
      case Iop_Recip32x4:
      case Iop_Abs32Fx4:
      case Iop_Neg32Fx4:
      case Iop_Rsqrte32Fx4:
         return unary32Fx4(mce, vatom);

      case Iop_I32UtoFx2:
      case Iop_I32StoFx2:
      case Iop_Recip32Fx2:
      case Iop_Recip32x2:
      case Iop_Abs32Fx2:
      case Iop_Neg32Fx2:
      case Iop_Rsqrte32Fx2:
         return unary32Fx2(mce, vatom);

      case Iop_Sqrt32F0x4:
      case Iop_RSqrt32F0x4:
      case Iop_Recip32F0x4:
         return unary32F0x4(mce, vatom);

      case Iop_32UtoV128:
      case Iop_64UtoV128:
      case Iop_Dup8x16:
      case Iop_Dup16x8:
      case Iop_Dup32x4:
      case Iop_Reverse16_8x16:
      case Iop_Reverse32_8x16:
      case Iop_Reverse32_16x8:
      case Iop_Reverse64_8x16:
      case Iop_Reverse64_16x8:
      case Iop_Reverse64_32x4:
      case Iop_V256toV128_1: case Iop_V256toV128_0:
         return assignNew('V', mce, Ity_V128, unop(op, vatom));

      case Iop_F128HItoF64:  /* F128 -> high half of F128 */
      case Iop_D128HItoD64:  /* D128 -> high half of D128 */
         return assignNew('V', mce, Ity_I64, unop(Iop_128HIto64, vatom));
      case Iop_F128LOtoF64:  /* F128 -> low  half of F128 */
      case Iop_D128LOtoD64:  /* D128 -> low  half of D128 */
         return assignNew('V', mce, Ity_I64, unop(Iop_128to64, vatom));

      case Iop_NegF128:
      case Iop_AbsF128:
         return mkPCastTo(mce, Ity_I128, vatom);

      case Iop_I32StoF128: /* signed I32 -> F128 */
      case Iop_I64StoF128: /* signed I64 -> F128 */
      case Iop_I32UtoF128: /* unsigned I32 -> F128 */
      case Iop_I64UtoF128: /* unsigned I64 -> F128 */
      case Iop_F32toF128:  /* F32 -> F128 */
      case Iop_F64toF128:  /* F64 -> F128 */
      case Iop_I32StoD128: /* signed I64 -> D128 */
      case Iop_I64StoD128: /* signed I64 -> D128 */
      case Iop_I32UtoD128: /* unsigned I32 -> D128 */
      case Iop_I64UtoD128: /* unsigned I64 -> D128 */
         return mkPCastTo(mce, Ity_I128, vatom);

      case Iop_F32toF64: 
      case Iop_I32StoF64:
      case Iop_I32UtoF64:
      case Iop_NegF64:
      case Iop_AbsF64:
      case Iop_Est5FRSqrt:
      case Iop_RoundF64toF64_NEAREST:
      case Iop_RoundF64toF64_NegINF:
      case Iop_RoundF64toF64_PosINF:
      case Iop_RoundF64toF64_ZERO:
      case Iop_Clz64:
      case Iop_D32toD64:
      case Iop_I32StoD64:
      case Iop_I32UtoD64:
      case Iop_ExtractExpD64:    /* D64  -> I64 */
      case Iop_ExtractExpD128:   /* D128 -> I64 */
      case Iop_ExtractSigD64:    /* D64  -> I64 */
      case Iop_ExtractSigD128:   /* D128 -> I64 */
      case Iop_DPBtoBCD:
      case Iop_BCDtoDPB:
         return mkPCastTo(mce, Ity_I64, vatom);

      case Iop_D64toD128:
         return mkPCastTo(mce, Ity_I128, vatom);

      case Iop_Clz32:
      case Iop_TruncF64asF32:
      case Iop_NegF32:
      case Iop_AbsF32:
         return mkPCastTo(mce, Ity_I32, vatom);

      case Iop_Ctz32:
      case Iop_Ctz64:
         return expensiveCountTrailingZeroes(mce, op, atom, vatom);

      case Iop_1Uto64:
      case Iop_1Sto64:
      case Iop_8Uto64:
      case Iop_8Sto64:
      case Iop_16Uto64:
      case Iop_16Sto64:
      case Iop_32Sto64:
      case Iop_32Uto64:
      case Iop_V128to64:
      case Iop_V128HIto64:
      case Iop_128HIto64:
      case Iop_128to64:
      case Iop_Dup8x8:
      case Iop_Dup16x4:
      case Iop_Dup32x2:
      case Iop_Reverse16_8x8:
      case Iop_Reverse32_8x8:
      case Iop_Reverse32_16x4:
      case Iop_Reverse64_8x8:
      case Iop_Reverse64_16x4:
      case Iop_Reverse64_32x2:
      case Iop_V256to64_0: case Iop_V256to64_1:
      case Iop_V256to64_2: case Iop_V256to64_3:
         return assignNew('V', mce, Ity_I64, unop(op, vatom));

      case Iop_64to32:
      case Iop_64HIto32:
      case Iop_1Uto32:
      case Iop_1Sto32:
      case Iop_8Uto32:
      case Iop_16Uto32:
      case Iop_16Sto32:
      case Iop_8Sto32:
      case Iop_V128to32:
         return assignNew('V', mce, Ity_I32, unop(op, vatom));

      case Iop_8Sto16:
      case Iop_8Uto16:
      case Iop_32to16:
      case Iop_32HIto16:
      case Iop_64to16:
      case Iop_GetMSBs8x16:
         return assignNew('V', mce, Ity_I16, unop(op, vatom));

      case Iop_1Uto8:
      case Iop_1Sto8:
      case Iop_16to8:
      case Iop_16HIto8:
      case Iop_32to8:
      case Iop_64to8:
      case Iop_GetMSBs8x8:
         return assignNew('V', mce, Ity_I8, unop(op, vatom));

      case Iop_32to1:
         return assignNew('V', mce, Ity_I1, unop(Iop_32to1, vatom));

      case Iop_64to1:
         return assignNew('V', mce, Ity_I1, unop(Iop_64to1, vatom));

      case Iop_ReinterpF64asI64:
      case Iop_ReinterpI64asF64:
      case Iop_ReinterpI32asF32:
      case Iop_ReinterpF32asI32:
      case Iop_ReinterpI64asD64:
      case Iop_ReinterpD64asI64:
      case Iop_NotV256:
      case Iop_NotV128:
      case Iop_Not64:
      case Iop_Not32:
      case Iop_Not16:
      case Iop_Not8:
      case Iop_Not1:
         return vatom;

      case Iop_CmpNEZ8x8:
      case Iop_Cnt8x8:
      case Iop_Clz8Sx8:
      case Iop_Cls8Sx8:
      case Iop_Abs8x8:
         return mkPCast8x8(mce, vatom);

      case Iop_CmpNEZ8x16:
      case Iop_Cnt8x16:
      case Iop_Clz8Sx16:
      case Iop_Cls8Sx16:
      case Iop_Abs8x16:
         return mkPCast8x16(mce, vatom);

      case Iop_CmpNEZ16x4:
      case Iop_Clz16Sx4:
      case Iop_Cls16Sx4:
      case Iop_Abs16x4:
         return mkPCast16x4(mce, vatom);

      case Iop_CmpNEZ16x8:
      case Iop_Clz16Sx8:
      case Iop_Cls16Sx8:
      case Iop_Abs16x8:
         return mkPCast16x8(mce, vatom);

      case Iop_CmpNEZ32x2:
      case Iop_Clz32Sx2:
      case Iop_Cls32Sx2:
      case Iop_FtoI32Ux2_RZ:
      case Iop_FtoI32Sx2_RZ:
      case Iop_Abs32x2:
         return mkPCast32x2(mce, vatom);

      case Iop_CmpNEZ32x4:
      case Iop_Clz32Sx4:
      case Iop_Cls32Sx4:
      case Iop_FtoI32Ux4_RZ:
      case Iop_FtoI32Sx4_RZ:
      case Iop_Abs32x4:
         return mkPCast32x4(mce, vatom);

      case Iop_CmpwNEZ32:
         return mkPCastTo(mce, Ity_I32, vatom);

      case Iop_CmpwNEZ64:
         return mkPCastTo(mce, Ity_I64, vatom);

      case Iop_CmpNEZ64x2:
      case Iop_CipherSV128:
      case Iop_Clz64x2:
         return mkPCast64x2(mce, vatom);

      case Iop_PwBitMtxXpose64x2:
         return assignNew('V', mce, Ity_V128, unop(op, vatom));

      case Iop_NarrowUn16to8x8:
      case Iop_NarrowUn32to16x4:
      case Iop_NarrowUn64to32x2:
      case Iop_QNarrowUn16Sto8Sx8:
      case Iop_QNarrowUn16Sto8Ux8:
      case Iop_QNarrowUn16Uto8Ux8:
      case Iop_QNarrowUn32Sto16Sx4:
      case Iop_QNarrowUn32Sto16Ux4:
      case Iop_QNarrowUn32Uto16Ux4:
      case Iop_QNarrowUn64Sto32Sx2:
      case Iop_QNarrowUn64Sto32Ux2:
      case Iop_QNarrowUn64Uto32Ux2:
         return vectorNarrowUnV128(mce, op, vatom);

      case Iop_Widen8Sto16x8:
      case Iop_Widen8Uto16x8:
      case Iop_Widen16Sto32x4:
      case Iop_Widen16Uto32x4:
      case Iop_Widen32Sto64x2:
      case Iop_Widen32Uto64x2:
         return vectorWidenI64(mce, op, vatom);

      case Iop_PwAddL32Ux2:
      case Iop_PwAddL32Sx2:
         return mkPCastTo(mce, Ity_I64,
               assignNew('V', mce, Ity_I64, unop(op, mkPCast32x2(mce, vatom))));

      case Iop_PwAddL16Ux4:
      case Iop_PwAddL16Sx4:
         return mkPCast32x2(mce,
               assignNew('V', mce, Ity_I64, unop(op, mkPCast16x4(mce, vatom))));

      case Iop_PwAddL8Ux8:
      case Iop_PwAddL8Sx8:
         return mkPCast16x4(mce,
               assignNew('V', mce, Ity_I64, unop(op, mkPCast8x8(mce, vatom))));

      case Iop_PwAddL32Ux4:
      case Iop_PwAddL32Sx4:
         return mkPCast64x2(mce,
               assignNew('V', mce, Ity_V128, unop(op, mkPCast32x4(mce, vatom))));

      case Iop_PwAddL16Ux8:
      case Iop_PwAddL16Sx8:
         return mkPCast32x4(mce,
               assignNew('V', mce, Ity_V128, unop(op, mkPCast16x8(mce, vatom))));

      case Iop_PwAddL8Ux16:
      case Iop_PwAddL8Sx16:
         return mkPCast16x8(mce,
               assignNew('V', mce, Ity_V128, unop(op, mkPCast8x16(mce, vatom))));

      case Iop_I64UtoF32:
      default:
         ppIROp(op);
         VG_(tool_panic)("memcheck:expr2vbits_Unop");
   }
}


/* Worker function -- do not call directly.  See comments on
   expr2vbits_Load for the meaning of |guard|.

   Generates IR to (1) perform a definedness test of |addr|, (2)
   perform a validity test of |addr|, and (3) return the Vbits for the
   location indicated by |addr|.  All of this only happens when
   |guard| is NULL or |guard| evaluates to True at run time.

   If |guard| evaluates to False at run time, the returned value is
   the IR-mandated 0x55..55 value, and no checks nor shadow loads are
   performed.

   The definedness of |guard| itself is not checked.  That is assumed
   to have been done before this point, by the caller. */
static
IRAtom* expr2vbits_Load_WRK ( MCEnv* mce,
                              IREndness end, IRType ty,
                              IRAtom* addr, UInt bias, IRAtom* guard )
{
   tl_assert(isOriginalAtom(mce,addr));
   tl_assert(end == Iend_LE || end == Iend_BE);

   /* First, emit a definedness test for the address.  This also sets
      the address (shadow) to 'defined' following the test. */
   complainIfUndefined( mce, addr, guard );

   /* Now cook up a call to the relevant helper function, to read the
      data V bits from shadow memory. */
   ty = shadowTypeV(ty);

   void*        helper           = NULL;
   const HChar* hname            = NULL;
   Bool         ret_via_outparam = False;

   if (end == Iend_LE) {
      switch (ty) {
         case Ity_V256: helper = &MC_(helperc_LOADV256le);
                        hname = "MC_(helperc_LOADV256le)";
                        ret_via_outparam = True;
                        break;
         case Ity_V128: helper = &MC_(helperc_LOADV128le);
                        hname = "MC_(helperc_LOADV128le)";
                        ret_via_outparam = True;
                        break;
         case Ity_I64:  helper = &MC_(helperc_LOADV64le);
                        hname = "MC_(helperc_LOADV64le)";
                        break;
         case Ity_I32:  helper = &MC_(helperc_LOADV32le);
                        hname = "MC_(helperc_LOADV32le)";
                        break;
         case Ity_I16:  helper = &MC_(helperc_LOADV16le);
                        hname = "MC_(helperc_LOADV16le)";
                        break;
         case Ity_I8:   helper = &MC_(helperc_LOADV8);
                        hname = "MC_(helperc_LOADV8)";
                        break;
         default:       ppIRType(ty);
                        VG_(tool_panic)("memcheck:expr2vbits_Load_WRK(LE)");
      }
   } else {
      switch (ty) {
         case Ity_V256: helper = &MC_(helperc_LOADV256be);
                        hname = "MC_(helperc_LOADV256be)";
                        ret_via_outparam = True;
                        break;
         case Ity_V128: helper = &MC_(helperc_LOADV128be);
                        hname = "MC_(helperc_LOADV128be)";
                        ret_via_outparam = True;
                        break;
         case Ity_I64:  helper = &MC_(helperc_LOADV64be);
                        hname = "MC_(helperc_LOADV64be)";
                        break;
         case Ity_I32:  helper = &MC_(helperc_LOADV32be);
                        hname = "MC_(helperc_LOADV32be)";
                        break;
         case Ity_I16:  helper = &MC_(helperc_LOADV16be);
                        hname = "MC_(helperc_LOADV16be)";
                        break;
         case Ity_I8:   helper = &MC_(helperc_LOADV8);
                        hname = "MC_(helperc_LOADV8)";
                        break;
         default:       ppIRType(ty);
                        VG_(tool_panic)("memcheck:expr2vbits_Load_WRK(BE)");
      }
   }

   tl_assert(helper);
   tl_assert(hname);

   /* Generate the actual address into addrAct. */
   IRAtom* addrAct;
   if (bias == 0) {
      addrAct = addr;
   } else {
      IROp    mkAdd;
      IRAtom* eBias;
      IRType  tyAddr  = mce->hWordTy;
      tl_assert( tyAddr == Ity_I32 || tyAddr == Ity_I64 );
      mkAdd   = tyAddr==Ity_I32 ? Iop_Add32 : Iop_Add64;
      eBias   = tyAddr==Ity_I32 ? mkU32(bias) : mkU64(bias);
      addrAct = assignNew('V', mce, tyAddr, binop(mkAdd, addr, eBias) );
   }

   /* We need to have a place to park the V bits we're just about to
      read. */
   IRTemp datavbits = newTemp(mce, ty, VSh);

   /* Here's the call. */
   IRDirty* di;
   if (ret_via_outparam) {
      di = unsafeIRDirty_1_N( datavbits, 
                              2/*regparms*/, 
                              hname, VG_(fnptr_to_fnentry)( helper ), 
                              mkIRExprVec_2( IRExpr_VECRET(), addrAct ) );
   } else {
      di = unsafeIRDirty_1_N( datavbits, 
                              1/*regparms*/, 
                              hname, VG_(fnptr_to_fnentry)( helper ), 
                              mkIRExprVec_1( addrAct ) );
   }

   setHelperAnns( mce, di );
   if (guard) {
      di->guard = guard;
      /* Ideally the didn't-happen return value here would be all-ones
         (all-undefined), so it'd be obvious if it got used
         inadvertantly.  We can get by with the IR-mandated default
         value (0b01 repeating, 0x55 etc) as that'll still look pretty
         undefined if it ever leaks out. */
   }
   stmt( 'V', mce, IRStmt_Dirty(di) );

   return mkexpr(datavbits);
}


/* Generate IR to do a shadow load.  The helper is expected to check
   the validity of the address and return the V bits for that address.
   This can optionally be controlled by a guard, which is assumed to
   be True if NULL.  In the case where the guard is False at runtime,
   the helper will return the didn't-do-the-call value of 0x55..55.
   Since that means "completely undefined result", the caller of
   this function will need to fix up the result somehow in that
   case.

   Caller of this function is also expected to have checked the
   definedness of |guard| before this point.
*/
static
IRAtom* expr2vbits_Load ( MCEnv* mce,
                          IREndness end, IRType ty,
                          IRAtom* addr, UInt bias,
                          IRAtom* guard )
{
   tl_assert(end == Iend_LE || end == Iend_BE);
   switch (shadowTypeV(ty)) {
      case Ity_I8:
      case Ity_I16:
      case Ity_I32:
      case Ity_I64:
      case Ity_V128:
      case Ity_V256:
         return expr2vbits_Load_WRK(mce, end, ty, addr, bias, guard);
      default:
         VG_(tool_panic)("expr2vbits_Load");
   }
}


/* The most general handler for guarded loads.  Assumes the
   definedness of GUARD has already been checked by the caller.  A
   GUARD of NULL is assumed to mean "always True".  Generates code to
   check the definedness and validity of ADDR.

   Generate IR to do a shadow load from ADDR and return the V bits.
   The loaded type is TY.  The loaded data is then (shadow) widened by
   using VWIDEN, which can be Iop_INVALID to denote a no-op.  If GUARD
   evaluates to False at run time then the returned Vbits are simply
   VALT instead.  Note therefore that the argument type of VWIDEN must
   be TY and the result type of VWIDEN must equal the type of VALT.
*/
static
IRAtom* expr2vbits_Load_guarded_General ( MCEnv* mce,
                                          IREndness end, IRType ty,
                                          IRAtom* addr, UInt bias,
                                          IRAtom* guard,
                                          IROp vwiden, IRAtom* valt )
{
   /* Sanity check the conversion operation, and also set TYWIDE. */
   IRType tyWide = Ity_INVALID;
   switch (vwiden) {
      case Iop_INVALID:
         tyWide = ty;
         break;
      case Iop_16Uto32: case Iop_16Sto32: case Iop_8Uto32: case Iop_8Sto32:
         tyWide = Ity_I32; 
         break;
      default:
         VG_(tool_panic)("memcheck:expr2vbits_Load_guarded_General");
   }

   /* If the guard evaluates to True, this will hold the loaded V bits
      at TY.  If the guard evaluates to False, this will be all
      ones, meaning "all undefined", in which case we will have to
      replace it using an ITE below. */
   IRAtom* iftrue1
      = assignNew('V', mce, ty,
                  expr2vbits_Load(mce, end, ty, addr, bias, guard));
   /* Now (shadow-) widen the loaded V bits to the desired width.  In
      the guard-is-False case, the allowable widening operators will
      in the worst case (unsigned widening) at least leave the
      pre-widened part as being marked all-undefined, and in the best
      case (signed widening) mark the whole widened result as
      undefined.  Anyway, it doesn't matter really, since in this case
      we will replace said value with the default value |valt| using an
      ITE. */
   IRAtom* iftrue2
      = vwiden == Iop_INVALID
           ? iftrue1
           : assignNew('V', mce, tyWide, unop(vwiden, iftrue1));
   /* These are the V bits we will return if the load doesn't take
      place. */
   IRAtom* iffalse 
      = valt;
   /* Prepare the cond for the ITE.  Convert a NULL cond into
      something that iropt knows how to fold out later. */
   IRAtom* cond
      = guard == NULL  ? mkU1(1)  : guard;
   /* And assemble the final result. */
   return assignNew('V', mce, tyWide, IRExpr_ITE(cond, iftrue2, iffalse));
}


/* A simpler handler for guarded loads, in which there is no
   conversion operation, and the default V bit return (when the guard
   evaluates to False at runtime) is "all defined".  If there is no
   guard expression or the guard is always TRUE this function behaves
   like expr2vbits_Load.  It is assumed that definedness of GUARD has
   already been checked at the call site. */
static
IRAtom* expr2vbits_Load_guarded_Simple ( MCEnv* mce, 
                                         IREndness end, IRType ty, 
                                         IRAtom* addr, UInt bias,
                                         IRAtom *guard )
{
   return expr2vbits_Load_guarded_General(
             mce, end, ty, addr, bias, guard, Iop_INVALID, definedOfType(ty)
          );
}


static
IRAtom* expr2vbits_ITE ( MCEnv* mce, 
                         IRAtom* cond, IRAtom* iftrue, IRAtom* iffalse )
{
   IRAtom *vbitsC, *vbits0, *vbits1;
   IRType ty;
   /* Given ITE(cond, iftrue,  iffalse),  generate
            ITE(cond, iftrue#, iffalse#) `UifU` PCast(cond#)
      That is, steer the V bits like the originals, but trash the 
      result if the steering value is undefined.  This gives 
      lazy propagation. */
   tl_assert(isOriginalAtom(mce, cond));
   tl_assert(isOriginalAtom(mce, iftrue));
   tl_assert(isOriginalAtom(mce, iffalse));

   vbitsC = expr2vbits(mce, cond);
   vbits1 = expr2vbits(mce, iftrue);
   vbits0 = expr2vbits(mce, iffalse);
   ty = typeOfIRExpr(mce->sb->tyenv, vbits0);

   return
      mkUifU(mce, ty, assignNew('V', mce, ty, 
                                     IRExpr_ITE(cond, vbits1, vbits0)),
                      mkPCastTo(mce, ty, vbitsC) );
}      

/* --------- This is the main expression-handling function. --------- */

static
IRExpr* expr2vbits ( MCEnv* mce, IRExpr* e )
{
   switch (e->tag) {

      case Iex_Get:
         return shadow_GET( mce, e->Iex.Get.offset, e->Iex.Get.ty );

      case Iex_GetI:
         return shadow_GETI( mce, e->Iex.GetI.descr, 
                                  e->Iex.GetI.ix, e->Iex.GetI.bias );

      case Iex_RdTmp:
         return IRExpr_RdTmp( findShadowTmpV(mce, e->Iex.RdTmp.tmp) );

      case Iex_Const:
         return definedOfType(shadowTypeV(typeOfIRExpr(mce->sb->tyenv, e)));

      case Iex_Qop:
         return expr2vbits_Qop(
                   mce,
                   e->Iex.Qop.details->op,
                   e->Iex.Qop.details->arg1, e->Iex.Qop.details->arg2,
                   e->Iex.Qop.details->arg3, e->Iex.Qop.details->arg4
                );

      case Iex_Triop:
         return expr2vbits_Triop(
                   mce,
                   e->Iex.Triop.details->op,
                   e->Iex.Triop.details->arg1, e->Iex.Triop.details->arg2,
                   e->Iex.Triop.details->arg3
                );

      case Iex_Binop:
         return expr2vbits_Binop(
                   mce,
                   e->Iex.Binop.op,
                   e->Iex.Binop.arg1, e->Iex.Binop.arg2
                );

      case Iex_Unop:
         return expr2vbits_Unop( mce, e->Iex.Unop.op, e->Iex.Unop.arg );

      case Iex_Load:
         return expr2vbits_Load( mce, e->Iex.Load.end,
                                      e->Iex.Load.ty, 
                                      e->Iex.Load.addr, 0/*addr bias*/, 
                                      NULL/* guard == "always True"*/ );

      case Iex_CCall:
         return mkLazyN( mce, e->Iex.CCall.args, 
                              e->Iex.CCall.retty,
                              e->Iex.CCall.cee );

      case Iex_ITE:
         return expr2vbits_ITE( mce, e->Iex.ITE.cond, e->Iex.ITE.iftrue, 
                                     e->Iex.ITE.iffalse);

      default: 
         VG_(printf)("\n");
         ppIRExpr(e);
         VG_(printf)("\n");
         VG_(tool_panic)("memcheck: expr2vbits");
   }
}

/*------------------------------------------------------------*/
/*--- Generate shadow stmts from all kinds of IRStmts.     ---*/
/*------------------------------------------------------------*/

/* Widen a value to the host word size. */

static
IRExpr* zwidenToHostWord ( MCEnv* mce, IRAtom* vatom )
{
   IRType ty, tyH;

   /* vatom is vbits-value and as such can only have a shadow type. */
   tl_assert(isShadowAtom(mce,vatom));

   ty  = typeOfIRExpr(mce->sb->tyenv, vatom);
   tyH = mce->hWordTy;

   if (tyH == Ity_I32) {
      switch (ty) {
         case Ity_I32:
            return vatom;
         case Ity_I16:
            return assignNew('V', mce, tyH, unop(Iop_16Uto32, vatom));
         case Ity_I8:
            return assignNew('V', mce, tyH, unop(Iop_8Uto32, vatom));
         default:
            goto unhandled;
      }
   } else
   if (tyH == Ity_I64) {
      switch (ty) {
         case Ity_I32:
            return assignNew('V', mce, tyH, unop(Iop_32Uto64, vatom));
         case Ity_I16:
            return assignNew('V', mce, tyH, unop(Iop_32Uto64, 
                   assignNew('V', mce, Ity_I32, unop(Iop_16Uto32, vatom))));
         case Ity_I8:
            return assignNew('V', mce, tyH, unop(Iop_32Uto64, 
                   assignNew('V', mce, Ity_I32, unop(Iop_8Uto32, vatom))));
         default:
            goto unhandled;
      }
   } else {
      goto unhandled;
   }
  unhandled:
   VG_(printf)("\nty = "); ppIRType(ty); VG_(printf)("\n");
   VG_(tool_panic)("zwidenToHostWord");
}


/* Generate a shadow store.  |addr| is always the original address
   atom.  You can pass in either originals or V-bits for the data
   atom, but obviously not both.  This function generates a check for
   the definedness and (indirectly) the validity of |addr|, but only
   when |guard| evaluates to True at run time (or is NULL).

   |guard| :: Ity_I1 controls whether the store really happens; NULL
   means it unconditionally does.  Note that |guard| itself is not
   checked for definedness; the caller of this function must do that
   if necessary.
*/
static 
void do_shadow_Store ( MCEnv* mce, 
                       IREndness end,
                       IRAtom* addr, UInt bias,
                       IRAtom* data, IRAtom* vdata,
                       IRAtom* guard )
{
   IROp     mkAdd;
   IRType   ty, tyAddr;
   void*    helper = NULL;
   const HChar* hname = NULL;
   IRConst* c;

   tyAddr = mce->hWordTy;
   mkAdd  = tyAddr==Ity_I32 ? Iop_Add32 : Iop_Add64;
   tl_assert( tyAddr == Ity_I32 || tyAddr == Ity_I64 );
   tl_assert( end == Iend_LE || end == Iend_BE );

   if (data) {
      tl_assert(!vdata);
      tl_assert(isOriginalAtom(mce, data));
      tl_assert(bias == 0);
      vdata = expr2vbits( mce, data );
   } else {
      tl_assert(vdata);
   }

   tl_assert(isOriginalAtom(mce,addr));
   tl_assert(isShadowAtom(mce,vdata));

   if (guard) {
      tl_assert(isOriginalAtom(mce, guard));
      tl_assert(typeOfIRExpr(mce->sb->tyenv, guard) == Ity_I1);
   }

   ty = typeOfIRExpr(mce->sb->tyenv, vdata);

   // If we're not doing undefined value checking, pretend that this value
   // is "all valid".  That lets Vex's optimiser remove some of the V bit
   // shadow computation ops that precede it.
   if (MC_(clo_mc_level) == 1) {
      switch (ty) {
         case Ity_V256: // V256 weirdness -- used four times
                        c = IRConst_V256(V_BITS32_DEFINED); break;
         case Ity_V128: // V128 weirdness -- used twice
                        c = IRConst_V128(V_BITS16_DEFINED); break;
         case Ity_I64:  c = IRConst_U64 (V_BITS64_DEFINED); break;
         case Ity_I32:  c = IRConst_U32 (V_BITS32_DEFINED); break;
         case Ity_I16:  c = IRConst_U16 (V_BITS16_DEFINED); break;
         case Ity_I8:   c = IRConst_U8  (V_BITS8_DEFINED);  break;
         default:       VG_(tool_panic)("memcheck:do_shadow_Store(LE)");
      }
      vdata = IRExpr_Const( c );
   }

   /* First, emit a definedness test for the address.  This also sets
      the address (shadow) to 'defined' following the test.  Both of
      those actions are gated on |guard|. */
   complainIfUndefined( mce, addr, guard );

   /* Now decide which helper function to call to write the data V
      bits into shadow memory. */
   if (end == Iend_LE) {
      switch (ty) {
         case Ity_V256: /* we'll use the helper four times */
         case Ity_V128: /* we'll use the helper twice */
         case Ity_I64: helper = &MC_(helperc_STOREV64le);
                       hname = "MC_(helperc_STOREV64le)";
                       break;
         case Ity_I32: helper = &MC_(helperc_STOREV32le);
                       hname = "MC_(helperc_STOREV32le)";
                       break;
         case Ity_I16: helper = &MC_(helperc_STOREV16le);
                       hname = "MC_(helperc_STOREV16le)";
                       break;
         case Ity_I8:  helper = &MC_(helperc_STOREV8);
                       hname = "MC_(helperc_STOREV8)";
                       break;
         default:      VG_(tool_panic)("memcheck:do_shadow_Store(LE)");
      }
   } else {
      switch (ty) {
         case Ity_V128: /* we'll use the helper twice */
         case Ity_I64: helper = &MC_(helperc_STOREV64be);
                       hname = "MC_(helperc_STOREV64be)";
                       break;
         case Ity_I32: helper = &MC_(helperc_STOREV32be);
                       hname = "MC_(helperc_STOREV32be)";
                       break;
         case Ity_I16: helper = &MC_(helperc_STOREV16be);
                       hname = "MC_(helperc_STOREV16be)";
                       break;
         case Ity_I8:  helper = &MC_(helperc_STOREV8);
                       hname = "MC_(helperc_STOREV8)";
                       break;
         /* Note, no V256 case here, because no big-endian target that
            we support, has 256 vectors. */
         default:      VG_(tool_panic)("memcheck:do_shadow_Store(BE)");
      }
   }

   if (UNLIKELY(ty == Ity_V256)) {

      /* V256-bit case -- phrased in terms of 64 bit units (Qs), with
         Q3 being the most significant lane. */
      /* These are the offsets of the Qs in memory. */
      Int     offQ0, offQ1, offQ2, offQ3;

      /* Various bits for constructing the 4 lane helper calls */
      IRDirty *diQ0,    *diQ1,    *diQ2,    *diQ3;
      IRAtom  *addrQ0,  *addrQ1,  *addrQ2,  *addrQ3;
      IRAtom  *vdataQ0, *vdataQ1, *vdataQ2, *vdataQ3;
      IRAtom  *eBiasQ0, *eBiasQ1, *eBiasQ2, *eBiasQ3;

      if (end == Iend_LE) {
         offQ0 = 0; offQ1 = 8; offQ2 = 16; offQ3 = 24;
      } else {
         offQ3 = 0; offQ2 = 8; offQ1 = 16; offQ0 = 24;
      }

      eBiasQ0 = tyAddr==Ity_I32 ? mkU32(bias+offQ0) : mkU64(bias+offQ0);
      addrQ0  = assignNew('V', mce, tyAddr, binop(mkAdd, addr, eBiasQ0) );
      vdataQ0 = assignNew('V', mce, Ity_I64, unop(Iop_V256to64_0, vdata));
      diQ0    = unsafeIRDirty_0_N( 
                   1/*regparms*/, 
                   hname, VG_(fnptr_to_fnentry)( helper ), 
                   mkIRExprVec_2( addrQ0, vdataQ0 )
                );

      eBiasQ1 = tyAddr==Ity_I32 ? mkU32(bias+offQ1) : mkU64(bias+offQ1);
      addrQ1  = assignNew('V', mce, tyAddr, binop(mkAdd, addr, eBiasQ1) );
      vdataQ1 = assignNew('V', mce, Ity_I64, unop(Iop_V256to64_1, vdata));
      diQ1    = unsafeIRDirty_0_N( 
                   1/*regparms*/, 
                   hname, VG_(fnptr_to_fnentry)( helper ), 
                   mkIRExprVec_2( addrQ1, vdataQ1 )
                );

      eBiasQ2 = tyAddr==Ity_I32 ? mkU32(bias+offQ2) : mkU64(bias+offQ2);
      addrQ2  = assignNew('V', mce, tyAddr, binop(mkAdd, addr, eBiasQ2) );
      vdataQ2 = assignNew('V', mce, Ity_I64, unop(Iop_V256to64_2, vdata));
      diQ2    = unsafeIRDirty_0_N( 
                   1/*regparms*/, 
                   hname, VG_(fnptr_to_fnentry)( helper ), 
                   mkIRExprVec_2( addrQ2, vdataQ2 )
                );

      eBiasQ3 = tyAddr==Ity_I32 ? mkU32(bias+offQ3) : mkU64(bias+offQ3);
      addrQ3  = assignNew('V', mce, tyAddr, binop(mkAdd, addr, eBiasQ3) );
      vdataQ3 = assignNew('V', mce, Ity_I64, unop(Iop_V256to64_3, vdata));
      diQ3    = unsafeIRDirty_0_N( 
                   1/*regparms*/, 
                   hname, VG_(fnptr_to_fnentry)( helper ), 
                   mkIRExprVec_2( addrQ3, vdataQ3 )
                );

      if (guard)
         diQ0->guard = diQ1->guard = diQ2->guard = diQ3->guard = guard;

      setHelperAnns( mce, diQ0 );
      setHelperAnns( mce, diQ1 );
      setHelperAnns( mce, diQ2 );
      setHelperAnns( mce, diQ3 );
      stmt( 'V', mce, IRStmt_Dirty(diQ0) );
      stmt( 'V', mce, IRStmt_Dirty(diQ1) );
      stmt( 'V', mce, IRStmt_Dirty(diQ2) );
      stmt( 'V', mce, IRStmt_Dirty(diQ3) );

   } 
   else if (UNLIKELY(ty == Ity_V128)) {

      /* V128-bit case */
      /* See comment in next clause re 64-bit regparms */
      /* also, need to be careful about endianness */

      Int     offLo64, offHi64;
      IRDirty *diLo64, *diHi64;
      IRAtom  *addrLo64, *addrHi64;
      IRAtom  *vdataLo64, *vdataHi64;
      IRAtom  *eBiasLo64, *eBiasHi64;

      if (end == Iend_LE) {
         offLo64 = 0;
         offHi64 = 8;
      } else {
         offLo64 = 8;
         offHi64 = 0;
      }

      eBiasLo64 = tyAddr==Ity_I32 ? mkU32(bias+offLo64) : mkU64(bias+offLo64);
      addrLo64  = assignNew('V', mce, tyAddr, binop(mkAdd, addr, eBiasLo64) );
      vdataLo64 = assignNew('V', mce, Ity_I64, unop(Iop_V128to64, vdata));
      diLo64    = unsafeIRDirty_0_N( 
                     1/*regparms*/, 
                     hname, VG_(fnptr_to_fnentry)( helper ), 
                     mkIRExprVec_2( addrLo64, vdataLo64 )
                  );
      eBiasHi64 = tyAddr==Ity_I32 ? mkU32(bias+offHi64) : mkU64(bias+offHi64);
      addrHi64  = assignNew('V', mce, tyAddr, binop(mkAdd, addr, eBiasHi64) );
      vdataHi64 = assignNew('V', mce, Ity_I64, unop(Iop_V128HIto64, vdata));
      diHi64    = unsafeIRDirty_0_N( 
                     1/*regparms*/, 
                     hname, VG_(fnptr_to_fnentry)( helper ), 
                     mkIRExprVec_2( addrHi64, vdataHi64 )
                  );
      if (guard) diLo64->guard = guard;
      if (guard) diHi64->guard = guard;
      setHelperAnns( mce, diLo64 );
      setHelperAnns( mce, diHi64 );
      stmt( 'V', mce, IRStmt_Dirty(diLo64) );
      stmt( 'V', mce, IRStmt_Dirty(diHi64) );

   } else {

      IRDirty *di;
      IRAtom  *addrAct;

      /* 8/16/32/64-bit cases */
      /* Generate the actual address into addrAct. */
      if (bias == 0) {
         addrAct = addr;
      } else {
         IRAtom* eBias   = tyAddr==Ity_I32 ? mkU32(bias) : mkU64(bias);
         addrAct = assignNew('V', mce, tyAddr, binop(mkAdd, addr, eBias));
      }

      if (ty == Ity_I64) {
         /* We can't do this with regparm 2 on 32-bit platforms, since
            the back ends aren't clever enough to handle 64-bit
            regparm args.  Therefore be different. */
         di = unsafeIRDirty_0_N( 
                 1/*regparms*/, 
                 hname, VG_(fnptr_to_fnentry)( helper ), 
                 mkIRExprVec_2( addrAct, vdata )
              );
      } else {
         di = unsafeIRDirty_0_N( 
                 2/*regparms*/, 
                 hname, VG_(fnptr_to_fnentry)( helper ), 
                 mkIRExprVec_2( addrAct,
                                zwidenToHostWord( mce, vdata ))
              );
      }
      if (guard) di->guard = guard;
      setHelperAnns( mce, di );
      stmt( 'V', mce, IRStmt_Dirty(di) );
   }

}


/* Do lazy pessimistic propagation through a dirty helper call, by
   looking at the annotations on it.  This is the most complex part of
   Memcheck. */

static IRType szToITy ( Int n )
{
   switch (n) {
      case 1: return Ity_I8;
      case 2: return Ity_I16;
      case 4: return Ity_I32;
      case 8: return Ity_I64;
      default: VG_(tool_panic)("szToITy(memcheck)");
   }
}

static
void do_shadow_Dirty ( MCEnv* mce, IRDirty* d )
{
   Int       i, k, n, toDo, gSz, gOff;
   IRAtom    *src, *here, *curr;
   IRType    tySrc, tyDst;
   IRTemp    dst;
   IREndness end;

   /* What's the native endianness?  We need to know this. */
#  if defined(VG_BIGENDIAN)
   end = Iend_BE;
#  elif defined(VG_LITTLEENDIAN)
   end = Iend_LE;
#  else
#    error "Unknown endianness"
#  endif

   /* First check the guard. */
   complainIfUndefined(mce, d->guard, NULL);

   /* Now round up all inputs and PCast over them. */
   curr = definedOfType(Ity_I32);

   /* Inputs: unmasked args
      Note: arguments are evaluated REGARDLESS of the guard expression */
   for (i = 0; d->args[i]; i++) {
      IRAtom* arg = d->args[i];
      if ( (d->cee->mcx_mask & (1<<i))
           || UNLIKELY(is_IRExpr_VECRET_or_BBPTR(arg)) ) {
         /* ignore this arg */
      } else {
         here = mkPCastTo( mce, Ity_I32, expr2vbits(mce, arg) );
         curr = mkUifU32(mce, here, curr);
      }
   }

   /* Inputs: guest state that we read. */
   for (i = 0; i < d->nFxState; i++) {
      tl_assert(d->fxState[i].fx != Ifx_None);
      if (d->fxState[i].fx == Ifx_Write)
         continue;

      /* Enumerate the described state segments */
      for (k = 0; k < 1 + d->fxState[i].nRepeats; k++) {
         gOff = d->fxState[i].offset + k * d->fxState[i].repeatLen;
         gSz  = d->fxState[i].size;

         /* Ignore any sections marked as 'always defined'. */
         if (isAlwaysDefd(mce, gOff, gSz)) {
            if (0)
            VG_(printf)("memcheck: Dirty gst: ignored off %d, sz %d\n",
                        gOff, gSz);
            continue;
         }

         /* This state element is read or modified.  So we need to
            consider it.  If larger than 8 bytes, deal with it in
            8-byte chunks. */
         while (True) {
            tl_assert(gSz >= 0);
            if (gSz == 0) break;
            n = gSz <= 8 ? gSz : 8;
            /* update 'curr' with UifU of the state slice 
               gOff .. gOff+n-1 */
            tySrc = szToITy( n );

            /* Observe the guard expression. If it is false use an
               all-bits-defined bit pattern */
            IRAtom *cond, *iffalse, *iftrue;

            cond    = assignNew('V', mce, Ity_I1, d->guard);
            iftrue  = assignNew('V', mce, tySrc, shadow_GET(mce, gOff, tySrc));
            iffalse = assignNew('V', mce, tySrc, definedOfType(tySrc));
            src     = assignNew('V', mce, tySrc,
                                IRExpr_ITE(cond, iftrue, iffalse));

            here = mkPCastTo( mce, Ity_I32, src );
            curr = mkUifU32(mce, here, curr);
            gSz -= n;
            gOff += n;
         }
      }
   }

   /* Inputs: memory.  First set up some info needed regardless of
      whether we're doing reads or writes. */

   if (d->mFx != Ifx_None) {
      /* Because we may do multiple shadow loads/stores from the same
         base address, it's best to do a single test of its
         definedness right now.  Post-instrumentation optimisation
         should remove all but this test. */
      IRType tyAddr;
      tl_assert(d->mAddr);
      complainIfUndefined(mce, d->mAddr, d->guard);

      tyAddr = typeOfIRExpr(mce->sb->tyenv, d->mAddr);
      tl_assert(tyAddr == Ity_I32 || tyAddr == Ity_I64);
      tl_assert(tyAddr == mce->hWordTy); /* not really right */
   }

   /* Deal with memory inputs (reads or modifies) */
   if (d->mFx == Ifx_Read || d->mFx == Ifx_Modify) {
      toDo   = d->mSize;
      /* chew off 32-bit chunks.  We don't care about the endianness
         since it's all going to be condensed down to a single bit,
         but nevertheless choose an endianness which is hopefully
         native to the platform. */
      while (toDo >= 4) {
         here = mkPCastTo( 
                   mce, Ity_I32,
                   expr2vbits_Load_guarded_Simple(
                      mce, end, Ity_I32, d->mAddr, d->mSize - toDo, d->guard )
                );
         curr = mkUifU32(mce, here, curr);
         toDo -= 4;
      }
      /* chew off 16-bit chunks */
      while (toDo >= 2) {
         here = mkPCastTo( 
                   mce, Ity_I32,
                   expr2vbits_Load_guarded_Simple(
                      mce, end, Ity_I16, d->mAddr, d->mSize - toDo, d->guard )
                );
         curr = mkUifU32(mce, here, curr);
         toDo -= 2;
      }
      /* chew off the remaining 8-bit chunk, if any */
      if (toDo == 1) {
         here = mkPCastTo( 
                   mce, Ity_I32,
                   expr2vbits_Load_guarded_Simple(
                      mce, end, Ity_I8, d->mAddr, d->mSize - toDo, d->guard )
                );
         curr = mkUifU32(mce, here, curr);
         toDo -= 1;
      }
      tl_assert(toDo == 0);
   }

   /* Whew!  So curr is a 32-bit V-value summarising pessimistically
      all the inputs to the helper.  Now we need to re-distribute the
      results to all destinations. */

   /* Outputs: the destination temporary, if there is one. */
   if (d->tmp != IRTemp_INVALID) {
      dst   = findShadowTmpV(mce, d->tmp);
      tyDst = typeOfIRTemp(mce->sb->tyenv, d->tmp);
      assign( 'V', mce, dst, mkPCastTo( mce, tyDst, curr) );
   }

   /* Outputs: guest state that we write or modify. */
   for (i = 0; i < d->nFxState; i++) {
      tl_assert(d->fxState[i].fx != Ifx_None);
      if (d->fxState[i].fx == Ifx_Read)
         continue;

      /* Enumerate the described state segments */
      for (k = 0; k < 1 + d->fxState[i].nRepeats; k++) {
         gOff = d->fxState[i].offset + k * d->fxState[i].repeatLen;
         gSz  = d->fxState[i].size;

         /* Ignore any sections marked as 'always defined'. */
         if (isAlwaysDefd(mce, gOff, gSz))
            continue;

         /* This state element is written or modified.  So we need to
            consider it.  If larger than 8 bytes, deal with it in
            8-byte chunks. */
         while (True) {
            tl_assert(gSz >= 0);
            if (gSz == 0) break;
            n = gSz <= 8 ? gSz : 8;
            /* Write suitably-casted 'curr' to the state slice 
               gOff .. gOff+n-1 */
            tyDst = szToITy( n );
            do_shadow_PUT( mce, gOff,
                                NULL, /* original atom */
                                mkPCastTo( mce, tyDst, curr ), d->guard );
            gSz -= n;
            gOff += n;
         }
      }
   }

   /* Outputs: memory that we write or modify.  Same comments about
      endianness as above apply. */
   if (d->mFx == Ifx_Write || d->mFx == Ifx_Modify) {
      toDo   = d->mSize;
      /* chew off 32-bit chunks */
      while (toDo >= 4) {
         do_shadow_Store( mce, end, d->mAddr, d->mSize - toDo,
                          NULL, /* original data */
                          mkPCastTo( mce, Ity_I32, curr ),
                          d->guard );
         toDo -= 4;
      }
      /* chew off 16-bit chunks */
      while (toDo >= 2) {
         do_shadow_Store( mce, end, d->mAddr, d->mSize - toDo,
                          NULL, /* original data */
                          mkPCastTo( mce, Ity_I16, curr ),
                          d->guard );
         toDo -= 2;
      }
      /* chew off the remaining 8-bit chunk, if any */
      if (toDo == 1) {
         do_shadow_Store( mce, end, d->mAddr, d->mSize - toDo,
                          NULL, /* original data */
                          mkPCastTo( mce, Ity_I8, curr ),
                          d->guard );
         toDo -= 1;
      }
      tl_assert(toDo == 0);
   }

}


/* We have an ABI hint telling us that [base .. base+len-1] is to
   become undefined ("writable").  Generate code to call a helper to
   notify the A/V bit machinery of this fact.

   We call 
   void MC_(helperc_MAKE_STACK_UNINIT) ( Addr base, UWord len,
                                                    Addr nia );
*/
static
void do_AbiHint ( MCEnv* mce, IRExpr* base, Int len, IRExpr* nia )
{
   IRDirty* di;
   /* Minor optimisation: if not doing origin tracking, ignore the
      supplied nia and pass zero instead.  This is on the basis that
      MC_(helperc_MAKE_STACK_UNINIT) will ignore it anyway, and we can
      almost always generate a shorter instruction to put zero into a
      register than any other value. */
   if (MC_(clo_mc_level) < 3)
      nia = mkIRExpr_HWord(0);

   di = unsafeIRDirty_0_N(
           0/*regparms*/,
           "MC_(helperc_MAKE_STACK_UNINIT)",
           VG_(fnptr_to_fnentry)( &MC_(helperc_MAKE_STACK_UNINIT) ),
           mkIRExprVec_3( base, mkIRExpr_HWord( (UInt)len), nia )
        );
   stmt( 'V', mce, IRStmt_Dirty(di) );
}


/* ------ Dealing with IRCAS (big and complex) ------ */

/* FWDS */
static IRAtom* gen_load_b  ( MCEnv* mce, Int szB, 
                             IRAtom* baseaddr, Int offset );
static IRAtom* gen_maxU32  ( MCEnv* mce, IRAtom* b1, IRAtom* b2 );
static void    gen_store_b ( MCEnv* mce, Int szB,
                             IRAtom* baseaddr, Int offset, IRAtom* dataB,
                             IRAtom* guard );

static void do_shadow_CAS_single ( MCEnv* mce, IRCAS* cas );
static void do_shadow_CAS_double ( MCEnv* mce, IRCAS* cas );


/* Either ORIG and SHADOW are both IRExpr.RdTmps, or they are both
   IRExpr.Consts, else this asserts.  If they are both Consts, it
   doesn't do anything.  So that just leaves the RdTmp case.

   In which case: this assigns the shadow value SHADOW to the IR
   shadow temporary associated with ORIG.  That is, ORIG, being an
   original temporary, will have a shadow temporary associated with
   it.  However, in the case envisaged here, there will so far have
   been no IR emitted to actually write a shadow value into that
   temporary.  What this routine does is to (emit IR to) copy the
   value in SHADOW into said temporary, so that after this call,
   IRExpr.RdTmps of ORIG's shadow temp will correctly pick up the
   value in SHADOW.

   Point is to allow callers to compute "by hand" a shadow value for
   ORIG, and force it to be associated with ORIG.

   How do we know that that shadow associated with ORIG has not so far
   been assigned to?  Well, we don't per se know that, but supposing
   it had.  Then this routine would create a second assignment to it,
   and later the IR sanity checker would barf.  But that never
   happens.  QED.
*/
static void bind_shadow_tmp_to_orig ( UChar how,
                                      MCEnv* mce,
                                      IRAtom* orig, IRAtom* shadow )
{
   tl_assert(isOriginalAtom(mce, orig));
   tl_assert(isShadowAtom(mce, shadow));
   switch (orig->tag) {
      case Iex_Const:
         tl_assert(shadow->tag == Iex_Const);
         break;
      case Iex_RdTmp:
         tl_assert(shadow->tag == Iex_RdTmp);
         if (how == 'V') {
            assign('V', mce, findShadowTmpV(mce,orig->Iex.RdTmp.tmp),
                   shadow);
         } else {
            tl_assert(how == 'B');
            assign('B', mce, findShadowTmpB(mce,orig->Iex.RdTmp.tmp),
                   shadow);
         }
         break;
      default:
         tl_assert(0);
   }
}


static
void do_shadow_CAS ( MCEnv* mce, IRCAS* cas )
{
   /* Scheme is (both single- and double- cases):

      1. fetch data#,dataB (the proposed new value)

      2. fetch expd#,expdB (what we expect to see at the address)

      3. check definedness of address

      4. load old#,oldB from shadow memory; this also checks
         addressibility of the address

      5. the CAS itself

      6. compute "expected == old".  See COMMENT_ON_CasCmpEQ below.

      7. if "expected == old" (as computed by (6))
            store data#,dataB to shadow memory

      Note that 5 reads 'old' but 4 reads 'old#'.  Similarly, 5 stores
      'data' but 7 stores 'data#'.  Hence it is possible for the
      shadow data to be incorrectly checked and/or updated:

      * 7 is at least gated correctly, since the 'expected == old'
        condition is derived from outputs of 5.  However, the shadow
        write could happen too late: imagine after 5 we are
        descheduled, a different thread runs, writes a different
        (shadow) value at the address, and then we resume, hence
        overwriting the shadow value written by the other thread.

      Because the original memory access is atomic, there's no way to
      make both the original and shadow accesses into a single atomic
      thing, hence this is unavoidable.

      At least as Valgrind stands, I don't think it's a problem, since
      we're single threaded *and* we guarantee that there are no
      context switches during the execution of any specific superblock
      -- context switches can only happen at superblock boundaries.

      If Valgrind ever becomes MT in the future, then it might be more
      of a problem.  A possible kludge would be to artificially
      associate with the location, a lock, which we must acquire and
      release around the transaction as a whole.  Hmm, that probably
      would't work properly since it only guards us against other
      threads doing CASs on the same location, not against other
      threads doing normal reads and writes.

      ------------------------------------------------------------

      COMMENT_ON_CasCmpEQ:

      Note two things.  Firstly, in the sequence above, we compute
      "expected == old", but we don't check definedness of it.  Why
      not?  Also, the x86 and amd64 front ends use
      Iop_CasCmp{EQ,NE}{8,16,32,64} comparisons to make the equivalent
      determination (expected == old ?) for themselves, and we also
      don't check definedness for those primops; we just say that the
      result is defined.  Why?  Details follow.

      x86/amd64 contains various forms of locked insns:
      * lock prefix before all basic arithmetic insn; 
        eg lock xorl %reg1,(%reg2)
      * atomic exchange reg-mem
      * compare-and-swaps

      Rather than attempt to represent them all, which would be a
      royal PITA, I used a result from Maurice Herlihy
      (http://en.wikipedia.org/wiki/Maurice_Herlihy), in which he
      demonstrates that compare-and-swap is a primitive more general
      than the other two, and so can be used to represent all of them.
      So the translation scheme for (eg) lock incl (%reg) is as
      follows:

        again:
         old = * %reg
         new = old + 1
         atomically { if (* %reg == old) { * %reg = new } else { goto again } }

      The "atomically" is the CAS bit.  The scheme is always the same:
      get old value from memory, compute new value, atomically stuff
      new value back in memory iff the old value has not changed (iow,
      no other thread modified it in the meantime).  If it has changed
      then we've been out-raced and we have to start over.

      Now that's all very neat, but it has the bad side effect of
      introducing an explicit equality test into the translation.
      Consider the behaviour of said code on a memory location which
      is uninitialised.  We will wind up doing a comparison on
      uninitialised data, and mc duly complains.

      What's difficult about this is, the common case is that the
      location is uncontended, and so we're usually comparing the same
      value (* %reg) with itself.  So we shouldn't complain even if it
      is undefined.  But mc doesn't know that.

      My solution is to mark the == in the IR specially, so as to tell
      mc that it almost certainly compares a value with itself, and we
      should just regard the result as always defined.  Rather than
      add a bit to all IROps, I just cloned Iop_CmpEQ{8,16,32,64} into
      Iop_CasCmpEQ{8,16,32,64} so as not to disturb anything else.

      So there's always the question of, can this give a false
      negative?  eg, imagine that initially, * %reg is defined; and we
      read that; but then in the gap between the read and the CAS, a
      different thread writes an undefined (and different) value at
      the location.  Then the CAS in this thread will fail and we will
      go back to "again:", but without knowing that the trip back
      there was based on an undefined comparison.  No matter; at least
      the other thread won the race and the location is correctly
      marked as undefined.  What if it wrote an uninitialised version
      of the same value that was there originally, though?

      etc etc.  Seems like there's a small corner case in which we
      might lose the fact that something's defined -- we're out-raced
      in between the "old = * reg" and the "atomically {", _and_ the
      other thread is writing in an undefined version of what's
      already there.  Well, that seems pretty unlikely.

      ---

      If we ever need to reinstate it .. code which generates a
      definedness test for "expected == old" was removed at r10432 of
      this file.
   */
   if (cas->oldHi == IRTemp_INVALID) {
      do_shadow_CAS_single( mce, cas );
   } else {
      do_shadow_CAS_double( mce, cas );
   }
}


static void do_shadow_CAS_single ( MCEnv* mce, IRCAS* cas )
{
   IRAtom *vdataLo = NULL, *bdataLo = NULL;
   IRAtom *vexpdLo = NULL, *bexpdLo = NULL;
   IRAtom *voldLo  = NULL, *boldLo  = NULL;
   IRAtom *expd_eq_old = NULL;
   IROp   opCasCmpEQ;
   Int    elemSzB;
   IRType elemTy;
   Bool   otrak = MC_(clo_mc_level) >= 3; /* a shorthand */

   /* single CAS */
   tl_assert(cas->oldHi == IRTemp_INVALID);
   tl_assert(cas->expdHi == NULL);
   tl_assert(cas->dataHi == NULL);

   elemTy = typeOfIRExpr(mce->sb->tyenv, cas->expdLo);
   switch (elemTy) {
      case Ity_I8:  elemSzB = 1; opCasCmpEQ = Iop_CasCmpEQ8;  break;
      case Ity_I16: elemSzB = 2; opCasCmpEQ = Iop_CasCmpEQ16; break;
      case Ity_I32: elemSzB = 4; opCasCmpEQ = Iop_CasCmpEQ32; break;
      case Ity_I64: elemSzB = 8; opCasCmpEQ = Iop_CasCmpEQ64; break;
      default: tl_assert(0); /* IR defn disallows any other types */
   }

   /* 1. fetch data# (the proposed new value) */
   tl_assert(isOriginalAtom(mce, cas->dataLo));
   vdataLo
      = assignNew('V', mce, elemTy, expr2vbits(mce, cas->dataLo));
   tl_assert(isShadowAtom(mce, vdataLo));
   if (otrak) {
      bdataLo
         = assignNew('B', mce, Ity_I32, schemeE(mce, cas->dataLo));
      tl_assert(isShadowAtom(mce, bdataLo));
   }

   /* 2. fetch expected# (what we expect to see at the address) */
   tl_assert(isOriginalAtom(mce, cas->expdLo));
   vexpdLo
      = assignNew('V', mce, elemTy, expr2vbits(mce, cas->expdLo));
   tl_assert(isShadowAtom(mce, vexpdLo));
   if (otrak) {
      bexpdLo
         = assignNew('B', mce, Ity_I32, schemeE(mce, cas->expdLo));
      tl_assert(isShadowAtom(mce, bexpdLo));
   }

   /* 3. check definedness of address */
   /* 4. fetch old# from shadow memory; this also checks
         addressibility of the address */
   voldLo
      = assignNew(
           'V', mce, elemTy,
           expr2vbits_Load( 
              mce,
              cas->end, elemTy, cas->addr, 0/*Addr bias*/,
              NULL/*always happens*/
        ));
   bind_shadow_tmp_to_orig('V', mce, mkexpr(cas->oldLo), voldLo);
   if (otrak) {
      boldLo
         = assignNew('B', mce, Ity_I32,
                     gen_load_b(mce, elemSzB, cas->addr, 0/*addr bias*/));
      bind_shadow_tmp_to_orig('B', mce, mkexpr(cas->oldLo), boldLo);
   }

   /* 5. the CAS itself */
   stmt( 'C', mce, IRStmt_CAS(cas) );

   /* 6. compute "expected == old" */
   /* See COMMENT_ON_CasCmpEQ in this file background/rationale. */
   /* Note that 'C' is kinda faking it; it is indeed a non-shadow
      tree, but it's not copied from the input block. */
   expd_eq_old
      = assignNew('C', mce, Ity_I1,
                  binop(opCasCmpEQ, cas->expdLo, mkexpr(cas->oldLo)));

   /* 7. if "expected == old"
            store data# to shadow memory */
   do_shadow_Store( mce, cas->end, cas->addr, 0/*bias*/,
                    NULL/*data*/, vdataLo/*vdata*/,
                    expd_eq_old/*guard for store*/ );
   if (otrak) {
      gen_store_b( mce, elemSzB, cas->addr, 0/*offset*/,
                   bdataLo/*bdata*/,
                   expd_eq_old/*guard for store*/ );
   }
}


static void do_shadow_CAS_double ( MCEnv* mce, IRCAS* cas )
{
   IRAtom *vdataHi = NULL, *bdataHi = NULL;
   IRAtom *vdataLo = NULL, *bdataLo = NULL;
   IRAtom *vexpdHi = NULL, *bexpdHi = NULL;
   IRAtom *vexpdLo = NULL, *bexpdLo = NULL;
   IRAtom *voldHi  = NULL, *boldHi  = NULL;
   IRAtom *voldLo  = NULL, *boldLo  = NULL;
   IRAtom *xHi = NULL, *xLo = NULL, *xHL = NULL;
   IRAtom *expd_eq_old = NULL, *zero = NULL;
   IROp   opCasCmpEQ, opOr, opXor;
   Int    elemSzB, memOffsLo, memOffsHi;
   IRType elemTy;
   Bool   otrak = MC_(clo_mc_level) >= 3; /* a shorthand */

   /* double CAS */
   tl_assert(cas->oldHi != IRTemp_INVALID);
   tl_assert(cas->expdHi != NULL);
   tl_assert(cas->dataHi != NULL);

   elemTy = typeOfIRExpr(mce->sb->tyenv, cas->expdLo);
   switch (elemTy) {
      case Ity_I8:
         opCasCmpEQ = Iop_CasCmpEQ8; opOr = Iop_Or8; opXor = Iop_Xor8; 
         elemSzB = 1; zero = mkU8(0);
         break;
      case Ity_I16:
         opCasCmpEQ = Iop_CasCmpEQ16; opOr = Iop_Or16; opXor = Iop_Xor16;
         elemSzB = 2; zero = mkU16(0);
         break;
      case Ity_I32:
         opCasCmpEQ = Iop_CasCmpEQ32; opOr = Iop_Or32; opXor = Iop_Xor32;
         elemSzB = 4; zero = mkU32(0);
         break;
      case Ity_I64:
         opCasCmpEQ = Iop_CasCmpEQ64; opOr = Iop_Or64; opXor = Iop_Xor64;
         elemSzB = 8; zero = mkU64(0);
         break;
      default:
         tl_assert(0); /* IR defn disallows any other types */
   }

   /* 1. fetch data# (the proposed new value) */
   tl_assert(isOriginalAtom(mce, cas->dataHi));
   tl_assert(isOriginalAtom(mce, cas->dataLo));
   vdataHi
      = assignNew('V', mce, elemTy, expr2vbits(mce, cas->dataHi));
   vdataLo
      = assignNew('V', mce, elemTy, expr2vbits(mce, cas->dataLo));
   tl_assert(isShadowAtom(mce, vdataHi));
   tl_assert(isShadowAtom(mce, vdataLo));
   if (otrak) {
      bdataHi
         = assignNew('B', mce, Ity_I32, schemeE(mce, cas->dataHi));
      bdataLo
         = assignNew('B', mce, Ity_I32, schemeE(mce, cas->dataLo));
      tl_assert(isShadowAtom(mce, bdataHi));
      tl_assert(isShadowAtom(mce, bdataLo));
   }

   /* 2. fetch expected# (what we expect to see at the address) */
   tl_assert(isOriginalAtom(mce, cas->expdHi));
   tl_assert(isOriginalAtom(mce, cas->expdLo));
   vexpdHi
      = assignNew('V', mce, elemTy, expr2vbits(mce, cas->expdHi));
   vexpdLo
      = assignNew('V', mce, elemTy, expr2vbits(mce, cas->expdLo));
   tl_assert(isShadowAtom(mce, vexpdHi));
   tl_assert(isShadowAtom(mce, vexpdLo));
   if (otrak) {
      bexpdHi
         = assignNew('B', mce, Ity_I32, schemeE(mce, cas->expdHi));
      bexpdLo
         = assignNew('B', mce, Ity_I32, schemeE(mce, cas->expdLo));
      tl_assert(isShadowAtom(mce, bexpdHi));
      tl_assert(isShadowAtom(mce, bexpdLo));
   }

   /* 3. check definedness of address */
   /* 4. fetch old# from shadow memory; this also checks
         addressibility of the address */
   if (cas->end == Iend_LE) {
      memOffsLo = 0;
      memOffsHi = elemSzB;
   } else {
      tl_assert(cas->end == Iend_BE);
      memOffsLo = elemSzB;
      memOffsHi = 0;
   }
   voldHi
      = assignNew(
           'V', mce, elemTy,
           expr2vbits_Load( 
              mce,
              cas->end, elemTy, cas->addr, memOffsHi/*Addr bias*/,
              NULL/*always happens*/
        ));
   voldLo
      = assignNew(
           'V', mce, elemTy,
           expr2vbits_Load( 
              mce,
              cas->end, elemTy, cas->addr, memOffsLo/*Addr bias*/,
              NULL/*always happens*/
        ));
   bind_shadow_tmp_to_orig('V', mce, mkexpr(cas->oldHi), voldHi);
   bind_shadow_tmp_to_orig('V', mce, mkexpr(cas->oldLo), voldLo);
   if (otrak) {
      boldHi
         = assignNew('B', mce, Ity_I32,
                     gen_load_b(mce, elemSzB, cas->addr,
                                memOffsHi/*addr bias*/));
      boldLo
         = assignNew('B', mce, Ity_I32,
                     gen_load_b(mce, elemSzB, cas->addr,
                                memOffsLo/*addr bias*/));
      bind_shadow_tmp_to_orig('B', mce, mkexpr(cas->oldHi), boldHi);
      bind_shadow_tmp_to_orig('B', mce, mkexpr(cas->oldLo), boldLo);
   }

   /* 5. the CAS itself */
   stmt( 'C', mce, IRStmt_CAS(cas) );

   /* 6. compute "expected == old" */
   /* See COMMENT_ON_CasCmpEQ in this file background/rationale. */
   /* Note that 'C' is kinda faking it; it is indeed a non-shadow
      tree, but it's not copied from the input block. */
   /*
      xHi = oldHi ^ expdHi;
      xLo = oldLo ^ expdLo;
      xHL = xHi | xLo;
      expd_eq_old = xHL == 0;
   */
   xHi = assignNew('C', mce, elemTy,
                   binop(opXor, cas->expdHi, mkexpr(cas->oldHi))); 
   xLo = assignNew('C', mce, elemTy,
                   binop(opXor, cas->expdLo, mkexpr(cas->oldLo)));
   xHL = assignNew('C', mce, elemTy,
                   binop(opOr, xHi, xLo));
   expd_eq_old
      = assignNew('C', mce, Ity_I1,
                  binop(opCasCmpEQ, xHL, zero));

   /* 7. if "expected == old"
            store data# to shadow memory */
   do_shadow_Store( mce, cas->end, cas->addr, memOffsHi/*bias*/,
                    NULL/*data*/, vdataHi/*vdata*/,
                    expd_eq_old/*guard for store*/ );
   do_shadow_Store( mce, cas->end, cas->addr, memOffsLo/*bias*/,
                    NULL/*data*/, vdataLo/*vdata*/,
                    expd_eq_old/*guard for store*/ );
   if (otrak) {
      gen_store_b( mce, elemSzB, cas->addr, memOffsHi/*offset*/,
                   bdataHi/*bdata*/,
                   expd_eq_old/*guard for store*/ );
      gen_store_b( mce, elemSzB, cas->addr, memOffsLo/*offset*/,
                   bdataLo/*bdata*/,
                   expd_eq_old/*guard for store*/ );
   }
}


/* ------ Dealing with LL/SC (not difficult) ------ */

static void do_shadow_LLSC ( MCEnv*    mce,
                             IREndness stEnd,
                             IRTemp    stResult,
                             IRExpr*   stAddr,
                             IRExpr*   stStoredata )
{
   /* In short: treat a load-linked like a normal load followed by an
      assignment of the loaded (shadow) data to the result temporary.
      Treat a store-conditional like a normal store, and mark the
      result temporary as defined. */
   IRType resTy  = typeOfIRTemp(mce->sb->tyenv, stResult);
   IRTemp resTmp = findShadowTmpV(mce, stResult);

   tl_assert(isIRAtom(stAddr));
   if (stStoredata)
      tl_assert(isIRAtom(stStoredata));

   if (stStoredata == NULL) {
      /* Load Linked */
      /* Just treat this as a normal load, followed by an assignment of
         the value to .result. */
      /* Stay sane */
      tl_assert(resTy == Ity_I64 || resTy == Ity_I32
                || resTy == Ity_I16 || resTy == Ity_I8);
      assign( 'V', mce, resTmp,
                   expr2vbits_Load(
                      mce, stEnd, resTy, stAddr, 0/*addr bias*/,
                      NULL/*always happens*/) );
   } else {
      /* Store Conditional */
      /* Stay sane */
      IRType dataTy = typeOfIRExpr(mce->sb->tyenv,
                                   stStoredata);
      tl_assert(dataTy == Ity_I64 || dataTy == Ity_I32
                || dataTy == Ity_I16 || dataTy == Ity_I8);
      do_shadow_Store( mce, stEnd,
                            stAddr, 0/* addr bias */,
                            stStoredata,
                            NULL /* shadow data */,
                            NULL/*guard*/ );
      /* This is a store conditional, so it writes to .result a value
         indicating whether or not the store succeeded.  Just claim
         this value is always defined.  In the PowerPC interpretation
         of store-conditional, definedness of the success indication
         depends on whether the address of the store matches the
         reservation address.  But we can't tell that here (and
         anyway, we're not being PowerPC-specific).  At least we are
         guaranteed that the definedness of the store address, and its
         addressibility, will be checked as per normal.  So it seems
         pretty safe to just say that the success indication is always
         defined.

         In schemeS, for origin tracking, we must correspondingly set
         a no-origin value for the origin shadow of .result.
      */
      tl_assert(resTy == Ity_I1);
      assign( 'V', mce, resTmp, definedOfType(resTy) );
   }
}


/* ---- Dealing with LoadG/StoreG (not entirely simple) ---- */

static void do_shadow_StoreG ( MCEnv* mce, IRStoreG* sg )
{
   complainIfUndefined(mce, sg->guard, NULL);
   /* do_shadow_Store will generate code to check the definedness and
      validity of sg->addr, in the case where sg->guard evaluates to
      True at run-time. */
   do_shadow_Store( mce, sg->end,
                    sg->addr, 0/* addr bias */,
                    sg->data,
                    NULL /* shadow data */,
                    sg->guard );
}

static void do_shadow_LoadG ( MCEnv* mce, IRLoadG* lg )
{
   complainIfUndefined(mce, lg->guard, NULL);
   /* expr2vbits_Load_guarded_General will generate code to check the
      definedness and validity of lg->addr, in the case where
      lg->guard evaluates to True at run-time. */

   /* Look at the LoadG's built-in conversion operation, to determine
      the source (actual loaded data) type, and the equivalent IROp.
      NOTE that implicitly we are taking a widening operation to be
      applied to original atoms and producing one that applies to V
      bits.  Since signed and unsigned widening are self-shadowing,
      this is a straight copy of the op (modulo swapping from the
      IRLoadGOp form to the IROp form).  Note also therefore that this
      implicitly duplicates the logic to do with said widening ops in
      expr2vbits_Unop.  See comment at the start of expr2vbits_Unop. */
   IROp   vwiden   = Iop_INVALID;
   IRType loadedTy = Ity_INVALID;
   switch (lg->cvt) {
      case ILGop_Ident32: loadedTy = Ity_I32; vwiden = Iop_INVALID; break;
      case ILGop_16Uto32: loadedTy = Ity_I16; vwiden = Iop_16Uto32; break;
      case ILGop_16Sto32: loadedTy = Ity_I16; vwiden = Iop_16Sto32; break;
      case ILGop_8Uto32:  loadedTy = Ity_I8;  vwiden = Iop_8Uto32;  break;
      case ILGop_8Sto32:  loadedTy = Ity_I8;  vwiden = Iop_8Sto32;  break;
      default: VG_(tool_panic)("do_shadow_LoadG");
   }

   IRAtom* vbits_alt
      = expr2vbits( mce, lg->alt );
   IRAtom* vbits_final
      = expr2vbits_Load_guarded_General(mce, lg->end, loadedTy,
                                        lg->addr, 0/*addr bias*/,
                                        lg->guard, vwiden, vbits_alt );
   /* And finally, bind the V bits to the destination temporary. */
   assign( 'V', mce, findShadowTmpV(mce, lg->dst), vbits_final );
}


/*------------------------------------------------------------*/
/*--- Memcheck main                                        ---*/
/*------------------------------------------------------------*/

static void schemeS ( MCEnv* mce, IRStmt* st );

static Bool isBogusAtom ( IRAtom* at )
{
   ULong n = 0;
   IRConst* con;
   tl_assert(isIRAtom(at));
   if (at->tag == Iex_RdTmp)
      return False;
   tl_assert(at->tag == Iex_Const);
   con = at->Iex.Const.con;
   switch (con->tag) {
      case Ico_U1:   return False;
      case Ico_U8:   n = (ULong)con->Ico.U8; break;
      case Ico_U16:  n = (ULong)con->Ico.U16; break;
      case Ico_U32:  n = (ULong)con->Ico.U32; break;
      case Ico_U64:  n = (ULong)con->Ico.U64; break;
      case Ico_F64:  return False;
      case Ico_F32i: return False;
      case Ico_F64i: return False;
      case Ico_V128: return False;
      case Ico_V256: return False;
      default: ppIRExpr(at); tl_assert(0);
   }
   /* VG_(printf)("%llx\n", n); */
   return (/*32*/    n == 0xFEFEFEFFULL
           /*32*/ || n == 0x80808080ULL
           /*32*/ || n == 0x7F7F7F7FULL
           /*32*/ || n == 0x7EFEFEFFULL
           /*32*/ || n == 0x81010100ULL
           /*64*/ || n == 0xFFFFFFFFFEFEFEFFULL
           /*64*/ || n == 0xFEFEFEFEFEFEFEFFULL
           /*64*/ || n == 0x0000000000008080ULL
           /*64*/ || n == 0x8080808080808080ULL
           /*64*/ || n == 0x0101010101010101ULL
          );
}

static Bool checkForBogusLiterals ( /*FLAT*/ IRStmt* st )
{
   Int      i;
   IRExpr*  e;
   IRDirty* d;
   IRCAS*   cas;
   switch (st->tag) {
      case Ist_WrTmp:
         e = st->Ist.WrTmp.data;
         switch (e->tag) {
            case Iex_Get:
            case Iex_RdTmp:
               return False;
            case Iex_Const:
               return isBogusAtom(e);
            case Iex_Unop: 
               return isBogusAtom(e->Iex.Unop.arg)
                      || e->Iex.Unop.op == Iop_GetMSBs8x16;
            case Iex_GetI:
               return isBogusAtom(e->Iex.GetI.ix);
            case Iex_Binop: 
               return isBogusAtom(e->Iex.Binop.arg1)
                      || isBogusAtom(e->Iex.Binop.arg2);
            case Iex_Triop: 
               return isBogusAtom(e->Iex.Triop.details->arg1)
                      || isBogusAtom(e->Iex.Triop.details->arg2)
                      || isBogusAtom(e->Iex.Triop.details->arg3);
            case Iex_Qop: 
               return isBogusAtom(e->Iex.Qop.details->arg1)
                      || isBogusAtom(e->Iex.Qop.details->arg2)
                      || isBogusAtom(e->Iex.Qop.details->arg3)
                      || isBogusAtom(e->Iex.Qop.details->arg4);
            case Iex_ITE:
               return isBogusAtom(e->Iex.ITE.cond)
                      || isBogusAtom(e->Iex.ITE.iftrue)
                      || isBogusAtom(e->Iex.ITE.iffalse);
            case Iex_Load: 
               return isBogusAtom(e->Iex.Load.addr);
            case Iex_CCall:
               for (i = 0; e->Iex.CCall.args[i]; i++)
                  if (isBogusAtom(e->Iex.CCall.args[i]))
                     return True;
               return False;
            default: 
               goto unhandled;
         }
      case Ist_Dirty:
         d = st->Ist.Dirty.details;
         for (i = 0; d->args[i]; i++) {
            IRAtom* atom = d->args[i];
            if (LIKELY(!is_IRExpr_VECRET_or_BBPTR(atom))) {
               if (isBogusAtom(atom))
                  return True;
            }
         }
         if (isBogusAtom(d->guard))
            return True;
         if (d->mAddr && isBogusAtom(d->mAddr))
            return True;
         return False;
      case Ist_Put:
         return isBogusAtom(st->Ist.Put.data);
      case Ist_PutI:
         return isBogusAtom(st->Ist.PutI.details->ix) 
                || isBogusAtom(st->Ist.PutI.details->data);
      case Ist_Store:
         return isBogusAtom(st->Ist.Store.addr) 
                || isBogusAtom(st->Ist.Store.data);
      case Ist_StoreG: {
         IRStoreG* sg = st->Ist.StoreG.details;
         return isBogusAtom(sg->addr) || isBogusAtom(sg->data)
                || isBogusAtom(sg->guard);
      }
      case Ist_LoadG: {
         IRLoadG* lg = st->Ist.LoadG.details;
         return isBogusAtom(lg->addr) || isBogusAtom(lg->alt)
                || isBogusAtom(lg->guard);
      }
      case Ist_Exit:
         return isBogusAtom(st->Ist.Exit.guard);
      case Ist_AbiHint:
         return isBogusAtom(st->Ist.AbiHint.base)
                || isBogusAtom(st->Ist.AbiHint.nia);
      case Ist_NoOp:
      case Ist_IMark:
      case Ist_MBE:
         return False;
      case Ist_CAS:
         cas = st->Ist.CAS.details;
         return isBogusAtom(cas->addr)
                || (cas->expdHi ? isBogusAtom(cas->expdHi) : False)
                || isBogusAtom(cas->expdLo)
                || (cas->dataHi ? isBogusAtom(cas->dataHi) : False)
                || isBogusAtom(cas->dataLo);
      case Ist_LLSC:
         return isBogusAtom(st->Ist.LLSC.addr)
                || (st->Ist.LLSC.storedata
                       ? isBogusAtom(st->Ist.LLSC.storedata)
                       : False);
      default: 
      unhandled:
         ppIRStmt(st);
         VG_(tool_panic)("hasBogusLiterals");
   }
}


IRSB* MC_(instrument) ( VgCallbackClosure* closure,
                        IRSB* sb_in, 
                        VexGuestLayout* layout, 
                        VexGuestExtents* vge,
                        VexArchInfo* archinfo_host,
                        IRType gWordTy, IRType hWordTy )
{
   Bool    verboze = 0||False;
   Bool    bogus;
   Int     i, j, first_stmt;
   IRStmt* st;
   MCEnv   mce;
   IRSB*   sb_out;

   if (gWordTy != hWordTy) {
      /* We don't currently support this case. */
      VG_(tool_panic)("host/guest word size mismatch");
   }

   /* Check we're not completely nuts */
   tl_assert(sizeof(UWord)  == sizeof(void*));
   tl_assert(sizeof(Word)   == sizeof(void*));
   tl_assert(sizeof(Addr)   == sizeof(void*));
   tl_assert(sizeof(ULong)  == 8);
   tl_assert(sizeof(Long)   == 8);
   tl_assert(sizeof(Addr64) == 8);
   tl_assert(sizeof(UInt)   == 4);
   tl_assert(sizeof(Int)    == 4);

   tl_assert(MC_(clo_mc_level) >= 1 && MC_(clo_mc_level) <= 3);

   /* Set up SB */
   sb_out = deepCopyIRSBExceptStmts(sb_in);

   /* Set up the running environment.  Both .sb and .tmpMap are
      modified as we go along.  Note that tmps are added to both
      .sb->tyenv and .tmpMap together, so the valid index-set for
      those two arrays should always be identical. */
   VG_(memset)(&mce, 0, sizeof(mce));
   mce.sb             = sb_out;
   mce.trace          = verboze;
   mce.layout         = layout;
   mce.hWordTy        = hWordTy;
   mce.bogusLiterals  = False;

   /* Do expensive interpretation for Iop_Add32 and Iop_Add64 on
      Darwin.  10.7 is mostly built with LLVM, which uses these for
      bitfield inserts, and we get a lot of false errors if the cheap
      interpretation is used, alas.  Could solve this much better if
      we knew which of such adds came from x86/amd64 LEA instructions,
      since these are the only ones really needing the expensive
      interpretation, but that would require some way to tag them in
      the _toIR.c front ends, which is a lot of faffing around.  So
      for now just use the slow and blunt-instrument solution. */
   mce.useLLVMworkarounds = False;
#  if defined(VGO_darwin)
   mce.useLLVMworkarounds = True;
#  endif

   mce.tmpMap = VG_(newXA)( VG_(malloc), "mc.MC_(instrument).1", VG_(free),
                            sizeof(TempMapEnt));
   for (i = 0; i < sb_in->tyenv->types_used; i++) {
      TempMapEnt ent;
      ent.kind    = Orig;
      ent.shadowV = IRTemp_INVALID;
      ent.shadowB = IRTemp_INVALID;
      VG_(addToXA)( mce.tmpMap, &ent );
   }
   tl_assert( VG_(sizeXA)( mce.tmpMap ) == sb_in->tyenv->types_used );

   /* Make a preliminary inspection of the statements, to see if there
      are any dodgy-looking literals.  If there are, we generate
      extra-detailed (hence extra-expensive) instrumentation in
      places.  Scan the whole bb even if dodgyness is found earlier,
      so that the flatness assertion is applied to all stmts. */

   bogus = False;

   for (i = 0; i < sb_in->stmts_used; i++) {

      st = sb_in->stmts[i];
      tl_assert(st);
      tl_assert(isFlatIRStmt(st));

      if (!bogus) {
         bogus = checkForBogusLiterals(st);
         if (0 && bogus) {
            VG_(printf)("bogus: ");
            ppIRStmt(st);
            VG_(printf)("\n");
         }
      }

   }

   mce.bogusLiterals = bogus;

   /* Copy verbatim any IR preamble preceding the first IMark */

   tl_assert(mce.sb == sb_out);
   tl_assert(mce.sb != sb_in);

   i = 0;
   while (i < sb_in->stmts_used && sb_in->stmts[i]->tag != Ist_IMark) {

      st = sb_in->stmts[i];
      tl_assert(st);
      tl_assert(isFlatIRStmt(st));

      stmt( 'C', &mce, sb_in->stmts[i] );
      i++;
   }

   /* Nasty problem.  IR optimisation of the pre-instrumented IR may
      cause the IR following the preamble to contain references to IR
      temporaries defined in the preamble.  Because the preamble isn't
      instrumented, these temporaries don't have any shadows.
      Nevertheless uses of them following the preamble will cause
      memcheck to generate references to their shadows.  End effect is
      to cause IR sanity check failures, due to references to
      non-existent shadows.  This is only evident for the complex
      preambles used for function wrapping on TOC-afflicted platforms
      (ppc64-linux).

      The following loop therefore scans the preamble looking for
      assignments to temporaries.  For each one found it creates an
      assignment to the corresponding (V) shadow temp, marking it as
      'defined'.  This is the same resulting IR as if the main
      instrumentation loop before had been applied to the statement
      'tmp = CONSTANT'.

      Similarly, if origin tracking is enabled, we must generate an
      assignment for the corresponding origin (B) shadow, claiming
      no-origin, as appropriate for a defined value.
   */
   for (j = 0; j < i; j++) {
      if (sb_in->stmts[j]->tag == Ist_WrTmp) {
         /* findShadowTmpV checks its arg is an original tmp;
            no need to assert that here. */
         IRTemp tmp_o = sb_in->stmts[j]->Ist.WrTmp.tmp;
         IRTemp tmp_v = findShadowTmpV(&mce, tmp_o);
         IRType ty_v  = typeOfIRTemp(sb_out->tyenv, tmp_v);
         assign( 'V', &mce, tmp_v, definedOfType( ty_v ) );
         if (MC_(clo_mc_level) == 3) {
            IRTemp tmp_b = findShadowTmpB(&mce, tmp_o);
            tl_assert(typeOfIRTemp(sb_out->tyenv, tmp_b) == Ity_I32);
            assign( 'B', &mce, tmp_b, mkU32(0)/* UNKNOWN ORIGIN */);
         }
         if (0) {
            VG_(printf)("create shadow tmp(s) for preamble tmp [%d] ty ", j);
            ppIRType( ty_v );
            VG_(printf)("\n");
         }
      }
   }

   /* Iterate over the remaining stmts to generate instrumentation. */

   tl_assert(sb_in->stmts_used > 0);
   tl_assert(i >= 0);
   tl_assert(i < sb_in->stmts_used);
   tl_assert(sb_in->stmts[i]->tag == Ist_IMark);

   for (/* use current i*/; i < sb_in->stmts_used; i++) {

      st = sb_in->stmts[i];
      first_stmt = sb_out->stmts_used;

      if (verboze) {
         VG_(printf)("\n");
         ppIRStmt(st);
         VG_(printf)("\n");
      }

      if (MC_(clo_mc_level) == 3) {
         /* See comments on case Ist_CAS below. */
         if (st->tag != Ist_CAS) 
            schemeS( &mce, st );
      }

      /* Generate instrumentation code for each stmt ... */

      switch (st->tag) {

         case Ist_WrTmp:
            assign( 'V', &mce, findShadowTmpV(&mce, st->Ist.WrTmp.tmp), 
                               expr2vbits( &mce, st->Ist.WrTmp.data) );
            break;

         case Ist_Put:
            do_shadow_PUT( &mce, 
                           st->Ist.Put.offset,
                           st->Ist.Put.data,
                           NULL /* shadow atom */, NULL /* guard */ );
            break;

         case Ist_PutI:
            do_shadow_PUTI( &mce, st->Ist.PutI.details);
            break;

         case Ist_Store:
            do_shadow_Store( &mce, st->Ist.Store.end,
                                   st->Ist.Store.addr, 0/* addr bias */,
                                   st->Ist.Store.data,
                                   NULL /* shadow data */,
                                   NULL/*guard*/ );
            break;

         case Ist_StoreG:
            do_shadow_StoreG( &mce, st->Ist.StoreG.details );
            break;

         case Ist_LoadG:
            do_shadow_LoadG( &mce, st->Ist.LoadG.details );
            break;

         case Ist_Exit:
            complainIfUndefined( &mce, st->Ist.Exit.guard, NULL );
            break;

         case Ist_IMark:
            break;

         case Ist_NoOp:
         case Ist_MBE:
            break;

         case Ist_Dirty:
            do_shadow_Dirty( &mce, st->Ist.Dirty.details );
            break;

         case Ist_AbiHint:
            do_AbiHint( &mce, st->Ist.AbiHint.base,
                              st->Ist.AbiHint.len,
                              st->Ist.AbiHint.nia );
            break;

         case Ist_CAS:
            do_shadow_CAS( &mce, st->Ist.CAS.details );
            /* Note, do_shadow_CAS copies the CAS itself to the output
               block, because it needs to add instrumentation both
               before and after it.  Hence skip the copy below.  Also
               skip the origin-tracking stuff (call to schemeS) above,
               since that's all tangled up with it too; do_shadow_CAS
               does it all. */
            break;

         case Ist_LLSC:
            do_shadow_LLSC( &mce,
                            st->Ist.LLSC.end,
                            st->Ist.LLSC.result,
                            st->Ist.LLSC.addr,
                            st->Ist.LLSC.storedata );
            break;

         default:
            VG_(printf)("\n");
            ppIRStmt(st);
            VG_(printf)("\n");
            VG_(tool_panic)("memcheck: unhandled IRStmt");

      } /* switch (st->tag) */

      if (0 && verboze) {
         for (j = first_stmt; j < sb_out->stmts_used; j++) {
            VG_(printf)("   ");
            ppIRStmt(sb_out->stmts[j]);
            VG_(printf)("\n");
         }
         VG_(printf)("\n");
      }

      /* ... and finally copy the stmt itself to the output.  Except,
         skip the copy of IRCASs; see comments on case Ist_CAS
         above. */
      if (st->tag != Ist_CAS)
         stmt('C', &mce, st);
   }

   /* Now we need to complain if the jump target is undefined. */
   first_stmt = sb_out->stmts_used;

   if (verboze) {
      VG_(printf)("sb_in->next = ");
      ppIRExpr(sb_in->next);
      VG_(printf)("\n\n");
   }

   complainIfUndefined( &mce, sb_in->next, NULL );

   if (0 && verboze) {
      for (j = first_stmt; j < sb_out->stmts_used; j++) {
         VG_(printf)("   ");
         ppIRStmt(sb_out->stmts[j]);
         VG_(printf)("\n");
      }
      VG_(printf)("\n");
   }

   /* If this fails, there's been some serious snafu with tmp management,
      that should be investigated. */
   tl_assert( VG_(sizeXA)( mce.tmpMap ) == mce.sb->tyenv->types_used );
   VG_(deleteXA)( mce.tmpMap );

   tl_assert(mce.sb == sb_out);
   return sb_out;
}

/*------------------------------------------------------------*/
/*--- Post-tree-build final tidying                        ---*/
/*------------------------------------------------------------*/

/* This exploits the observation that Memcheck often produces
   repeated conditional calls of the form

   Dirty G MC_(helperc_value_check0/1/4/8_fail)(UInt otag)

   with the same guard expression G guarding the same helper call.
   The second and subsequent calls are redundant.  This usually
   results from instrumentation of guest code containing multiple
   memory references at different constant offsets from the same base
   register.  After optimisation of the instrumentation, you get a
   test for the definedness of the base register for each memory
   reference, which is kinda pointless.  MC_(final_tidy) therefore
   looks for such repeated calls and removes all but the first. */

/* A struct for recording which (helper, guard) pairs we have already
   seen. */
typedef
   struct { void* entry; IRExpr* guard; }
   Pair;

/* Return True if e1 and e2 definitely denote the same value (used to
   compare guards).  Return False if unknown; False is the safe
   answer.  Since guest registers and guest memory do not have the
   SSA property we must return False if any Gets or Loads appear in
   the expression. */

static Bool sameIRValue ( IRExpr* e1, IRExpr* e2 )
{
   if (e1->tag != e2->tag)
      return False;
   switch (e1->tag) {
      case Iex_Const:
         return eqIRConst( e1->Iex.Const.con, e2->Iex.Const.con );
      case Iex_Binop:
         return e1->Iex.Binop.op == e2->Iex.Binop.op 
                && sameIRValue(e1->Iex.Binop.arg1, e2->Iex.Binop.arg1)
                && sameIRValue(e1->Iex.Binop.arg2, e2->Iex.Binop.arg2);
      case Iex_Unop:
         return e1->Iex.Unop.op == e2->Iex.Unop.op 
                && sameIRValue(e1->Iex.Unop.arg, e2->Iex.Unop.arg);
      case Iex_RdTmp:
         return e1->Iex.RdTmp.tmp == e2->Iex.RdTmp.tmp;
      case Iex_ITE:
         return sameIRValue( e1->Iex.ITE.cond, e2->Iex.ITE.cond )
                && sameIRValue( e1->Iex.ITE.iftrue,  e2->Iex.ITE.iftrue )
                && sameIRValue( e1->Iex.ITE.iffalse, e2->Iex.ITE.iffalse );
      case Iex_Qop:
      case Iex_Triop:
      case Iex_CCall:
         /* be lazy.  Could define equality for these, but they never
            appear to be used. */
         return False;
      case Iex_Get:
      case Iex_GetI:
      case Iex_Load:
         /* be conservative - these may not give the same value each
            time */
         return False;
      case Iex_Binder:
         /* should never see this */
         /* fallthrough */
      default:
         VG_(printf)("mc_translate.c: sameIRValue: unhandled: ");
         ppIRExpr(e1); 
         VG_(tool_panic)("memcheck:sameIRValue");
         return False;
   }
}

/* See if 'pairs' already has an entry for (entry, guard).  Return
   True if so.  If not, add an entry. */

static 
Bool check_or_add ( XArray* /*of Pair*/ pairs, IRExpr* guard, void* entry )
{
   Pair  p;
   Pair* pp;
   Int   i, n = VG_(sizeXA)( pairs );
   for (i = 0; i < n; i++) {
      pp = VG_(indexXA)( pairs, i );
      if (pp->entry == entry && sameIRValue(pp->guard, guard))
         return True;
   }
   p.guard = guard;
   p.entry = entry;
   VG_(addToXA)( pairs, &p );
   return False;
}

static Bool is_helperc_value_checkN_fail ( const HChar* name )
{
   return
      0==VG_(strcmp)(name, "MC_(helperc_value_check0_fail_no_o)")
      || 0==VG_(strcmp)(name, "MC_(helperc_value_check1_fail_no_o)")
      || 0==VG_(strcmp)(name, "MC_(helperc_value_check4_fail_no_o)")
      || 0==VG_(strcmp)(name, "MC_(helperc_value_check8_fail_no_o)")
      || 0==VG_(strcmp)(name, "MC_(helperc_value_check0_fail_w_o)")
      || 0==VG_(strcmp)(name, "MC_(helperc_value_check1_fail_w_o)")
      || 0==VG_(strcmp)(name, "MC_(helperc_value_check4_fail_w_o)")
      || 0==VG_(strcmp)(name, "MC_(helperc_value_check8_fail_w_o)");
}

IRSB* MC_(final_tidy) ( IRSB* sb_in )
{
   Int i;
   IRStmt*   st;
   IRDirty*  di;
   IRExpr*   guard;
   IRCallee* cee;
   Bool      alreadyPresent;
   XArray*   pairs = VG_(newXA)( VG_(malloc), "mc.ft.1",
                                 VG_(free), sizeof(Pair) );
   /* Scan forwards through the statements.  Each time a call to one
      of the relevant helpers is seen, check if we have made a
      previous call to the same helper using the same guard
      expression, and if so, delete the call. */
   for (i = 0; i < sb_in->stmts_used; i++) {
      st = sb_in->stmts[i];
      tl_assert(st);
      if (st->tag != Ist_Dirty)
         continue;
      di = st->Ist.Dirty.details;
      guard = di->guard;
      tl_assert(guard);
      if (0) { ppIRExpr(guard); VG_(printf)("\n"); }
      cee = di->cee;
      if (!is_helperc_value_checkN_fail( cee->name )) 
         continue;
       /* Ok, we have a call to helperc_value_check0/1/4/8_fail with
          guard 'guard'.  Check if we have already seen a call to this
          function with the same guard.  If so, delete it.  If not,
          add it to the set of calls we do know about. */
      alreadyPresent = check_or_add( pairs, guard, cee->addr );
      if (alreadyPresent) {
         sb_in->stmts[i] = IRStmt_NoOp();
         if (0) VG_(printf)("XX\n");
      }
   }
   VG_(deleteXA)( pairs );
   return sb_in;
}


/*------------------------------------------------------------*/
/*--- Origin tracking stuff                                ---*/
/*------------------------------------------------------------*/

/* Almost identical to findShadowTmpV. */
static IRTemp findShadowTmpB ( MCEnv* mce, IRTemp orig )
{
   TempMapEnt* ent;
   /* VG_(indexXA) range-checks 'orig', hence no need to check
      here. */
   ent = (TempMapEnt*)VG_(indexXA)( mce->tmpMap, (Word)orig );
   tl_assert(ent->kind == Orig);
   if (ent->shadowB == IRTemp_INVALID) {
      IRTemp tmpB
        = newTemp( mce, Ity_I32, BSh );
      /* newTemp may cause mce->tmpMap to resize, hence previous results
         from VG_(indexXA) are invalid. */
      ent = (TempMapEnt*)VG_(indexXA)( mce->tmpMap, (Word)orig );
      tl_assert(ent->kind == Orig);
      tl_assert(ent->shadowB == IRTemp_INVALID);
      ent->shadowB = tmpB;
   }
   return ent->shadowB;
}

static IRAtom* gen_maxU32 ( MCEnv* mce, IRAtom* b1, IRAtom* b2 )
{
   return assignNew( 'B', mce, Ity_I32, binop(Iop_Max32U, b1, b2) );
}


/* Make a guarded origin load, with no special handling in the
   didn't-happen case.  A GUARD of NULL is assumed to mean "always
   True".

   Generate IR to do a shadow origins load from BASEADDR+OFFSET and
   return the otag.  The loaded size is SZB.  If GUARD evaluates to
   False at run time then the returned otag is zero.
*/
static IRAtom* gen_guarded_load_b ( MCEnv* mce, Int szB, 
                                    IRAtom* baseaddr, 
                                    Int offset, IRExpr* guard )
{
   void*    hFun;
   const HChar* hName;
   IRTemp   bTmp;
   IRDirty* di;
   IRType   aTy   = typeOfIRExpr( mce->sb->tyenv, baseaddr );
   IROp     opAdd = aTy == Ity_I32 ? Iop_Add32 : Iop_Add64;
   IRAtom*  ea    = baseaddr;
   if (offset != 0) {
      IRAtom* off = aTy == Ity_I32 ? mkU32( offset )
                                   : mkU64( (Long)(Int)offset );
      ea = assignNew( 'B', mce, aTy, binop(opAdd, ea, off));
   }
   bTmp = newTemp(mce, mce->hWordTy, BSh);

   switch (szB) {
      case 1: hFun  = (void*)&MC_(helperc_b_load1);
              hName = "MC_(helperc_b_load1)";
              break;
      case 2: hFun  = (void*)&MC_(helperc_b_load2);
              hName = "MC_(helperc_b_load2)";
              break;
      case 4: hFun  = (void*)&MC_(helperc_b_load4);
              hName = "MC_(helperc_b_load4)";
              break;
      case 8: hFun  = (void*)&MC_(helperc_b_load8);
              hName = "MC_(helperc_b_load8)";
              break;
      case 16: hFun  = (void*)&MC_(helperc_b_load16);
               hName = "MC_(helperc_b_load16)";
               break;
      case 32: hFun  = (void*)&MC_(helperc_b_load32);
               hName = "MC_(helperc_b_load32)";
               break;
      default:
         VG_(printf)("mc_translate.c: gen_load_b: unhandled szB == %d\n", szB);
         tl_assert(0);
   }
   di = unsafeIRDirty_1_N(
           bTmp, 1/*regparms*/, hName, VG_(fnptr_to_fnentry)( hFun ),
           mkIRExprVec_1( ea )
        );
   if (guard) {
      di->guard = guard;
      /* Ideally the didn't-happen return value here would be
         all-zeroes (unknown-origin), so it'd be harmless if it got
         used inadvertantly.  We slum it out with the IR-mandated
         default value (0b01 repeating, 0x55 etc) as that'll probably
         trump all legitimate otags via Max32, and it's pretty
         obviously bogus. */
   }
   /* no need to mess with any annotations.  This call accesses
      neither guest state nor guest memory. */
   stmt( 'B', mce, IRStmt_Dirty(di) );
   if (mce->hWordTy == Ity_I64) {
      /* 64-bit host */
      IRTemp bTmp32 = newTemp(mce, Ity_I32, BSh);
      assign( 'B', mce, bTmp32, unop(Iop_64to32, mkexpr(bTmp)) );
      return mkexpr(bTmp32);
   } else {
      /* 32-bit host */
      return mkexpr(bTmp);
   }
}


/* Generate IR to do a shadow origins load from BASEADDR+OFFSET.  The
   loaded size is SZB.  The load is regarded as unconditional (always
   happens).
*/
static IRAtom* gen_load_b ( MCEnv* mce, Int szB, IRAtom* baseaddr,
                            Int offset )
{
   return gen_guarded_load_b(mce, szB, baseaddr, offset, NULL/*guard*/);
}


/* The most general handler for guarded origin loads.  A GUARD of NULL
   is assumed to mean "always True".

   Generate IR to do a shadow origin load from ADDR+BIAS and return
   the B bits.  The loaded type is TY.  If GUARD evaluates to False at
   run time then the returned B bits are simply BALT instead.
*/
static
IRAtom* expr2ori_Load_guarded_General ( MCEnv* mce,
                                        IRType ty,
                                        IRAtom* addr, UInt bias,
                                        IRAtom* guard, IRAtom* balt )
{
   /* If the guard evaluates to True, this will hold the loaded
      origin.  If the guard evaluates to False, this will be zero,
      meaning "unknown origin", in which case we will have to replace
      it using an ITE below. */
   IRAtom* iftrue
      = assignNew('B', mce, Ity_I32,
                  gen_guarded_load_b(mce, sizeofIRType(ty),
                                     addr, bias, guard));
   /* These are the bits we will return if the load doesn't take
      place. */
   IRAtom* iffalse 
      = balt;
   /* Prepare the cond for the ITE.  Convert a NULL cond into
      something that iropt knows how to fold out later. */
   IRAtom* cond
      = guard == NULL  ? mkU1(1)  : guard;
   /* And assemble the final result. */
   return assignNew('B', mce, Ity_I32, IRExpr_ITE(cond, iftrue, iffalse));
}


/* Generate a shadow origins store.  guard :: Ity_I1 controls whether
   the store really happens; NULL means it unconditionally does. */
static void gen_store_b ( MCEnv* mce, Int szB,
                          IRAtom* baseaddr, Int offset, IRAtom* dataB,
                          IRAtom* guard )
{
   void*    hFun;
   const HChar* hName;
   IRDirty* di;
   IRType   aTy   = typeOfIRExpr( mce->sb->tyenv, baseaddr );
   IROp     opAdd = aTy == Ity_I32 ? Iop_Add32 : Iop_Add64;
   IRAtom*  ea    = baseaddr;
   if (guard) {
      tl_assert(isOriginalAtom(mce, guard));
      tl_assert(typeOfIRExpr(mce->sb->tyenv, guard) == Ity_I1);
   }
   if (offset != 0) {
      IRAtom* off = aTy == Ity_I32 ? mkU32( offset )
                                   : mkU64( (Long)(Int)offset );
      ea = assignNew(  'B', mce, aTy, binop(opAdd, ea, off));
   }
   if (mce->hWordTy == Ity_I64)
      dataB = assignNew( 'B', mce, Ity_I64, unop(Iop_32Uto64, dataB));

   switch (szB) {
      case 1: hFun  = (void*)&MC_(helperc_b_store1);
              hName = "MC_(helperc_b_store1)";
              break;
      case 2: hFun  = (void*)&MC_(helperc_b_store2);
              hName = "MC_(helperc_b_store2)";
              break;
      case 4: hFun  = (void*)&MC_(helperc_b_store4);
              hName = "MC_(helperc_b_store4)";
              break;
      case 8: hFun  = (void*)&MC_(helperc_b_store8);
              hName = "MC_(helperc_b_store8)";
              break;
      case 16: hFun  = (void*)&MC_(helperc_b_store16);
               hName = "MC_(helperc_b_store16)";
               break;
      case 32: hFun  = (void*)&MC_(helperc_b_store32);
               hName = "MC_(helperc_b_store32)";
               break;
      default:
         tl_assert(0);
   }
   di = unsafeIRDirty_0_N( 2/*regparms*/,
           hName, VG_(fnptr_to_fnentry)( hFun ),
           mkIRExprVec_2( ea, dataB )
        );
   /* no need to mess with any annotations.  This call accesses
      neither guest state nor guest memory. */
   if (guard) di->guard = guard;
   stmt( 'B', mce, IRStmt_Dirty(di) );
}

static IRAtom* narrowTo32 ( MCEnv* mce, IRAtom* e ) {
   IRType eTy = typeOfIRExpr(mce->sb->tyenv, e);
   if (eTy == Ity_I64)
      return assignNew( 'B', mce, Ity_I32, unop(Iop_64to32, e) );
   if (eTy == Ity_I32)
      return e;
   tl_assert(0);
}

static IRAtom* zWidenFrom32 ( MCEnv* mce, IRType dstTy, IRAtom* e ) {
   IRType eTy = typeOfIRExpr(mce->sb->tyenv, e);
   tl_assert(eTy == Ity_I32);
   if (dstTy == Ity_I64)
      return assignNew( 'B', mce, Ity_I64, unop(Iop_32Uto64, e) );
   tl_assert(0);
}


static IRAtom* schemeE ( MCEnv* mce, IRExpr* e )
{
   tl_assert(MC_(clo_mc_level) == 3);

   switch (e->tag) {

      case Iex_GetI: {
         IRRegArray* descr_b;
         IRAtom      *t1, *t2, *t3, *t4;
         IRRegArray* descr      = e->Iex.GetI.descr;
         IRType equivIntTy 
            = MC_(get_otrack_reg_array_equiv_int_type)(descr);
         /* If this array is unshadowable for whatever reason, use the
            usual approximation. */
         if (equivIntTy == Ity_INVALID)
            return mkU32(0);
         tl_assert(sizeofIRType(equivIntTy) >= 4);
         tl_assert(sizeofIRType(equivIntTy) == sizeofIRType(descr->elemTy));
         descr_b = mkIRRegArray( descr->base + 2*mce->layout->total_sizeB,
                                 equivIntTy, descr->nElems );
         /* Do a shadow indexed get of the same size, giving t1.  Take
            the bottom 32 bits of it, giving t2.  Compute into t3 the
            origin for the index (almost certainly zero, but there's
            no harm in being completely general here, since iropt will
            remove any useless code), and fold it in, giving a final
            value t4. */
         t1 = assignNew( 'B', mce, equivIntTy, 
                          IRExpr_GetI( descr_b, e->Iex.GetI.ix, 
                                                e->Iex.GetI.bias ));
         t2 = narrowTo32( mce, t1 );
         t3 = schemeE( mce, e->Iex.GetI.ix );
         t4 = gen_maxU32( mce, t2, t3 );
         return t4;
      }
      case Iex_CCall: {
         Int i;
         IRAtom*  here;
         IRExpr** args = e->Iex.CCall.args;
         IRAtom*  curr = mkU32(0);
         for (i = 0; args[i]; i++) {
            tl_assert(i < 32);
            tl_assert(isOriginalAtom(mce, args[i]));
            /* Only take notice of this arg if the callee's
               mc-exclusion mask does not say it is to be excluded. */
            if (e->Iex.CCall.cee->mcx_mask & (1<<i)) {
               /* the arg is to be excluded from definedness checking.
                  Do nothing. */
               if (0) VG_(printf)("excluding %s(%d)\n",
                                  e->Iex.CCall.cee->name, i);
            } else {
               /* calculate the arg's definedness, and pessimistically
                  merge it in. */
               here = schemeE( mce, args[i] );
               curr = gen_maxU32( mce, curr, here );
            }
         }
         return curr;
      }
      case Iex_Load: {
         Int dszB;
         dszB = sizeofIRType(e->Iex.Load.ty);
         /* assert that the B value for the address is already
            available (somewhere) */
         tl_assert(isIRAtom(e->Iex.Load.addr));
         tl_assert(mce->hWordTy == Ity_I32 || mce->hWordTy == Ity_I64);
         return gen_load_b( mce, dszB, e->Iex.Load.addr, 0 );
      }
      case Iex_ITE: {
         IRAtom* b1 = schemeE( mce, e->Iex.ITE.cond );
         IRAtom* b3 = schemeE( mce, e->Iex.ITE.iftrue );
         IRAtom* b2 = schemeE( mce, e->Iex.ITE.iffalse );
         return gen_maxU32( mce, b1, gen_maxU32( mce, b2, b3 ));
      }
      case Iex_Qop: {
         IRAtom* b1 = schemeE( mce, e->Iex.Qop.details->arg1 );
         IRAtom* b2 = schemeE( mce, e->Iex.Qop.details->arg2 );
         IRAtom* b3 = schemeE( mce, e->Iex.Qop.details->arg3 );
         IRAtom* b4 = schemeE( mce, e->Iex.Qop.details->arg4 );
         return gen_maxU32( mce, gen_maxU32( mce, b1, b2 ),
                                 gen_maxU32( mce, b3, b4 ) );
      }
      case Iex_Triop: {
         IRAtom* b1 = schemeE( mce, e->Iex.Triop.details->arg1 );
         IRAtom* b2 = schemeE( mce, e->Iex.Triop.details->arg2 );
         IRAtom* b3 = schemeE( mce, e->Iex.Triop.details->arg3 );
         return gen_maxU32( mce, b1, gen_maxU32( mce, b2, b3 ) );
      }
      case Iex_Binop: {
         switch (e->Iex.Binop.op) {
            case Iop_CasCmpEQ8:  case Iop_CasCmpNE8:
            case Iop_CasCmpEQ16: case Iop_CasCmpNE16:
            case Iop_CasCmpEQ32: case Iop_CasCmpNE32:
            case Iop_CasCmpEQ64: case Iop_CasCmpNE64:
               /* Just say these all produce a defined result,
                  regardless of their arguments.  See
                  COMMENT_ON_CasCmpEQ in this file. */
               return mkU32(0);
            default: {
               IRAtom* b1 = schemeE( mce, e->Iex.Binop.arg1 );
               IRAtom* b2 = schemeE( mce, e->Iex.Binop.arg2 );
               return gen_maxU32( mce, b1, b2 );
            }
         }
         tl_assert(0);
         /*NOTREACHED*/
      }
      case Iex_Unop: {
         IRAtom* b1 = schemeE( mce, e->Iex.Unop.arg );
         return b1;
      }
      case Iex_Const:
         return mkU32(0);
      case Iex_RdTmp:
         return mkexpr( findShadowTmpB( mce, e->Iex.RdTmp.tmp ));
      case Iex_Get: {
         Int b_offset = MC_(get_otrack_shadow_offset)( 
                           e->Iex.Get.offset,
                           sizeofIRType(e->Iex.Get.ty) 
                        );
         tl_assert(b_offset >= -1
                   && b_offset <= mce->layout->total_sizeB -4);
         if (b_offset >= 0) {
            /* FIXME: this isn't an atom! */
            return IRExpr_Get( b_offset + 2*mce->layout->total_sizeB,
                               Ity_I32 );
         }
         return mkU32(0);
      }
      default:
         VG_(printf)("mc_translate.c: schemeE: unhandled: ");
         ppIRExpr(e); 
         VG_(tool_panic)("memcheck:schemeE");
   }
}


static void do_origins_Dirty ( MCEnv* mce, IRDirty* d )
{
   // This is a hacked version of do_shadow_Dirty
   Int       i, k, n, toDo, gSz, gOff;
   IRAtom    *here, *curr;
   IRTemp    dst;

   /* First check the guard. */
   curr = schemeE( mce, d->guard );

   /* Now round up all inputs and maxU32 over them. */

   /* Inputs: unmasked args
      Note: arguments are evaluated REGARDLESS of the guard expression */
   for (i = 0; d->args[i]; i++) {
      IRAtom* arg = d->args[i];
      if ( (d->cee->mcx_mask & (1<<i))
           || UNLIKELY(is_IRExpr_VECRET_or_BBPTR(arg)) ) {
         /* ignore this arg */
      } else {
         here = schemeE( mce, arg );
         curr = gen_maxU32( mce, curr, here );
      }
   }

   /* Inputs: guest state that we read. */
   for (i = 0; i < d->nFxState; i++) {
      tl_assert(d->fxState[i].fx != Ifx_None);
      if (d->fxState[i].fx == Ifx_Write)
         continue;

      /* Enumerate the described state segments */
      for (k = 0; k < 1 + d->fxState[i].nRepeats; k++) {
         gOff = d->fxState[i].offset + k * d->fxState[i].repeatLen;
         gSz  = d->fxState[i].size;

         /* Ignore any sections marked as 'always defined'. */
         if (isAlwaysDefd(mce, gOff, gSz)) {
            if (0)
            VG_(printf)("memcheck: Dirty gst: ignored off %d, sz %d\n",
                        gOff, gSz);
            continue;
         }

         /* This state element is read or modified.  So we need to
            consider it.  If larger than 4 bytes, deal with it in
            4-byte chunks. */
         while (True) {
            Int b_offset;
            tl_assert(gSz >= 0);
            if (gSz == 0) break;
            n = gSz <= 4 ? gSz : 4;
            /* update 'curr' with maxU32 of the state slice 
               gOff .. gOff+n-1 */
            b_offset = MC_(get_otrack_shadow_offset)(gOff, 4);
            if (b_offset != -1) {
               /* Observe the guard expression. If it is false use 0, i.e.
                  nothing is known about the origin */
               IRAtom *cond, *iffalse, *iftrue;

               cond = assignNew( 'B', mce, Ity_I1, d->guard);
               iffalse = mkU32(0);
               iftrue  = assignNew( 'B', mce, Ity_I32,
                                    IRExpr_Get(b_offset
                                                 + 2*mce->layout->total_sizeB,
                                               Ity_I32));
               here = assignNew( 'B', mce, Ity_I32,
                                 IRExpr_ITE(cond, iftrue, iffalse));
               curr = gen_maxU32( mce, curr, here );
            }
            gSz -= n;
            gOff += n;
         }
      }
   }

   /* Inputs: memory */

   if (d->mFx != Ifx_None) {
      /* Because we may do multiple shadow loads/stores from the same
         base address, it's best to do a single test of its
         definedness right now.  Post-instrumentation optimisation
         should remove all but this test. */
      tl_assert(d->mAddr);
      here = schemeE( mce, d->mAddr );
      curr = gen_maxU32( mce, curr, here );
   }

   /* Deal with memory inputs (reads or modifies) */
   if (d->mFx == Ifx_Read || d->mFx == Ifx_Modify) {
      toDo   = d->mSize;
      /* chew off 32-bit chunks.  We don't care about the endianness
         since it's all going to be condensed down to a single bit,
         but nevertheless choose an endianness which is hopefully
         native to the platform. */
      while (toDo >= 4) {
         here = gen_guarded_load_b( mce, 4, d->mAddr, d->mSize - toDo,
                                    d->guard );
         curr = gen_maxU32( mce, curr, here );
         toDo -= 4;
      }
      /* handle possible 16-bit excess */
      while (toDo >= 2) {
         here = gen_guarded_load_b( mce, 2, d->mAddr, d->mSize - toDo,
                                    d->guard );
         curr = gen_maxU32( mce, curr, here );
         toDo -= 2;
      }
      /* chew off the remaining 8-bit chunk, if any */
      if (toDo == 1) {
         here = gen_guarded_load_b( mce, 1, d->mAddr, d->mSize - toDo,
                                    d->guard );
         curr = gen_maxU32( mce, curr, here );
         toDo -= 1;
      }
      tl_assert(toDo == 0);
   }

   /* Whew!  So curr is a 32-bit B-value which should give an origin
      of some use if any of the inputs to the helper are undefined.
      Now we need to re-distribute the results to all destinations. */

   /* Outputs: the destination temporary, if there is one. */
   if (d->tmp != IRTemp_INVALID) {
      dst   = findShadowTmpB(mce, d->tmp);
      assign( 'V', mce, dst, curr );
   }

   /* Outputs: guest state that we write or modify. */
   for (i = 0; i < d->nFxState; i++) {
      tl_assert(d->fxState[i].fx != Ifx_None);
      if (d->fxState[i].fx == Ifx_Read)
         continue;

      /* Enumerate the described state segments */
      for (k = 0; k < 1 + d->fxState[i].nRepeats; k++) {
         gOff = d->fxState[i].offset + k * d->fxState[i].repeatLen;
         gSz  = d->fxState[i].size;

         /* Ignore any sections marked as 'always defined'. */
         if (isAlwaysDefd(mce, gOff, gSz))
            continue;

         /* This state element is written or modified.  So we need to
            consider it.  If larger than 4 bytes, deal with it in
            4-byte chunks. */
         while (True) {
            Int b_offset;
            tl_assert(gSz >= 0);
            if (gSz == 0) break;
            n = gSz <= 4 ? gSz : 4;
            /* Write 'curr' to the state slice gOff .. gOff+n-1 */
            b_offset = MC_(get_otrack_shadow_offset)(gOff, 4);
            if (b_offset != -1) {

               /* If the guard expression evaluates to false we simply Put
                  the value that is already stored in the guest state slot */
               IRAtom *cond, *iffalse;

               cond    = assignNew('B', mce, Ity_I1,
                                   d->guard);
               iffalse = assignNew('B', mce, Ity_I32,
                                   IRExpr_Get(b_offset +
                                              2*mce->layout->total_sizeB,
                                              Ity_I32));
               curr = assignNew('V', mce, Ity_I32,
                                IRExpr_ITE(cond, curr, iffalse));

               stmt( 'B', mce, IRStmt_Put(b_offset
                                          + 2*mce->layout->total_sizeB,
                                          curr ));
            }
            gSz -= n;
            gOff += n;
         }
      }
   }

   /* Outputs: memory that we write or modify.  Same comments about
      endianness as above apply. */
   if (d->mFx == Ifx_Write || d->mFx == Ifx_Modify) {
      toDo   = d->mSize;
      /* chew off 32-bit chunks */
      while (toDo >= 4) {
         gen_store_b( mce, 4, d->mAddr, d->mSize - toDo, curr,
                      d->guard );
         toDo -= 4;
      }
      /* handle possible 16-bit excess */
      while (toDo >= 2) {
         gen_store_b( mce, 2, d->mAddr, d->mSize - toDo, curr,
                      d->guard );
         toDo -= 2;
      }
      /* chew off the remaining 8-bit chunk, if any */
      if (toDo == 1) {
         gen_store_b( mce, 1, d->mAddr, d->mSize - toDo, curr,
                      d->guard );
         toDo -= 1;
      }
      tl_assert(toDo == 0);
   }
}


/* Generate IR for origin shadowing for a general guarded store. */
static void do_origins_Store_guarded ( MCEnv* mce,
                                       IREndness stEnd,
                                       IRExpr* stAddr,
                                       IRExpr* stData,
                                       IRExpr* guard )
{
   Int     dszB;
   IRAtom* dataB;
   /* assert that the B value for the address is already available
      (somewhere), since the call to schemeE will want to see it.
      XXXX how does this actually ensure that?? */
   tl_assert(isIRAtom(stAddr));
   tl_assert(isIRAtom(stData));
   dszB  = sizeofIRType( typeOfIRExpr(mce->sb->tyenv, stData ) );
   dataB = schemeE( mce, stData );
   gen_store_b( mce, dszB, stAddr, 0/*offset*/, dataB, guard );
}


/* Generate IR for origin shadowing for a plain store. */
static void do_origins_Store_plain ( MCEnv* mce,
                                     IREndness stEnd,
                                     IRExpr* stAddr,
                                     IRExpr* stData )
{
   do_origins_Store_guarded ( mce, stEnd, stAddr, stData,
                              NULL/*guard*/ );
}


/* ---- Dealing with LoadG/StoreG (not entirely simple) ---- */

static void do_origins_StoreG ( MCEnv* mce, IRStoreG* sg )
{
   do_origins_Store_guarded( mce, sg->end, sg->addr,
                             sg->data, sg->guard );
}

static void do_origins_LoadG ( MCEnv* mce, IRLoadG* lg )
{
   IRType loadedTy = Ity_INVALID;
   switch (lg->cvt) {
      case ILGop_Ident32: loadedTy = Ity_I32; break;
      case ILGop_16Uto32: loadedTy = Ity_I16; break;
      case ILGop_16Sto32: loadedTy = Ity_I16; break;
      case ILGop_8Uto32:  loadedTy = Ity_I8;  break;
      case ILGop_8Sto32:  loadedTy = Ity_I8;  break;
      default: VG_(tool_panic)("schemeS.IRLoadG");
   }
   IRAtom* ori_alt
      = schemeE( mce,lg->alt );
   IRAtom* ori_final
      = expr2ori_Load_guarded_General(mce, loadedTy,
                                      lg->addr, 0/*addr bias*/,
                                      lg->guard, ori_alt );
   /* And finally, bind the origin to the destination temporary. */
   assign( 'B', mce, findShadowTmpB(mce, lg->dst), ori_final );
}


static void schemeS ( MCEnv* mce, IRStmt* st )
{
   tl_assert(MC_(clo_mc_level) == 3);

   switch (st->tag) {

      case Ist_AbiHint:
         /* The value-check instrumenter handles this - by arranging
            to pass the address of the next instruction to
            MC_(helperc_MAKE_STACK_UNINIT).  This is all that needs to
            happen for origin tracking w.r.t. AbiHints.  So there is
            nothing to do here. */
         break;

      case Ist_PutI: {
         IRPutI *puti = st->Ist.PutI.details;
         IRRegArray* descr_b;
         IRAtom      *t1, *t2, *t3, *t4;
         IRRegArray* descr = puti->descr;
         IRType equivIntTy
            = MC_(get_otrack_reg_array_equiv_int_type)(descr);
         /* If this array is unshadowable for whatever reason,
            generate no code. */
         if (equivIntTy == Ity_INVALID)
            break;
         tl_assert(sizeofIRType(equivIntTy) >= 4);
         tl_assert(sizeofIRType(equivIntTy) == sizeofIRType(descr->elemTy));
         descr_b
            = mkIRRegArray( descr->base + 2*mce->layout->total_sizeB,
                            equivIntTy, descr->nElems );
         /* Compute a value to Put - the conjoinment of the origin for
            the data to be Put-ted (obviously) and of the index value
            (not so obviously). */
         t1 = schemeE( mce, puti->data );
         t2 = schemeE( mce, puti->ix );
         t3 = gen_maxU32( mce, t1, t2 );
         t4 = zWidenFrom32( mce, equivIntTy, t3 );
         stmt( 'B', mce, IRStmt_PutI( mkIRPutI(descr_b, puti->ix,
                                               puti->bias, t4) ));
         break;
      }

      case Ist_Dirty:
         do_origins_Dirty( mce, st->Ist.Dirty.details );
         break;

      case Ist_Store:
         do_origins_Store_plain( mce, st->Ist.Store.end,
                                      st->Ist.Store.addr,
                                      st->Ist.Store.data );
         break;

      case Ist_StoreG:
         do_origins_StoreG( mce, st->Ist.StoreG.details );
         break;

      case Ist_LoadG:
         do_origins_LoadG( mce, st->Ist.LoadG.details );
         break;

      case Ist_LLSC: {
         /* In short: treat a load-linked like a normal load followed
            by an assignment of the loaded (shadow) data the result
            temporary.  Treat a store-conditional like a normal store,
            and mark the result temporary as defined. */
         if (st->Ist.LLSC.storedata == NULL) {
            /* Load Linked */
            IRType resTy 
               = typeOfIRTemp(mce->sb->tyenv, st->Ist.LLSC.result);
            IRExpr* vanillaLoad
               = IRExpr_Load(st->Ist.LLSC.end, resTy, st->Ist.LLSC.addr);
            tl_assert(resTy == Ity_I64 || resTy == Ity_I32
                      || resTy == Ity_I16 || resTy == Ity_I8);
            assign( 'B', mce, findShadowTmpB(mce, st->Ist.LLSC.result),
                              schemeE(mce, vanillaLoad));
         } else {
            /* Store conditional */
            do_origins_Store_plain( mce, st->Ist.LLSC.end,
                                    st->Ist.LLSC.addr,
                                    st->Ist.LLSC.storedata );
            /* For the rationale behind this, see comments at the
               place where the V-shadow for .result is constructed, in
               do_shadow_LLSC.  In short, we regard .result as
               always-defined. */
            assign( 'B', mce, findShadowTmpB(mce, st->Ist.LLSC.result),
                              mkU32(0) );
         }
         break;
      }

      case Ist_Put: {
         Int b_offset
            = MC_(get_otrack_shadow_offset)(
                 st->Ist.Put.offset,
                 sizeofIRType(typeOfIRExpr(mce->sb->tyenv, st->Ist.Put.data))
              );
         if (b_offset >= 0) {
            /* FIXME: this isn't an atom! */
            stmt( 'B', mce, IRStmt_Put(b_offset + 2*mce->layout->total_sizeB, 
                                       schemeE( mce, st->Ist.Put.data )) );
         }
         break;
      }

      case Ist_WrTmp:
         assign( 'B', mce, findShadowTmpB(mce, st->Ist.WrTmp.tmp),
                           schemeE(mce, st->Ist.WrTmp.data) );
         break;

      case Ist_MBE:
      case Ist_NoOp:
      case Ist_Exit:
      case Ist_IMark:
         break;

      default:
         VG_(printf)("mc_translate.c: schemeS: unhandled: ");
         ppIRStmt(st); 
         VG_(tool_panic)("memcheck:schemeS");
   }
}


/*--------------------------------------------------------------------*/
/*--- end                                           mc_translate.c ---*/
/*--------------------------------------------------------------------*/