[llvm-commits] [llvm] r133022 - in /llvm/trunk: lib/CodeGen/SelectionDAG/DAGCombiner.cpp test/CodeGen/X86/shl_undef.ll

[Jay Foad]

>> IMO it would be better to change the Lang Ref so that the result of
>> "shl undef, 1" is undef.
>
> But then front-ends would not be able to output "shl" for a left-shift because
> the semantics would be wrong.

C doesn't guarantee that this function returns 0:

int f(void) {
  int x; // uninitialised
  return (x << 1) & 1;
}

Does it? So the semantics would be just fine. Am I missing something?

Thanks,
Jay.