PING^1: [PATCH GCC 8] x86: Re-enable partial_reg_dependency and movx for Haswell

[H.J. Lu]

On Sun, May 20, 2018 at 11:51 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> r254152 disabled partial_reg_dependency and movx for Haswell and newer
>> Intel processors.  r258972 restored them for skylake-avx512.  For Haswell,
>> movx improves performance.  But partial_reg_stall may be better than
>> partial_reg_dependency in theory.  We will investigate performance impact
>> of partial_reg_stall vs partial_reg_dependency on Haswell for GCC 9.  In
>> the meantime, this patch restores both partial_reg_dependency and mox for
>> Haswell in GCC 8.
>>
>> OK for GCC 8?
>
> I would still like to know in what situations/bechnarks it improves the performance.
> The change was benchmarked on spec2000/2006 plus some additional benchmarks and, so
> it would be nice to know where it hurts.

From

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85829#c5:

I have made measurements on HSW comparing
-mtune-ctrl=movx,partial_reg_dependency -Ofast -march=haswell to
-Ofast -mtune=haswell and I see improvements on EEMBC benchmarks.

automotive
=========
  aifftr01 (default) - goodperf: Runtime improvement of   2.6% (time).
  aiifft01 (default) - goodperf: Runtime improvement of   2.2% (time).

networking
=========
  ip_pktcheckb1m (default) - goodperf: Runtime improvement of   3.8% (time).
  ip_pktcheckb2m (default) - goodperf: Runtime improvement of   5.2% (time).
  ip_pktcheckb4m (default) - goodperf: Runtime improvement of   4.4% (time).
  ip_pktcheckb512k (default) - goodperf: Runtime improvement of   4.2% (time).

telecom
=========
  fft00data_1 (default) - goodperf: Runtime improvement of   8.4% (time).
  fft00data_2 (default) - goodperf: Runtime improvement of   8.6% (time).
  fft00data_3 (default) - goodperf: Runtime improvement of   9.0% (time).

OK for GCC 8?

H.J.
> Honza
>>
>> H.J.
>> ---
>>       PR target/85829
>>       * config/i386/x86-tune.def: Re-enable partial_reg_dependency
>>       and movx for Haswell.
>> ---
>>  gcc/config/i386/x86-tune.def | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/gcc/config/i386/x86-tune.def b/gcc/config/i386/x86-tune.def
>> index 5649fdcf416..60625668236 100644
>> --- a/gcc/config/i386/x86-tune.def
>> +++ b/gcc/config/i386/x86-tune.def
>> @@ -48,7 +48,7 @@ DEF_TUNE (X86_TUNE_SCHEDULE, "schedule",
>>     over partial stores.  For example preffer MOVZBL or MOVQ to load 8bit
>>     value over movb.  */
>>  DEF_TUNE (X86_TUNE_PARTIAL_REG_DEPENDENCY, "partial_reg_dependency",
>> -          m_P4_NOCONA | m_CORE2 | m_NEHALEM  | m_SANDYBRIDGE
>> +          m_P4_NOCONA | m_CORE2 | m_NEHALEM  | m_SANDYBRIDGE | m_HASWELL
>>         | m_BONNELL | m_SILVERMONT | m_INTEL
>>         | m_KNL | m_KNM | m_AMD_MULTIPLE | m_SKYLAKE_AVX512 | m_GENERIC)
>>
>> @@ -84,7 +84,7 @@ DEF_TUNE (X86_TUNE_PARTIAL_FLAG_REG_STALL, "partial_flag_reg_stall",
>>     partial dependencies.  */
>>  DEF_TUNE (X86_TUNE_MOVX, "movx",
>>            m_PPRO | m_P4_NOCONA | m_CORE2 | m_NEHALEM  | m_SANDYBRIDGE
>> -       | m_BONNELL | m_SILVERMONT | m_KNL | m_KNM | m_INTEL
>> +       | m_BONNELL | m_SILVERMONT | m_KNL | m_KNM | m_INTEL | m_HASWELL
>>         | m_GEODE | m_AMD_MULTIPLE | m_SKYLAKE_AVX512 | m_GENERIC)
>>
>>  /* X86_TUNE_MEMORY_MISMATCH_STALL: Avoid partial stores that are followed by
>> --
>> 2.17.0
>>



-- 
H.J.