RFR: 8282711: Accelerate Math.signum function for AVX and AVX512 target. [v6]

[Sandhya Viswanathan]

On Wed, 13 Apr 2022 18:53:18 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:
>> 
>>  - 8282711: Review comments resolutions.
>>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8282711
>>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8282711
>>  - 8282711: Replacing vector length based predicate.
>>  - 8282711: Making the changes more generic (removing AVX512DQ restriction), adding new IR level test.
>>  - 8282711: Review comments resolved.
>>  - 8282711: Accelerate Math.signum function for AVX and AVX512 target.
>
> src/hotspot/cpu/x86/x86.ad line 6114:
> 
>> 6112: 
>> 6113: instruct signumV_reg_evex(vec dst, vec src, vec zero, vec one, kReg ktmp1) %{
>> 6114:   predicate(Matcher::vector_length_in_bytes(n) ==  64);
> 
> avx512vl check is needed here. vector_signum_evex needs avx512vl support.

Further clarification here: The vector_signum_evex code is faster than vector_signum_vex. On AVX=3 platforms vector_signum_evex should be used for all vector lengths.
So the predicate for signumV_reg_evex should be:
    ((VM_Version::supports_avx512vl()) || (Matcher::vector_length_in_bytes(n) == 64))
Accordingly the predicate for signumV_reg_avx should be adjusted to be reverse of this.

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PR: https://git.openjdk.java.net/jdk/pull/7717