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llvm-6502/lib/Transforms/InstCombine/InstCombineCasts.cpp
Chris Lattner e0e4cc7fd5 Teach instcombine's sext elimination logic to be more aggressive. 
Previously, instcombine would only promote an expression tree to
the larger type if doing so eliminated two casts.  This is because
a need to manually do the sign extend after the promoted expression
tree with two shifts.  Now, we keep track of whether the result of
the computation is going to be properly sign extended already.  If
so, we can unconditionally promote the expression, which allows us
to zap more sext's.

This implements rdar://6598839 (aka gcc pr38751)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92815 91177308-0d34-0410-b5e6-96231b3b80d8
2010-01-06 01:56:21 +00:00

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//===- InstCombineCasts.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 visit functions for cast operations.
//
//===----------------------------------------------------------------------===//
#include "InstCombine.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Support/PatternMatch.h"
using namespace llvm;
using namespace PatternMatch;
/// DecomposeSimpleLinearExpr - Analyze 'Val', seeing if it is a simple linear
/// expression. If so, decompose it, returning some value X, such that Val is
/// X*Scale+Offset.
///
static Value *DecomposeSimpleLinearExpr(Value *Val, unsigned &Scale,
int &Offset) {
assert(Val->getType()->isInteger(32) && "Unexpected allocation size type!");
if (ConstantInt *CI = dyn_cast<ConstantInt>(Val)) {
Offset = CI->getZExtValue();
Scale = 0;
return ConstantInt::get(Type::getInt32Ty(Val->getContext()), 0);
}
if (BinaryOperator *I = dyn_cast<BinaryOperator>(Val)) {
if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
if (I->getOpcode() == Instruction::Shl) {
// This is a value scaled by '1 << the shift amt'.
Scale = 1U << RHS->getZExtValue();
Offset = 0;
return I->getOperand(0);
}
if (I->getOpcode() == Instruction::Mul) {
// This value is scaled by 'RHS'.
Scale = RHS->getZExtValue();
Offset = 0;
return I->getOperand(0);
}
if (I->getOpcode() == Instruction::Add) {
// We have X+C. Check to see if we really have (X*C2)+C1,
// where C1 is divisible by C2.
unsigned SubScale;
Value *SubVal =
DecomposeSimpleLinearExpr(I->getOperand(0), SubScale, Offset);
Offset += RHS->getZExtValue();
Scale = SubScale;
return SubVal;
}
}
}
// Otherwise, we can't look past this.
Scale = 1;
Offset = 0;
return Val;
}
/// PromoteCastOfAllocation - If we find a cast of an allocation instruction,
/// try to eliminate the cast by moving the type information into the alloc.
Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI,
AllocaInst &AI) {
// This requires TargetData to get the alloca alignment and size information.
if (!TD) return 0;
const PointerType *PTy = cast<PointerType>(CI.getType());
BuilderTy AllocaBuilder(*Builder);
AllocaBuilder.SetInsertPoint(AI.getParent(), &AI);
// Get the type really allocated and the type casted to.
const Type *AllocElTy = AI.getAllocatedType();
const Type *CastElTy = PTy->getElementType();
if (!AllocElTy->isSized() || !CastElTy->isSized()) return 0;
unsigned AllocElTyAlign = TD->getABITypeAlignment(AllocElTy);
unsigned CastElTyAlign = TD->getABITypeAlignment(CastElTy);
if (CastElTyAlign < AllocElTyAlign) return 0;
// If the allocation has multiple uses, only promote it if we are strictly
// increasing the alignment of the resultant allocation. If we keep it the
// same, we open the door to infinite loops of various kinds. (A reference
// from a dbg.declare doesn't count as a use for this purpose.)
if (!AI.hasOneUse() && !hasOneUsePlusDeclare(&AI) &&
CastElTyAlign == AllocElTyAlign) return 0;
uint64_t AllocElTySize = TD->getTypeAllocSize(AllocElTy);
uint64_t CastElTySize = TD->getTypeAllocSize(CastElTy);
if (CastElTySize == 0 || AllocElTySize == 0) return 0;
// See if we can satisfy the modulus by pulling a scale out of the array
// size argument.
unsigned ArraySizeScale;
int ArrayOffset;
Value *NumElements = // See if the array size is a decomposable linear expr.
DecomposeSimpleLinearExpr(AI.getOperand(0), ArraySizeScale, ArrayOffset);
// If we can now satisfy the modulus, by using a non-1 scale, we really can
// do the xform.
if ((AllocElTySize*ArraySizeScale) % CastElTySize != 0 ||
(AllocElTySize*ArrayOffset ) % CastElTySize != 0) return 0;
unsigned Scale = (AllocElTySize*ArraySizeScale)/CastElTySize;
Value *Amt = 0;
if (Scale == 1) {
Amt = NumElements;
} else {
Amt = ConstantInt::get(Type::getInt32Ty(CI.getContext()), Scale);
// Insert before the alloca, not before the cast.
Amt = AllocaBuilder.CreateMul(Amt, NumElements, "tmp");
}
if (int Offset = (AllocElTySize*ArrayOffset)/CastElTySize) {
Value *Off = ConstantInt::get(Type::getInt32Ty(CI.getContext()),
Offset, true);
Amt = AllocaBuilder.CreateAdd(Amt, Off, "tmp");
}
AllocaInst *New = AllocaBuilder.CreateAlloca(CastElTy, Amt);
New->setAlignment(AI.getAlignment());
New->takeName(&AI);
// If the allocation has one real use plus a dbg.declare, just remove the
// declare.
if (DbgDeclareInst *DI = hasOneUsePlusDeclare(&AI)) {
EraseInstFromFunction(*(Instruction*)DI);
}
// If the allocation has multiple real uses, insert a cast and change all
// things that used it to use the new cast. This will also hack on CI, but it
// will die soon.
else if (!AI.hasOneUse()) {
// New is the allocation instruction, pointer typed. AI is the original
// allocation instruction, also pointer typed. Thus, cast to use is BitCast.
Value *NewCast = AllocaBuilder.CreateBitCast(New, AI.getType(), "tmpcast");
AI.replaceAllUsesWith(NewCast);
}
return ReplaceInstUsesWith(CI, New);
}
/// CanEvaluateInDifferentType - Return true if we can take the specified value
/// and return it as type Ty without inserting any new casts and without
/// changing the computed value. This is used by code that tries to decide
/// whether promoting or shrinking integer operations to wider or smaller types
/// will allow us to eliminate a truncate or extend.
///
/// This is a truncation operation if Ty is smaller than V->getType(), or a zero
/// extension operation if Ty is larger.
///
/// If CastOpc is a truncation, then Ty will be a type smaller than V. We
/// should return true if trunc(V) can be computed by computing V in the smaller
/// type. If V is an instruction, then trunc(inst(x,y)) can be computed as
/// inst(trunc(x),trunc(y)), which only makes sense if x and y can be
/// efficiently truncated.
///
/// If CastOpc is zext, we are asking if the low bits of the value can bit
/// computed in a larger type, which is then and'd to get the final result.
static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
unsigned CastOpc,
unsigned &NumCastsRemoved) {
assert(CastOpc == Instruction::ZExt || CastOpc == Instruction::Trunc);
// We can always evaluate constants in another type.
if (isa<Constant>(V))
return true;
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return false;
const Type *OrigTy = V->getType();
// If this is an extension or truncate, we can often eliminate it.
if (isa<TruncInst>(I) || isa<ZExtInst>(I) || isa<SExtInst>(I)) {
// If this is a cast from the destination type, we can trivially eliminate
// it, and this will remove a cast overall.
if (I->getOperand(0)->getType() == Ty) {
// If the first operand is itself a cast, and is eliminable, do not count
// this as an eliminable cast. We would prefer to eliminate those two
// casts first.
if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse())
++NumCastsRemoved;
return true;
}
}
// We can't extend or shrink something that has multiple uses: doing so would
// require duplicating the instruction in general, which isn't profitable.
if (!I->hasOneUse()) return false;
unsigned Opc = I->getOpcode();
switch (Opc) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// These operators can all arbitrarily be extended or truncated.
return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
NumCastsRemoved) &&
CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
NumCastsRemoved);
case Instruction::UDiv:
case Instruction::URem: {
// UDiv and URem can be truncated if all the truncated bits are zero.
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
uint32_t BitWidth = Ty->getScalarSizeInBits();
if (BitWidth < OrigBitWidth) {
APInt Mask = APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth);
if (MaskedValueIsZero(I->getOperand(0), Mask) &&
MaskedValueIsZero(I->getOperand(1), Mask)) {
return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
NumCastsRemoved) &&
CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
NumCastsRemoved);
}
}
break;
}
case Instruction::Shl:
// If we are truncating the result of this SHL, and if it's a shift of a
// constant amount, we can always perform a SHL in a smaller type.
if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
uint32_t BitWidth = Ty->getScalarSizeInBits();
if (BitWidth < OrigTy->getScalarSizeInBits() &&
CI->getLimitedValue(BitWidth) < BitWidth)
return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
NumCastsRemoved);
}
break;
case Instruction::LShr:
// If this is a truncate of a logical shr, we can truncate it to a smaller
// lshr iff we know that the bits we would otherwise be shifting in are
// already zeros.
if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
uint32_t BitWidth = Ty->getScalarSizeInBits();
if (BitWidth < OrigBitWidth &&
MaskedValueIsZero(I->getOperand(0),
APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
CI->getLimitedValue(BitWidth) < BitWidth) {
return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
NumCastsRemoved);
}
}
break;
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::Trunc:
// If this is the same kind of case as our original (e.g. zext+zext), we
// can safely replace it. Note that replacing it does not reduce the number
// of casts in the input.
if (Opc == CastOpc)
return true;
// sext (zext ty1), ty2 -> zext ty2
if (CastOpc == Instruction::SExt && Opc == Instruction::ZExt)
return true;
break;
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
return CanEvaluateInDifferentType(SI->getTrueValue(), Ty, CastOpc,
NumCastsRemoved) &&
CanEvaluateInDifferentType(SI->getFalseValue(), Ty, CastOpc,
NumCastsRemoved);
}
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (!CanEvaluateInDifferentType(PN->getIncomingValue(i), Ty, CastOpc,
NumCastsRemoved))
return false;
return true;
}
default:
// TODO: Can handle more cases here.
break;
}
return false;
}
/// CanEvaluateSExtd - Return true if we can take the specified value
/// and return it as type Ty without inserting any new casts and without
/// changing the computed value of the common low bits. This is used by code
/// that tries to promote integer operations to a wider types will allow us to
/// eliminate the extension.
///
/// This returns 0 if we can't do this or the number of sign bits that would be
/// set if we can. For example, CanEvaluateSExtd(i16 1, i64) would return 63,
/// because the computation can be extended (to "i64 1") and the resulting
/// computation has 63 equal sign bits.
///
/// This function works on both vectors and scalars. For vectors, the result is
/// the number of bits known sign extended in each element.
///
static unsigned CanEvaluateSExtd(Value *V, const Type *Ty,
unsigned &NumCastsRemoved, TargetData *TD) {
assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() &&
"Can't sign extend type to a smaller type");
// If this is a constant, return the number of sign bits the extended version
// of it would have.
if (Constant *C = dyn_cast<Constant>(V))
return ComputeNumSignBits(ConstantExpr::getSExt(C, Ty), TD);
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return 0;
// If this is a truncate from the destination type, we can trivially eliminate
// it, and this will remove a cast overall.
if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty) {
// If the operand of the truncate is itself a cast, and is eliminable, do
// not count this as an eliminable cast. We would prefer to eliminate those
// two casts first.
if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse())
++NumCastsRemoved;
return ComputeNumSignBits(I->getOperand(0), TD);
}
// We can't extend or shrink something that has multiple uses: doing so would
// require duplicating the instruction in general, which isn't profitable.
if (!I->hasOneUse()) return 0;
const Type *OrigTy = V->getType();
unsigned Opc = I->getOpcode();
unsigned Tmp1, Tmp2;
switch (Opc) {
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// These operators can all arbitrarily be extended or truncated.
Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD);
if (Tmp1 == 0) return 0;
Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
return std::min(Tmp1, Tmp2);
case Instruction::Add:
case Instruction::Sub:
// Add/Sub can have at most one carry/borrow bit.
Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD);
if (Tmp1 == 0) return 0;
Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
if (Tmp2 == 0) return 0;
return std::min(Tmp1, Tmp2)-1;
case Instruction::Mul:
// These operators can all arbitrarily be extended or truncated.
if (!CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD))
return 0;
if (!CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD))
return 0;
return 1; // IMPROVE?
//case Instruction::Shl: TODO
//case Instruction::LShr: TODO
//case Instruction::Trunc: TODO
case Instruction::SExt:
case Instruction::ZExt: {
// sext(sext(x)) -> sext(x)
// sext(zext(x)) -> zext(x)
// Note that replacing a cast does not reduce the number of casts in the
// input.
unsigned InSignBits = ComputeNumSignBits(I, TD);
unsigned ExtBits = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits();
// We'll end up extending it all the way out.
return InSignBits+ExtBits;
}
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
Tmp1 = CanEvaluateSExtd(SI->getTrueValue(), Ty, NumCastsRemoved, TD);
if (Tmp1 == 0) return 0;
Tmp2 = CanEvaluateSExtd(SI->getFalseValue(), Ty, NumCastsRemoved,TD);
return std::min(Tmp1, Tmp2);
}
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
unsigned Result = ~0U;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Result = std::min(Result,
CanEvaluateSExtd(PN->getIncomingValue(i), Ty,
NumCastsRemoved, TD));
if (Result == 0) return 0;
}
return Result;
}
default:
// TODO: Can handle more cases here.
break;
}
return 0;
}
/// EvaluateInDifferentType - Given an expression that
/// CanEvaluateInDifferentType or CanEvaluateSExtd returns true for, actually
/// insert the code to evaluate the expression.
Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty,
bool isSigned) {
if (Constant *C = dyn_cast<Constant>(V))
return ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/);
// Otherwise, it must be an instruction.
Instruction *I = cast<Instruction>(V);
Instruction *Res = 0;
unsigned Opc = I->getOpcode();
switch (Opc) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
case Instruction::AShr:
case Instruction::LShr:
case Instruction::Shl:
case Instruction::UDiv:
case Instruction::URem: {
Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS);
break;
}
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
// If the source type of the cast is the type we're trying for then we can
// just return the source. There's no need to insert it because it is not
// new.
if (I->getOperand(0)->getType() == Ty)
return I->getOperand(0);
// Otherwise, must be the same type of cast, so just reinsert a new one.
Res = CastInst::Create(cast<CastInst>(I)->getOpcode(), I->getOperand(0),Ty);
break;
case Instruction::Select: {
Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned);
Res = SelectInst::Create(I->getOperand(0), True, False);
break;
}
case Instruction::PHI: {
PHINode *OPN = cast<PHINode>(I);
PHINode *NPN = PHINode::Create(Ty);
for (unsigned i = 0, e = OPN->getNumIncomingValues(); i != e; ++i) {
Value *V =EvaluateInDifferentType(OPN->getIncomingValue(i), Ty, isSigned);
NPN->addIncoming(V, OPN->getIncomingBlock(i));
}
Res = NPN;
break;
}
default:
// TODO: Can handle more cases here.
llvm_unreachable("Unreachable!");
break;
}
Res->takeName(I);
return InsertNewInstBefore(Res, *I);
}
/// This function is a wrapper around CastInst::isEliminableCastPair. It
/// simply extracts arguments and returns what that function returns.
static Instruction::CastOps
isEliminableCastPair(
const CastInst *CI, ///< The first cast instruction
unsigned opcode, ///< The opcode of the second cast instruction
const Type *DstTy, ///< The target type for the second cast instruction
TargetData *TD ///< The target data for pointer size
) {
const Type *SrcTy = CI->getOperand(0)->getType(); // A from above
const Type *MidTy = CI->getType(); // B from above
// Get the opcodes of the two Cast instructions
Instruction::CastOps firstOp = Instruction::CastOps(CI->getOpcode());
Instruction::CastOps secondOp = Instruction::CastOps(opcode);
unsigned Res = CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy,
DstTy,
TD ? TD->getIntPtrType(CI->getContext()) : 0);
// We don't want to form an inttoptr or ptrtoint that converts to an integer
// type that differs from the pointer size.
if ((Res == Instruction::IntToPtr &&
(!TD || SrcTy != TD->getIntPtrType(CI->getContext()))) ||
(Res == Instruction::PtrToInt &&
(!TD || DstTy != TD->getIntPtrType(CI->getContext()))))
Res = 0;
return Instruction::CastOps(Res);
}
/// ValueRequiresCast - Return true if the cast from "V to Ty" actually results
/// in any code being generated. It does not require codegen if V is simple
/// enough or if the cast can be folded into other casts.
bool InstCombiner::ValueRequiresCast(Instruction::CastOps opcode,const Value *V,
const Type *Ty) {
if (V->getType() == Ty || isa<Constant>(V)) return false;
// If this is another cast that can be eliminated, it isn't codegen either.
if (const CastInst *CI = dyn_cast<CastInst>(V))
if (isEliminableCastPair(CI, opcode, Ty, TD))
return false;
return true;
}
/// @brief Implement the transforms common to all CastInst visitors.
Instruction *InstCombiner::commonCastTransforms(CastInst &CI) {
Value *Src = CI.getOperand(0);
// Many cases of "cast of a cast" are eliminable. If it's eliminable we just
// eliminate it now.
if (CastInst *CSrc = dyn_cast<CastInst>(Src)) { // A->B->C cast
if (Instruction::CastOps opc =
isEliminableCastPair(CSrc, CI.getOpcode(), CI.getType(), TD)) {
// The first cast (CSrc) is eliminable so we need to fix up or replace
// the second cast (CI). CSrc will then have a good chance of being dead.
return CastInst::Create(opc, CSrc->getOperand(0), CI.getType());
}
}
// If we are casting a select then fold the cast into the select
if (SelectInst *SI = dyn_cast<SelectInst>(Src))
if (Instruction *NV = FoldOpIntoSelect(CI, SI))
return NV;
// If we are casting a PHI then fold the cast into the PHI
if (isa<PHINode>(Src)) {
// We don't do this if this would create a PHI node with an illegal type if
// it is currently legal.
if (!isa<IntegerType>(Src->getType()) ||
!isa<IntegerType>(CI.getType()) ||
ShouldChangeType(CI.getType(), Src->getType()))
if (Instruction *NV = FoldOpIntoPhi(CI))
return NV;
}
return 0;
}
/// commonIntCastTransforms - This function implements the common transforms
/// for trunc, zext, and sext.
Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
if (Instruction *Result = commonCastTransforms(CI))
return Result;
// See if we can simplify any instructions used by the LHS whose sole
// purpose is to compute bits we don't care about.
if (SimplifyDemandedInstructionBits(CI))
return &CI;
// If the source isn't an instruction or has more than one use then we
// can't do anything more.
Instruction *Src = dyn_cast<Instruction>(CI.getOperand(0));
if (!Src || !Src->hasOneUse())
return 0;
// Check to see if we can eliminate the cast by changing the entire
// computation chain to do the computation in the result type.
const Type *SrcTy = Src->getType();
const Type *DestTy = CI.getType();
// Only do this if the dest type is a simple type, don't convert the
// expression tree to something weird like i93 unless the source is also
// strange.
if (!isa<VectorType>(DestTy) && !ShouldChangeType(SrcTy, DestTy))
return 0;
// Attempt to propagate the cast into the instruction for int->int casts.
unsigned NumCastsRemoved = 0;
switch (CI.getOpcode()) {
default: assert(0 && "not an integer cast");
case Instruction::Trunc:
if (!CanEvaluateInDifferentType(Src, DestTy,
Instruction::Trunc, NumCastsRemoved))
return 0;
// If this cast is a truncate, evaluting in a different type always
// eliminates the cast, so it is always a win.
break;
case Instruction::ZExt:
if (!CanEvaluateInDifferentType(Src, DestTy,
Instruction::ZExt, NumCastsRemoved))
return 0;
// If this is a zero-extension, we need to do an AND to maintain the clear
// top-part of the computation, so we require that the input have eliminated
// at least one cast.
if (NumCastsRemoved < 1)
return 0;
break;
case Instruction::SExt: {
// Check to see if we can do this transformation, and if so, how many bits
// of the promoted expression will be known copies of the sign bit in the
// result.
unsigned NumBitsSExt = CanEvaluateSExtd(Src, DestTy, NumCastsRemoved, TD);
if (NumBitsSExt == 0)
return 0;
uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
uint32_t DestBitSize = DestTy->getScalarSizeInBits();
// Because this is a sign extension, we can always transform it by inserting
// two new shifts (to do the extension). However, this is only profitable
// if we've eliminated two or more casts from the input. If we know the
// result will be sign-extendy enough to not require these shifts, we can
// always do the transformation.
if (NumCastsRemoved < 2 &&
NumBitsSExt <= DestBitSize-SrcBitSize)
return 0;
// Okay, we can transform this! Insert the new expression now.
DEBUG(errs() << "ICE: EvaluateInDifferentType converting expression type"
" to avoid sign extend: " << CI);
Value *Res = EvaluateInDifferentType(Src, DestTy, true);
assert(Res->getType() == DestTy);
// If the high bits are already filled with sign bit, just replace this
// cast with the result.
if (NumBitsSExt > DestBitSize - SrcBitSize ||
ComputeNumSignBits(Res) > DestBitSize - SrcBitSize)
return ReplaceInstUsesWith(CI, Res);
// We need to emit a cast to truncate, then a cast to sext.
return new SExtInst(Builder->CreateTrunc(Res, Src->getType()), DestTy);
}
}
DEBUG(errs() << "ICE: EvaluateInDifferentType converting expression type"
" to avoid cast: " << CI);
Value *Res = EvaluateInDifferentType(Src, DestTy, false);
assert(Res->getType() == DestTy);
uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
uint32_t DestBitSize = DestTy->getScalarSizeInBits();
switch (CI.getOpcode()) {
default: assert(0 && "Unknown cast type!");
case Instruction::Trunc:
// Just replace this cast with the result.
return ReplaceInstUsesWith(CI, Res);
case Instruction::ZExt: {
// If the high bits are already zero, just replace this cast with the
// result.
APInt Mask(APInt::getBitsSet(DestBitSize, SrcBitSize, DestBitSize));
if (MaskedValueIsZero(Res, Mask))
return ReplaceInstUsesWith(CI, Res);
// We need to emit an AND to clear the high bits.
Constant *C = ConstantInt::get(CI.getContext(),
APInt::getLowBitsSet(DestBitSize, SrcBitSize));
return BinaryOperator::CreateAnd(Res, C);
}
case Instruction::SExt: {
// If the high bits are already filled with sign bit, just replace this
// cast with the result.
unsigned NumSignBits = ComputeNumSignBits(Res);
if (NumSignBits > (DestBitSize - SrcBitSize))
return ReplaceInstUsesWith(CI, Res);
// We need to emit a cast to truncate, then a cast to sext.
return new SExtInst(Builder->CreateTrunc(Res, Src->getType()), DestTy);
}
}
}
Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
if (Instruction *Result = commonIntCastTransforms(CI))
return Result;
Value *Src = CI.getOperand(0);
const Type *DestTy = CI.getType();
// Canonicalize trunc x to i1 -> (icmp ne (and x, 1), 0), likewise for vector.
if (DestTy->getScalarSizeInBits() == 1) {
Constant *One = ConstantInt::get(Src->getType(), 1);
Src = Builder->CreateAnd(Src, One, "tmp");
Value *Zero = Constant::getNullValue(Src->getType());
return new ICmpInst(ICmpInst::ICMP_NE, Src, Zero);
}
return 0;
}
/// transformZExtICmp - Transform (zext icmp) to bitwise / integer operations
/// in order to eliminate the icmp.
Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
bool DoXform) {
// If we are just checking for a icmp eq of a single bit and zext'ing it
// to an integer, then shift the bit to the appropriate place and then
// cast to integer to avoid the comparison.
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
const APInt &Op1CV = Op1C->getValue();
// zext (x <s 0) to i32 --> x>>u31 true if signbit set.
// zext (x >s -1) to i32 --> (x>>u31)^1 true if signbit clear.
if ((ICI->getPredicate() == ICmpInst::ICMP_SLT && Op1CV == 0) ||
(ICI->getPredicate() == ICmpInst::ICMP_SGT &&Op1CV.isAllOnesValue())) {
if (!DoXform) return ICI;
Value *In = ICI->getOperand(0);
Value *Sh = ConstantInt::get(In->getType(),
In->getType()->getScalarSizeInBits()-1);
In = Builder->CreateLShr(In, Sh, In->getName()+".lobit");
if (In->getType() != CI.getType())
In = Builder->CreateIntCast(In, CI.getType(), false/*ZExt*/, "tmp");
if (ICI->getPredicate() == ICmpInst::ICMP_SGT) {
Constant *One = ConstantInt::get(In->getType(), 1);
In = Builder->CreateXor(In, One, In->getName()+".not");
}
return ReplaceInstUsesWith(CI, In);
}
// zext (X == 0) to i32 --> X^1 iff X has only the low bit set.
// zext (X == 0) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
// zext (X == 1) to i32 --> X iff X has only the low bit set.
// zext (X == 2) to i32 --> X>>1 iff X has only the 2nd bit set.
// zext (X != 0) to i32 --> X iff X has only the low bit set.
// zext (X != 0) to i32 --> X>>1 iff X has only the 2nd bit set.
// zext (X != 1) to i32 --> X^1 iff X has only the low bit set.
// zext (X != 2) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
if ((Op1CV == 0 || Op1CV.isPowerOf2()) &&
// This only works for EQ and NE
ICI->isEquality()) {
// If Op1C some other power of two, convert:
uint32_t BitWidth = Op1C->getType()->getBitWidth();
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
APInt TypeMask(APInt::getAllOnesValue(BitWidth));
ComputeMaskedBits(ICI->getOperand(0), TypeMask, KnownZero, KnownOne);
APInt KnownZeroMask(~KnownZero);
if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
if (!DoXform) return ICI;
bool isNE = ICI->getPredicate() == ICmpInst::ICMP_NE;
if (Op1CV != 0 && (Op1CV != KnownZeroMask)) {
// (X&4) == 2 --> false
// (X&4) != 2 --> true
Constant *Res = ConstantInt::get(Type::getInt1Ty(CI.getContext()),
isNE);
Res = ConstantExpr::getZExt(Res, CI.getType());
return ReplaceInstUsesWith(CI, Res);
}
uint32_t ShiftAmt = KnownZeroMask.logBase2();
Value *In = ICI->getOperand(0);
if (ShiftAmt) {
// Perform a logical shr by shiftamt.
// Insert the shift to put the result in the low bit.
In = Builder->CreateLShr(In, ConstantInt::get(In->getType(),ShiftAmt),
In->getName()+".lobit");
}
if ((Op1CV != 0) == isNE) { // Toggle the low bit.
Constant *One = ConstantInt::get(In->getType(), 1);
In = Builder->CreateXor(In, One, "tmp");
}
if (CI.getType() == In->getType())
return ReplaceInstUsesWith(CI, In);
else
return CastInst::CreateIntegerCast(In, CI.getType(), false/*ZExt*/);
}
}
}
// icmp ne A, B is equal to xor A, B when A and B only really have one bit.
// It is also profitable to transform icmp eq into not(xor(A, B)) because that
// may lead to additional simplifications.
if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) {
if (const IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) {
uint32_t BitWidth = ITy->getBitWidth();
Value *LHS = ICI->getOperand(0);
Value *RHS = ICI->getOperand(1);
APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0);
APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0);
APInt TypeMask(APInt::getAllOnesValue(BitWidth));
ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS);
ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS);
if (KnownZeroLHS == KnownZeroRHS && KnownOneLHS == KnownOneRHS) {
APInt KnownBits = KnownZeroLHS | KnownOneLHS;
APInt UnknownBit = ~KnownBits;
if (UnknownBit.countPopulation() == 1) {
if (!DoXform) return ICI;
Value *Result = Builder->CreateXor(LHS, RHS);
// Mask off any bits that are set and won't be shifted away.
if (KnownOneLHS.uge(UnknownBit))
Result = Builder->CreateAnd(Result,
ConstantInt::get(ITy, UnknownBit));
// Shift the bit we're testing down to the lsb.
Result = Builder->CreateLShr(
Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros()));
if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
Result = Builder->CreateXor(Result, ConstantInt::get(ITy, 1));
Result->takeName(ICI);
return ReplaceInstUsesWith(CI, Result);
}
}
}
}
return 0;
}
Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
// If one of the common conversion will work, do it.
if (Instruction *Result = commonIntCastTransforms(CI))
return Result;
Value *Src = CI.getOperand(0);
// If this is a TRUNC followed by a ZEXT then we are dealing with integral
// types and if the sizes are just right we can convert this into a logical
// 'and' which will be much cheaper than the pair of casts.
if (TruncInst *CSrc = dyn_cast<TruncInst>(Src)) { // A->B->C cast
// Get the sizes of the types involved. We know that the intermediate type
// will be smaller than A or C, but don't know the relation between A and C.
Value *A = CSrc->getOperand(0);
unsigned SrcSize = A->getType()->getScalarSizeInBits();
unsigned MidSize = CSrc->getType()->getScalarSizeInBits();
unsigned DstSize = CI.getType()->getScalarSizeInBits();
// If we're actually extending zero bits, then if
// SrcSize < DstSize: zext(a & mask)
// SrcSize == DstSize: a & mask
// SrcSize > DstSize: trunc(a) & mask
if (SrcSize < DstSize) {
APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
Constant *AndConst = ConstantInt::get(A->getType(), AndValue);
Value *And = Builder->CreateAnd(A, AndConst, CSrc->getName()+".mask");
return new ZExtInst(And, CI.getType());
}
if (SrcSize == DstSize) {
APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
return BinaryOperator::CreateAnd(A, ConstantInt::get(A->getType(),
AndValue));
}
if (SrcSize > DstSize) {
Value *Trunc = Builder->CreateTrunc(A, CI.getType(), "tmp");
APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize));
return BinaryOperator::CreateAnd(Trunc,
ConstantInt::get(Trunc->getType(),
AndValue));
}
}
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))
return transformZExtICmp(ICI, CI);
BinaryOperator *SrcI = dyn_cast<BinaryOperator>(Src);
if (SrcI && SrcI->getOpcode() == Instruction::Or) {
// zext (or icmp, icmp) --> or (zext icmp), (zext icmp) if at least one
// of the (zext icmp) will be transformed.
ICmpInst *LHS = dyn_cast<ICmpInst>(SrcI->getOperand(0));
ICmpInst *RHS = dyn_cast<ICmpInst>(SrcI->getOperand(1));
if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() &&
(transformZExtICmp(LHS, CI, false) ||
transformZExtICmp(RHS, CI, false))) {
Value *LCast = Builder->CreateZExt(LHS, CI.getType(), LHS->getName());
Value *RCast = Builder->CreateZExt(RHS, CI.getType(), RHS->getName());
return BinaryOperator::Create(Instruction::Or, LCast, RCast);
}
}
// zext(trunc(t) & C) -> (t & zext(C)).
if (SrcI && SrcI->getOpcode() == Instruction::And && SrcI->hasOneUse())
if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1)))
if (TruncInst *TI = dyn_cast<TruncInst>(SrcI->getOperand(0))) {
Value *TI0 = TI->getOperand(0);
if (TI0->getType() == CI.getType())
return
BinaryOperator::CreateAnd(TI0,
ConstantExpr::getZExt(C, CI.getType()));
}
// zext((trunc(t) & C) ^ C) -> ((t & zext(C)) ^ zext(C)).
if (SrcI && SrcI->getOpcode() == Instruction::Xor && SrcI->hasOneUse())
if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1)))
if (BinaryOperator *And = dyn_cast<BinaryOperator>(SrcI->getOperand(0)))
if (And->getOpcode() == Instruction::And && And->hasOneUse() &&
And->getOperand(1) == C)
if (TruncInst *TI = dyn_cast<TruncInst>(And->getOperand(0))) {
Value *TI0 = TI->getOperand(0);
if (TI0->getType() == CI.getType()) {
Constant *ZC = ConstantExpr::getZExt(C, CI.getType());
Value *NewAnd = Builder->CreateAnd(TI0, ZC, "tmp");
return BinaryOperator::CreateXor(NewAnd, ZC);
}
}
// zext (xor i1 X, true) to i32 --> xor (zext i1 X to i32), 1
Value *X;
if (SrcI && SrcI->hasOneUse() && SrcI->getType()->isInteger(1) &&
match(SrcI, m_Not(m_Value(X))) &&
(!X->hasOneUse() || !isa<CmpInst>(X))) {
Value *New = Builder->CreateZExt(X, CI.getType());
return BinaryOperator::CreateXor(New, ConstantInt::get(CI.getType(), 1));
}
return 0;
}
Instruction *InstCombiner::visitSExt(SExtInst &CI) {
if (Instruction *I = commonIntCastTransforms(CI))
return I;
Value *Src = CI.getOperand(0);
// Canonicalize sign-extend from i1 to a select.
if (Src->getType()->isInteger(1))
return SelectInst::Create(Src,
Constant::getAllOnesValue(CI.getType()),
Constant::getNullValue(CI.getType()));
// See if the value being truncated is already sign extended. If so, just
// eliminate the trunc/sext pair.
if (Operator::getOpcode(Src) == Instruction::Trunc) {
Value *Op = cast<User>(Src)->getOperand(0);
unsigned OpBits = Op->getType()->getScalarSizeInBits();
unsigned MidBits = Src->getType()->getScalarSizeInBits();
unsigned DestBits = CI.getType()->getScalarSizeInBits();
unsigned NumSignBits = ComputeNumSignBits(Op);
if (OpBits == DestBits) {
// Op is i32, Mid is i8, and Dest is i32. If Op has more than 24 sign
// bits, it is already ready.
if (NumSignBits > DestBits-MidBits)
return ReplaceInstUsesWith(CI, Op);
} else if (OpBits < DestBits) {
// Op is i32, Mid is i8, and Dest is i64. If Op has more than 24 sign
// bits, just sext from i32.
if (NumSignBits > OpBits-MidBits)
return new SExtInst(Op, CI.getType(), "tmp");
} else {
// Op is i64, Mid is i8, and Dest is i32. If Op has more than 56 sign
// bits, just truncate to i32.
if (NumSignBits > OpBits-MidBits)
return new TruncInst(Op, CI.getType(), "tmp");
}
}
// If the input is a shl/ashr pair of a same constant, then this is a sign
// extension from a smaller value. If we could trust arbitrary bitwidth
// integers, we could turn this into a truncate to the smaller bit and then
// use a sext for the whole extension. Since we don't, look deeper and check
// for a truncate. If the source and dest are the same type, eliminate the
// trunc and extend and just do shifts. For example, turn:
// %a = trunc i32 %i to i8
// %b = shl i8 %a, 6
// %c = ashr i8 %b, 6
// %d = sext i8 %c to i32
// into:
// %a = shl i32 %i, 30
// %d = ashr i32 %a, 30
Value *A = 0;
ConstantInt *BA = 0, *CA = 0;
if (match(Src, m_AShr(m_Shl(m_Value(A), m_ConstantInt(BA)),
m_ConstantInt(CA))) &&
BA == CA && isa<TruncInst>(A)) {
Value *I = cast<TruncInst>(A)->getOperand(0);
if (I->getType() == CI.getType()) {
unsigned MidSize = Src->getType()->getScalarSizeInBits();
unsigned SrcDstSize = CI.getType()->getScalarSizeInBits();
unsigned ShAmt = CA->getZExtValue()+SrcDstSize-MidSize;
Constant *ShAmtV = ConstantInt::get(CI.getType(), ShAmt);
I = Builder->CreateShl(I, ShAmtV, CI.getName());
return BinaryOperator::CreateAShr(I, ShAmtV);
}
}
return 0;
}
/// FitsInFPType - Return a Constant* for the specified FP constant if it fits
/// in the specified FP type without changing its value.
static Constant *FitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) {
bool losesInfo;
APFloat F = CFP->getValueAPF();
(void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo);
if (!losesInfo)
return ConstantFP::get(CFP->getContext(), F);
return 0;
}
/// LookThroughFPExtensions - If this is an fp extension instruction, look
/// through it until we get the source value.
static Value *LookThroughFPExtensions(Value *V) {
if (Instruction *I = dyn_cast<Instruction>(V))
if (I->getOpcode() == Instruction::FPExt)
return LookThroughFPExtensions(I->getOperand(0));
// If this value is a constant, return the constant in the smallest FP type
// that can accurately represent it. This allows us to turn
// (float)((double)X+2.0) into x+2.0f.
if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
if (CFP->getType() == Type::getPPC_FP128Ty(V->getContext()))
return V; // No constant folding of this.
// See if the value can be truncated to float and then reextended.
if (Value *V = FitsInFPType(CFP, APFloat::IEEEsingle))
return V;
if (CFP->getType()->isDoubleTy())
return V; // Won't shrink.
if (Value *V = FitsInFPType(CFP, APFloat::IEEEdouble))
return V;
// Don't try to shrink to various long double types.
}
return V;
}
Instruction *InstCombiner::visitFPTrunc(FPTruncInst &CI) {
if (Instruction *I = commonCastTransforms(CI))
return I;
// If we have fptrunc(fadd (fpextend x), (fpextend y)), where x and y are
// smaller than the destination type, we can eliminate the truncate by doing
// the add as the smaller type. This applies to fadd/fsub/fmul/fdiv as well
// as many builtins (sqrt, etc).
BinaryOperator *OpI = dyn_cast<BinaryOperator>(CI.getOperand(0));
if (OpI && OpI->hasOneUse()) {
switch (OpI->getOpcode()) {
default: break;
case Instruction::FAdd:
case Instruction::FSub:
case Instruction::FMul:
case Instruction::FDiv:
case Instruction::FRem:
const Type *SrcTy = OpI->getType();
Value *LHSTrunc = LookThroughFPExtensions(OpI->getOperand(0));
Value *RHSTrunc = LookThroughFPExtensions(OpI->getOperand(1));
if (LHSTrunc->getType() != SrcTy &&
RHSTrunc->getType() != SrcTy) {
unsigned DstSize = CI.getType()->getScalarSizeInBits();
// If the source types were both smaller than the destination type of
// the cast, do this xform.
if (LHSTrunc->getType()->getScalarSizeInBits() <= DstSize &&
RHSTrunc->getType()->getScalarSizeInBits() <= DstSize) {
LHSTrunc = Builder->CreateFPExt(LHSTrunc, CI.getType());
RHSTrunc = Builder->CreateFPExt(RHSTrunc, CI.getType());
return BinaryOperator::Create(OpI->getOpcode(), LHSTrunc, RHSTrunc);
}
}
break;
}
}
return 0;
}
Instruction *InstCombiner::visitFPExt(CastInst &CI) {
return commonCastTransforms(CI);
}
Instruction *InstCombiner::visitFPToUI(FPToUIInst &FI) {
Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0));
if (OpI == 0)
return commonCastTransforms(FI);
// fptoui(uitofp(X)) --> X
// fptoui(sitofp(X)) --> X
// This is safe if the intermediate type has enough bits in its mantissa to
// accurately represent all values of X. For example, do not do this with
// i64->float->i64. This is also safe for sitofp case, because any negative
// 'X' value would cause an undefined result for the fptoui.
if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) &&
OpI->getOperand(0)->getType() == FI.getType() &&
(int)FI.getType()->getScalarSizeInBits() < /*extra bit for sign */
OpI->getType()->getFPMantissaWidth())
return ReplaceInstUsesWith(FI, OpI->getOperand(0));
return commonCastTransforms(FI);
}
Instruction *InstCombiner::visitFPToSI(FPToSIInst &FI) {
Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0));
if (OpI == 0)
return commonCastTransforms(FI);
// fptosi(sitofp(X)) --> X
// fptosi(uitofp(X)) --> X
// This is safe if the intermediate type has enough bits in its mantissa to
// accurately represent all values of X. For example, do not do this with
// i64->float->i64. This is also safe for sitofp case, because any negative
// 'X' value would cause an undefined result for the fptoui.
if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) &&
OpI->getOperand(0)->getType() == FI.getType() &&
(int)FI.getType()->getScalarSizeInBits() <=
OpI->getType()->getFPMantissaWidth())
return ReplaceInstUsesWith(FI, OpI->getOperand(0));
return commonCastTransforms(FI);
}
Instruction *InstCombiner::visitUIToFP(CastInst &CI) {
return commonCastTransforms(CI);
}
Instruction *InstCombiner::visitSIToFP(CastInst &CI) {
return commonCastTransforms(CI);
}
Instruction *InstCombiner::visitIntToPtr(IntToPtrInst &CI) {
// If the source integer type is larger than the intptr_t type for
// this target, do a trunc to the intptr_t type, then inttoptr of it. This
// allows the trunc to be exposed to other transforms. Don't do this for
// extending inttoptr's, because we don't know if the target sign or zero
// extends to pointers.
if (TD && CI.getOperand(0)->getType()->getScalarSizeInBits() >
TD->getPointerSizeInBits()) {
Value *P = Builder->CreateTrunc(CI.getOperand(0),
TD->getIntPtrType(CI.getContext()), "tmp");
return new IntToPtrInst(P, CI.getType());
}
if (Instruction *I = commonCastTransforms(CI))
return I;
return 0;
}
/// @brief Implement the transforms for cast of pointer (bitcast/ptrtoint)
Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) {
Value *Src = CI.getOperand(0);
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) {
// If casting the result of a getelementptr instruction with no offset, turn
// this into a cast of the original pointer!
if (GEP->hasAllZeroIndices()) {
// Changing the cast operand is usually not a good idea but it is safe
// here because the pointer operand is being replaced with another
// pointer operand so the opcode doesn't need to change.
Worklist.Add(GEP);
CI.setOperand(0, GEP->getOperand(0));
return &CI;
}
// If the GEP has a single use, and the base pointer is a bitcast, and the
// GEP computes a constant offset, see if we can convert these three
// instructions into fewer. This typically happens with unions and other
// non-type-safe code.
if (TD && GEP->hasOneUse() && isa<BitCastInst>(GEP->getOperand(0)) &&
GEP->hasAllConstantIndices()) {
// We are guaranteed to get a constant from EmitGEPOffset.
ConstantInt *OffsetV = cast<ConstantInt>(EmitGEPOffset(GEP));
int64_t Offset = OffsetV->getSExtValue();
// Get the base pointer input of the bitcast, and the type it points to.
Value *OrigBase = cast<BitCastInst>(GEP->getOperand(0))->getOperand(0);
const Type *GEPIdxTy =
cast<PointerType>(OrigBase->getType())->getElementType();
SmallVector<Value*, 8> NewIndices;
if (FindElementAtOffset(GEPIdxTy, Offset, NewIndices)) {
// If we were able to index down into an element, create the GEP
// and bitcast the result. This eliminates one bitcast, potentially
// two.
Value *NGEP = cast<GEPOperator>(GEP)->isInBounds() ?
Builder->CreateInBoundsGEP(OrigBase,
NewIndices.begin(), NewIndices.end()) :
Builder->CreateGEP(OrigBase, NewIndices.begin(), NewIndices.end());
NGEP->takeName(GEP);
if (isa<BitCastInst>(CI))
return new BitCastInst(NGEP, CI.getType());
assert(isa<PtrToIntInst>(CI));
return new PtrToIntInst(NGEP, CI.getType());
}
}
}
return commonCastTransforms(CI);
}
Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) {
// If the destination integer type is smaller than the intptr_t type for
// this target, do a ptrtoint to intptr_t then do a trunc. This allows the
// trunc to be exposed to other transforms. Don't do this for extending
// ptrtoint's, because we don't know if the target sign or zero extends its
// pointers.
if (TD &&
CI.getType()->getScalarSizeInBits() < TD->getPointerSizeInBits()) {
Value *P = Builder->CreatePtrToInt(CI.getOperand(0),
TD->getIntPtrType(CI.getContext()),
"tmp");
return new TruncInst(P, CI.getType());
}
return commonPointerCastTransforms(CI);
}
Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
// If the operands are integer typed then apply the integer transforms,
// otherwise just apply the common ones.
Value *Src = CI.getOperand(0);
const Type *SrcTy = Src->getType();
const Type *DestTy = CI.getType();
// Get rid of casts from one type to the same type. These are useless and can
// be replaced by the operand.
if (DestTy == Src->getType())
return ReplaceInstUsesWith(CI, Src);
if (const PointerType *DstPTy = dyn_cast<PointerType>(DestTy)) {
const PointerType *SrcPTy = cast<PointerType>(SrcTy);
const Type *DstElTy = DstPTy->getElementType();
const Type *SrcElTy = SrcPTy->getElementType();
// If the address spaces don't match, don't eliminate the bitcast, which is
// required for changing types.
if (SrcPTy->getAddressSpace() != DstPTy->getAddressSpace())
return 0;
// If we are casting a alloca to a pointer to a type of the same
// size, rewrite the allocation instruction to allocate the "right" type.
// There is no need to modify malloc calls because it is their bitcast that
// needs to be cleaned up.
if (AllocaInst *AI = dyn_cast<AllocaInst>(Src))
if (Instruction *V = PromoteCastOfAllocation(CI, *AI))
return V;
// If the source and destination are pointers, and this cast is equivalent
// to a getelementptr X, 0, 0, 0... turn it into the appropriate gep.
// This can enhance SROA and other transforms that want type-safe pointers.
Constant *ZeroUInt =
Constant::getNullValue(Type::getInt32Ty(CI.getContext()));
unsigned NumZeros = 0;
while (SrcElTy != DstElTy &&
isa<CompositeType>(SrcElTy) && !isa<PointerType>(SrcElTy) &&
SrcElTy->getNumContainedTypes() /* not "{}" */) {
SrcElTy = cast<CompositeType>(SrcElTy)->getTypeAtIndex(ZeroUInt);
++NumZeros;
}
// If we found a path from the src to dest, create the getelementptr now.
if (SrcElTy == DstElTy) {
SmallVector<Value*, 8> Idxs(NumZeros+1, ZeroUInt);
return GetElementPtrInst::CreateInBounds(Src, Idxs.begin(), Idxs.end(),"",
((Instruction*)NULL));
}
}
if (const VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) {
if (DestVTy->getNumElements() == 1 && !isa<VectorType>(SrcTy)) {
Value *Elem = Builder->CreateBitCast(Src, DestVTy->getElementType());
return InsertElementInst::Create(UndefValue::get(DestTy), Elem,
Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
// FIXME: Canonicalize bitcast(insertelement) -> insertelement(bitcast)
}
}
if (const VectorType *SrcVTy = dyn_cast<VectorType>(SrcTy)) {
if (SrcVTy->getNumElements() == 1 && !isa<VectorType>(DestTy)) {
Value *Elem =
Builder->CreateExtractElement(Src,
Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
return CastInst::Create(Instruction::BitCast, Elem, DestTy);
}
}
if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(Src)) {
// Okay, we have (bitcast (shuffle ..)). Check to see if this is
// a bitconvert to a vector with the same # elts.
if (SVI->hasOneUse() && isa<VectorType>(DestTy) &&
cast<VectorType>(DestTy)->getNumElements() ==
SVI->getType()->getNumElements() &&
SVI->getType()->getNumElements() ==
cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements()) {
BitCastInst *Tmp;
// If either of the operands is a cast from CI.getType(), then
// evaluating the shuffle in the casted destination's type will allow
// us to eliminate at least one cast.
if (((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(0))) &&
Tmp->getOperand(0)->getType() == DestTy) ||
((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(1))) &&
Tmp->getOperand(0)->getType() == DestTy)) {
Value *LHS = Builder->CreateBitCast(SVI->getOperand(0), DestTy);
Value *RHS = Builder->CreateBitCast(SVI->getOperand(1), DestTy);
// Return a new shuffle vector. Use the same element ID's, as we
// know the vector types match #elts.
return new ShuffleVectorInst(LHS, RHS, SVI->getOperand(2));
}
}
}
if (isa<PointerType>(SrcTy))
return commonPointerCastTransforms(CI);
return commonCastTransforms(CI);
}
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