RFR: 8288047: Accelerate Poly1305 on x86_64 using AVX512 instructions [v6]

[Vladimir Ivanov]

On Tue, 1 Nov 2022 23:17:46 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> vpaprotsk has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   invalidkeyexception and some review comments
>
> src/hotspot/cpu/x86/stubGenerator_x86_64.cpp line 2002:
> 
>> 2000: }
>> 2001: 
>> 2002: address StubGenerator::generate_poly1305_masksCP() {
> 
> I suggest to turn it into a C++ literal constant and move the declaration next to `poly1305_process_blocks_avx512` where they are used. As an example, here's how it is handled in GHASH stubs:
>   https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/stubGenerator_x86_64_ghash.cpp#L35
> 
> That would allow to avoid to simplify the code a bit (no need in `StubRoutines::x86::_poly1305_mask_addr`/`poly1305_mask_addr()` and no need to generate the constants during VM startup).
> 
> You could split it into 3 constants, but then using a single base register (`polyCP`) won't work anymore.
> Thinking more about it, I'm not sure why you can't just do the split and use address literals instead  to access individual constants (and repurpose `r13` to be used as a scratch register when RIP-relative addressing mode doesn't work).

The case of AES stubs may be even a better fit here:
https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/stubGenerator_x86_64_aes.cpp#L47

It doesn't use/introduce any shared constants, so declaring a constant and a local accessor (to save on pointer to address casts at use sites) is enough.

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PR: https://git.openjdk.org/jdk/pull/10582