lib/Target/ARM/ARMFastISel.cpp

//===-- ARMFastISel.cpp - ARM FastISel implementation ---------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the ARM-specific support for the FastISel class. Some
// of the target-specific code is generated by tablegen in the file
// ARMGenFastISel.inc, which is #included here.
//
//===----------------------------------------------------------------------===//

#include "ARM.h"
#include "ARMBaseInstrInfo.h"
#include "ARMRegisterInfo.h"
#include "ARMTargetMachine.h"
#include "ARMSubtarget.h"
#include "llvm/CallingConv.h"
#include "llvm/DerivedTypes.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/FastISel.h"
#include "llvm/CodeGen/FunctionLoweringInfo.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
using namespace llvm;

static cl::opt<bool>
EnableARMFastISel("arm-fast-isel",
                  cl::desc("Turn on experimental ARM fast-isel support"),
                  cl::init(false), cl::Hidden);

namespace {

class ARMFastISel : public FastISel {

  /// Subtarget - Keep a pointer to the ARMSubtarget around so that we can
  /// make the right decision when generating code for different targets.
  const ARMSubtarget *Subtarget;
  const TargetMachine &TM;
  const TargetInstrInfo &TII;
  const TargetLowering &TLI;
  const ARMFunctionInfo *AFI;

  // Convenience variable to avoid checking all the time.
  bool isThumb;

  public:
    explicit ARMFastISel(FunctionLoweringInfo &funcInfo) 
    : FastISel(funcInfo),
      TM(funcInfo.MF->getTarget()),
      TII(*TM.getInstrInfo()),
      TLI(*TM.getTargetLowering()) {
      Subtarget = &TM.getSubtarget<ARMSubtarget>();
      AFI = funcInfo.MF->getInfo<ARMFunctionInfo>();
      isThumb = AFI->isThumbFunction();
    }

    // Code from FastISel.cpp.
    virtual unsigned FastEmitInst_(unsigned MachineInstOpcode,
                                   const TargetRegisterClass *RC);
    virtual unsigned FastEmitInst_r(unsigned MachineInstOpcode,
                                    const TargetRegisterClass *RC,
                                    unsigned Op0, bool Op0IsKill);
    virtual unsigned FastEmitInst_rr(unsigned MachineInstOpcode,
                                     const TargetRegisterClass *RC,
                                     unsigned Op0, bool Op0IsKill,
                                     unsigned Op1, bool Op1IsKill);
    virtual unsigned FastEmitInst_ri(unsigned MachineInstOpcode,
                                     const TargetRegisterClass *RC,
                                     unsigned Op0, bool Op0IsKill,
                                     uint64_t Imm);
    virtual unsigned FastEmitInst_rf(unsigned MachineInstOpcode,
                                     const TargetRegisterClass *RC,
                                     unsigned Op0, bool Op0IsKill,
                                     const ConstantFP *FPImm);
    virtual unsigned FastEmitInst_i(unsigned MachineInstOpcode,
                                    const TargetRegisterClass *RC,
                                    uint64_t Imm);
    virtual unsigned FastEmitInst_rri(unsigned MachineInstOpcode,
                                      const TargetRegisterClass *RC,
                                      unsigned Op0, bool Op0IsKill,
                                      unsigned Op1, bool Op1IsKill,
                                      uint64_t Imm);
    virtual unsigned FastEmitInst_extractsubreg(MVT RetVT,
                                                unsigned Op0, bool Op0IsKill,
                                                uint32_t Idx);
                                                
    // Backend specific FastISel code.
    virtual bool TargetSelectInstruction(const Instruction *I);
    virtual unsigned TargetMaterializeConstant(const Constant *C);

  #include "ARMGenFastISel.inc"
  
    // Instruction selection routines.
    virtual bool ARMSelectLoad(const Instruction *I);
    virtual bool ARMSelectStore(const Instruction *I);

    // Utility routines.
  private:
    bool isTypeLegal(const Type *Ty, EVT &VT);
    bool isLoadTypeLegal(const Type *Ty, EVT &VT);
    bool ARMEmitLoad(EVT VT, unsigned &ResultReg, unsigned Reg, int Offset);
    bool ARMEmitStore(EVT VT, unsigned SrcReg, unsigned Reg, int Offset);
    bool ARMLoadAlloca(const Instruction *I);
    bool ARMStoreAlloca(const Instruction *I, unsigned SrcReg);
    bool ARMComputeRegOffset(const Value *Obj, unsigned &Reg, int &Offset);
    bool ARMMaterializeConstant(const ConstantInt *Val, unsigned &Reg);
    
    bool DefinesOptionalPredicate(MachineInstr *MI, bool *CPSR);
    const MachineInstrBuilder &AddOptionalDefs(const MachineInstrBuilder &MIB);
};

} // end anonymous namespace

// #include "ARMGenCallingConv.inc"

// DefinesOptionalPredicate - This is different from DefinesPredicate in that
// we don't care about implicit defs here, just places we'll need to add a
// default CCReg argument. Sets CPSR if we're setting CPSR instead of CCR.
bool ARMFastISel::DefinesOptionalPredicate(MachineInstr *MI, bool *CPSR) {
  const TargetInstrDesc &TID = MI->getDesc();
  if (!TID.hasOptionalDef())
    return false;

  // Look to see if our OptionalDef is defining CPSR or CCR.
  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
    const MachineOperand &MO = MI->getOperand(i);
    if (!MO.isReg() || !MO.isDef()) continue;
    if (MO.getReg() == ARM::CPSR)
      *CPSR = true;
  }
  return true;
}

// If the machine is predicable go ahead and add the predicate operands, if
// it needs default CC operands add those.
const MachineInstrBuilder &
ARMFastISel::AddOptionalDefs(const MachineInstrBuilder &MIB) {
  MachineInstr *MI = &*MIB;

  // Do we use a predicate?
  if (TII.isPredicable(MI))
    AddDefaultPred(MIB);
  
  // Do we optionally set a predicate?  Preds is size > 0 iff the predicate
  // defines CPSR. All other OptionalDefines in ARM are the CCR register.
  bool CPSR = false;
  if (DefinesOptionalPredicate(MI, &CPSR)) {
    if (CPSR)
      AddDefaultT1CC(MIB);
    else
      AddDefaultCC(MIB);
  }
  return MIB;
}

unsigned ARMFastISel::FastEmitInst_(unsigned MachineInstOpcode,
                                    const TargetRegisterClass* RC) {
  unsigned ResultReg = createResultReg(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);

  AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II, ResultReg));
  return ResultReg;
}

unsigned ARMFastISel::FastEmitInst_r(unsigned MachineInstOpcode,
                                     const TargetRegisterClass *RC,
                                     unsigned Op0, bool Op0IsKill) {
  unsigned ResultReg = createResultReg(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);

  if (II.getNumDefs() >= 1)
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II, ResultReg)
                   .addReg(Op0, Op0IsKill * RegState::Kill));
  else {
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II)
                   .addReg(Op0, Op0IsKill * RegState::Kill));
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                   TII.get(TargetOpcode::COPY), ResultReg)
                   .addReg(II.ImplicitDefs[0]));
  }
  return ResultReg;
}

unsigned ARMFastISel::FastEmitInst_rr(unsigned MachineInstOpcode,
                                      const TargetRegisterClass *RC,
                                      unsigned Op0, bool Op0IsKill,
                                      unsigned Op1, bool Op1IsKill) {
  unsigned ResultReg = createResultReg(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);

  if (II.getNumDefs() >= 1)
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II, ResultReg)
                   .addReg(Op0, Op0IsKill * RegState::Kill)
                   .addReg(Op1, Op1IsKill * RegState::Kill));
  else {
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II)
                   .addReg(Op0, Op0IsKill * RegState::Kill)
                   .addReg(Op1, Op1IsKill * RegState::Kill));
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                           TII.get(TargetOpcode::COPY), ResultReg)
                   .addReg(II.ImplicitDefs[0]));
  }
  return ResultReg;
}

unsigned ARMFastISel::FastEmitInst_ri(unsigned MachineInstOpcode,
                                      const TargetRegisterClass *RC,
                                      unsigned Op0, bool Op0IsKill,
                                      uint64_t Imm) {
  unsigned ResultReg = createResultReg(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);

  if (II.getNumDefs() >= 1)
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II, ResultReg)
                   .addReg(Op0, Op0IsKill * RegState::Kill)
                   .addImm(Imm));
  else {
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II)
                   .addReg(Op0, Op0IsKill * RegState::Kill)
                   .addImm(Imm));
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                           TII.get(TargetOpcode::COPY), ResultReg)
                   .addReg(II.ImplicitDefs[0]));
  }
  return ResultReg;
}

unsigned ARMFastISel::FastEmitInst_rf(unsigned MachineInstOpcode,
                                      const TargetRegisterClass *RC,
                                      unsigned Op0, bool Op0IsKill,
                                      const ConstantFP *FPImm) {
  unsigned ResultReg = createResultReg(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);

  if (II.getNumDefs() >= 1)
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II, ResultReg)
                   .addReg(Op0, Op0IsKill * RegState::Kill)
                   .addFPImm(FPImm));
  else {
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II)
                   .addReg(Op0, Op0IsKill * RegState::Kill)
                   .addFPImm(FPImm));
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                           TII.get(TargetOpcode::COPY), ResultReg)
                   .addReg(II.ImplicitDefs[0]));
  }
  return ResultReg;
}

unsigned ARMFastISel::FastEmitInst_rri(unsigned MachineInstOpcode,
                                       const TargetRegisterClass *RC,
                                       unsigned Op0, bool Op0IsKill,
                                       unsigned Op1, bool Op1IsKill,
                                       uint64_t Imm) {
  unsigned ResultReg = createResultReg(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);

  if (II.getNumDefs() >= 1)
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II, ResultReg)
                   .addReg(Op0, Op0IsKill * RegState::Kill)
                   .addReg(Op1, Op1IsKill * RegState::Kill)
                   .addImm(Imm));
  else {
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II)
                   .addReg(Op0, Op0IsKill * RegState::Kill)
                   .addReg(Op1, Op1IsKill * RegState::Kill)
                   .addImm(Imm));
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                           TII.get(TargetOpcode::COPY), ResultReg)
                   .addReg(II.ImplicitDefs[0]));
  }
  return ResultReg;
}

unsigned ARMFastISel::FastEmitInst_i(unsigned MachineInstOpcode,
                                     const TargetRegisterClass *RC,
                                     uint64_t Imm) {
  unsigned ResultReg = createResultReg(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);
  
  if (II.getNumDefs() >= 1)
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II, ResultReg)
                   .addImm(Imm));
  else {
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II)
                   .addImm(Imm));
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                           TII.get(TargetOpcode::COPY), ResultReg)
                   .addReg(II.ImplicitDefs[0]));
  }
  return ResultReg;
}

unsigned ARMFastISel::FastEmitInst_extractsubreg(MVT RetVT,
                                                 unsigned Op0, bool Op0IsKill,
                                                 uint32_t Idx) {
  unsigned ResultReg = createResultReg(TLI.getRegClassFor(RetVT));
  assert(TargetRegisterInfo::isVirtualRegister(Op0) &&
         "Cannot yet extract from physregs");
  AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt,
                         DL, TII.get(TargetOpcode::COPY), ResultReg)
                 .addReg(Op0, getKillRegState(Op0IsKill), Idx));
  return ResultReg;
}

unsigned ARMFastISel::TargetMaterializeConstant(const Constant *C) {
  EVT VT = TLI.getValueType(C->getType(), true);

  // Only handle simple types.
  if (!VT.isSimple()) return 0;
  
  // TODO: This should be safe for fp because they're just bits from the
  // Constant.
  // TODO: Theoretically we could materialize fp constants with instructions
  // from VFP3.

  // MachineConstantPool wants an explicit alignment.
  unsigned Align = TD.getPrefTypeAlignment(C->getType());
  if (Align == 0) {
    // TODO: Figure out if this is correct.
    Align = TD.getTypeAllocSize(C->getType());
  }
  unsigned Idx = MCP.getConstantPoolIndex(C, Align);

  unsigned DestReg = createResultReg(TLI.getRegClassFor(VT));
  // Different addressing modes between ARM/Thumb2 for constant pool loads.
  if (isThumb)
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                            TII.get(ARM::t2LDRpci))
                    .addReg(DestReg).addConstantPoolIndex(Idx));
  else
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                            TII.get(ARM::LDRcp))
                    .addReg(DestReg).addConstantPoolIndex(Idx)
                    .addReg(0).addImm(0));
    
  return DestReg;
}

bool ARMFastISel::isTypeLegal(const Type *Ty, EVT &VT) {
  VT = TLI.getValueType(Ty, true);
  
  // Only handle simple types.
  if (VT == MVT::Other || !VT.isSimple()) return false;
    
  // Handle all legal types, i.e. a register that will directly hold this
  // value.
  return TLI.isTypeLegal(VT);
}

bool ARMFastISel::isLoadTypeLegal(const Type *Ty, EVT &VT) {
  if (isTypeLegal(Ty, VT)) return true;
  
  // If this is a type than can be sign or zero-extended to a basic operation
  // go ahead and accept it now.
  if (VT == MVT::i8 || VT == MVT::i16)
    return true;
  
  return false;
}

// Computes the Reg+Offset to get to an object.
bool ARMFastISel::ARMComputeRegOffset(const Value *Obj, unsigned &Reg,
                                      int &Offset) {
  // Some boilerplate from the X86 FastISel.
  const User *U = NULL;
  unsigned Opcode = Instruction::UserOp1;
  if (const Instruction *I = dyn_cast<Instruction>(Obj)) {
    // Don't walk into other basic blocks; it's possible we haven't
    // visited them yet, so the instructions may not yet be assigned
    // virtual registers.
    if (FuncInfo.MBBMap[I->getParent()] != FuncInfo.MBB)
      return false;

    Opcode = I->getOpcode();
    U = I;
  } else if (const ConstantExpr *C = dyn_cast<ConstantExpr>(Obj)) {
    Opcode = C->getOpcode();
    U = C;
  }

  if (const PointerType *Ty = dyn_cast<PointerType>(Obj->getType()))
    if (Ty->getAddressSpace() > 255)
      // Fast instruction selection doesn't support the special
      // address spaces.
      return false;
  
  switch (Opcode) {
    default: 
    //errs() << "Failing Opcode is: " << *Op1 << "\n";
    break;
    case Instruction::Alloca: {
      assert(false && "Alloca should have been handled earlier!");
      return false;
    }
  }
  
  if (const GlobalValue *GV = dyn_cast<GlobalValue>(Obj)) {
    //errs() << "Failing GV is: " << GV << "\n";
    (void)GV;
    return false;
  }
  
  // Try to get this in a register if nothing else has worked.
  Reg = getRegForValue(Obj);
  if (Reg == 0) return false;

  // Since the offset may be too large for the load instruction
  // get the reg+offset into a register.
  // TODO: Verify the additions work, otherwise we'll need to add the
  // offset instead of 0 to the instructions and do all sorts of operand
  // munging.
  // TODO: Optimize this somewhat.
  if (Offset != 0) {
    ARMCC::CondCodes Pred = ARMCC::AL;
    unsigned PredReg = 0;

    if (!isThumb)
      emitARMRegPlusImmediate(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                              Reg, Reg, Offset, Pred, PredReg,
                              static_cast<const ARMBaseInstrInfo&>(TII));
    else {
      assert(AFI->isThumb2Function());
      emitT2RegPlusImmediate(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                             Reg, Reg, Offset, Pred, PredReg,
                             static_cast<const ARMBaseInstrInfo&>(TII));
    }
  }
  
  return true;
}

bool ARMFastISel::ARMLoadAlloca(const Instruction *I) {
  Value *Op0 = I->getOperand(0);

  // Verify it's an alloca.
  if (const AllocaInst *AI = dyn_cast<AllocaInst>(Op0)) {
    DenseMap<const AllocaInst*, int>::iterator SI =
      FuncInfo.StaticAllocaMap.find(AI);

    if (SI != FuncInfo.StaticAllocaMap.end()) {
      TargetRegisterClass* RC = TLI.getRegClassFor(TLI.getPointerTy());
      unsigned ResultReg = createResultReg(RC);
      TII.loadRegFromStackSlot(*FuncInfo.MBB, *FuncInfo.InsertPt,
                               ResultReg, SI->second, RC,
                               TM.getRegisterInfo());
      UpdateValueMap(I, ResultReg);
      return true;
    }
  }
  return false;
}

bool ARMFastISel::ARMEmitLoad(EVT VT, unsigned &ResultReg,
                              unsigned Reg, int Offset) {
  
  assert(VT.isSimple() && "Non-simple types are invalid here!");
  unsigned Opc;
  
  switch (VT.getSimpleVT().SimpleTy) {
    default: 
      assert(false && "Trying to emit for an unhandled type!");
      return false;
    case MVT::i16:
      Opc = isThumb ? ARM::tLDRH : ARM::LDRH;
      VT = MVT::i32;
      break;
    case MVT::i8:
      Opc = isThumb ? ARM::tLDRB : ARM::LDRB;
      VT = MVT::i32;
      break;
    case MVT::i32:
      Opc = isThumb ? ARM::tLDR : ARM::LDR;
      break;
  }
  
  ResultReg = createResultReg(TLI.getRegClassFor(VT));
  
  // TODO: Fix the Addressing modes so that these can share some code.
  // Since this is a Thumb1 load this will work in Thumb1 or 2 mode.
  if (isThumb)
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                            TII.get(Opc), ResultReg)
                    .addReg(Reg).addImm(Offset).addReg(0));
  else
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                            TII.get(Opc), ResultReg)
                    .addReg(Reg).addReg(0).addImm(Offset));
                    
  return true;
}

bool ARMFastISel::ARMStoreAlloca(const Instruction *I, unsigned SrcReg) {
  Value *Op1 = I->getOperand(1);

  // Verify it's an alloca.
  if (const AllocaInst *AI = dyn_cast<AllocaInst>(Op1)) {
    DenseMap<const AllocaInst*, int>::iterator SI =
      FuncInfo.StaticAllocaMap.find(AI);

    if (SI != FuncInfo.StaticAllocaMap.end()) {
      TargetRegisterClass* RC = TLI.getRegClassFor(TLI.getPointerTy());
      assert(SrcReg != 0 && "Nothing to store!");
      TII.storeRegToStackSlot(*FuncInfo.MBB, *FuncInfo.InsertPt,
                              SrcReg, true /*isKill*/, SI->second, RC,
                              TM.getRegisterInfo());
      return true;
    }
  }
  return false;
}

bool ARMFastISel::ARMEmitStore(EVT VT, unsigned SrcReg,
                               unsigned DstReg, int Offset) {
  unsigned StrOpc;
  switch (VT.getSimpleVT().SimpleTy) {
    default: return false;
    case MVT::i1:
    case MVT::i8: StrOpc = isThumb ? ARM::tSTRB : ARM::STRB; break;
    case MVT::i16: StrOpc = isThumb ? ARM::tSTRH : ARM::STRH; break;
    case MVT::i32: StrOpc = isThumb ? ARM::tSTR : ARM::STR; break;
    case MVT::f32:
      if (!Subtarget->hasVFP2()) return false;
      StrOpc = ARM::VSTRS;
      break;
    case MVT::f64:
      if (!Subtarget->hasVFP2()) return false;
      StrOpc = ARM::VSTRD;
      break;
  }
  
  if (isThumb)
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                            TII.get(StrOpc), SrcReg)
                    .addReg(DstReg).addImm(Offset).addReg(0));
  else
    AddOptionalDefs(BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
                            TII.get(StrOpc), SrcReg)
                    .addReg(DstReg).addReg(0).addImm(Offset));
  
  return true;
}

bool ARMFastISel::ARMSelectStore(const Instruction *I) {
  Value *Op0 = I->getOperand(0);
  unsigned SrcReg = 0;

  // Yay type legalization
  EVT VT;
  if (!isLoadTypeLegal(I->getOperand(0)->getType(), VT))
    return false;

  // Get the value to be stored into a register.
  SrcReg = getRegForValue(Op0);
  if (SrcReg == 0)
    return false;
    
  // If we're an alloca we know we have a frame index and can emit the store
  // quickly.
  if (ARMStoreAlloca(I, SrcReg))
    return true;
    
  // Our register and offset with innocuous defaults.
  unsigned Reg = 0;
  int Offset = 0;
  
  // See if we can handle this as Reg + Offset
  if (!ARMComputeRegOffset(I->getOperand(1), Reg, Offset))
    return false;
    
  if (!ARMEmitStore(VT, SrcReg, Reg, Offset /* 0 */)) return false;
    
  return false;
  
}

bool ARMFastISel::ARMSelectLoad(const Instruction *I) {
  // If we're an alloca we know we have a frame index and can emit the load
  // directly in short order.
  if (ARMLoadAlloca(I))
    return true;
    
  // Verify we have a legal type before going any further.
  EVT VT;
  if (!isLoadTypeLegal(I->getType(), VT))
    return false;
  
  // Our register and offset with innocuous defaults.
  unsigned Reg = 0;
  int Offset = 0;
  
  // See if we can handle this as Reg + Offset
  if (!ARMComputeRegOffset(I->getOperand(0), Reg, Offset))
    return false;
  
  unsigned ResultReg;
  if (!ARMEmitLoad(VT, ResultReg, Reg, Offset /* 0 */)) return false;
  
  UpdateValueMap(I, ResultReg);
  return true;
}

// TODO: SoftFP support.
bool ARMFastISel::TargetSelectInstruction(const Instruction *I) {
  // No Thumb-1 for now.
  if (isThumb && !AFI->isThumb2Function()) return false;
  
  switch (I->getOpcode()) {
    case Instruction::Load:
      return ARMSelectLoad(I);
    case Instruction::Store:
      return ARMSelectStore(I);
    default: break;
  }
  return false;
}

namespace llvm {
  llvm::FastISel *ARM::createFastISel(FunctionLoweringInfo &funcInfo) {
    if (EnableARMFastISel) return new ARMFastISel(funcInfo);
    return 0;
  }
}