Transforms/InstCombine/InstCombineCalls.cpp

//===- InstCombineCalls.cpp -----------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the visitCall and visitInvoke functions.
//
//===----------------------------------------------------------------------===//

#include "InstCombine.h"
#include "llvm/Support/CallSite.h"
#include "llvm/DataLayout.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Transforms/Utils/BuildLibCalls.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;

STATISTIC(NumSimplified, "Number of library calls simplified");

/// getPromotedType - Return the specified type promoted as it would be to pass
/// though a va_arg area.
static Type *getPromotedType(Type *Ty) {
  if (IntegerType* ITy = dyn_cast<IntegerType>(Ty)) {
    if (ITy->getBitWidth() < 32)
      return Type::getInt32Ty(Ty->getContext());
  }
  return Ty;
}

/// reduceToSingleValueType - Given an aggregate type which ultimately holds a
/// single scalar element, like {{{type}}} or [1 x type], return type.
static Type *reduceToSingleValueType(Type *T) {
  while (!T->isSingleValueType()) {
    if (StructType *STy = dyn_cast<StructType>(T)) {
      if (STy->getNumElements() == 1)
        T = STy->getElementType(0);
      else
        break;
    } else if (ArrayType *ATy = dyn_cast<ArrayType>(T)) {
      if (ATy->getNumElements() == 1)
        T = ATy->getElementType();
      else
        break;
    } else
      break;
  }

  return T;
}

Instruction *InstCombiner::SimplifyMemTransfer(MemIntrinsic *MI) {
  unsigned DstAlign = getKnownAlignment(MI->getArgOperand(0), TD);
  unsigned SrcAlign = getKnownAlignment(MI->getArgOperand(1), TD);
  unsigned MinAlign = std::min(DstAlign, SrcAlign);
  unsigned CopyAlign = MI->getAlignment();

  if (CopyAlign < MinAlign) {
    MI->setAlignment(ConstantInt::get(MI->getAlignmentType(),
                                             MinAlign, false));
    return MI;
  }

  // If MemCpyInst length is 1/2/4/8 bytes then replace memcpy with
  // load/store.
  ConstantInt *MemOpLength = dyn_cast<ConstantInt>(MI->getArgOperand(2));
  if (MemOpLength == 0) return 0;

  // Source and destination pointer types are always "i8*" for intrinsic.  See
  // if the size is something we can handle with a single primitive load/store.
  // A single load+store correctly handles overlapping memory in the memmove
  // case.
  uint64_t Size = MemOpLength->getLimitedValue();
  assert(Size && "0-sized memory transfering should be removed already.");

  if (Size > 8 || (Size&(Size-1)))
    return 0;  // If not 1/2/4/8 bytes, exit.

  // Use an integer load+store unless we can find something better.
  unsigned SrcAddrSp =
    cast<PointerType>(MI->getArgOperand(1)->getType())->getAddressSpace();
  unsigned DstAddrSp =
    cast<PointerType>(MI->getArgOperand(0)->getType())->getAddressSpace();

  IntegerType* IntType = IntegerType::get(MI->getContext(), Size<<3);
  Type *NewSrcPtrTy = PointerType::get(IntType, SrcAddrSp);
  Type *NewDstPtrTy = PointerType::get(IntType, DstAddrSp);

  // Memcpy forces the use of i8* for the source and destination.  That means
  // that if you're using memcpy to move one double around, you'll get a cast
  // from double* to i8*.  We'd much rather use a double load+store rather than
  // an i64 load+store, here because this improves the odds that the source or
  // dest address will be promotable.  See if we can find a better type than the
  // integer datatype.
  Value *StrippedDest = MI->getArgOperand(0)->stripPointerCasts();
  MDNode *CopyMD = 0;
  if (StrippedDest != MI->getArgOperand(0)) {
    Type *SrcETy = cast<PointerType>(StrippedDest->getType())
                                    ->getElementType();
    if (TD && SrcETy->isSized() && TD->getTypeStoreSize(SrcETy) == Size) {
      // The SrcETy might be something like {{{double}}} or [1 x double].  Rip
      // down through these levels if so.
      SrcETy = reduceToSingleValueType(SrcETy);

      if (SrcETy->isSingleValueType()) {
        NewSrcPtrTy = PointerType::get(SrcETy, SrcAddrSp);
        NewDstPtrTy = PointerType::get(SrcETy, DstAddrSp);

        // If the memcpy has metadata describing the members, see if we can
        // get the TBAA tag describing our copy.
        if (MDNode *M = MI->getMetadata(LLVMContext::MD_tbaa_struct)) {
          if (M->getNumOperands() == 3 &&
              M->getOperand(0) &&
              isa<ConstantInt>(M->getOperand(0)) &&
              cast<ConstantInt>(M->getOperand(0))->isNullValue() &&
              M->getOperand(1) &&
              isa<ConstantInt>(M->getOperand(1)) &&
              cast<ConstantInt>(M->getOperand(1))->getValue() == Size &&
              M->getOperand(2) &&
              isa<MDNode>(M->getOperand(2)))
            CopyMD = cast<MDNode>(M->getOperand(2));
        }
      }
    }
  }

  // If the memcpy/memmove provides better alignment info than we can
  // infer, use it.
  SrcAlign = std::max(SrcAlign, CopyAlign);
  DstAlign = std::max(DstAlign, CopyAlign);

  Value *Src = Builder->CreateBitCast(MI->getArgOperand(1), NewSrcPtrTy);
  Value *Dest = Builder->CreateBitCast(MI->getArgOperand(0), NewDstPtrTy);
  LoadInst *L = Builder->CreateLoad(Src, MI->isVolatile());
  L->setAlignment(SrcAlign);
  if (CopyMD)
    L->setMetadata(LLVMContext::MD_tbaa, CopyMD);
  StoreInst *S = Builder->CreateStore(L, Dest, MI->isVolatile());
  S->setAlignment(DstAlign);
  if (CopyMD)
    S->setMetadata(LLVMContext::MD_tbaa, CopyMD);

  // Set the size of the copy to 0, it will be deleted on the next iteration.
  MI->setArgOperand(2, Constant::getNullValue(MemOpLength->getType()));
  return MI;
}

Instruction *InstCombiner::SimplifyMemSet(MemSetInst *MI) {
  unsigned Alignment = getKnownAlignment(MI->getDest(), TD);
  if (MI->getAlignment() < Alignment) {
    MI->setAlignment(ConstantInt::get(MI->getAlignmentType(),
                                             Alignment, false));
    return MI;
  }

  // Extract the length and alignment and fill if they are constant.
  ConstantInt *LenC = dyn_cast<ConstantInt>(MI->getLength());
  ConstantInt *FillC = dyn_cast<ConstantInt>(MI->getValue());
  if (!LenC || !FillC || !FillC->getType()->isIntegerTy(8))
    return 0;
  uint64_t Len = LenC->getLimitedValue();
  Alignment = MI->getAlignment();
  assert(Len && "0-sized memory setting should be removed already.");

  // memset(s,c,n) -> store s, c (for n=1,2,4,8)
  if (Len <= 8 && isPowerOf2_32((uint32_t)Len)) {
    Type *ITy = IntegerType::get(MI->getContext(), Len*8);  // n=1 -> i8.

    Value *Dest = MI->getDest();
    unsigned DstAddrSp = cast<PointerType>(Dest->getType())->getAddressSpace();
    Type *NewDstPtrTy = PointerType::get(ITy, DstAddrSp);
    Dest = Builder->CreateBitCast(Dest, NewDstPtrTy);

    // Alignment 0 is identity for alignment 1 for memset, but not store.
    if (Alignment == 0) Alignment = 1;

    // Extract the fill value and store.
    uint64_t Fill = FillC->getZExtValue()*0x0101010101010101ULL;
    StoreInst *S = Builder->CreateStore(ConstantInt::get(ITy, Fill), Dest,
                                        MI->isVolatile());
    S->setAlignment(Alignment);

    // Set the size of the copy to 0, it will be deleted on the next iteration.
    MI->setLength(Constant::getNullValue(LenC->getType()));
    return MI;
  }

  return 0;
}

/// visitCallInst - CallInst simplification.  This mostly only handles folding
/// of intrinsic instructions.  For normal calls, it allows visitCallSite to do
/// the heavy lifting.
///
Instruction *InstCombiner::visitCallInst(CallInst &CI) {
  if (isFreeCall(&CI, TLI))
    return visitFree(CI);

  // If the caller function is nounwind, mark the call as nounwind, even if the
  // callee isn't.
  if (CI.getParent()->getParent()->doesNotThrow() &&
      !CI.doesNotThrow()) {
    CI.setDoesNotThrow();
    return &CI;
  }

  IntrinsicInst *II = dyn_cast<IntrinsicInst>(&CI);
  if (!II) return visitCallSite(&CI);

  // Intrinsics cannot occur in an invoke, so handle them here instead of in
  // visitCallSite.
  if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(II)) {
    bool Changed = false;

    // memmove/cpy/set of zero bytes is a noop.
    if (Constant *NumBytes = dyn_cast<Constant>(MI->getLength())) {
      if (NumBytes->isNullValue())
        return EraseInstFromFunction(CI);

      if (ConstantInt *CI = dyn_cast<ConstantInt>(NumBytes))
        if (CI->getZExtValue() == 1) {
          // Replace the instruction with just byte operations.  We would
          // transform other cases to loads/stores, but we don't know if
          // alignment is sufficient.
        }
    }

    // No other transformations apply to volatile transfers.
    if (MI->isVolatile())
      return 0;

    // If we have a memmove and the source operation is a constant global,
    // then the source and dest pointers can't alias, so we can change this
    // into a call to memcpy.
    if (MemMoveInst *MMI = dyn_cast<MemMoveInst>(MI)) {
      if (GlobalVariable *GVSrc = dyn_cast<GlobalVariable>(MMI->getSource()))
        if (GVSrc->isConstant()) {
          Module *M = CI.getParent()->getParent()->getParent();
          Intrinsic::ID MemCpyID = Intrinsic::memcpy;
          Type *Tys[3] = { CI.getArgOperand(0)->getType(),
                           CI.getArgOperand(1)->getType(),
                           CI.getArgOperand(2)->getType() };
          CI.setCalledFunction(Intrinsic::getDeclaration(M, MemCpyID, Tys));
          Changed = true;
        }
    }

    if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) {
      // memmove(x,x,size) -> noop.
      if (MTI->getSource() == MTI->getDest())
        return EraseInstFromFunction(CI);
    }

    // If we can determine a pointer alignment that is bigger than currently
    // set, update the alignment.
    if (isa<MemTransferInst>(MI)) {
      if (Instruction *I = SimplifyMemTransfer(MI))
        return I;
    } else if (MemSetInst *MSI = dyn_cast<MemSetInst>(MI)) {
      if (Instruction *I = SimplifyMemSet(MSI))
        return I;
    }

    if (Changed) return II;
  }

  switch (II->getIntrinsicID()) {
  default: break;
  case Intrinsic::objectsize: {
    uint64_t Size;
    if (getObjectSize(II->getArgOperand(0), Size, TD, TLI))
      return ReplaceInstUsesWith(CI, ConstantInt::get(CI.getType(), Size));
    return 0;
  }
  case Intrinsic::bswap:
    // bswap(bswap(x)) -> x
    if (IntrinsicInst *Operand = dyn_cast<IntrinsicInst>(II->getArgOperand(0)))
      if (Operand->getIntrinsicID() == Intrinsic::bswap)
        return ReplaceInstUsesWith(CI, Operand->getArgOperand(0));

    // bswap(trunc(bswap(x))) -> trunc(lshr(x, c))
    if (TruncInst *TI = dyn_cast<TruncInst>(II->getArgOperand(0))) {
      if (IntrinsicInst *Operand = dyn_cast<IntrinsicInst>(TI->getOperand(0)))
        if (Operand->getIntrinsicID() == Intrinsic::bswap) {
          unsigned C = Operand->getType()->getPrimitiveSizeInBits() -
                       TI->getType()->getPrimitiveSizeInBits();
          Value *CV = ConstantInt::get(Operand->getType(), C);
          Value *V = Builder->CreateLShr(Operand->getArgOperand(0), CV);
          return new TruncInst(V, TI->getType());
        }
    }

    break;
  case Intrinsic::powi:
    if (ConstantInt *Power = dyn_cast<ConstantInt>(II->getArgOperand(1))) {
      // powi(x, 0) -> 1.0
      if (Power->isZero())
        return ReplaceInstUsesWith(CI, ConstantFP::get(CI.getType(), 1.0));
      // powi(x, 1) -> x
      if (Power->isOne())
        return ReplaceInstUsesWith(CI, II->getArgOperand(0));
      // powi(x, -1) -> 1/x
      if (Power->isAllOnesValue())
        return BinaryOperator::CreateFDiv(ConstantFP::get(CI.getType(), 1.0),
                                          II->getArgOperand(0));
    }
    break;
  case Intrinsic::cttz: {
    // If all bits below the first known one are known zero,
    // this value is constant.
    IntegerType *IT = dyn_cast<IntegerType>(II->getArgOperand(0)->getType());
    // FIXME: Try to simplify vectors of integers.
    if (!IT) break;
    uint32_t BitWidth = IT->getBitWidth();
    APInt KnownZero(BitWidth, 0);
    APInt KnownOne(BitWidth, 0);
    ComputeMaskedBits(II->getArgOperand(0), KnownZero, KnownOne);
    unsigned TrailingZeros = KnownOne.countTrailingZeros();
    APInt Mask(APInt::getLowBitsSet(BitWidth, TrailingZeros));
    if ((Mask & KnownZero) == Mask)
      return ReplaceInstUsesWith(CI, ConstantInt::get(IT,
                                 APInt(BitWidth, TrailingZeros)));

    }
    break;
  case Intrinsic::ctlz: {
    // If all bits above the first known one are known zero,
    // this value is constant.
    IntegerType *IT = dyn_cast<IntegerType>(II->getArgOperand(0)->getType());
    // FIXME: Try to simplify vectors of integers.
    if (!IT) break;
    uint32_t BitWidth = IT->getBitWidth();
    APInt KnownZero(BitWidth, 0);
    APInt KnownOne(BitWidth, 0);
    ComputeMaskedBits(II->getArgOperand(0), KnownZero, KnownOne);
    unsigned LeadingZeros = KnownOne.countLeadingZeros();
    APInt Mask(APInt::getHighBitsSet(BitWidth, LeadingZeros));
    if ((Mask & KnownZero) == Mask)
      return ReplaceInstUsesWith(CI, ConstantInt::get(IT,
                                 APInt(BitWidth, LeadingZeros)));

    }
    break;
  case Intrinsic::uadd_with_overflow: {
    Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
    IntegerType *IT = cast<IntegerType>(II->getArgOperand(0)->getType());
    uint32_t BitWidth = IT->getBitWidth();
    APInt LHSKnownZero(BitWidth, 0);
    APInt LHSKnownOne(BitWidth, 0);
    ComputeMaskedBits(LHS, LHSKnownZero, LHSKnownOne);
    bool LHSKnownNegative = LHSKnownOne[BitWidth - 1];
    bool LHSKnownPositive = LHSKnownZero[BitWidth - 1];

    if (LHSKnownNegative || LHSKnownPositive) {
      APInt RHSKnownZero(BitWidth, 0);
      APInt RHSKnownOne(BitWidth, 0);
      ComputeMaskedBits(RHS, RHSKnownZero, RHSKnownOne);
      bool RHSKnownNegative = RHSKnownOne[BitWidth - 1];
      bool RHSKnownPositive = RHSKnownZero[BitWidth - 1];
      if (LHSKnownNegative && RHSKnownNegative) {
        // The sign bit is set in both cases: this MUST overflow.
        // Create a simple add instruction, and insert it into the struct.
        Value *Add = Builder->CreateAdd(LHS, RHS);
        Add->takeName(&CI);
        Constant *V[] = {
          UndefValue::get(LHS->getType()),
          ConstantInt::getTrue(II->getContext())
        };
        StructType *ST = cast<StructType>(II->getType());
        Constant *Struct = ConstantStruct::get(ST, V);
        return InsertValueInst::Create(Struct, Add, 0);
      }

      if (LHSKnownPositive && RHSKnownPositive) {
        // The sign bit is clear in both cases: this CANNOT overflow.
        // Create a simple add instruction, and insert it into the struct.
        Value *Add = Builder->CreateNUWAdd(LHS, RHS);
        Add->takeName(&CI);
        Constant *V[] = {
          UndefValue::get(LHS->getType()),
          ConstantInt::getFalse(II->getContext())
        };
        StructType *ST = cast<StructType>(II->getType());
        Constant *Struct = ConstantStruct::get(ST, V);
        return InsertValueInst::Create(Struct, Add, 0);
      }
    }
  }
  // FALL THROUGH uadd into sadd
  case Intrinsic::sadd_with_overflow:
    // Canonicalize constants into the RHS.
    if (isa<Constant>(II->getArgOperand(0)) &&
        !isa<Constant>(II->getArgOperand(1))) {
      Value *LHS = II->getArgOperand(0);
      II->setArgOperand(0, II->getArgOperand(1));
      II->setArgOperand(1, LHS);
      return II;
    }

    // X + undef -> undef
    if (isa<UndefValue>(II->getArgOperand(1)))
      return ReplaceInstUsesWith(CI, UndefValue::get(II->getType()));

    if (ConstantInt *RHS = dyn_cast<ConstantInt>(II->getArgOperand(1))) {
      // X + 0 -> {X, false}
      if (RHS->isZero()) {
        Constant *V[] = {
          UndefValue::get(II->getArgOperand(0)->getType()),
          ConstantInt::getFalse(II->getContext())
        };
        Constant *Struct =
          ConstantStruct::get(cast<StructType>(II->getType()), V);
        return InsertValueInst::Create(Struct, II->getArgOperand(0), 0);
      }
    }
    break;
  case Intrinsic::usub_with_overflow:
  case Intrinsic::ssub_with_overflow:
    // undef - X -> undef
    // X - undef -> undef
    if (isa<UndefValue>(II->getArgOperand(0)) ||
        isa<UndefValue>(II->getArgOperand(1)))
      return ReplaceInstUsesWith(CI, UndefValue::get(II->getType()));

    if (ConstantInt *RHS = dyn_cast<ConstantInt>(II->getArgOperand(1))) {
      // X - 0 -> {X, false}
      if (RHS->isZero()) {
        Constant *V[] = {
          UndefValue::get(II->getArgOperand(0)->getType()),
          ConstantInt::getFalse(II->getContext())
        };
        Constant *Struct =
          ConstantStruct::get(cast<StructType>(II->getType()), V);
        return InsertValueInst::Create(Struct, II->getArgOperand(0), 0);
      }
    }
    break;
  case Intrinsic::umul_with_overflow: {
    Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
    unsigned BitWidth = cast<IntegerType>(LHS->getType())->getBitWidth();

    APInt LHSKnownZero(BitWidth, 0);
    APInt LHSKnownOne(BitWidth, 0);
    ComputeMaskedBits(LHS, LHSKnownZero, LHSKnownOne);
    APInt RHSKnownZero(BitWidth, 0);
    APInt RHSKnownOne(BitWidth, 0);
    ComputeMaskedBits(RHS, RHSKnownZero, RHSKnownOne);

    // Get the largest possible values for each operand.
    APInt LHSMax = ~LHSKnownZero;
    APInt RHSMax = ~RHSKnownZero;

    // If multiplying the maximum values does not overflow then we can turn
    // this into a plain NUW mul.
    bool Overflow;
    LHSMax.umul_ov(RHSMax, Overflow);
    if (!Overflow) {
      Value *Mul = Builder->CreateNUWMul(LHS, RHS, "umul_with_overflow");
      Constant *V[] = {
        UndefValue::get(LHS->getType()),
        Builder->getFalse()
      };
      Constant *Struct = ConstantStruct::get(cast<StructType>(II->getType()),V);
      return InsertValueInst::Create(Struct, Mul, 0);
    }
  } // FALL THROUGH
  case Intrinsic::smul_with_overflow:
    // Canonicalize constants into the RHS.
    if (isa<Constant>(II->getArgOperand(0)) &&
        !isa<Constant>(II->getArgOperand(1))) {
      Value *LHS = II->getArgOperand(0);
      II->setArgOperand(0, II->getArgOperand(1));
      II->setArgOperand(1, LHS);
      return II;
    }

    // X * undef -> undef
    if (isa<UndefValue>(II->getArgOperand(1)))
      return ReplaceInstUsesWith(CI, UndefValue::get(II->getType()));

    if (ConstantInt *RHSI = dyn_cast<ConstantInt>(II->getArgOperand(1))) {
      // X*0 -> {0, false}
      if (RHSI->isZero())
        return ReplaceInstUsesWith(CI, Constant::getNullValue(II->getType()));

      // X * 1 -> {X, false}
      if (RHSI->equalsInt(1)) {
        Constant *V[] = {
          UndefValue::get(II->getArgOperand(0)->getType()),
          ConstantInt::getFalse(II->getContext())
        };
        Constant *Struct =
          ConstantStruct::get(cast<StructType>(II->getType()), V);
        return InsertValueInst::Create(Struct, II->getArgOperand(0), 0);
      }
    }
    break;
  case Intrinsic::ppc_altivec_lvx:
  case Intrinsic::ppc_altivec_lvxl:
    // Turn PPC lvx -> load if the pointer is known aligned.
    if (getOrEnforceKnownAlignment(II->getArgOperand(0), 16, TD) >= 16) {
      Value *Ptr = Builder->CreateBitCast(II->getArgOperand(0),
                                         PointerType::getUnqual(II->getType()));
      return new LoadInst(Ptr);
    }
    break;
  case Intrinsic::ppc_altivec_stvx:
  case Intrinsic::ppc_altivec_stvxl:
    // Turn stvx -> store if the pointer is known aligned.
    if (getOrEnforceKnownAlignment(II->getArgOperand(1), 16, TD) >= 16) {
      Type *OpPtrTy =
        PointerType::getUnqual(II->getArgOperand(0)->getType());
      Value *Ptr = Builder->CreateBitCast(II->getArgOperand(1), OpPtrTy);
      return new StoreInst(II->getArgOperand(0), Ptr);
    }
    break;
  case Intrinsic::x86_sse_storeu_ps:
  case Intrinsic::x86_sse2_storeu_pd:
  case Intrinsic::x86_sse2_storeu_dq:
    // Turn X86 storeu -> store if the pointer is known aligned.
    if (getOrEnforceKnownAlignment(II->getArgOperand(0), 16, TD) >= 16) {
      Type *OpPtrTy =
        PointerType::getUnqual(II->getArgOperand(1)->getType());
      Value *Ptr = Builder->CreateBitCast(II->getArgOperand(0), OpPtrTy);
      return new StoreInst(II->getArgOperand(1), Ptr);
    }
    break;

  case Intrinsic::x86_sse_cvtss2si:
  case Intrinsic::x86_sse_cvtss2si64:
  case Intrinsic::x86_sse_cvttss2si:
  case Intrinsic::x86_sse_cvttss2si64:
  case Intrinsic::x86_sse2_cvtsd2si:
  case Intrinsic::x86_sse2_cvtsd2si64:
  case Intrinsic::x86_sse2_cvttsd2si:
  case Intrinsic::x86_sse2_cvttsd2si64: {
    // These intrinsics only demand the 0th element of their input vectors. If
    // we can simplify the input based on that, do so now.
    unsigned VWidth =
      cast<VectorType>(II->getArgOperand(0)->getType())->getNumElements();
    APInt DemandedElts(VWidth, 1);
    APInt UndefElts(VWidth, 0);
    if (Value *V = SimplifyDemandedVectorElts(II->getArgOperand(0),
                                              DemandedElts, UndefElts)) {
      II->setArgOperand(0, V);
      return II;
    }
    break;
  }


  case Intrinsic::x86_sse41_pmovsxbw:
  case Intrinsic::x86_sse41_pmovsxwd:
  case Intrinsic::x86_sse41_pmovsxdq:
  case Intrinsic::x86_sse41_pmovzxbw:
  case Intrinsic::x86_sse41_pmovzxwd:
  case Intrinsic::x86_sse41_pmovzxdq: {
    // pmov{s|z}x ignores the upper half of their input vectors.
    unsigned VWidth =
      cast<VectorType>(II->getArgOperand(0)->getType())->getNumElements();
    unsigned LowHalfElts = VWidth / 2;
    APInt InputDemandedElts(APInt::getBitsSet(VWidth, 0, LowHalfElts));
    APInt UndefElts(VWidth, 0);
    if (Value *TmpV = SimplifyDemandedVectorElts(II->getArgOperand(0),
                                                 InputDemandedElts,
                                                 UndefElts)) {
      II->setArgOperand(0, TmpV);
      return II;
    }
    break;
  }

  case Intrinsic::ppc_altivec_vperm:
    // Turn vperm(V1,V2,mask) -> shuffle(V1,V2,mask) if mask is a constant.
    if (Constant *Mask = dyn_cast<Constant>(II->getArgOperand(2))) {
      assert(Mask->getType()->getVectorNumElements() == 16 &&
             "Bad type for intrinsic!");

      // Check that all of the elements are integer constants or undefs.
      bool AllEltsOk = true;
      for (unsigned i = 0; i != 16; ++i) {
        Constant *Elt = Mask->getAggregateElement(i);
        if (Elt == 0 ||
            !(isa<ConstantInt>(Elt) || isa<UndefValue>(Elt))) {
          AllEltsOk = false;
          break;
        }
      }

      if (AllEltsOk) {
        // Cast the input vectors to byte vectors.
        Value *Op0 = Builder->CreateBitCast(II->getArgOperand(0),
                                            Mask->getType());
        Value *Op1 = Builder->CreateBitCast(II->getArgOperand(1),
                                            Mask->getType());
        Value *Result = UndefValue::get(Op0->getType());

        // Only extract each element once.
        Value *ExtractedElts[32];
        memset(ExtractedElts, 0, sizeof(ExtractedElts));

        for (unsigned i = 0; i != 16; ++i) {
          if (isa<UndefValue>(Mask->getAggregateElement(i)))
            continue;
          unsigned Idx =
            cast<ConstantInt>(Mask->getAggregateElement(i))->getZExtValue();
          Idx &= 31;  // Match the hardware behavior.

          if (ExtractedElts[Idx] == 0) {
            ExtractedElts[Idx] =
              Builder->CreateExtractElement(Idx < 16 ? Op0 : Op1,
                                            Builder->getInt32(Idx&15));
          }

          // Insert this value into the result vector.
          Result = Builder->CreateInsertElement(Result, ExtractedElts[Idx],
                                                Builder->getInt32(i));
        }
        return CastInst::Create(Instruction::BitCast, Result, CI.getType());
      }
    }
    break;

  case Intrinsic::arm_neon_vld1:
  case Intrinsic::arm_neon_vld2:
  case Intrinsic::arm_neon_vld3:
  case Intrinsic::arm_neon_vld4:
  case Intrinsic::arm_neon_vld2lane:
  case Intrinsic::arm_neon_vld3lane:
  case Intrinsic::arm_neon_vld4lane:
  case Intrinsic::arm_neon_vst1:
  case Intrinsic::arm_neon_vst2:
  case Intrinsic::arm_neon_vst3:
  case Intrinsic::arm_neon_vst4:
  case Intrinsic::arm_neon_vst2lane:
  case Intrinsic::arm_neon_vst3lane:
  case Intrinsic::arm_neon_vst4lane: {
    unsigned MemAlign = getKnownAlignment(II->getArgOperand(0), TD);
    unsigned AlignArg = II->getNumArgOperands() - 1;
    ConstantInt *IntrAlign = dyn_cast<ConstantInt>(II->getArgOperand(AlignArg));
    if (IntrAlign && IntrAlign->getZExtValue() < MemAlign) {
      II->setArgOperand(AlignArg,
                        ConstantInt::get(Type::getInt32Ty(II->getContext()),
                                         MemAlign, false));
      return II;
    }
    break;
  }

  case Intrinsic::arm_neon_vmulls:
  case Intrinsic::arm_neon_vmullu: {
    Value *Arg0 = II->getArgOperand(0);
    Value *Arg1 = II->getArgOperand(1);

    // Handle mul by zero first:
    if (isa<ConstantAggregateZero>(Arg0) || isa<ConstantAggregateZero>(Arg1)) {
      return ReplaceInstUsesWith(CI, ConstantAggregateZero::get(II->getType()));
    }

    // Check for constant LHS & RHS - in this case we just simplify.
    bool Zext = (II->getIntrinsicID() == Intrinsic::arm_neon_vmullu);
    VectorType *NewVT = cast<VectorType>(II->getType());
    unsigned NewWidth = NewVT->getElementType()->getIntegerBitWidth();
    if (ConstantDataVector *CV0 = dyn_cast<ConstantDataVector>(Arg0)) {
      if (ConstantDataVector *CV1 = dyn_cast<ConstantDataVector>(Arg1)) {
        VectorType* VT = cast<VectorType>(CV0->getType());
        SmallVector<Constant*, 4> NewElems;
        for (unsigned i = 0; i < VT->getNumElements(); ++i) {
          APInt CV0E =
            (cast<ConstantInt>(CV0->getAggregateElement(i)))->getValue();
          CV0E = Zext ? CV0E.zext(NewWidth) : CV0E.sext(NewWidth);
          APInt CV1E =
            (cast<ConstantInt>(CV1->getAggregateElement(i)))->getValue();
          CV1E = Zext ? CV1E.zext(NewWidth) : CV1E.sext(NewWidth);
          NewElems.push_back(
            ConstantInt::get(NewVT->getElementType(), CV0E * CV1E));
        }
        return ReplaceInstUsesWith(CI, ConstantVector::get(NewElems));
      }

      // Couldn't simplify - cannonicalize constant to the RHS.
      std::swap(Arg0, Arg1);
    }

    // Handle mul by one:
    if (ConstantDataVector *CV1 = dyn_cast<ConstantDataVector>(Arg1)) {
      if (ConstantInt *Splat =
            dyn_cast_or_null<ConstantInt>(CV1->getSplatValue())) {
        if (Splat->isOne()) {
          if (Zext)
            return CastInst::CreateZExtOrBitCast(Arg0, II->getType());
          // else
          return CastInst::CreateSExtOrBitCast(Arg0, II->getType());
        }
      }
    }

    break;
  }

  case Intrinsic::stackrestore: {
    // If the save is right next to the restore, remove the restore.  This can
    // happen when variable allocas are DCE'd.
    if (IntrinsicInst *SS = dyn_cast<IntrinsicInst>(II->getArgOperand(0))) {
      if (SS->getIntrinsicID() == Intrinsic::stacksave) {
        BasicBlock::iterator BI = SS;
        if (&*++BI == II)
          return EraseInstFromFunction(CI);
      }
    }

    // Scan down this block to see if there is another stack restore in the
    // same block without an intervening call/alloca.
    BasicBlock::iterator BI = II;
    TerminatorInst *TI = II->getParent()->getTerminator();
    bool CannotRemove = false;
    for (++BI; &*BI != TI; ++BI) {
      if (isa<AllocaInst>(BI)) {
        CannotRemove = true;
        break;
      }
      if (CallInst *BCI = dyn_cast<CallInst>(BI)) {
        if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(BCI)) {
          // If there is a stackrestore below this one, remove this one.
          if (II->getIntrinsicID() == Intrinsic::stackrestore)
            return EraseInstFromFunction(CI);
          // Otherwise, ignore the intrinsic.
        } else {
          // If we found a non-intrinsic call, we can't remove the stack
          // restore.
          CannotRemove = true;
          break;
        }
      }
    }

    // If the stack restore is in a return, resume, or unwind block and if there
    // are no allocas or calls between the restore and the return, nuke the
    // restore.
    if (!CannotRemove && (isa<ReturnInst>(TI) || isa<ResumeInst>(TI)))
      return EraseInstFromFunction(CI);
    break;
  }
  }

  return visitCallSite(II);
}

// InvokeInst simplification
//
Instruction *InstCombiner::visitInvokeInst(InvokeInst &II) {
  return visitCallSite(&II);
}

/// isSafeToEliminateVarargsCast - If this cast does not affect the value
/// passed through the varargs area, we can eliminate the use of the cast.
static bool isSafeToEliminateVarargsCast(const CallSite CS,
                                         const CastInst * const CI,
                                         const DataLayout * const TD,
                                         const int ix) {
  if (!CI->isLosslessCast())
    return false;

  // The size of ByVal arguments is derived from the type, so we
  // can't change to a type with a different size.  If the size were
  // passed explicitly we could avoid this check.
  if (!CS.isByValArgument(ix))
    return true;

  Type* SrcTy =
            cast<PointerType>(CI->getOperand(0)->getType())->getElementType();
  Type* DstTy = cast<PointerType>(CI->getType())->getElementType();
  if (!SrcTy->isSized() || !DstTy->isSized())
    return false;
  if (!TD || TD->getTypeAllocSize(SrcTy) != TD->getTypeAllocSize(DstTy))
    return false;
  return true;
}

// Try to fold some different type of calls here.
// Currently we're only working with the checking functions, memcpy_chk,
// mempcpy_chk, memmove_chk, memset_chk, strcpy_chk, stpcpy_chk, strncpy_chk,
// strcat_chk and strncat_chk.
Instruction *InstCombiner::tryOptimizeCall(CallInst *CI, const DataLayout *TD) {
  if (CI->getCalledFunction() == 0) return 0;

  if (Value *With = Simplifier->optimizeCall(CI)) {
    ++NumSimplified;
    return CI->use_empty() ? CI : ReplaceInstUsesWith(*CI, With);
  }

  return 0;
}

static IntrinsicInst *FindInitTrampolineFromAlloca(Value *TrampMem) {
  // Strip off at most one level of pointer casts, looking for an alloca.  This
  // is good enough in practice and simpler than handling any number of casts.
  Value *Underlying = TrampMem->stripPointerCasts();
  if (Underlying != TrampMem &&
      (!Underlying->hasOneUse() || *Underlying->use_begin() != TrampMem))
    return 0;
  if (!isa<AllocaInst>(Underlying))
    return 0;

  IntrinsicInst *InitTrampoline = 0;
  for (Value::use_iterator I = TrampMem->use_begin(), E = TrampMem->use_end();
       I != E; I++) {
    IntrinsicInst *II = dyn_cast<IntrinsicInst>(*I);
    if (!II)
      return 0;
    if (II->getIntrinsicID() == Intrinsic::init_trampoline) {
      if (InitTrampoline)
        // More than one init_trampoline writes to this value.  Give up.
        return 0;
      InitTrampoline = II;
      continue;
    }
    if (II->getIntrinsicID() == Intrinsic::adjust_trampoline)
      // Allow any number of calls to adjust.trampoline.
      continue;
    return 0;
  }

  // No call to init.trampoline found.
  if (!InitTrampoline)
    return 0;

  // Check that the alloca is being used in the expected way.
  if (InitTrampoline->getOperand(0) != TrampMem)
    return 0;

  return InitTrampoline;
}

static IntrinsicInst *FindInitTrampolineFromBB(IntrinsicInst *AdjustTramp,
                                               Value *TrampMem) {
  // Visit all the previous instructions in the basic block, and try to find a
  // init.trampoline which has a direct path to the adjust.trampoline.
  for (BasicBlock::iterator I = AdjustTramp,
       E = AdjustTramp->getParent()->begin(); I != E; ) {
    Instruction *Inst = --I;
    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
      if (II->getIntrinsicID() == Intrinsic::init_trampoline &&
          II->getOperand(0) == TrampMem)
        return II;
    if (Inst->mayWriteToMemory())
      return 0;
  }
  return 0;
}

// Given a call to llvm.adjust.trampoline, find and return the corresponding
// call to llvm.init.trampoline if the call to the trampoline can be optimized
// to a direct call to a function.  Otherwise return NULL.
//
static IntrinsicInst *FindInitTrampoline(Value *Callee) {
  Callee = Callee->stripPointerCasts();
  IntrinsicInst *AdjustTramp = dyn_cast<IntrinsicInst>(Callee);
  if (!AdjustTramp ||
      AdjustTramp->getIntrinsicID() != Intrinsic::adjust_trampoline)
    return 0;

  Value *TrampMem = AdjustTramp->getOperand(0);

  if (IntrinsicInst *IT = FindInitTrampolineFromAlloca(TrampMem))
    return IT;
  if (IntrinsicInst *IT = FindInitTrampolineFromBB(AdjustTramp, TrampMem))
    return IT;
  return 0;
}

// visitCallSite - Improvements for call and invoke instructions.
//
Instruction *InstCombiner::visitCallSite(CallSite CS) {
  if (isAllocLikeFn(CS.getInstruction(), TLI))
    return visitAllocSite(*CS.getInstruction());

  bool Changed = false;

  // If the callee is a pointer to a function, attempt to move any casts to the
  // arguments of the call/invoke.
  Value *Callee = CS.getCalledValue();
  if (!isa<Function>(Callee) && transformConstExprCastCall(CS))
    return 0;

  if (Function *CalleeF = dyn_cast<Function>(Callee))
    // If the call and callee calling conventions don't match, this call must
    // be unreachable, as the call is undefined.
    if (CalleeF->getCallingConv() != CS.getCallingConv() &&
        // Only do this for calls to a function with a body.  A prototype may
        // not actually end up matching the implementation's calling conv for a
        // variety of reasons (e.g. it may be written in assembly).
        !CalleeF->isDeclaration()) {
      Instruction *OldCall = CS.getInstruction();
      new StoreInst(ConstantInt::getTrue(Callee->getContext()),
                UndefValue::get(Type::getInt1PtrTy(Callee->getContext())),
                                  OldCall);
      // If OldCall dues not return void then replaceAllUsesWith undef.
      // This allows ValueHandlers and custom metadata to adjust itself.
      if (!OldCall->getType()->isVoidTy())
        ReplaceInstUsesWith(*OldCall, UndefValue::get(OldCall->getType()));
      if (isa<CallInst>(OldCall))
        return EraseInstFromFunction(*OldCall);

      // We cannot remove an invoke, because it would change the CFG, just
      // change the callee to a null pointer.
      cast<InvokeInst>(OldCall)->setCalledFunction(
                                    Constant::getNullValue(CalleeF->getType()));
      return 0;
    }

  if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
    // If CS does not return void then replaceAllUsesWith undef.
    // This allows ValueHandlers and custom metadata to adjust itself.
    if (!CS.getInstruction()->getType()->isVoidTy())
      ReplaceInstUsesWith(*CS.getInstruction(),
                          UndefValue::get(CS.getInstruction()->getType()));

    if (isa<InvokeInst>(CS.getInstruction())) {
      // Can't remove an invoke because we cannot change the CFG.
      return 0;
    }

    // This instruction is not reachable, just remove it.  We insert a store to
    // undef so that we know that this code is not reachable, despite the fact
    // that we can't modify the CFG here.
    new StoreInst(ConstantInt::getTrue(Callee->getContext()),
                  UndefValue::get(Type::getInt1PtrTy(Callee->getContext())),
                  CS.getInstruction());

    return EraseInstFromFunction(*CS.getInstruction());
  }

  if (IntrinsicInst *II = FindInitTrampoline(Callee))
    return transformCallThroughTrampoline(CS, II);

  PointerType *PTy = cast<PointerType>(Callee->getType());
  FunctionType *FTy = cast<FunctionType>(PTy->getElementType());
  if (FTy->isVarArg()) {
    int ix = FTy->getNumParams();
    // See if we can optimize any arguments passed through the varargs area of
    // the call.
    for (CallSite::arg_iterator I = CS.arg_begin()+FTy->getNumParams(),
           E = CS.arg_end(); I != E; ++I, ++ix) {
      CastInst *CI = dyn_cast<CastInst>(*I);
      if (CI && isSafeToEliminateVarargsCast(CS, CI, TD, ix)) {
        *I = CI->getOperand(0);
        Changed = true;
      }
    }
  }

  if (isa<InlineAsm>(Callee) && !CS.doesNotThrow()) {
    // Inline asm calls cannot throw - mark them 'nounwind'.
    CS.setDoesNotThrow();
    Changed = true;
  }

  // Try to optimize the call if possible, we require DataLayout for most of
  // this.  None of these calls are seen as possibly dead so go ahead and
  // delete the instruction now.
  if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction())) {
    Instruction *I = tryOptimizeCall(CI, TD);
    // If we changed something return the result, etc. Otherwise let
    // the fallthrough check.
    if (I) return EraseInstFromFunction(*I);
  }

  return Changed ? CS.getInstruction() : 0;
}

// transformConstExprCastCall - If the callee is a constexpr cast of a function,
// attempt to move the cast to the arguments of the call/invoke.
//
bool InstCombiner::transformConstExprCastCall(CallSite CS) {
  Function *Callee =
    dyn_cast<Function>(CS.getCalledValue()->stripPointerCasts());
  if (Callee == 0)
    return false;
  Instruction *Caller = CS.getInstruction();
  const AttrListPtr &CallerPAL = CS.getAttributes();

  // Okay, this is a cast from a function to a different type.  Unless doing so
  // would cause a type conversion of one of our arguments, change this call to
  // be a direct call with arguments casted to the appropriate types.
  //
  FunctionType *FT = Callee->getFunctionType();
  Type *OldRetTy = Caller->getType();
  Type *NewRetTy = FT->getReturnType();

  if (NewRetTy->isStructTy())
    return false; // TODO: Handle multiple return values.

  // Check to see if we are changing the return type...
  if (OldRetTy != NewRetTy) {
    if (Callee->isDeclaration() &&
        // Conversion is ok if changing from one pointer type to another or from
        // a pointer to an integer of the same size.
        !((OldRetTy->isPointerTy() || !TD ||
           OldRetTy == TD->getIntPtrType(Caller->getContext())) &&
          (NewRetTy->isPointerTy() || !TD ||
           NewRetTy == TD->getIntPtrType(Caller->getContext()))))
      return false;   // Cannot transform this return value.

    if (!Caller->use_empty() &&
        // void -> non-void is handled specially
        !NewRetTy->isVoidTy() && !CastInst::isCastable(NewRetTy, OldRetTy))
      return false;   // Cannot transform this return value.

    if (!CallerPAL.isEmpty() && !Caller->use_empty()) {
      AttrBuilder RAttrs = CallerPAL.getRetAttributes();
      if (RAttrs.hasAttributes(Attributes::typeIncompatible(NewRetTy)))
        return false;   // Attribute not compatible with transformed value.
    }

    // If the callsite is an invoke instruction, and the return value is used by
    // a PHI node in a successor, we cannot change the return type of the call
    // because there is no place to put the cast instruction (without breaking
    // the critical edge).  Bail out in this case.
    if (!Caller->use_empty())
      if (InvokeInst *II = dyn_cast<InvokeInst>(Caller))
        for (Value::use_iterator UI = II->use_begin(), E = II->use_end();
             UI != E; ++UI)
          if (PHINode *PN = dyn_cast<PHINode>(*UI))
            if (PN->getParent() == II->getNormalDest() ||
                PN->getParent() == II->getUnwindDest())
              return false;
  }

  unsigned NumActualArgs = unsigned(CS.arg_end()-CS.arg_begin());
  unsigned NumCommonArgs = std::min(FT->getNumParams(), NumActualArgs);

  CallSite::arg_iterator AI = CS.arg_begin();
  for (unsigned i = 0, e = NumCommonArgs; i != e; ++i, ++AI) {
    Type *ParamTy = FT->getParamType(i);
    Type *ActTy = (*AI)->getType();

    if (!CastInst::isCastable(ActTy, ParamTy))
      return false;   // Cannot transform this parameter value.

    Attributes Attrs = CallerPAL.getParamAttributes(i + 1);
    if (AttrBuilder(Attrs).
          hasAttributes(Attributes::typeIncompatible(ParamTy)))
      return false;   // Attribute not compatible with transformed value.

    // If the parameter is passed as a byval argument, then we have to have a
    // sized type and the sized type has to have the same size as the old type.
    if (ParamTy != ActTy && Attrs.hasAttribute(Attributes::ByVal)) {
      PointerType *ParamPTy = dyn_cast<PointerType>(ParamTy);
      if (ParamPTy == 0 || !ParamPTy->getElementType()->isSized() || TD == 0)
        return false;

      Type *CurElTy = cast<PointerType>(ActTy)->getElementType();
      if (TD->getTypeAllocSize(CurElTy) !=
          TD->getTypeAllocSize(ParamPTy->getElementType()))
        return false;
    }

    // Converting from one pointer type to another or between a pointer and an
    // integer of the same size is safe even if we do not have a body.
    bool isConvertible = ActTy == ParamTy ||
      (TD && ((ParamTy->isPointerTy() ||
      ParamTy == TD->getIntPtrType(Caller->getContext())) &&
              (ActTy->isPointerTy() ||
              ActTy == TD->getIntPtrType(Caller->getContext()))));
    if (Callee->isDeclaration() && !isConvertible) return false;
  }

  if (Callee->isDeclaration()) {
    // Do not delete arguments unless we have a function body.
    if (FT->getNumParams() < NumActualArgs && !FT->isVarArg())
      return false;

    // If the callee is just a declaration, don't change the varargsness of the
    // call.  We don't want to introduce a varargs call where one doesn't
    // already exist.
    PointerType *APTy = cast<PointerType>(CS.getCalledValue()->getType());
    if (FT->isVarArg()!=cast<FunctionType>(APTy->getElementType())->isVarArg())
      return false;

    // If both the callee and the cast type are varargs, we still have to make
    // sure the number of fixed parameters are the same or we have the same
    // ABI issues as if we introduce a varargs call.
    if (FT->isVarArg() &&
        cast<FunctionType>(APTy->getElementType())->isVarArg() &&
        FT->getNumParams() !=
        cast<FunctionType>(APTy->getElementType())->getNumParams())
      return false;
  }

  if (FT->getNumParams() < NumActualArgs && FT->isVarArg() &&
      !CallerPAL.isEmpty())
    // In this case we have more arguments than the new function type, but we
    // won't be dropping them.  Check that these extra arguments have attributes
    // that are compatible with being a vararg call argument.
    for (unsigned i = CallerPAL.getNumSlots(); i; --i) {
      if (CallerPAL.getSlot(i - 1).Index <= FT->getNumParams())
        break;
      Attributes PAttrs = CallerPAL.getSlot(i - 1).Attrs;
      if (PAttrs.hasIncompatibleWithVarArgsAttrs())
        return false;
    }


  // Okay, we decided that this is a safe thing to do: go ahead and start
  // inserting cast instructions as necessary.
  std::vector<Value*> Args;
  Args.reserve(NumActualArgs);
  SmallVector<AttributeWithIndex, 8> attrVec;
  attrVec.reserve(NumCommonArgs);

  // Get any return attributes.
  AttrBuilder RAttrs = CallerPAL.getRetAttributes();

  // If the return value is not being used, the type may not be compatible
  // with the existing attributes.  Wipe out any problematic attributes.
  RAttrs.removeAttributes(Attributes::typeIncompatible(NewRetTy));

  // Add the new return attributes.
  if (RAttrs.hasAttributes())
    attrVec.push_back(
      AttributeWithIndex::get(AttrListPtr::ReturnIndex,
                              Attributes::get(FT->getContext(), RAttrs)));

  AI = CS.arg_begin();
  for (unsigned i = 0; i != NumCommonArgs; ++i, ++AI) {
    Type *ParamTy = FT->getParamType(i);
    if ((*AI)->getType() == ParamTy) {
      Args.push_back(*AI);
    } else {
      Instruction::CastOps opcode = CastInst::getCastOpcode(*AI,
          false, ParamTy, false);
      Args.push_back(Builder->CreateCast(opcode, *AI, ParamTy));
    }

    // Add any parameter attributes.
    Attributes PAttrs = CallerPAL.getParamAttributes(i + 1);
    if (PAttrs.hasAttributes())
      attrVec.push_back(AttributeWithIndex::get(i + 1, PAttrs));
  }

  // If the function takes more arguments than the call was taking, add them
  // now.
  for (unsigned i = NumCommonArgs; i != FT->getNumParams(); ++i)
    Args.push_back(Constant::getNullValue(FT->getParamType(i)));

  // If we are removing arguments to the function, emit an obnoxious warning.
  if (FT->getNumParams() < NumActualArgs) {
    if (!FT->isVarArg()) {
      errs() << "WARNING: While resolving call to function '"
             << Callee->getName() << "' arguments were dropped!\n";
    } else {
      // Add all of the arguments in their promoted form to the arg list.
      for (unsigned i = FT->getNumParams(); i != NumActualArgs; ++i, ++AI) {
        Type *PTy = getPromotedType((*AI)->getType());
        if (PTy != (*AI)->getType()) {
          // Must promote to pass through va_arg area!
          Instruction::CastOps opcode =
            CastInst::getCastOpcode(*AI, false, PTy, false);
          Args.push_back(Builder->CreateCast(opcode, *AI, PTy));
        } else {
          Args.push_back(*AI);
        }

        // Add any parameter attributes.
        Attributes PAttrs = CallerPAL.getParamAttributes(i + 1);
        if (PAttrs.hasAttributes())
          attrVec.push_back(AttributeWithIndex::get(i + 1, PAttrs));
      }
    }
  }

  Attributes FnAttrs = CallerPAL.getFnAttributes();
  if (FnAttrs.hasAttributes())
    attrVec.push_back(AttributeWithIndex::get(AttrListPtr::FunctionIndex,
                                              FnAttrs));

  if (NewRetTy->isVoidTy())
    Caller->setName("");   // Void type should not have a name.

  const AttrListPtr &NewCallerPAL = AttrListPtr::get(Callee->getContext(),
                                                     attrVec);

  Instruction *NC;
  if (InvokeInst *II = dyn_cast<InvokeInst>(Caller)) {
    NC = Builder->CreateInvoke(Callee, II->getNormalDest(),
                               II->getUnwindDest(), Args);
    NC->takeName(II);
    cast<InvokeInst>(NC)->setCallingConv(II->getCallingConv());
    cast<InvokeInst>(NC)->setAttributes(NewCallerPAL);
  } else {
    CallInst *CI = cast<CallInst>(Caller);
    NC = Builder->CreateCall(Callee, Args);
    NC->takeName(CI);
    if (CI->isTailCall())
      cast<CallInst>(NC)->setTailCall();
    cast<CallInst>(NC)->setCallingConv(CI->getCallingConv());
    cast<CallInst>(NC)->setAttributes(NewCallerPAL);
  }

  // Insert a cast of the return type as necessary.
  Value *NV = NC;
  if (OldRetTy != NV->getType() && !Caller->use_empty()) {
    if (!NV->getType()->isVoidTy()) {
      Instruction::CastOps opcode =
        CastInst::getCastOpcode(NC, false, OldRetTy, false);
      NV = NC = CastInst::Create(opcode, NC, OldRetTy);
      NC->setDebugLoc(Caller->getDebugLoc());

      // If this is an invoke instruction, we should insert it after the first
      // non-phi, instruction in the normal successor block.
      if (InvokeInst *II = dyn_cast<InvokeInst>(Caller)) {
        BasicBlock::iterator I = II->getNormalDest()->getFirstInsertionPt();
        InsertNewInstBefore(NC, *I);
      } else {
        // Otherwise, it's a call, just insert cast right after the call.
        InsertNewInstBefore(NC, *Caller);
      }
      Worklist.AddUsersToWorkList(*Caller);
    } else {
      NV = UndefValue::get(Caller->getType());
    }
  }

  if (!Caller->use_empty())
    ReplaceInstUsesWith(*Caller, NV);

  EraseInstFromFunction(*Caller);
  return true;
}

// transformCallThroughTrampoline - Turn a call to a function created by
// init_trampoline / adjust_trampoline intrinsic pair into a direct call to the
// underlying function.
//
Instruction *
InstCombiner::transformCallThroughTrampoline(CallSite CS,
                                             IntrinsicInst *Tramp) {
  Value *Callee = CS.getCalledValue();
  PointerType *PTy = cast<PointerType>(Callee->getType());
  FunctionType *FTy = cast<FunctionType>(PTy->getElementType());
  const AttrListPtr &Attrs = CS.getAttributes();

  // If the call already has the 'nest' attribute somewhere then give up -
  // otherwise 'nest' would occur twice after splicing in the chain.
  for (unsigned I = 0, E = Attrs.getNumAttrs(); I != E; ++I)
    if (Attrs.getAttributesAtIndex(I).hasAttribute(Attributes::Nest))
      return 0;

  assert(Tramp &&
         "transformCallThroughTrampoline called with incorrect CallSite.");

  Function *NestF =cast<Function>(Tramp->getArgOperand(1)->stripPointerCasts());
  PointerType *NestFPTy = cast<PointerType>(NestF->getType());
  FunctionType *NestFTy = cast<FunctionType>(NestFPTy->getElementType());

  const AttrListPtr &NestAttrs = NestF->getAttributes();
  if (!NestAttrs.isEmpty()) {
    unsigned NestIdx = 1;
    Type *NestTy = 0;
    Attributes NestAttr;

    // Look for a parameter marked with the 'nest' attribute.
    for (FunctionType::param_iterator I = NestFTy->param_begin(),
         E = NestFTy->param_end(); I != E; ++NestIdx, ++I)
      if (NestAttrs.getParamAttributes(NestIdx).hasAttribute(Attributes::Nest)){
        // Record the parameter type and any other attributes.
        NestTy = *I;
        NestAttr = NestAttrs.getParamAttributes(NestIdx);
        break;
      }

    if (NestTy) {
      Instruction *Caller = CS.getInstruction();
      std::vector<Value*> NewArgs;
      NewArgs.reserve(unsigned(CS.arg_end()-CS.arg_begin())+1);

      SmallVector<AttributeWithIndex, 8> NewAttrs;
      NewAttrs.reserve(Attrs.getNumSlots() + 1);

      // Insert the nest argument into the call argument list, which may
      // mean appending it.  Likewise for attributes.

      // Add any result attributes.
      Attributes Attr = Attrs.getRetAttributes();
      if (Attr.hasAttributes())
        NewAttrs.push_back(AttributeWithIndex::get(AttrListPtr::ReturnIndex,
                                                   Attr));

      {
        unsigned Idx = 1;
        CallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
        do {
          if (Idx == NestIdx) {
            // Add the chain argument and attributes.
            Value *NestVal = Tramp->getArgOperand(2);
            if (NestVal->getType() != NestTy)
              NestVal = Builder->CreateBitCast(NestVal, NestTy, "nest");
            NewArgs.push_back(NestVal);
            NewAttrs.push_back(AttributeWithIndex::get(NestIdx, NestAttr));
          }

          if (I == E)
            break;

          // Add the original argument and attributes.
          NewArgs.push_back(*I);
          Attr = Attrs.getParamAttributes(Idx);
          if (Attr.hasAttributes())
            NewAttrs.push_back
              (AttributeWithIndex::get(Idx + (Idx >= NestIdx), Attr));

          ++Idx, ++I;
        } while (1);
      }

      // Add any function attributes.
      Attr = Attrs.getFnAttributes();
      if (Attr.hasAttributes())
        NewAttrs.push_back(AttributeWithIndex::get(AttrListPtr::FunctionIndex,
                                                   Attr));

      // The trampoline may have been bitcast to a bogus type (FTy).
      // Handle this by synthesizing a new function type, equal to FTy
      // with the chain parameter inserted.

      std::vector<Type*> NewTypes;
      NewTypes.reserve(FTy->getNumParams()+1);

      // Insert the chain's type into the list of parameter types, which may
      // mean appending it.
      {
        unsigned Idx = 1;
        FunctionType::param_iterator I = FTy->param_begin(),
          E = FTy->param_end();

        do {
          if (Idx == NestIdx)
            // Add the chain's type.
            NewTypes.push_back(NestTy);

          if (I == E)
            break;

          // Add the original type.
          NewTypes.push_back(*I);

          ++Idx, ++I;
        } while (1);
      }

      // Replace the trampoline call with a direct call.  Let the generic
      // code sort out any function type mismatches.
      FunctionType *NewFTy = FunctionType::get(FTy->getReturnType(), NewTypes,
                                                FTy->isVarArg());
      Constant *NewCallee =
        NestF->getType() == PointerType::getUnqual(NewFTy) ?
        NestF : ConstantExpr::getBitCast(NestF,
                                         PointerType::getUnqual(NewFTy));
      const AttrListPtr &NewPAL = AttrListPtr::get(FTy->getContext(), NewAttrs);

      Instruction *NewCaller;
      if (InvokeInst *II = dyn_cast<InvokeInst>(Caller)) {
        NewCaller = InvokeInst::Create(NewCallee,
                                       II->getNormalDest(), II->getUnwindDest(),
                                       NewArgs);
        cast<InvokeInst>(NewCaller)->setCallingConv(II->getCallingConv());
        cast<InvokeInst>(NewCaller)->setAttributes(NewPAL);
      } else {
        NewCaller = CallInst::Create(NewCallee, NewArgs);
        if (cast<CallInst>(Caller)->isTailCall())
          cast<CallInst>(NewCaller)->setTailCall();
        cast<CallInst>(NewCaller)->
          setCallingConv(cast<CallInst>(Caller)->getCallingConv());
        cast<CallInst>(NewCaller)->setAttributes(NewPAL);
      }

      return NewCaller;
    }
  }

  // Replace the trampoline call with a direct call.  Since there is no 'nest'
  // parameter, there is no need to adjust the argument list.  Let the generic
  // code sort out any function type mismatches.
  Constant *NewCallee =
    NestF->getType() == PTy ? NestF :
                              ConstantExpr::getBitCast(NestF, PTy);
  CS.setCalledFunction(NewCallee);
  return CS.getInstruction();
}