RFR: 8288047: Accelerate Poly1305 on x86_64 using AVX512 instructions [v6]
Volodymyr Paprotski
duke at openjdk.org
Wed Nov 9 22:00:40 UTC 2022
On Wed, 9 Nov 2022 02:19:29 GMT, Volodymyr Paprotski <duke at openjdk.org> wrote:
>>> Did not split it up into individual constants. The main 'problem' is that Address and ExternalAddress are not compatible.
>>
>> There's a reason for that and it's because RIP-relative addressing doesn't always work, so additional register may be needed.
>>
>>> Most instructions do not take AddressLiteral, so can't use ExternalAddress to refer to those constants.
>>
>> I counted 4 instructions accessing the constants (`evpandq`, `andq`, `evporq`, and `vpternlogq`) in your patch.
>>
>> `macroAssembler_x86.hpp` is the place for `AddressLiteral`-related overloads (there are already numerous cases present) and it's trivial to add new ones.
>>
>>> (If I did get the instructions I use to take AddressLiteral, I think we would end up with more lea(rscratch)s generated; but that's more of a silver-lining)
>>
>> It depends on memory layout. If constants end up placed close enough in the address space, there'll be no additional instructions generated.
>>
>> Anyway, it doesn't look like something important from throughput perspective. Overall, I find it clearer when the code refers to individual constants through `AddressLiteral`s, but I'm also fine with it as it is now.
>
> Makes sense to me, that would indeed be cleaner, will add a couple more overloads. (Still getting used to what is 'clean' in this code base).
done
-------------
PR: https://git.openjdk.org/jdk/pull/10582
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