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Generalize this code to turn any cast-to-first-element-of into a gep constexpr 

llvm-svn: 17914
This commit is contained in:
Chris Lattner 2004-11-17 17:59:35 +00:00
parent c368b63515
commit ba18b9a0da
1 changed files with 21 additions and 8 deletions
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29
llvm/lib/VMCore/ConstantFolding.cpp
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@ -565,16 +565,29 @@ Constant *llvm::ConstantFoldCastInstruction(const Constant *V,
return UndefValue::get(DestTy);
}
// Check to see if we are casting an array of X to a pointer to X. If so, use
// a GEP to get to the first element of the array instead of a cast!
// Check to see if we are casting an pointer to an aggregate to a pointer to
// the first element. If so, return the appropriate GEP instruction.
if (const PointerType *PTy = dyn_cast<PointerType>(V->getType()))
if (const ArrayType *ATy = dyn_cast<ArrayType>(PTy->getElementType()))
if (const PointerType *DPTy = dyn_cast<PointerType>(DestTy))
if (DPTy->getElementType() == ATy->getElementType()) {
std::vector<Constant*> IdxList(2,Constant::getNullValue(Type::IntTy));
return ConstantExpr::getGetElementPtr(const_cast<Constant*>(V),
IdxList);
if (const PointerType *DPTy = dyn_cast<PointerType>(DestTy)) {
std::vector<Value*> IdxList;
IdxList.push_back(Constant::getNullValue(Type::IntTy));
const Type *ElTy = PTy->getElementType();
while (ElTy != DPTy->getElementType()) {
if (const StructType *STy = dyn_cast<StructType>(ElTy)) {
ElTy = STy->getElementType(0);
IdxList.push_back(Constant::getNullValue(Type::UIntTy));
} else if (const SequentialType *STy = dyn_cast<SequentialType>(ElTy)) {
if (isa<PointerType>(ElTy)) break; // Can't index into pointers!
ElTy = STy->getElementType();
IdxList.push_back(IdxList[0]);
} else {
break;
}
}
if (ElTy == DPTy->getElementType())
return ConstantExpr::getGetElementPtr(const_cast<Constant*>(V),IdxList);
}
ConstRules &Rules = ConstRules::get(V, V);