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Fix part 3/2 of PR3290, making instcombine zap (gep(bitcast)) when possible. 

llvm-svn: 61980
This commit is contained in:
Chris Lattner 2009-01-09 05:44:56 +00:00
parent 9170731cb7
commit fef138b140
2 changed files with 127 additions and 81 deletions
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145
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -7695,6 +7695,66 @@ Instruction *InstCombiner::commonCastTransforms(CastInst &CI) {
return 0;
}
/// FindElementAtOffset - Given a type and a constant offset, determine whether
/// or not there is a sequence of GEP indices into the type that will land us at
/// the specified offset. If so, fill them into NewIndices and return true,
/// otherwise return false.
static bool FindElementAtOffset(const Type *Ty, int64_t Offset,
SmallVectorImpl<Value*> &NewIndices,
const TargetData *TD) {
if (!Ty->isSized()) return false;
// Start with the index over the outer type. Note that the type size
// might be zero (even if the offset isn't zero) if the indexed type
// is something like [0 x {int, int}]
const Type *IntPtrTy = TD->getIntPtrType();
int64_t FirstIdx = 0;
if (int64_t TySize = TD->getABITypeSize(Ty)) {
FirstIdx = Offset/TySize;
Offset %= TySize;
// Handle silly modulus not returning values values [0..TySize).
if (Offset < 0) {
--FirstIdx;
Offset += TySize;
assert(Offset >= 0);
}
assert((uint64_t)Offset < (uint64_t)TySize && "Out of range offset");
}
NewIndices.push_back(ConstantInt::get(IntPtrTy, FirstIdx));
// Index into the types. If we fail, set OrigBase to null.
while (Offset) {
if (const StructType *STy = dyn_cast<StructType>(Ty)) {
const StructLayout *SL = TD->getStructLayout(STy);
if (Offset >= (int64_t)SL->getSizeInBytes()) {
// We can't index into this, bail out.
return false;
}
unsigned Elt = SL->getElementContainingOffset(Offset);
NewIndices.push_back(ConstantInt::get(Type::Int32Ty, Elt));
Offset -= SL->getElementOffset(Elt);
Ty = STy->getElementType(Elt);
} else if (isa<ArrayType>(Ty) || isa<VectorType>(Ty)) {
const SequentialType *STy = cast<SequentialType>(Ty);
if (uint64_t EltSize = TD->getABITypeSize(STy->getElementType())) {
NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize));
Offset %= EltSize;
} else {
NewIndices.push_back(ConstantInt::get(IntPtrTy, 0));
}
Ty = STy->getElementType();
} else {
// Otherwise, we can't index into this, bail out.
return false;
}
}
return true;
}
/// @brief Implement the transforms for cast of pointer (bitcast/ptrtoint)
Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) {
Value *Src = CI.getOperand(0);
@ -7725,60 +7785,8 @@ Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) {
Value *OrigBase = cast<BitCastInst>(GEP->getOperand(0))->getOperand(0);
const Type *GEPIdxTy =
cast<PointerType>(OrigBase->getType())->getElementType();
if (GEPIdxTy->isSized()) {
SmallVector<Value*, 8> NewIndices;
// Start with the index over the outer type. Note that the type size
// might be zero (even if the offset isn't zero) if the indexed type
// is something like [0 x {int, int}]
const Type *IntPtrTy = TD->getIntPtrType();
int64_t FirstIdx = 0;
if (int64_t TySize = TD->getABITypeSize(GEPIdxTy)) {
FirstIdx = Offset/TySize;
Offset %= TySize;
// Handle silly modulus not returning values values [0..TySize).
if (Offset < 0) {
--FirstIdx;
Offset += TySize;
assert(Offset >= 0);
}
assert((uint64_t)Offset < (uint64_t)TySize &&"Out of range offset");
}
NewIndices.push_back(ConstantInt::get(IntPtrTy, FirstIdx));
// Index into the types. If we fail, set OrigBase to null.
while (Offset) {
if (const StructType *STy = dyn_cast<StructType>(GEPIdxTy)) {
const StructLayout *SL = TD->getStructLayout(STy);
if (Offset < (int64_t)SL->getSizeInBytes()) {
unsigned Elt = SL->getElementContainingOffset(Offset);
NewIndices.push_back(ConstantInt::get(Type::Int32Ty, Elt));
Offset -= SL->getElementOffset(Elt);
GEPIdxTy = STy->getElementType(Elt);
} else {
// Otherwise, we can't index into this, bail out.
Offset = 0;
OrigBase = 0;
}
} else if (isa<ArrayType>(GEPIdxTy) || isa<VectorType>(GEPIdxTy)) {
const SequentialType *STy = cast<SequentialType>(GEPIdxTy);
if (uint64_t EltSize = TD->getABITypeSize(STy->getElementType())){
NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize));
Offset %= EltSize;
} else {
NewIndices.push_back(ConstantInt::get(IntPtrTy, 0));
}
GEPIdxTy = STy->getElementType();
} else {
// Otherwise, we can't index into this, bail out.
Offset = 0;
OrigBase = 0;
}
}
if (OrigBase) {
if (FindElementAtOffset(GEPIdxTy, Offset, NewIndices, TD)) {
// If we were able to index down into an element, create the GEP
// and bitcast the result. This eliminates one bitcast, potentially
// two.
@ -7796,7 +7804,6 @@ Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) {
}
}
}
}
return commonCastTransforms(CI);
}
@ -10675,10 +10682,21 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
}
}
/// See if we can simplify:
/// X = bitcast A to B*
/// Y = gep X, <...constant indices...>
/// into a gep of the original struct. This is important for SROA and alias
/// analysis of unions. If "A" is also a bitcast, wait for A/X to be merged.
if (BitCastInst *BCI = dyn_cast<BitCastInst>(PtrOp)) {
if (!isa<BitCastInst>(BCI->getOperand(0)) && GEP.hasAllConstantIndices()) {
// Determine how much the GEP moves the pointer. We are guaranteed to get
// a constant back from EmitGEPOffset.
ConstantInt *OffsetV = cast<ConstantInt>(EmitGEPOffset(&GEP, GEP, *this));
int64_t Offset = OffsetV->getSExtValue();
// If this GEP instruction doesn't move the pointer, just replace the GEP
// with a bitcast of the real input to the dest type.
if (GEP.hasAllZeroIndices()) {
if (Offset == 0) {
// If the bitcast is of an allocation, and the allocation will be
// converted to match the type of the cast, don't touch this.
if (isa<AllocationInst>(BCI->getOperand(0))) {
@ -10694,6 +10712,23 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
}
return new BitCastInst(BCI->getOperand(0), GEP.getType());
}
// Otherwise, if the offset is non-zero, we need to find out if there is a
// field at Offset in 'A's type. If so, we can pull the cast through the
// GEP.
SmallVector<Value*, 8> NewIndices;
const Type *InTy =
cast<PointerType>(BCI->getOperand(0)->getType())->getElementType();
if (FindElementAtOffset(InTy, Offset, NewIndices, TD)) {
Instruction *NGEP =
GetElementPtrInst::Create(BCI->getOperand(0), NewIndices.begin(),
NewIndices.end());
if (NGEP->getType() == GEP.getType()) return NGEP;
InsertNewInstBefore(NGEP, GEP);
NGEP->takeName(&GEP);
return new BitCastInst(NGEP, GEP.getType());
}
}
}
return 0;

11
llvm/test/Transforms/InstCombine/bitcast-gep.ll
View File

@ -17,3 +17,14 @@ define i8* @test(i8* %v) {
%G = load i8** %F ; <i8*> [#uses=1]
ret i8* %G
}
; PR3290
%struct.Key = type { { i32, i32 } }
%struct.anon = type <{ i8, [3 x i8], i32 }>
define i32 *@test2(%struct.Key *%A) {
%B = bitcast %struct.Key* %A to %struct.anon*
%C = getelementptr %struct.anon* %B, i32 0, i32 2
ret i32 *%C
}