Re: x86: making better use of vpternlog{d,q}

[Jan Beulich <jbeulich@suse.com>]

On 24.05.2023 11:01, Hongtao Liu wrote:
> On Wed, May 24, 2023 at 3:58 PM Jan Beulich via Gcc <gcc@gcc.gnu.org> wrote:
>>
>> Hello,
>>
>> for a couple of years I was meaning to extend the use of these AVX512F
>> insns beyond the pretty minimalistic ones there are so far. Now that I've
>> got around to at least draft something, I ran into a couple of issues I
>> cannot explain. I'd like to start with understanding the unexpected
>> effects of a change to an existing insn I have made (reproduced at the
>> bottom). I certainly was prepared to observe testsuite failures, but it
>> ends up failing tests I didn't expect it would fail, and - upon looking
>> at sibling ones - also ends up leaving intact tests which I would expect
>> would then need adjustment (because of using the new alternative).
>>
>> In particular (all mentioned tests are in gcc.target/i386/)
>> - avx512f-andn-si-zmm-1.c (and its AVX512VL counterparts) fails because
>>   for whatever reason generated code reverts back to using vpbroadcastd,
>> - avx512f-andn-di-zmm-1.c, otoh, is unaffected (i.e. continues to use
>>   vpandnq with embedded broadcast),
>> - avx512f-andn-si-zmm-2.c doesn't use the new 4th insn alternative when
>>   at the same time a made-up DI variant of the test (akin to what might
>>   be an avx512f-andn-di-zmm-2.c testcase) does.
>> IOW: How is SI mode element size different here from DI mode one? Is
>> there anything wrong with the 4th alternative I'm adding, or is this
>> hinting at some anomaly elsewhere?
> __m512i is defined as __v8di, when it's used for _mm512_andnot_epi32,
> it's explicitlt converted to (__v16si) and creates an extra subreg
> which is not needed for DImode cases.
> And pass_combine try to match the below pattern but failed due to the
> condition REG_P (operands[1]) || REG_P (operands[2]). Here I think you
> want register_operand instead of REG_P.

Thanks, this has indeed made things match my expectations wrt testsuite
results. Sadly similar adjustments for other (new) insns didn't make
any difference with the further issues I'm facing. I may therefore need
to ask more questions; I hope they're not going to be too dumb.

Jan