Re: x86: Prepare `strrchr-evex` and `strrchr-evex512` for AVX10

[Florian Weimer <fw@deneb.enyo.de>]

* Florian Weimer:

> * Noah Goldstein:
>
>> This commit refactors `strrchr-evex` and `strrchr-evex512` to use a
>> common implementation: `strrchr-evex-base.S`.
>>
>> The motivation is `strrchr-evex` needed to be refactored to not use
>> 64-bit masked registers in preperation for AVX10.
>>
>> Once vec-width masked register combining was removed, the EVEX and
>> EVEX512 implementations can easily be implemented in the same file
>> without any major overhead.
>>
>> The net result is performance improvements (measured on TGL) for both
>> `strrchr-evex` and `strrchr-evex512`. Although, note there are some
>> regressions in the test suite and it may be many of the cases that
>> make the total-geomean of improvement/regression across bench-strrchr
>> are cold. The point of the performance measurement is to show there
>> are no major regressions, but the primary motivation is preperation
>> for AVX10.
>>
>> Benchmarks where taken on TGL:
>> https://www.intel.com/content/www/us/en/products/sku/213799/intel-core-i711850h-processor-24m-cache-up-to-4-80-ghz/specifications.html
>>
>> EVEX geometric_mean(N=5) of all benchmarks New / Original   : 0.74
>> EVEX512 geometric_mean(N=5) of all benchmarks New / Original: 0.87
>>
>> Full check passes on x86.
>
> I believe this caused some sort of regression because when we upgraded
> glibc in the Fedora rawhide buildroot, a lot of things started failing:
>
>   glibc-2.38.9000-13.fc40 broke rawhide buildroot on x86_64
>   <https://bugzilla.redhat.com/show_bug.cgi?id=2244688>
>
> The list of changes relative to the previous version is rather short:
>
> - stdlib: fix grouping verification with multi-byte thousands separator (bug 30964)
> - build-many-glibcs: Check for required system tools
> - x86: Prepare `strrchr-evex` and `strrchr-evex512` for AVX10
> - aarch64: Optimise vecmath logs
> - aarch64: Cosmetic change in SVE exp routines
> - aarch64: Optimize SVE cos & cosf
> - aarch64: Improve vecmath sin routines
> - nss: Get rid of alloca usage in makedb's write_output.
> - debug: Add regression tests for BZ 30932
> - Fix FORTIFY_SOURCE false positive
> - nss: Rearrange and sort Makefile variables
> - inet: Rearrange and sort Makefile variables
> - Fix off-by-one OOB write in iconv/tst-iconv-mt
>
> And this patch is the most likely one to cause issues.  I will try to
> revert the patch and see if it fixes the observed issues.

We did the revert and the issues were gone.  So I think this commit is
faulty.