[crac] RFR: 8374491: CPUFeatures: check performance regression of AVX_Fast_Unaligned_Load [v3]

[Jan Kratochvil]

On Mon, 5 Jan 2026 07:21:01 GMT, Timofei Pushkin <tpushkin at openjdk.org> wrote:

>> Jan Kratochvil has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Adjust the 'xem_xcr0_eax.bits.sse != 0 && xem_xcr0_eax.bits.ymm != 0' detection
>
> src/hotspot/cpu/x86/vm_version_x86.cpp line 1232:
> 
>> 1230:   // There is no CPU_FEATURE_ACTIVE() available for this symbol.
>> 1231:   // There is no check for 'xem_xcr0_eax.bits.sse != 0 && xem_xcr0_eax.bits.ymm != 0' but FEATURE_ACTIVE(AVX) depends on it so it can be assumed.
>> 1232:   EXCESSIVE2(AVX_Fast_Unaligned_Load, FEATURE_ACTIVE(OSXSAVE) && FEATURE_ACTIVE(AVX) && FEATURE_ACTIVE(AVX2));
> 
> Since we check it like this here, I'd again suggest simplifying the detection of `AVX_Fast_Unaligned_Load` in `feature_flags()` to `vm_features.supports_feature(CPU_OSXSAVE) && vm_features.supports_feature(CPU_AVX) && vm_features.supports_feature(CPU_AVX2)` (maybe with `assert(xem_xcr0_eax.bits.sse != 0 && xem_xcr0_eax.bits.ymm != 0)`), but I don't insist.

I have adjusted it somehow.

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PR Review Comment: https://git.openjdk.org/crac/pull/283#discussion_r2662899045