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zext(undef) = 0 and sext(undef) = 0, not undef.

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This hopefully fixes a miscompilation of TargetData.cpp when self hosting.

llvm-svn: 40125
This commit is contained in:
Chris Lattner 2007-07-20 22:09:02 +00:00
parent 9663eb4a5b
commit c157b172c1
1 changed files with 6 additions and 1 deletions
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7
lib/VMCore/ConstantFold.cpp
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@ -140,8 +140,13 @@ Constant *llvm::ConstantFoldCastInstruction(unsigned opc, const Constant *V,
const Type *DestTy) {
const Type *SrcTy = V->getType();
if (isa<UndefValue>(V))
if (isa<UndefValue>(V)) {
// zext(undef) = 0, because the top bits will be zero.
// sext(undef) = 0, because the top bits will all be the same.
if (opc == Instruction::ZExt || opc == Instruction::SExt)
return Constant::getNullValue(DestTy);
return UndefValue::get(DestTy);
}
// If the cast operand is a constant expression, there's a few things we can
// do to try to simplify it.