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Turn casts into getelementptr's when possible. This enables SROA to be more

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aggressive in some cases where LLVMGCC 4 is inserting casts for no reason.

This implements InstCombine/cast.ll:test27/28.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27620 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-04-12 18:09:35 +00:00
parent 1c62195c98
commit 9fb9213083
1 changed files with 23 additions and 0 deletions
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23
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -4814,6 +4814,29 @@ Instruction *InstCombiner::visitCastInst(CastInst &CI) {
if (Instruction *NV = FoldOpIntoPhi(CI)) if (Instruction *NV = FoldOpIntoPhi(CI))
return NV; return NV;
// If the source and destination are pointers, and this cast is equivalent to
// a getelementptr X, 0, 0, 0... turn it into the appropriate getelementptr.
// This can enhance SROA and other transforms that want type-safe pointers.
if (const PointerType *DstPTy = dyn_cast<PointerType>(CI.getType()))
if (const PointerType *SrcPTy = dyn_cast<PointerType>(Src->getType())) {
const Type *DstTy = DstPTy->getElementType();
const Type *SrcTy = SrcPTy->getElementType();
Constant *ZeroUInt = Constant::getNullValue(Type::UIntTy);
unsigned NumZeros = 0;
while (SrcTy != DstTy &&
isa<CompositeType>(SrcTy) && !isa<PointerType>(SrcTy)) {
SrcTy = cast<CompositeType>(SrcTy)->getTypeAtIndex(ZeroUInt);
++NumZeros;
}
// If we found a path from the src to dest, create the getelementptr now.
if (SrcTy == DstTy) {
std::vector<Value*> Idxs(NumZeros+1, ZeroUInt);
return new GetElementPtrInst(Src, Idxs);
}
}
// If the source value is an instruction with only this use, we can attempt to // If the source value is an instruction with only this use, we can attempt to
// propagate the cast into the instruction. Also, only handle integral types // propagate the cast into the instruction. Also, only handle integral types
// for now. // for now.