RFR: 8258932: AArch64: Enhance floating-point Min/MaxReductionV with fminp/fmaxp [v2]

[Andrew Haley]

On Tue, 5 Jan 2021 03:43:15 GMT, Dong Bo <dongbo at openjdk.org> wrote:

>> This patch optimizes vectorial Min/Max reduction of two floating-point numbers on aarch64 with NEON instructions `fmaxp` and `fminp`.
>> 
>> Passed jtreg tier1-3 tests with `linux-aarch64-server-fastdebug` build.
>> Tests under `test/jdk/jdk/incubator/vector/` runned specially for the correctness and passed.
>> 
>> Introduced a new JMH micro `test/micro/org/openjdk/bench/vm/compiler/VectorReductionFloatingMinMax.java` for performance test.
>> Witnessed abount `37%` performance improvements on Kunpeng916. The JMH Results:
>> Benchmark                (COUNT)  (seed)  Mode  Cnt    Score   Error  Units
>> # Kunpeng 916, default
>> VectorReduction.maxRedD      512       0  avgt   10  678.126 ± 0.815  ns/op
>> VectorReduction.maxRedF      512       0  avgt   10  242.958 ± 0.212  ns/op
>> VectorReduction.minRedD      512       0  avgt   10  678.554 ± 0.824  ns/op
>> VectorReduction.minRedF      512       0  avgt   10  243.368 ± 0.205  ns/op
>> 
>> # Kunpeng 916, with fmaxp/fminp
>> VectorReduction.maxRedD      512       0  avgt   10  430.201 ± 0.353  ns/op => 36.56%
>> VectorReduction.maxRedF      512       0  avgt   10  243.404 ± 0.297  ns/op
>> VectorReduction.minRedD      512       0  avgt   10  427.805 ± 0.528  ns/op => 36.89%
>> VectorReduction.minRedF      512       0  avgt   10  242.963 ± 0.210  ns/op
>
> Dong Bo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   rebase the .m4 entry

This all looks reasonable. With the assembler change I think we should be good to go.

src/hotspot/cpu/aarch64/assembler_aarch64.hpp line 2451:

> 2449: #undef INSN
> 2450: 
> 2451: #define INSN(NAME, opc) \

This should be in an "AdvSIMD scalar pairwise" instruction group with faddp.

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PR: https://git.openjdk.java.net/jdk/pull/1925