[llvm] r207088 - X86: Emit test instead of constant shift + compare if the shift result is unused.

[Tobias Grosser]

On 24/04/2014 22:59, Benjamin Kramer wrote:
>
> On 24.04.2014, at 22:01, Tobias Grosser <tobias at grosser.es> wrote:
>
>> On 24/04/2014 10:15, Benjamin Kramer wrote:
>>> Author: d0k
>>> Date: Thu Apr 24 03:15:31 2014
>>> New Revision: 207088
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=207088&view=rev
>>> Log:
>>> X86: Emit test instead of constant shift + compare if the shift result is unused.
>>>
>>> This allows us to compile
>>>    return (mask & 0x8 ? a : b);
>>> into
>>>    testb $8, %dil
>>>    cmovnel %edx, %esi
>>> instead of
>>>    andl  $8, %edi
>>>    shrl  $3, %edi
>>>    cmovnel %edx, %esi
>>>
>>> which we formed previously because dag combiner canonicalizes setcc of and into shift.
>>
>> After this commit, my -O3 test-suite buildbot showed a miscompare during the execution of MultiSource/Benchmarks/mediabench/g721/g721encode/encode.
>>
>> http://lab.llvm.org:8011/builders/polly-perf-O3/builds/2811
>>
>> The only other two commits in this batch are 207090 and 207091 from Chandler, but I guess they should not cause this.
>>
>> I did not investigate further.
>
> Good catch, r207145 should help.

It did. Everything is back to green.

Thanks,
Tobias