Another epic optimiser failure

Stefan Kanthak stefan.kanthak@nexgo.de
Sat May 27 22:00:41 GMT 2023


"Andrew Pinski" <pinskia@gmail.com> wrote:

> On Sat, May 27, 2023 at 2:38 PM Stefan Kanthak <stefan.kanthak@nexgo.de> wrote:
>>
>> "Jakub Jelinek" <jakub@redhat.com> wrote, completely clueless:
>>
>>> On Sat, May 27, 2023 at 11:04:11PM +0200, Stefan Kanthak wrote:
>>>> OUCH: popcnt writes the WHOLE result register, there is ABSOLUTELY
>>>>       no need to clear it beforehand nor to clear the higher 24 bits
>>>>       afterwards!
>>>
>>> Except that there is.  See https://gcc.gnu.org/PR62011 for details.
>>
>> GUESS WHY I EXPLICITLY WROTE
>>
>> | JFTR: before GCC zealots write nonsense: see -march= or -mtune=
>>
>> NOT AMUSED ABOUT YOUR CRYING INCOMPETENCE!
>
> So you want to complain about GCC knowing about an Intel performance errata????

Ever heard about cargo cult?

Read the options I used CAREFULLY

| gcc -m32 -march=alderlake -O3
| gcc -m32 -march=sapphirerapids -O3
| gcc -m32 -mpopcnt -mtune=sapphirerapids -O3

> If you read that bug report, you would have learned why the zeroing is
> done. I am sorry you hate GCC for actually following advice from the
> processor maker after all.

HSD146 does NOT apply to Alder Lake or Sapphire Rapids!

NOT AMUSED ABOUT YOUR INCOMPETENCE TOO!
Stefan



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