llvm-project/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

///===-- FastISel.cpp - Implementation of the FastISel class --------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the implementation of the FastISel class.
//
// "Fast" instruction selection is designed to emit very poor code quickly.
// Also, it is not designed to be able to do much lowering, so most illegal
// types (e.g. i64 on 32-bit targets) and operations are not supported.  It is
// also not intended to be able to do much optimization, except in a few cases
// where doing optimizations reduces overall compile time.  For example, folding
// constants into immediate fields is often done, because it's cheap and it
// reduces the number of instructions later phases have to examine.
//
// "Fast" instruction selection is able to fail gracefully and transfer
// control to the SelectionDAG selector for operations that it doesn't
// support.  In many cases, this allows us to avoid duplicating a lot of
// the complicated lowering logic that SelectionDAG currently has.
//
// The intended use for "fast" instruction selection is "-O0" mode
// compilation, where the quality of the generated code is irrelevant when
// weighed against the speed at which the code can be generated.  Also,
// at -O0, the LLVM optimizers are not running, and this makes the
// compile time of codegen a much higher portion of the overall compile
// time.  Despite its limitations, "fast" instruction selection is able to
// handle enough code on its own to provide noticeable overall speedups
// in -O0 compiles.
//
// Basic operations are supported in a target-independent way, by reading
// the same instruction descriptions that the SelectionDAG selector reads,
// and identifying simple arithmetic operations that can be directly selected
// from simple operators.  More complicated operations currently require
// target-specific code.
//
//===----------------------------------------------------------------------===//

#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/CodeGen/FastISel.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/DebugLoc.h"
#include "llvm/CodeGen/DwarfWriter.h"
#include "llvm/Analysis/DebugInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "SelectionDAGBuild.h"
using namespace llvm;

unsigned FastISel::getRegForValue(Value *V) {
  MVT RealVT = TLI.getValueType(V->getType(), /*AllowUnknown=*/true);
  // Don't handle non-simple values in FastISel.
  if (!RealVT.isSimple())
    return 0;

  // Ignore illegal types. We must do this before looking up the value
  // in ValueMap because Arguments are given virtual registers regardless
  // of whether FastISel can handle them.
  MVT::SimpleValueType VT = RealVT.getSimpleVT();
  if (!TLI.isTypeLegal(VT)) {
    // Promote MVT::i1 to a legal type though, because it's common and easy.
    if (VT == MVT::i1)
      VT = TLI.getTypeToTransformTo(VT).getSimpleVT();
    else
      return 0;
  }

  // Look up the value to see if we already have a register for it. We
  // cache values defined by Instructions across blocks, and other values
  // only locally. This is because Instructions already have the SSA
  // def-dominatess-use requirement enforced.
  if (ValueMap.count(V))
    return ValueMap[V];
  unsigned Reg = LocalValueMap[V];
  if (Reg != 0)
    return Reg;

  if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
    if (CI->getValue().getActiveBits() <= 64)
      Reg = FastEmit_i(VT, VT, ISD::Constant, CI->getZExtValue());
  } else if (isa<AllocaInst>(V)) {
    Reg = TargetMaterializeAlloca(cast<AllocaInst>(V));
  } else if (isa<ConstantPointerNull>(V)) {
    // Translate this as an integer zero so that it can be
    // local-CSE'd with actual integer zeros.
    Reg = getRegForValue(Constant::getNullValue(TD.getIntPtrType()));
  } else if (ConstantFP *CF = dyn_cast<ConstantFP>(V)) {
    Reg = FastEmit_f(VT, VT, ISD::ConstantFP, CF);

    if (!Reg) {
      const APFloat &Flt = CF->getValueAPF();
      MVT IntVT = TLI.getPointerTy();

      uint64_t x[2];
      uint32_t IntBitWidth = IntVT.getSizeInBits();
      bool isExact;
      (void) Flt.convertToInteger(x, IntBitWidth, /*isSigned=*/true,
                                APFloat::rmTowardZero, &isExact);
      if (isExact) {
        APInt IntVal(IntBitWidth, 2, x);

        unsigned IntegerReg = getRegForValue(ConstantInt::get(IntVal));
        if (IntegerReg != 0)
          Reg = FastEmit_r(IntVT.getSimpleVT(), VT, ISD::SINT_TO_FP, IntegerReg);
      }
    }
  } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
    if (!SelectOperator(CE, CE->getOpcode())) return 0;
    Reg = LocalValueMap[CE];
  } else if (isa<UndefValue>(V)) {
    Reg = createResultReg(TLI.getRegClassFor(VT));
    BuildMI(MBB, DL, TII.get(TargetInstrInfo::IMPLICIT_DEF), Reg);
  }
  
  // If target-independent code couldn't handle the value, give target-specific
  // code a try.
  if (!Reg && isa<Constant>(V))
    Reg = TargetMaterializeConstant(cast<Constant>(V));
  
  // Don't cache constant materializations in the general ValueMap.
  // To do so would require tracking what uses they dominate.
  if (Reg != 0)
    LocalValueMap[V] = Reg;
  return Reg;
}

unsigned FastISel::lookUpRegForValue(Value *V) {
  // Look up the value to see if we already have a register for it. We
  // cache values defined by Instructions across blocks, and other values
  // only locally. This is because Instructions already have the SSA
  // def-dominatess-use requirement enforced.
  if (ValueMap.count(V))
    return ValueMap[V];
  return LocalValueMap[V];
}

/// UpdateValueMap - Update the value map to include the new mapping for this
/// instruction, or insert an extra copy to get the result in a previous
/// determined register.
/// NOTE: This is only necessary because we might select a block that uses
/// a value before we select the block that defines the value.  It might be
/// possible to fix this by selecting blocks in reverse postorder.
unsigned FastISel::UpdateValueMap(Value* I, unsigned Reg) {
  if (!isa<Instruction>(I)) {
    LocalValueMap[I] = Reg;
    return Reg;
  }
  
  unsigned &AssignedReg = ValueMap[I];
  if (AssignedReg == 0)
    AssignedReg = Reg;
  else if (Reg != AssignedReg) {
    const TargetRegisterClass *RegClass = MRI.getRegClass(Reg);
    TII.copyRegToReg(*MBB, MBB->end(), AssignedReg,
                     Reg, RegClass, RegClass);
  }
  return AssignedReg;
}

unsigned FastISel::getRegForGEPIndex(Value *Idx) {
  unsigned IdxN = getRegForValue(Idx);
  if (IdxN == 0)
    // Unhandled operand. Halt "fast" selection and bail.
    return 0;

  // If the index is smaller or larger than intptr_t, truncate or extend it.
  MVT PtrVT = TLI.getPointerTy();
  MVT IdxVT = MVT::getMVT(Idx->getType(), /*HandleUnknown=*/false);
  if (IdxVT.bitsLT(PtrVT))
    IdxN = FastEmit_r(IdxVT.getSimpleVT(), PtrVT.getSimpleVT(),
                      ISD::SIGN_EXTEND, IdxN);
  else if (IdxVT.bitsGT(PtrVT))
    IdxN = FastEmit_r(IdxVT.getSimpleVT(), PtrVT.getSimpleVT(),
                      ISD::TRUNCATE, IdxN);
  return IdxN;
}

/// SelectBinaryOp - Select and emit code for a binary operator instruction,
/// which has an opcode which directly corresponds to the given ISD opcode.
///
bool FastISel::SelectBinaryOp(User *I, ISD::NodeType ISDOpcode) {
  MVT VT = MVT::getMVT(I->getType(), /*HandleUnknown=*/true);
  if (VT == MVT::Other || !VT.isSimple())
    // Unhandled type. Halt "fast" selection and bail.
    return false;

  // We only handle legal types. For example, on x86-32 the instruction
  // selector contains all of the 64-bit instructions from x86-64,
  // under the assumption that i64 won't be used if the target doesn't
  // support it.
  if (!TLI.isTypeLegal(VT)) {
    // MVT::i1 is special. Allow AND, OR, or XOR because they
    // don't require additional zeroing, which makes them easy.
    if (VT == MVT::i1 &&
        (ISDOpcode == ISD::AND || ISDOpcode == ISD::OR ||
         ISDOpcode == ISD::XOR))
      VT = TLI.getTypeToTransformTo(VT);
    else
      return false;
  }

  unsigned Op0 = getRegForValue(I->getOperand(0));
  if (Op0 == 0)
    // Unhandled operand. Halt "fast" selection and bail.
    return false;

  // Check if the second operand is a constant and handle it appropriately.
  if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
    unsigned ResultReg = FastEmit_ri(VT.getSimpleVT(), VT.getSimpleVT(),
                                     ISDOpcode, Op0, CI->getZExtValue());
    if (ResultReg != 0) {
      // We successfully emitted code for the given LLVM Instruction.
      UpdateValueMap(I, ResultReg);
      return true;
    }
  }

  // Check if the second operand is a constant float.
  if (ConstantFP *CF = dyn_cast<ConstantFP>(I->getOperand(1))) {
    unsigned ResultReg = FastEmit_rf(VT.getSimpleVT(), VT.getSimpleVT(),
                                     ISDOpcode, Op0, CF);
    if (ResultReg != 0) {
      // We successfully emitted code for the given LLVM Instruction.
      UpdateValueMap(I, ResultReg);
      return true;
    }
  }

  unsigned Op1 = getRegForValue(I->getOperand(1));
  if (Op1 == 0)
    // Unhandled operand. Halt "fast" selection and bail.
    return false;

  // Now we have both operands in registers. Emit the instruction.
  unsigned ResultReg = FastEmit_rr(VT.getSimpleVT(), VT.getSimpleVT(),
                                   ISDOpcode, Op0, Op1);
  if (ResultReg == 0)
    // Target-specific code wasn't able to find a machine opcode for
    // the given ISD opcode and type. Halt "fast" selection and bail.
    return false;

  // We successfully emitted code for the given LLVM Instruction.
  UpdateValueMap(I, ResultReg);
  return true;
}

bool FastISel::SelectGetElementPtr(User *I) {
  unsigned N = getRegForValue(I->getOperand(0));
  if (N == 0)
    // Unhandled operand. Halt "fast" selection and bail.
    return false;

  const Type *Ty = I->getOperand(0)->getType();
  MVT::SimpleValueType VT = TLI.getPointerTy().getSimpleVT();
  for (GetElementPtrInst::op_iterator OI = I->op_begin()+1, E = I->op_end();
       OI != E; ++OI) {
    Value *Idx = *OI;
    if (const StructType *StTy = dyn_cast<StructType>(Ty)) {
      unsigned Field = cast<ConstantInt>(Idx)->getZExtValue();
      if (Field) {
        // N = N + Offset
        uint64_t Offs = TD.getStructLayout(StTy)->getElementOffset(Field);
        // FIXME: This can be optimized by combining the add with a
        // subsequent one.
        N = FastEmit_ri_(VT, ISD::ADD, N, Offs, VT);
        if (N == 0)
          // Unhandled operand. Halt "fast" selection and bail.
          return false;
      }
      Ty = StTy->getElementType(Field);
    } else {
      Ty = cast<SequentialType>(Ty)->getElementType();

      // If this is a constant subscript, handle it quickly.
      if (ConstantInt *CI = dyn_cast<ConstantInt>(Idx)) {
        if (CI->getZExtValue() == 0) continue;
        uint64_t Offs = 
          TD.getTypeAllocSize(Ty)*cast<ConstantInt>(CI)->getSExtValue();
        N = FastEmit_ri_(VT, ISD::ADD, N, Offs, VT);
        if (N == 0)
          // Unhandled operand. Halt "fast" selection and bail.
          return false;
        continue;
      }
      
      // N = N + Idx * ElementSize;
      uint64_t ElementSize = TD.getTypeAllocSize(Ty);
      unsigned IdxN = getRegForGEPIndex(Idx);
      if (IdxN == 0)
        // Unhandled operand. Halt "fast" selection and bail.
        return false;

      if (ElementSize != 1) {
        IdxN = FastEmit_ri_(VT, ISD::MUL, IdxN, ElementSize, VT);
        if (IdxN == 0)
          // Unhandled operand. Halt "fast" selection and bail.
          return false;
      }
      N = FastEmit_rr(VT, VT, ISD::ADD, N, IdxN);
      if (N == 0)
        // Unhandled operand. Halt "fast" selection and bail.
        return false;
    }
  }

  // We successfully emitted code for the given LLVM Instruction.
  UpdateValueMap(I, N);
  return true;
}

bool FastISel::SelectCall(User *I) {
  Function *F = cast<CallInst>(I)->getCalledFunction();
  if (!F) return false;

  unsigned IID = F->getIntrinsicID();
  switch (IID) {
  default: break;
  case Intrinsic::dbg_stoppoint: {
    DbgStopPointInst *SPI = cast<DbgStopPointInst>(I);
    if (DIDescriptor::ValidDebugInfo(SPI->getContext(), CodeGenOpt::None)) {
      DICompileUnit CU(cast<GlobalVariable>(SPI->getContext()));
      unsigned Line = SPI->getLine();
      unsigned Col = SPI->getColumn();
      unsigned Idx = MF.getOrCreateDebugLocID(CU.getGV(),
                                              DbgScopeTrack.getCurScope(),
                                              Line, Col);
      setCurDebugLoc(DebugLoc::get(Idx));
    }
    return true;
  }
  case Intrinsic::dbg_region_start: {
    DbgRegionStartInst *RSI = cast<DbgRegionStartInst>(I);
    if (!DIDescriptor::ValidDebugInfo(RSI->getContext(), CodeGenOpt::None))
      return true;

    GlobalVariable *Rgn = cast<GlobalVariable>(RSI->getContext());
    DbgScopeTrack.EnterDebugScope(Rgn, MF);
    if (DW && DW->ShouldEmitDwarfDebug()) {
      unsigned ID = DW->RecordRegionStart(Rgn);
      const TargetInstrDesc &II = TII.get(TargetInstrInfo::DBG_LABEL);
      BuildMI(MBB, DL, II).addImm(ID);
    }
    return true;
  }
  case Intrinsic::dbg_region_end: {
    DbgRegionEndInst *REI = cast<DbgRegionEndInst>(I);
    if (!DIDescriptor::ValidDebugInfo(REI->getContext(), CodeGenOpt::None))
      return true;

    GlobalVariable *Rgn = cast<GlobalVariable>(REI->getContext());
    DbgScopeTrack.ExitDebugScope(Rgn, MF);
    if (DW && DW->ShouldEmitDwarfDebug()) {
     unsigned ID = 0;
     DISubprogram Subprogram(Rgn);
     if (!Subprogram.isNull() && !Subprogram.describes(MF.getFunction())) {
        // This is end of an inlined function.
        const TargetInstrDesc &II = TII.get(TargetInstrInfo::DBG_LABEL);
        ID = DW->RecordInlinedFnEnd(Subprogram);
        if (ID)
          // Returned ID is 0 if this is unbalanced "end of inlined
          // scope". This could happen if optimizer eats dbg intrinsics
          // or "beginning of inlined scope" is not recoginized due to
          // missing location info. In such cases, do ignore this region.end.
          BuildMI(MBB, DL, II).addImm(ID);
      } else {
        const TargetInstrDesc &II = TII.get(TargetInstrInfo::DBG_LABEL);
        ID =  DW->RecordRegionEnd(cast<GlobalVariable>(REI->getContext()));
        BuildMI(MBB, DL, II).addImm(ID);
      }
    }
    return true;
  }
  case Intrinsic::dbg_func_start: {
    DbgFuncStartInst *FSI = cast<DbgFuncStartInst>(I);
    Value *SP = FSI->getSubprogram();
    if (!DIDescriptor::ValidDebugInfo(SP, CodeGenOpt::None))
      return true;

    // llvm.dbg.func.start implicitly defines a dbg_stoppoint which is what
    // (most?) gdb expects.
    DebugLoc PrevLoc = DL;
    DISubprogram Subprogram(cast<GlobalVariable>(SP));
    DICompileUnit CompileUnit = Subprogram.getCompileUnit();
    DbgScopeTrack.EnterDebugScope(Subprogram.getGV(), MF);

    if (!Subprogram.describes(MF.getFunction())) {
      // This is a beginning of an inlined function.

      // If llvm.dbg.func.start is seen in a new block before any
      // llvm.dbg.stoppoint intrinsic then the location info is unknown.
      // FIXME : Why DebugLoc is reset at the beginning of each block ?
      if (PrevLoc.isUnknown())
        return true;
      // Record the source line.
      unsigned Line = Subprogram.getLineNumber();
      setCurDebugLoc(
        DebugLoc::get(MF.getOrCreateDebugLocID(CompileUnit.getGV(),
                                               DbgScopeTrack.getCurScope(),
                                               Line, 0)));

      if (DW && DW->ShouldEmitDwarfDebug()) {
        DebugLocTuple PrevLocTpl = MF.getDebugLocTuple(PrevLoc);
        unsigned LabelID = DW->RecordInlinedFnStart(Subprogram,
                                          DICompileUnit(PrevLocTpl.CompileUnit),
                                          PrevLocTpl.Line,
                                          PrevLocTpl.Col);
        const TargetInstrDesc &II = TII.get(TargetInstrInfo::DBG_LABEL);
        BuildMI(MBB, DL, II).addImm(LabelID);
      }
    } else {
      // Record the source line.
      unsigned Line = Subprogram.getLineNumber();
      MF.setDefaultDebugLoc(
        DebugLoc::get(MF.getOrCreateDebugLocID(CompileUnit.getGV(),
                                               DbgScopeTrack.getCurScope(),
                                               Line, 0)));
      if (DW && DW->ShouldEmitDwarfDebug()) {
        // llvm.dbg.func_start also defines beginning of function scope.
        DW->RecordRegionStart(cast<GlobalVariable>(FSI->getSubprogram()));
      }
    }

    return true;
  }
  case Intrinsic::dbg_declare: {
    DbgDeclareInst *DI = cast<DbgDeclareInst>(I);
    Value *Variable = DI->getVariable();
    if (DIDescriptor::ValidDebugInfo(Variable, CodeGenOpt::None) &&
        DW && DW->ShouldEmitDwarfDebug()) {
      // Determine the address of the declared object.
      Value *Address = DI->getAddress();
      if (BitCastInst *BCI = dyn_cast<BitCastInst>(Address))
        Address = BCI->getOperand(0);
      AllocaInst *AI = dyn_cast<AllocaInst>(Address);
      // Don't handle byval struct arguments or VLAs, for example.
      if (!AI) break;
      DenseMap<const AllocaInst*, int>::iterator SI =
        StaticAllocaMap.find(AI);
      if (SI == StaticAllocaMap.end()) break; // VLAs.
      int FI = SI->second;

      // Determine the debug globalvariable.
      GlobalValue *GV = cast<GlobalVariable>(Variable);

      // Build the DECLARE instruction.
      const TargetInstrDesc &II = TII.get(TargetInstrInfo::DECLARE);
      MachineInstr *DeclareMI 
        = BuildMI(MBB, DL, II).addFrameIndex(FI).addGlobalAddress(GV);
      DIVariable DV(cast<GlobalVariable>(GV));
      if (!DV.isNull()) {
        // This is a local variable
        DW->RecordVariableScope(DV, DeclareMI);
      }
    }
    return true;
  }
  case Intrinsic::eh_exception: {
    MVT VT = TLI.getValueType(I->getType());
    switch (TLI.getOperationAction(ISD::EXCEPTIONADDR, VT)) {
    default: break;
    case TargetLowering::Expand: {
      if (!MBB->isLandingPad()) {
        // FIXME: Mark exception register as live in.  Hack for PR1508.
        unsigned Reg = TLI.getExceptionAddressRegister();
        if (Reg) MBB->addLiveIn(Reg);
      }
      unsigned Reg = TLI.getExceptionAddressRegister();
      const TargetRegisterClass *RC = TLI.getRegClassFor(VT);
      unsigned ResultReg = createResultReg(RC);
      bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                           Reg, RC, RC);
      assert(InsertedCopy && "Can't copy address registers!");
      InsertedCopy = InsertedCopy;
      UpdateValueMap(I, ResultReg);
      return true;
    }
    }
    break;
  }
  case Intrinsic::eh_selector_i32:
  case Intrinsic::eh_selector_i64: {
    MVT VT = TLI.getValueType(I->getType());
    switch (TLI.getOperationAction(ISD::EHSELECTION, VT)) {
    default: break;
    case TargetLowering::Expand: {
      MVT VT = (IID == Intrinsic::eh_selector_i32 ?
                           MVT::i32 : MVT::i64);

      if (MMI) {
        if (MBB->isLandingPad())
          AddCatchInfo(*cast<CallInst>(I), MMI, MBB);
        else {
#ifndef NDEBUG
          CatchInfoLost.insert(cast<CallInst>(I));
#endif
          // FIXME: Mark exception selector register as live in.  Hack for PR1508.
          unsigned Reg = TLI.getExceptionSelectorRegister();
          if (Reg) MBB->addLiveIn(Reg);
        }

        unsigned Reg = TLI.getExceptionSelectorRegister();
        const TargetRegisterClass *RC = TLI.getRegClassFor(VT);
        unsigned ResultReg = createResultReg(RC);
        bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                             Reg, RC, RC);
        assert(InsertedCopy && "Can't copy address registers!");
        InsertedCopy = InsertedCopy;
        UpdateValueMap(I, ResultReg);
      } else {
        unsigned ResultReg =
          getRegForValue(Constant::getNullValue(I->getType()));
        UpdateValueMap(I, ResultReg);
      }
      return true;
    }
    }
    break;
  }
  }
  return false;
}

bool FastISel::SelectCast(User *I, ISD::NodeType Opcode) {
  MVT SrcVT = TLI.getValueType(I->getOperand(0)->getType());
  MVT DstVT = TLI.getValueType(I->getType());
    
  if (SrcVT == MVT::Other || !SrcVT.isSimple() ||
      DstVT == MVT::Other || !DstVT.isSimple())
    // Unhandled type. Halt "fast" selection and bail.
    return false;
    
  // Check if the destination type is legal. Or as a special case,
  // it may be i1 if we're doing a truncate because that's
  // easy and somewhat common.
  if (!TLI.isTypeLegal(DstVT))
    if (DstVT != MVT::i1 || Opcode != ISD::TRUNCATE)
      // Unhandled type. Halt "fast" selection and bail.
      return false;

  // Check if the source operand is legal. Or as a special case,
  // it may be i1 if we're doing zero-extension because that's
  // easy and somewhat common.
  if (!TLI.isTypeLegal(SrcVT))
    if (SrcVT != MVT::i1 || Opcode != ISD::ZERO_EXTEND)
      // Unhandled type. Halt "fast" selection and bail.
      return false;

  unsigned InputReg = getRegForValue(I->getOperand(0));
  if (!InputReg)
    // Unhandled operand.  Halt "fast" selection and bail.
    return false;

  // If the operand is i1, arrange for the high bits in the register to be zero.
  if (SrcVT == MVT::i1) {
   SrcVT = TLI.getTypeToTransformTo(SrcVT);
   InputReg = FastEmitZExtFromI1(SrcVT.getSimpleVT(), InputReg);
   if (!InputReg)
     return false;
  }
  // If the result is i1, truncate to the target's type for i1 first.
  if (DstVT == MVT::i1)
    DstVT = TLI.getTypeToTransformTo(DstVT);

  unsigned ResultReg = FastEmit_r(SrcVT.getSimpleVT(),
                                  DstVT.getSimpleVT(),
                                  Opcode,
                                  InputReg);
  if (!ResultReg)
    return false;
    
  UpdateValueMap(I, ResultReg);
  return true;
}

bool FastISel::SelectBitCast(User *I) {
  // If the bitcast doesn't change the type, just use the operand value.
  if (I->getType() == I->getOperand(0)->getType()) {
    unsigned Reg = getRegForValue(I->getOperand(0));
    if (Reg == 0)
      return false;
    UpdateValueMap(I, Reg);
    return true;
  }

  // Bitcasts of other values become reg-reg copies or BIT_CONVERT operators.
  MVT SrcVT = TLI.getValueType(I->getOperand(0)->getType());
  MVT DstVT = TLI.getValueType(I->getType());
  
  if (SrcVT == MVT::Other || !SrcVT.isSimple() ||
      DstVT == MVT::Other || !DstVT.isSimple() ||
      !TLI.isTypeLegal(SrcVT) || !TLI.isTypeLegal(DstVT))
    // Unhandled type. Halt "fast" selection and bail.
    return false;
  
  unsigned Op0 = getRegForValue(I->getOperand(0));
  if (Op0 == 0)
    // Unhandled operand. Halt "fast" selection and bail.
    return false;
  
  // First, try to perform the bitcast by inserting a reg-reg copy.
  unsigned ResultReg = 0;
  if (SrcVT.getSimpleVT() == DstVT.getSimpleVT()) {
    TargetRegisterClass* SrcClass = TLI.getRegClassFor(SrcVT);
    TargetRegisterClass* DstClass = TLI.getRegClassFor(DstVT);
    ResultReg = createResultReg(DstClass);
    
    bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                         Op0, DstClass, SrcClass);
    if (!InsertedCopy)
      ResultReg = 0;
  }
  
  // If the reg-reg copy failed, select a BIT_CONVERT opcode.
  if (!ResultReg)
    ResultReg = FastEmit_r(SrcVT.getSimpleVT(), DstVT.getSimpleVT(),
                           ISD::BIT_CONVERT, Op0);
  
  if (!ResultReg)
    return false;
  
  UpdateValueMap(I, ResultReg);
  return true;
}

bool
FastISel::SelectInstruction(Instruction *I) {
  return SelectOperator(I, I->getOpcode());
}

/// FastEmitBranch - Emit an unconditional branch to the given block,
/// unless it is the immediate (fall-through) successor, and update
/// the CFG.
void
FastISel::FastEmitBranch(MachineBasicBlock *MSucc) {
  MachineFunction::iterator NextMBB =
     next(MachineFunction::iterator(MBB));

  if (MBB->isLayoutSuccessor(MSucc)) {
    // The unconditional fall-through case, which needs no instructions.
  } else {
    // The unconditional branch case.
    TII.InsertBranch(*MBB, MSucc, NULL, SmallVector<MachineOperand, 0>());
  }
  MBB->addSuccessor(MSucc);
}

bool
FastISel::SelectOperator(User *I, unsigned Opcode) {
  switch (Opcode) {
  case Instruction::Add: {
    ISD::NodeType Opc = I->getType()->isFPOrFPVector() ? ISD::FADD : ISD::ADD;
    return SelectBinaryOp(I, Opc);
  }
  case Instruction::Sub: {
    ISD::NodeType Opc = I->getType()->isFPOrFPVector() ? ISD::FSUB : ISD::SUB;
    return SelectBinaryOp(I, Opc);
  }
  case Instruction::Mul: {
    ISD::NodeType Opc = I->getType()->isFPOrFPVector() ? ISD::FMUL : ISD::MUL;
    return SelectBinaryOp(I, Opc);
  }
  case Instruction::SDiv:
    return SelectBinaryOp(I, ISD::SDIV);
  case Instruction::UDiv:
    return SelectBinaryOp(I, ISD::UDIV);
  case Instruction::FDiv:
    return SelectBinaryOp(I, ISD::FDIV);
  case Instruction::SRem:
    return SelectBinaryOp(I, ISD::SREM);
  case Instruction::URem:
    return SelectBinaryOp(I, ISD::UREM);
  case Instruction::FRem:
    return SelectBinaryOp(I, ISD::FREM);
  case Instruction::Shl:
    return SelectBinaryOp(I, ISD::SHL);
  case Instruction::LShr:
    return SelectBinaryOp(I, ISD::SRL);
  case Instruction::AShr:
    return SelectBinaryOp(I, ISD::SRA);
  case Instruction::And:
    return SelectBinaryOp(I, ISD::AND);
  case Instruction::Or:
    return SelectBinaryOp(I, ISD::OR);
  case Instruction::Xor:
    return SelectBinaryOp(I, ISD::XOR);

  case Instruction::GetElementPtr:
    return SelectGetElementPtr(I);

  case Instruction::Br: {
    BranchInst *BI = cast<BranchInst>(I);

    if (BI->isUnconditional()) {
      BasicBlock *LLVMSucc = BI->getSuccessor(0);
      MachineBasicBlock *MSucc = MBBMap[LLVMSucc];
      FastEmitBranch(MSucc);
      return true;
    }

    // Conditional branches are not handed yet.
    // Halt "fast" selection and bail.
    return false;
  }

  case Instruction::Unreachable:
    // Nothing to emit.
    return true;

  case Instruction::PHI:
    // PHI nodes are already emitted.
    return true;

  case Instruction::Alloca:
    // FunctionLowering has the static-sized case covered.
    if (StaticAllocaMap.count(cast<AllocaInst>(I)))
      return true;

    // Dynamic-sized alloca is not handled yet.
    return false;
    
  case Instruction::Call:
    return SelectCall(I);
  
  case Instruction::BitCast:
    return SelectBitCast(I);

  case Instruction::FPToSI:
    return SelectCast(I, ISD::FP_TO_SINT);
  case Instruction::ZExt:
    return SelectCast(I, ISD::ZERO_EXTEND);
  case Instruction::SExt:
    return SelectCast(I, ISD::SIGN_EXTEND);
  case Instruction::Trunc:
    return SelectCast(I, ISD::TRUNCATE);
  case Instruction::SIToFP:
    return SelectCast(I, ISD::SINT_TO_FP);

  case Instruction::IntToPtr: // Deliberate fall-through.
  case Instruction::PtrToInt: {
    MVT SrcVT = TLI.getValueType(I->getOperand(0)->getType());
    MVT DstVT = TLI.getValueType(I->getType());
    if (DstVT.bitsGT(SrcVT))
      return SelectCast(I, ISD::ZERO_EXTEND);
    if (DstVT.bitsLT(SrcVT))
      return SelectCast(I, ISD::TRUNCATE);
    unsigned Reg = getRegForValue(I->getOperand(0));
    if (Reg == 0) return false;
    UpdateValueMap(I, Reg);
    return true;
  }

  default:
    // Unhandled instruction. Halt "fast" selection and bail.
    return false;
  }
}

FastISel::FastISel(MachineFunction &mf,
                   MachineModuleInfo *mmi,
                   DwarfWriter *dw,
                   DenseMap<const Value *, unsigned> &vm,
                   DenseMap<const BasicBlock *, MachineBasicBlock *> &bm,
                   DenseMap<const AllocaInst *, int> &am
#ifndef NDEBUG
                   , SmallSet<Instruction*, 8> &cil
#endif
                   )
  : MBB(0),
    ValueMap(vm),
    MBBMap(bm),
    StaticAllocaMap(am),
#ifndef NDEBUG
    CatchInfoLost(cil),
#endif
    MF(mf),
    MMI(mmi),
    DW(dw),
    MRI(MF.getRegInfo()),
    MFI(*MF.getFrameInfo()),
    MCP(*MF.getConstantPool()),
    TM(MF.getTarget()),
    TD(*TM.getTargetData()),
    TII(*TM.getInstrInfo()),
    TLI(*TM.getTargetLowering()) {
}

FastISel::~FastISel() {}

unsigned FastISel::FastEmit_(MVT::SimpleValueType, MVT::SimpleValueType,
                             ISD::NodeType) {
  return 0;
}

unsigned FastISel::FastEmit_r(MVT::SimpleValueType, MVT::SimpleValueType,
                              ISD::NodeType, unsigned /*Op0*/) {
  return 0;
}

unsigned FastISel::FastEmit_rr(MVT::SimpleValueType, MVT::SimpleValueType, 
                               ISD::NodeType, unsigned /*Op0*/,
                               unsigned /*Op0*/) {
  return 0;
}

unsigned FastISel::FastEmit_i(MVT::SimpleValueType, MVT::SimpleValueType,
                              ISD::NodeType, uint64_t /*Imm*/) {
  return 0;
}

unsigned FastISel::FastEmit_f(MVT::SimpleValueType, MVT::SimpleValueType,
                              ISD::NodeType, ConstantFP * /*FPImm*/) {
  return 0;
}

unsigned FastISel::FastEmit_ri(MVT::SimpleValueType, MVT::SimpleValueType,
                               ISD::NodeType, unsigned /*Op0*/,
                               uint64_t /*Imm*/) {
  return 0;
}

unsigned FastISel::FastEmit_rf(MVT::SimpleValueType, MVT::SimpleValueType,
                               ISD::NodeType, unsigned /*Op0*/,
                               ConstantFP * /*FPImm*/) {
  return 0;
}

unsigned FastISel::FastEmit_rri(MVT::SimpleValueType, MVT::SimpleValueType,
                                ISD::NodeType,
                                unsigned /*Op0*/, unsigned /*Op1*/,
                                uint64_t /*Imm*/) {
  return 0;
}

/// FastEmit_ri_ - This method is a wrapper of FastEmit_ri. It first tries
/// to emit an instruction with an immediate operand using FastEmit_ri.
/// If that fails, it materializes the immediate into a register and try
/// FastEmit_rr instead.
unsigned FastISel::FastEmit_ri_(MVT::SimpleValueType VT, ISD::NodeType Opcode,
                                unsigned Op0, uint64_t Imm,
                                MVT::SimpleValueType ImmType) {
  // First check if immediate type is legal. If not, we can't use the ri form.
  unsigned ResultReg = FastEmit_ri(VT, VT, Opcode, Op0, Imm);
  if (ResultReg != 0)
    return ResultReg;
  unsigned MaterialReg = FastEmit_i(ImmType, ImmType, ISD::Constant, Imm);
  if (MaterialReg == 0)
    return 0;
  return FastEmit_rr(VT, VT, Opcode, Op0, MaterialReg);
}

/// FastEmit_rf_ - This method is a wrapper of FastEmit_ri. It first tries
/// to emit an instruction with a floating-point immediate operand using
/// FastEmit_rf. If that fails, it materializes the immediate into a register
/// and try FastEmit_rr instead.
unsigned FastISel::FastEmit_rf_(MVT::SimpleValueType VT, ISD::NodeType Opcode,
                                unsigned Op0, ConstantFP *FPImm,
                                MVT::SimpleValueType ImmType) {
  // First check if immediate type is legal. If not, we can't use the rf form.
  unsigned ResultReg = FastEmit_rf(VT, VT, Opcode, Op0, FPImm);
  if (ResultReg != 0)
    return ResultReg;

  // Materialize the constant in a register.
  unsigned MaterialReg = FastEmit_f(ImmType, ImmType, ISD::ConstantFP, FPImm);
  if (MaterialReg == 0) {
    // If the target doesn't have a way to directly enter a floating-point
    // value into a register, use an alternate approach.
    // TODO: The current approach only supports floating-point constants
    // that can be constructed by conversion from integer values. This should
    // be replaced by code that creates a load from a constant-pool entry,
    // which will require some target-specific work.
    const APFloat &Flt = FPImm->getValueAPF();
    MVT IntVT = TLI.getPointerTy();

    uint64_t x[2];
    uint32_t IntBitWidth = IntVT.getSizeInBits();
    bool isExact;
    (void) Flt.convertToInteger(x, IntBitWidth, /*isSigned=*/true,
                             APFloat::rmTowardZero, &isExact);
    if (!isExact)
      return 0;
    APInt IntVal(IntBitWidth, 2, x);

    unsigned IntegerReg = FastEmit_i(IntVT.getSimpleVT(), IntVT.getSimpleVT(),
                                     ISD::Constant, IntVal.getZExtValue());
    if (IntegerReg == 0)
      return 0;
    MaterialReg = FastEmit_r(IntVT.getSimpleVT(), VT,
                             ISD::SINT_TO_FP, IntegerReg);
    if (MaterialReg == 0)
      return 0;
  }
  return FastEmit_rr(VT, VT, Opcode, Op0, MaterialReg);
}

unsigned FastISel::createResultReg(const TargetRegisterClass* RC) {
  return MRI.createVirtualRegister(RC);
}

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

  BuildMI(MBB, DL, II, ResultReg);
  return ResultReg;
}

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

  if (II.getNumDefs() >= 1)
    BuildMI(MBB, DL, II, ResultReg).addReg(Op0);
  else {
    BuildMI(MBB, DL, II).addReg(Op0);
    bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                         II.ImplicitDefs[0], RC, RC);
    if (!InsertedCopy)
      ResultReg = 0;
  }

  return ResultReg;
}

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

  if (II.getNumDefs() >= 1)
    BuildMI(MBB, DL, II, ResultReg).addReg(Op0).addReg(Op1);
  else {
    BuildMI(MBB, DL, II).addReg(Op0).addReg(Op1);
    bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                         II.ImplicitDefs[0], RC, RC);
    if (!InsertedCopy)
      ResultReg = 0;
  }
  return ResultReg;
}

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

  if (II.getNumDefs() >= 1)
    BuildMI(MBB, DL, II, ResultReg).addReg(Op0).addImm(Imm);
  else {
    BuildMI(MBB, DL, II).addReg(Op0).addImm(Imm);
    bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                         II.ImplicitDefs[0], RC, RC);
    if (!InsertedCopy)
      ResultReg = 0;
  }
  return ResultReg;
}

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

  if (II.getNumDefs() >= 1)
    BuildMI(MBB, DL, II, ResultReg).addReg(Op0).addFPImm(FPImm);
  else {
    BuildMI(MBB, DL, II).addReg(Op0).addFPImm(FPImm);
    bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                         II.ImplicitDefs[0], RC, RC);
    if (!InsertedCopy)
      ResultReg = 0;
  }
  return ResultReg;
}

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

  if (II.getNumDefs() >= 1)
    BuildMI(MBB, DL, II, ResultReg).addReg(Op0).addReg(Op1).addImm(Imm);
  else {
    BuildMI(MBB, DL, II).addReg(Op0).addReg(Op1).addImm(Imm);
    bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                         II.ImplicitDefs[0], RC, RC);
    if (!InsertedCopy)
      ResultReg = 0;
  }
  return ResultReg;
}

unsigned FastISel::FastEmitInst_i(unsigned MachineInstOpcode,
                                  const TargetRegisterClass *RC,
                                  uint64_t Imm) {
  unsigned ResultReg = createResultReg(RC);
  const TargetInstrDesc &II = TII.get(MachineInstOpcode);
  
  if (II.getNumDefs() >= 1)
    BuildMI(MBB, DL, II, ResultReg).addImm(Imm);
  else {
    BuildMI(MBB, DL, II).addImm(Imm);
    bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                         II.ImplicitDefs[0], RC, RC);
    if (!InsertedCopy)
      ResultReg = 0;
  }
  return ResultReg;
}

unsigned FastISel::FastEmitInst_extractsubreg(MVT::SimpleValueType RetVT,
                                              unsigned Op0, uint32_t Idx) {
  const TargetRegisterClass* RC = MRI.getRegClass(Op0);
  
  unsigned ResultReg = createResultReg(TLI.getRegClassFor(RetVT));
  const TargetInstrDesc &II = TII.get(TargetInstrInfo::EXTRACT_SUBREG);
  
  if (II.getNumDefs() >= 1)
    BuildMI(MBB, DL, II, ResultReg).addReg(Op0).addImm(Idx);
  else {
    BuildMI(MBB, DL, II).addReg(Op0).addImm(Idx);
    bool InsertedCopy = TII.copyRegToReg(*MBB, MBB->end(), ResultReg,
                                         II.ImplicitDefs[0], RC, RC);
    if (!InsertedCopy)
      ResultReg = 0;
  }
  return ResultReg;
}

/// FastEmitZExtFromI1 - Emit MachineInstrs to compute the value of Op
/// with all but the least significant bit set to zero.
unsigned FastISel::FastEmitZExtFromI1(MVT::SimpleValueType VT, unsigned Op) {
  return FastEmit_ri(VT, VT, ISD::AND, Op, 1);
}