[llvm-commits] [llvm] r127598 - in /llvm/trunk: lib/CodeGen/SelectionDAG/SelectionDAG.cpp test/CodeGen/ARM/shifter_operand.ll test/CodeGen/ARM/undef-sext.ll

[Evan Cheng]

On Mar 14, 2011, at 11:25 AM, Frits van Bommel wrote:

> On Mon, Mar 14, 2011 at 7:15 PM, Evan Cheng <evan.cheng at apple.com> wrote:
>> Log:
>> Minor optimization. sign-ext/anyext of undef is still undef.
> 
> I can believe this for anyext, but a sext'ed undef should probably
> still have equal high bits, which is not a requirement for the bigger
> undef you're replacing it with.

I don't see the problem, the high-bit of an undef is an unknown value. zero-extend is definitely not safe, but sign-extend should be fine.

Evan