lib/Target/X86/X86AsmPrinter.cpp

//===-- X86AsmPrinter.cpp - Convert X86 LLVM code to AT&T assembly --------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains a printer that converts from our internal representation
// of machine-dependent LLVM code to X86 machine code.
//
//===----------------------------------------------------------------------===//

#include "X86AsmPrinter.h"
#include "InstPrinter/X86ATTInstPrinter.h"
#include "InstPrinter/X86IntelInstPrinter.h"
#include "X86MCInstLower.h"
#include "X86.h"
#include "X86COFFMachineModuleInfo.h"
#include "X86MachineFunctionInfo.h"
#include "X86TargetMachine.h"
#include "llvm/CallingConv.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Module.h"
#include "llvm/Type.h"
#include "llvm/Analysis/DebugInfo.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/CodeGen/MachineJumpTableInfo.h"
#include "llvm/CodeGen/MachineModuleInfoImpls.h"
#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
#include "llvm/Support/COFF.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Target/Mangler.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegistry.h"
#include "llvm/ADT/SmallString.h"
using namespace llvm;

//===----------------------------------------------------------------------===//
// Primitive Helper Functions.
//===----------------------------------------------------------------------===//

/// runOnMachineFunction - Emit the function body.
///
bool X86AsmPrinter::runOnMachineFunction(MachineFunction &MF) {
  SetupMachineFunction(MF);

  if (Subtarget->isTargetCOFF()) {
    bool Intrn = MF.getFunction()->hasInternalLinkage();
    OutStreamer.BeginCOFFSymbolDef(CurrentFnSym);
    OutStreamer.EmitCOFFSymbolStorageClass(Intrn ? COFF::IMAGE_SYM_CLASS_STATIC
                                              : COFF::IMAGE_SYM_CLASS_EXTERNAL);
    OutStreamer.EmitCOFFSymbolType(COFF::IMAGE_SYM_DTYPE_FUNCTION
                                               << COFF::SCT_COMPLEX_TYPE_SHIFT);
    OutStreamer.EndCOFFSymbolDef();
  }

  // Have common code print out the function header with linkage info etc.
  EmitFunctionHeader();

  // Emit the rest of the function body.
  EmitFunctionBody();

  // We didn't modify anything.
  return false;
}

/// printSymbolOperand - Print a raw symbol reference operand.  This handles
/// jump tables, constant pools, global address and external symbols, all of
/// which print to a label with various suffixes for relocation types etc.
void X86AsmPrinter::printSymbolOperand(const MachineOperand &MO,
                                       raw_ostream &O) {
  switch (MO.getType()) {
  default: llvm_unreachable("unknown symbol type!");
  case MachineOperand::MO_JumpTableIndex:
    O << *GetJTISymbol(MO.getIndex());
    break;
  case MachineOperand::MO_ConstantPoolIndex:
    O << *GetCPISymbol(MO.getIndex());
    printOffset(MO.getOffset(), O);
    break;
  case MachineOperand::MO_GlobalAddress: {
    const GlobalValue *GV = MO.getGlobal();

    MCSymbol *GVSym;
    if (MO.getTargetFlags() == X86II::MO_DARWIN_STUB)
      GVSym = GetSymbolWithGlobalValueBase(GV, "$stub");
    else if (MO.getTargetFlags() == X86II::MO_DARWIN_NONLAZY ||
             MO.getTargetFlags() == X86II::MO_DARWIN_NONLAZY_PIC_BASE ||
             MO.getTargetFlags() == X86II::MO_DARWIN_HIDDEN_NONLAZY_PIC_BASE)
      GVSym = GetSymbolWithGlobalValueBase(GV, "$non_lazy_ptr");
    else
      GVSym = Mang->getSymbol(GV);

    // Handle dllimport linkage.
    if (MO.getTargetFlags() == X86II::MO_DLLIMPORT)
      GVSym = OutContext.GetOrCreateSymbol(Twine("__imp_") + GVSym->getName());

    if (MO.getTargetFlags() == X86II::MO_DARWIN_NONLAZY ||
        MO.getTargetFlags() == X86II::MO_DARWIN_NONLAZY_PIC_BASE) {
      MCSymbol *Sym = GetSymbolWithGlobalValueBase(GV, "$non_lazy_ptr");
      MachineModuleInfoImpl::StubValueTy &StubSym =
        MMI->getObjFileInfo<MachineModuleInfoMachO>().getGVStubEntry(Sym);
      if (StubSym.getPointer() == 0)
        StubSym = MachineModuleInfoImpl::
          StubValueTy(Mang->getSymbol(GV), !GV->hasInternalLinkage());
    } else if (MO.getTargetFlags() == X86II::MO_DARWIN_HIDDEN_NONLAZY_PIC_BASE){
      MCSymbol *Sym = GetSymbolWithGlobalValueBase(GV, "$non_lazy_ptr");
      MachineModuleInfoImpl::StubValueTy &StubSym =
        MMI->getObjFileInfo<MachineModuleInfoMachO>().getHiddenGVStubEntry(Sym);
      if (StubSym.getPointer() == 0)
        StubSym = MachineModuleInfoImpl::
          StubValueTy(Mang->getSymbol(GV), !GV->hasInternalLinkage());
    } else if (MO.getTargetFlags() == X86II::MO_DARWIN_STUB) {
      MCSymbol *Sym = GetSymbolWithGlobalValueBase(GV, "$stub");
      MachineModuleInfoImpl::StubValueTy &StubSym =
        MMI->getObjFileInfo<MachineModuleInfoMachO>().getFnStubEntry(Sym);
      if (StubSym.getPointer() == 0)
        StubSym = MachineModuleInfoImpl::
          StubValueTy(Mang->getSymbol(GV), !GV->hasInternalLinkage());
    }

    // If the name begins with a dollar-sign, enclose it in parens.  We do this
    // to avoid having it look like an integer immediate to the assembler.
    if (GVSym->getName()[0] != '$')
      O << *GVSym;
    else
      O << '(' << *GVSym << ')';
    printOffset(MO.getOffset(), O);
    break;
  }
  case MachineOperand::MO_ExternalSymbol: {
    const MCSymbol *SymToPrint;
    if (MO.getTargetFlags() == X86II::MO_DARWIN_STUB) {
      SmallString<128> TempNameStr;
      TempNameStr += StringRef(MO.getSymbolName());
      TempNameStr += StringRef("$stub");

      MCSymbol *Sym = GetExternalSymbolSymbol(TempNameStr.str());
      MachineModuleInfoImpl::StubValueTy &StubSym =
        MMI->getObjFileInfo<MachineModuleInfoMachO>().getFnStubEntry(Sym);
      if (StubSym.getPointer() == 0) {
        TempNameStr.erase(TempNameStr.end()-5, TempNameStr.end());
        StubSym = MachineModuleInfoImpl::
          StubValueTy(OutContext.GetOrCreateSymbol(TempNameStr.str()),
                      true);
      }
      SymToPrint = StubSym.getPointer();
    } else {
      SymToPrint = GetExternalSymbolSymbol(MO.getSymbolName());
    }

    // If the name begins with a dollar-sign, enclose it in parens.  We do this
    // to avoid having it look like an integer immediate to the assembler.
    if (SymToPrint->getName()[0] != '$')
      O << *SymToPrint;
    else
      O << '(' << *SymToPrint << '(';
    break;
  }
  }

  switch (MO.getTargetFlags()) {
  default:
    llvm_unreachable("Unknown target flag on GV operand");
  case X86II::MO_NO_FLAG:    // No flag.
    break;
  case X86II::MO_DARWIN_NONLAZY:
  case X86II::MO_DLLIMPORT:
  case X86II::MO_DARWIN_STUB:
    // These affect the name of the symbol, not any suffix.
    break;
  case X86II::MO_GOT_ABSOLUTE_ADDRESS:
    O << " + [.-" << *MF->getPICBaseSymbol() << ']';
    break;
  case X86II::MO_PIC_BASE_OFFSET:
  case X86II::MO_DARWIN_NONLAZY_PIC_BASE:
  case X86II::MO_DARWIN_HIDDEN_NONLAZY_PIC_BASE:
    O << '-' << *MF->getPICBaseSymbol();
    break;
  case X86II::MO_TLSGD:     O << "@TLSGD";     break;
  case X86II::MO_GOTTPOFF:  O << "@GOTTPOFF";  break;
  case X86II::MO_INDNTPOFF: O << "@INDNTPOFF"; break;
  case X86II::MO_TPOFF:     O << "@TPOFF";     break;
  case X86II::MO_NTPOFF:    O << "@NTPOFF";    break;
  case X86II::MO_GOTPCREL:  O << "@GOTPCREL";  break;
  case X86II::MO_GOT:       O << "@GOT";       break;
  case X86II::MO_GOTOFF:    O << "@GOTOFF";    break;
  case X86II::MO_PLT:       O << "@PLT";       break;
  case X86II::MO_TLVP:      O << "@TLVP";      break;
  case X86II::MO_TLVP_PIC_BASE:
    O << "@TLVP" << '-' << *MF->getPICBaseSymbol();
    break;
  }
}

/// print_pcrel_imm - This is used to print an immediate value that ends up
/// being encoded as a pc-relative value.  These print slightly differently, for
/// example, a $ is not emitted.
void X86AsmPrinter::print_pcrel_imm(const MachineInstr *MI, unsigned OpNo,
                                    raw_ostream &O) {
  const MachineOperand &MO = MI->getOperand(OpNo);
  switch (MO.getType()) {
  default: llvm_unreachable("Unknown pcrel immediate operand");
  case MachineOperand::MO_Register:
    // pc-relativeness was handled when computing the value in the reg.
    printOperand(MI, OpNo, O);
    return;
  case MachineOperand::MO_Immediate:
    O << MO.getImm();
    return;
  case MachineOperand::MO_MachineBasicBlock:
    O << *MO.getMBB()->getSymbol();
    return;
  case MachineOperand::MO_GlobalAddress:
  case MachineOperand::MO_ExternalSymbol:
    printSymbolOperand(MO, O);
    return;
  }
}


void X86AsmPrinter::printOperand(const MachineInstr *MI, unsigned OpNo,
                                 raw_ostream &O, const char *Modifier) {
  const MachineOperand &MO = MI->getOperand(OpNo);
  switch (MO.getType()) {
  default: llvm_unreachable("unknown operand type!");
  case MachineOperand::MO_Register: {
    O << '%';
    unsigned Reg = MO.getReg();
    if (Modifier && strncmp(Modifier, "subreg", strlen("subreg")) == 0) {
      EVT VT = (strcmp(Modifier+6,"64") == 0) ?
        MVT::i64 : ((strcmp(Modifier+6, "32") == 0) ? MVT::i32 :
                    ((strcmp(Modifier+6,"16") == 0) ? MVT::i16 : MVT::i8));
      Reg = getX86SubSuperRegister(Reg, VT);
    }
    O << X86ATTInstPrinter::getRegisterName(Reg);
    return;
  }

  case MachineOperand::MO_Immediate:
    O << '$' << MO.getImm();
    return;

  case MachineOperand::MO_JumpTableIndex:
  case MachineOperand::MO_ConstantPoolIndex:
  case MachineOperand::MO_GlobalAddress:
  case MachineOperand::MO_ExternalSymbol: {
    O << '$';
    printSymbolOperand(MO, O);
    break;
  }
  }
}

void X86AsmPrinter::printSSECC(const MachineInstr *MI, unsigned Op,
                               raw_ostream &O) {
  unsigned char value = MI->getOperand(Op).getImm();
  assert(value <= 7 && "Invalid ssecc argument!");
  switch (value) {
  case 0: O << "eq"; break;
  case 1: O << "lt"; break;
  case 2: O << "le"; break;
  case 3: O << "unord"; break;
  case 4: O << "neq"; break;
  case 5: O << "nlt"; break;
  case 6: O << "nle"; break;
  case 7: O << "ord"; break;
  }
}

void X86AsmPrinter::printLeaMemReference(const MachineInstr *MI, unsigned Op,
                                         raw_ostream &O, const char *Modifier) {
  const MachineOperand &BaseReg  = MI->getOperand(Op);
  const MachineOperand &IndexReg = MI->getOperand(Op+2);
  const MachineOperand &DispSpec = MI->getOperand(Op+3);

  // If we really don't want to print out (rip), don't.
  bool HasBaseReg = BaseReg.getReg() != 0;
  if (HasBaseReg && Modifier && !strcmp(Modifier, "no-rip") &&
      BaseReg.getReg() == X86::RIP)
    HasBaseReg = false;

  // HasParenPart - True if we will print out the () part of the mem ref.
  bool HasParenPart = IndexReg.getReg() || HasBaseReg;

  if (DispSpec.isImm()) {
    int DispVal = DispSpec.getImm();
    if (DispVal || !HasParenPart)
      O << DispVal;
  } else {
    assert(DispSpec.isGlobal() || DispSpec.isCPI() ||
           DispSpec.isJTI() || DispSpec.isSymbol());
    printSymbolOperand(MI->getOperand(Op+3), O);
  }

  if (HasParenPart) {
    assert(IndexReg.getReg() != X86::ESP &&
           "X86 doesn't allow scaling by ESP");

    O << '(';
    if (HasBaseReg)
      printOperand(MI, Op, O, Modifier);

    if (IndexReg.getReg()) {
      O << ',';
      printOperand(MI, Op+2, O, Modifier);
      unsigned ScaleVal = MI->getOperand(Op+1).getImm();
      if (ScaleVal != 1)
        O << ',' << ScaleVal;
    }
    O << ')';
  }
}

void X86AsmPrinter::printMemReference(const MachineInstr *MI, unsigned Op,
                                      raw_ostream &O, const char *Modifier) {
  assert(isMem(MI, Op) && "Invalid memory reference!");
  const MachineOperand &Segment = MI->getOperand(Op+4);
  if (Segment.getReg()) {
    printOperand(MI, Op+4, O, Modifier);
    O << ':';
  }
  printLeaMemReference(MI, Op, O, Modifier);
}

void X86AsmPrinter::printPICLabel(const MachineInstr *MI, unsigned Op,
                                  raw_ostream &O) {
  O << *MF->getPICBaseSymbol() << '\n';
  O << *MF->getPICBaseSymbol() << ':';
}

bool X86AsmPrinter::printAsmMRegister(const MachineOperand &MO, char Mode,
                                      raw_ostream &O) {
  unsigned Reg = MO.getReg();
  switch (Mode) {
  default: return true;  // Unknown mode.
  case 'b': // Print QImode register
    Reg = getX86SubSuperRegister(Reg, MVT::i8);
    break;
  case 'h': // Print QImode high register
    Reg = getX86SubSuperRegister(Reg, MVT::i8, true);
    break;
  case 'w': // Print HImode register
    Reg = getX86SubSuperRegister(Reg, MVT::i16);
    break;
  case 'k': // Print SImode register
    Reg = getX86SubSuperRegister(Reg, MVT::i32);
    break;
  case 'q': // Print DImode register
    Reg = getX86SubSuperRegister(Reg, MVT::i64);
    break;
  }

  O << '%' << X86ATTInstPrinter::getRegisterName(Reg);
  return false;
}

/// PrintAsmOperand - Print out an operand for an inline asm expression.
///
bool X86AsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                                    unsigned AsmVariant,
                                    const char *ExtraCode, raw_ostream &O) {
  // Does this asm operand have a single letter operand modifier?
  if (ExtraCode && ExtraCode[0]) {
    if (ExtraCode[1] != 0) return true; // Unknown modifier.

    const MachineOperand &MO = MI->getOperand(OpNo);

    switch (ExtraCode[0]) {
    default: return true;  // Unknown modifier.
    case 'a': // This is an address.  Currently only 'i' and 'r' are expected.
      if (MO.isImm()) {
        O << MO.getImm();
        return false;
      }
      if (MO.isGlobal() || MO.isCPI() || MO.isJTI() || MO.isSymbol()) {
        printSymbolOperand(MO, O);
        if (Subtarget->isPICStyleRIPRel())
          O << "(%rip)";
        return false;
      }
      if (MO.isReg()) {
        O << '(';
        printOperand(MI, OpNo, O);
        O << ')';
        return false;
      }
      return true;

    case 'c': // Don't print "$" before a global var name or constant.
      if (MO.isImm())
        O << MO.getImm();
      else if (MO.isGlobal() || MO.isCPI() || MO.isJTI() || MO.isSymbol())
        printSymbolOperand(MO, O);
      else
        printOperand(MI, OpNo, O);
      return false;

    case 'A': // Print '*' before a register (it must be a register)
      if (MO.isReg()) {
        O << '*';
        printOperand(MI, OpNo, O);
        return false;
      }
      return true;

    case 'b': // Print QImode register
    case 'h': // Print QImode high register
    case 'w': // Print HImode register
    case 'k': // Print SImode register
    case 'q': // Print DImode register
      if (MO.isReg())
        return printAsmMRegister(MO, ExtraCode[0], O);
      printOperand(MI, OpNo, O);
      return false;

    case 'P': // This is the operand of a call, treat specially.
      print_pcrel_imm(MI, OpNo, O);
      return false;

    case 'n':  // Negate the immediate or print a '-' before the operand.
      // Note: this is a temporary solution. It should be handled target
      // independently as part of the 'MC' work.
      if (MO.isImm()) {
        O << -MO.getImm();
        return false;
      }
      O << '-';
    }
  }

  printOperand(MI, OpNo, O);
  return false;
}

bool X86AsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
                                          unsigned OpNo, unsigned AsmVariant,
                                          const char *ExtraCode,
                                          raw_ostream &O) {
  if (ExtraCode && ExtraCode[0]) {
    if (ExtraCode[1] != 0) return true; // Unknown modifier.

    switch (ExtraCode[0]) {
    default: return true;  // Unknown modifier.
    case 'b': // Print QImode register
    case 'h': // Print QImode high register
    case 'w': // Print HImode register
    case 'k': // Print SImode register
    case 'q': // Print SImode register
      // These only apply to registers, ignore on mem.
      break;
    case 'P': // Don't print @PLT, but do print as memory.
      printMemReference(MI, OpNo, O, "no-rip");
      return false;
    }
  }
  printMemReference(MI, OpNo, O);
  return false;
}

void X86AsmPrinter::EmitStartOfAsmFile(Module &M) {
  if (Subtarget->isTargetDarwin())
    OutStreamer.SwitchSection(getObjFileLowering().getTextSection());
}


void X86AsmPrinter::EmitEndOfAsmFile(Module &M) {
  if (Subtarget->isTargetDarwin()) {
    // All darwin targets use mach-o.
    MachineModuleInfoMachO &MMIMacho =
      MMI->getObjFileInfo<MachineModuleInfoMachO>();

    // Output stubs for dynamically-linked functions.
    MachineModuleInfoMachO::SymbolListTy Stubs;

    Stubs = MMIMacho.GetFnStubList();
    if (!Stubs.empty()) {
      const MCSection *TheSection =
        OutContext.getMachOSection("__IMPORT", "__jump_table",
                                   MCSectionMachO::S_SYMBOL_STUBS |
                                   MCSectionMachO::S_ATTR_SELF_MODIFYING_CODE |
                                   MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
                                   5, SectionKind::getMetadata());
      OutStreamer.SwitchSection(TheSection);

      for (unsigned i = 0, e = Stubs.size(); i != e; ++i) {
        // L_foo$stub:
        OutStreamer.EmitLabel(Stubs[i].first);
        //   .indirect_symbol _foo
        OutStreamer.EmitSymbolAttribute(Stubs[i].second.getPointer(),
                                        MCSA_IndirectSymbol);
        // hlt; hlt; hlt; hlt; hlt     hlt = 0xf4 = -12.
        const char HltInsts[] = { -12, -12, -12, -12, -12 };
        OutStreamer.EmitBytes(StringRef(HltInsts, 5), 0/*addrspace*/);
      }

      Stubs.clear();
      OutStreamer.AddBlankLine();
    }

    // Output stubs for external and common global variables.
    Stubs = MMIMacho.GetGVStubList();
    if (!Stubs.empty()) {
      const MCSection *TheSection =
        OutContext.getMachOSection("__IMPORT", "__pointers",
                                   MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS,
                                   SectionKind::getMetadata());
      OutStreamer.SwitchSection(TheSection);

      for (unsigned i = 0, e = Stubs.size(); i != e; ++i) {
        // L_foo$non_lazy_ptr:
        OutStreamer.EmitLabel(Stubs[i].first);
        // .indirect_symbol _foo
        MachineModuleInfoImpl::StubValueTy &MCSym = Stubs[i].second;
        OutStreamer.EmitSymbolAttribute(MCSym.getPointer(),
                                        MCSA_IndirectSymbol);
        // .long 0
        if (MCSym.getInt())
          // External to current translation unit.
          OutStreamer.EmitIntValue(0, 4/*size*/, 0/*addrspace*/);
        else
          // Internal to current translation unit.
          //
          // When we place the LSDA into the TEXT section, the type info
          // pointers need to be indirect and pc-rel. We accomplish this by
          // using NLPs.  However, sometimes the types are local to the file. So
          // we need to fill in the value for the NLP in those cases.
          OutStreamer.EmitValue(MCSymbolRefExpr::Create(MCSym.getPointer(),
                                                        OutContext),
                                4/*size*/, 0/*addrspace*/);
      }
      Stubs.clear();
      OutStreamer.AddBlankLine();
    }

    Stubs = MMIMacho.GetHiddenGVStubList();
    if (!Stubs.empty()) {
      OutStreamer.SwitchSection(getObjFileLowering().getDataSection());
      EmitAlignment(2);

      for (unsigned i = 0, e = Stubs.size(); i != e; ++i) {
        // L_foo$non_lazy_ptr:
        OutStreamer.EmitLabel(Stubs[i].first);
        // .long _foo
        OutStreamer.EmitValue(MCSymbolRefExpr::
                              Create(Stubs[i].second.getPointer(),
                                     OutContext),
                              4/*size*/, 0/*addrspace*/);
      }
      Stubs.clear();
      OutStreamer.AddBlankLine();
    }

    // Funny Darwin hack: This flag tells the linker that no global symbols
    // contain code that falls through to other global symbols (e.g. the obvious
    // implementation of multiple entry points).  If this doesn't occur, the
    // linker can safely perform dead code stripping.  Since LLVM never
    // generates code that does this, it is always safe to set.
    OutStreamer.EmitAssemblerFlag(MCAF_SubsectionsViaSymbols);
  }

  if (Subtarget->isTargetWindows() && !Subtarget->isTargetCygMing() &&
      MMI->callsExternalVAFunctionWithFloatingPointArguments()) {
    StringRef SymbolName = Subtarget->is64Bit() ? "_fltused" : "__fltused";
    MCSymbol *S = MMI->getContext().GetOrCreateSymbol(SymbolName);
    OutStreamer.EmitSymbolAttribute(S, MCSA_Global);
  }

  if (Subtarget->isTargetCOFF()) {
    X86COFFMachineModuleInfo &COFFMMI =
      MMI->getObjFileInfo<X86COFFMachineModuleInfo>();

    // Emit type information for external functions
    typedef X86COFFMachineModuleInfo::externals_iterator externals_iterator;
    for (externals_iterator I = COFFMMI.externals_begin(),
                            E = COFFMMI.externals_end();
                            I != E; ++I) {
      OutStreamer.BeginCOFFSymbolDef(CurrentFnSym);
      OutStreamer.EmitCOFFSymbolStorageClass(COFF::IMAGE_SYM_CLASS_EXTERNAL);
      OutStreamer.EmitCOFFSymbolType(COFF::IMAGE_SYM_DTYPE_FUNCTION
                                               << COFF::SCT_COMPLEX_TYPE_SHIFT);
      OutStreamer.EndCOFFSymbolDef();
    }

    // Necessary for dllexport support
    std::vector<const MCSymbol*> DLLExportedFns, DLLExportedGlobals;

    const TargetLoweringObjectFileCOFF &TLOFCOFF =
      static_cast<const TargetLoweringObjectFileCOFF&>(getObjFileLowering());

    for (Module::const_iterator I = M.begin(), E = M.end(); I != E; ++I)
      if (I->hasDLLExportLinkage())
        DLLExportedFns.push_back(Mang->getSymbol(I));

    for (Module::const_global_iterator I = M.global_begin(),
           E = M.global_end(); I != E; ++I)
      if (I->hasDLLExportLinkage())
        DLLExportedGlobals.push_back(Mang->getSymbol(I));

    // Output linker support code for dllexported globals on windows.
    if (!DLLExportedGlobals.empty() || !DLLExportedFns.empty()) {
      OutStreamer.SwitchSection(TLOFCOFF.getDrectveSection());
      SmallString<128> name;
      for (unsigned i = 0, e = DLLExportedGlobals.size(); i != e; ++i) {
        if (Subtarget->isTargetWindows())
          name = " /EXPORT:";
        else
          name = " -export:";
        name += DLLExportedGlobals[i]->getName();
        if (Subtarget->isTargetWindows())
          name += ",DATA";
        else
        name += ",data";
        OutStreamer.EmitBytes(name, 0);
      }

      for (unsigned i = 0, e = DLLExportedFns.size(); i != e; ++i) {
        if (Subtarget->isTargetWindows())
          name = " /EXPORT:";
        else
          name = " -export:";
        name += DLLExportedFns[i]->getName();
        OutStreamer.EmitBytes(name, 0);
      }
    }
  }

  if (Subtarget->isTargetELF()) {
    const TargetLoweringObjectFileELF &TLOFELF =
      static_cast<const TargetLoweringObjectFileELF &>(getObjFileLowering());

    MachineModuleInfoELF &MMIELF = MMI->getObjFileInfo<MachineModuleInfoELF>();

    // Output stubs for external and common global variables.
    MachineModuleInfoELF::SymbolListTy Stubs = MMIELF.GetGVStubList();
    if (!Stubs.empty()) {
      OutStreamer.SwitchSection(TLOFELF.getDataRelSection());
      const TargetData *TD = TM.getTargetData();

      for (unsigned i = 0, e = Stubs.size(); i != e; ++i) {
        OutStreamer.EmitLabel(Stubs[i].first);
        OutStreamer.EmitSymbolValue(Stubs[i].second.getPointer(),
                                    TD->getPointerSize(), 0);
      }
      Stubs.clear();
    }
  }
}

MachineLocation
X86AsmPrinter::getDebugValueLocation(const MachineInstr *MI) const {
  MachineLocation Location;
  assert (MI->getNumOperands() == 7 && "Invalid no. of machine operands!");
  // Frame address.  Currently handles register +- offset only.

  if (MI->getOperand(0).isReg() && MI->getOperand(3).isImm())
    Location.set(MI->getOperand(0).getReg(), MI->getOperand(3).getImm());
  else {
    DEBUG(dbgs() << "DBG_VALUE instruction ignored! " << *MI << "\n");
  }
  return Location;
}

void X86AsmPrinter::PrintDebugValueComment(const MachineInstr *MI,
                                           raw_ostream &O) {
  // Only the target-dependent form of DBG_VALUE should get here.
  // Referencing the offset and metadata as NOps-2 and NOps-1 is
  // probably portable to other targets; frame pointer location is not.
  unsigned NOps = MI->getNumOperands();
  assert(NOps==7);
  O << '\t' << MAI->getCommentString() << "DEBUG_VALUE: ";
  // cast away const; DIetc do not take const operands for some reason.
  DIVariable V(const_cast<MDNode *>(MI->getOperand(NOps-1).getMetadata()));
  if (V.getContext().isSubprogram())
    O << DISubprogram(V.getContext()).getDisplayName() << ":";
  O << V.getName();
  O << " <- ";
  // Frame address.  Currently handles register +- offset only.
  O << '[';
  if (MI->getOperand(0).isReg() && MI->getOperand(0).getReg())
    printOperand(MI, 0, O);
  else
    O << "undef";
  O << '+'; printOperand(MI, 3, O);
  O << ']';
  O << "+";
  printOperand(MI, NOps-2, O);
}



//===----------------------------------------------------------------------===//
// Target Registry Stuff
//===----------------------------------------------------------------------===//

static MCInstPrinter *createX86MCInstPrinter(const Target &T,
                                             unsigned SyntaxVariant,
                                             const MCAsmInfo &MAI) {
  if (SyntaxVariant == 0)
    return new X86ATTInstPrinter(MAI);
  if (SyntaxVariant == 1)
    return new X86IntelInstPrinter(MAI);
  return 0;
}

// Force static initialization.
extern "C" void LLVMInitializeX86AsmPrinter() {
  RegisterAsmPrinter<X86AsmPrinter> X(TheX86_32Target);
  RegisterAsmPrinter<X86AsmPrinter> Y(TheX86_64Target);

  TargetRegistry::RegisterMCInstPrinter(TheX86_32Target,createX86MCInstPrinter);
  TargetRegistry::RegisterMCInstPrinter(TheX86_64Target,createX86MCInstPrinter);
}