RFR: 8320347: Emulate vblendvp[sd] on ECore

[Volodymyr Paprotski]

On Mon, 20 Nov 2023 21:19:02 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Splitting vblendvp[sd] into boolean operations is bit faster on ECore, get up to 30% gain
>> 
>> 
>> =============== BEFORE ===============
>> Benchmark                 (SIZE)  Mode  Cnt    Score   Error  Units
>> VectorSignum.floatSignum     256  avgt    3   77.766 ± 0.049  ns/op
>> VectorSignum.floatSignum     512  avgt    3  154.889 ± 0.242  ns/op
>> VectorSignum.floatSignum    1024  avgt    3  306.130 ± 0.605  ns/op
>> VectorSignum.floatSignum    2048  avgt    3  609.965 ± 0.927  ns/op
>> VectorSignum.doubleSignum     256  avgt    3   151.874 ± 1.748  ns/op
>> VectorSignum.doubleSignum     512  avgt    3   303.080 ± 0.310  ns/op
>> VectorSignum.doubleSignum    1024  avgt    3   607.517 ± 0.597  ns/op
>> VectorSignum.doubleSignum    2048  avgt    3  1214.282 ± 1.834  ns/op
>> Benchmark                Mode  Cnt    Score   Error  Units
>> MaxMinOptimizeTest.dAdd  avgt    3   77.240 ± 0.029  us/op
>> MaxMinOptimizeTest.dMax  avgt    3  137.334 ± 0.128  us/op
>> MaxMinOptimizeTest.dMin  avgt    3  137.160 ± 0.465  us/op
>> MaxMinOptimizeTest.dMul  avgt    3   77.231 ± 0.051  us/op
>> MaxMinOptimizeTest.fAdd  avgt    3   77.165 ± 0.003  us/op
>> MaxMinOptimizeTest.fMax  avgt    3  107.428 ± 1.501  us/op
>> MaxMinOptimizeTest.fMin  avgt    3  107.186 ± 0.022  us/op
>> MaxMinOptimizeTest.fMul  avgt    3   77.164 ± 0.012  us/op
>> 
>> =============== AFTER ===============
>> Benchmark                 (SIZE)  Mode  Cnt    Score   Error  Units
>> VectorSignum.floatSignum     256  avgt    3   61.816 ± 1.980  ns/op
>> VectorSignum.floatSignum     512  avgt    3  117.251 ± 0.052  ns/op
>> VectorSignum.floatSignum    1024  avgt    3  231.356 ± 0.397  ns/op
>> VectorSignum.floatSignum    2048  avgt    3  458.904 ± 0.774  ns/op
>> VectorSignum.doubleSignum     256  avgt    3  121.449 ± 0.184  ns/op
>> VectorSignum.doubleSignum     512  avgt    3  241.662 ± 0.189  ns/op
>> VectorSignum.doubleSignum    1024  avgt    3  482.365 ± 0.165  ns/op
>> VectorSignum.doubleSignum    2048  avgt    3  962.412 ± 1.401  ns/op
>> Benchmark                Mode  Cnt    Score   Error  Units
>> MaxMinOptimizeTest.dAdd  avgt    3   77.240 ± 0.029  us/op
>> MaxMinOptimizeTest.dMax  avgt    3  125.701 ± 0.082  us/op
>> MaxMinOptimizeTest.dMin  avgt    3  124.704 ± 0.119  us/op
>> MaxMinOptimizeTest.dMul  avgt    3   77.232 ± 0.028  us/op
>> MaxMinOptimizeTest.fAdd  avgt    3   77.169 ± 0.103  us/op
>> MaxMinOptimizeTest.fMax  avgt    3   97.939 ± 0.477  us/op
>> MaxMinOptimizeTest.fMin  avgt    3   98.012 ± 0.154  us/op
>> MaxMinO...
>
> src/hotspot/cpu/x86/macroAssembler_x86.cpp line 3488:
> 
>> 3486:   // WARN: Allow dst == (src1|src2), mask == scratch
>> 3487:   bool scratch_available = scratch != xnoreg && scratch != src1 && scratch != src2 && scratch != dst;
>> 3488:   bool dst_available = dst != src1 || dst != src2;
> 
> What if it is fully masked and dst==mask? In that case also dst_available should be false.

Hmm.. thats a good catch.. but its also bad if `!fully_masked && mask==scratch` (i.e. both cases will destroy the mask before it can be used)

For readability, I think I will just keep a second half of the check: `bool dst_available = dst!=mask && (dst != src1 || dst != src2)` 
(i.e. whomever calls this function, really _should_ know better, just like all the other functions in this file that dont have input validation.. these checks started as asserts while developing to catch some confusing bugs..)

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PR Review Comment: https://git.openjdk.org/jdk/pull/16716#discussion_r1399802873