RFR: 8325991: Accelerate Poly1305 on x86_64 using AVX2 instructions [v10]

[Sandhya Viswanathan]

On Fri, 1 Mar 2024 08:15:50 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Srinivas Vamsi Parasa has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update description of Poly1305 algo
>
> src/hotspot/cpu/x86/assembler_x86.cpp line 5148:
> 
>> 5146:   assert(vector_len == AVX_512bit ? VM_Version::supports_avx512ifma() : VM_Version::supports_avxifma(), "");
>> 5147:   InstructionMark im(this);
>> 5148:   InstructionAttr attributes(vector_len, /* rex_w */ true, /* legacy_mode */ false, /* no_mask_reg */ false, /* uses_vl */ true);
> 
> uses_vl should be false here.
> 
> BTW, this assertion looks very fuzzy, you are checking for two target features in one instruction,  apparently, instruction is meant to use AVX512_IFMA only for 512 bit vector length, and for narrower vectors its needs AVX_IFMA.
> 
> Lets either keep this strictly for AVX_IFMA for AVX512_IFMA we already have evpmadd52[l/h]uq, if you truly want to make this generic one then split the assertion
> 
> `assert ( (avx_ifma && vector_len <= 256) || (avx512_ifma  && (vector_len == 512 || VM_Version::support_vl()));
> `
> 
> And then you may pass uses_vl at true.

It would be good to make this instruction generic.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17881#discussion_r1509271081