Re: [PATCH][RTL-ifcvt] Improve conditional select ops on immediates

[Uros Bizjak <ubizjak@gmail.com>]

On Mon, Aug 3, 2015 at 3:02 PM, Kyrill Tkachov <kyrylo.tkachov@arm.com> wrote:
>
> On 03/08/15 13:33, Uros Bizjak wrote:
>>
>> Hello!
>>
>>> 2015-07-30  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>>
>>>      * ifcvt.c (noce_try_store_flag_constants): Make logic of the case
>>>      when diff == STORE_FLAG_VALUE or diff == -STORE_FLAG_VALUE more
>>>      explicit.  Prefer to add the flag whenever possible.
>>>      (noce_process_if_block): Try noce_try_store_flag_constants before
>>>      noce_try_cmove.
>>>
>>> 2015-07-30  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>>
>>>      * gcc.target/aarch64/csel_bfx_1.c: New test.
>>>      * gcc.target/aarch64/csel_imms_inc_1.c: Likewise.
>>
>> This patch regressed following tests on x86_64:
>>
>> FAIL: gcc.target/i386/cmov2.c scan-assembler sbb
>> FAIL: gcc.target/i386/cmov3.c scan-assembler cmov[^3]

The difference for cmov3.c on x86_64 is:

       cmpl    %esi, %edi
       movl    $-5, %edx
       movl    $5, %eax
       cmovg   %edx, %eax
       ret

vs. new code:

       xorl    %eax, %eax
       cmpl    %esi, %edi
       setle   %al
       negl    %eax
       andl    $10, %eax
       subl    $5, %eax
       ret

I'm not sure old code is really better than new. HJ, do you have any
better insight?

Uros.