diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/VMCore/ConstantFold.cpp | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp index 53e5c69136..da4efcdaad 100644 --- a/lib/VMCore/ConstantFold.cpp +++ b/lib/VMCore/ConstantFold.cpp @@ -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. |