RFR: 8261542: X86 slice and unslice intrinsics for 256-bit byte/short vectors [v3]

[Vladimir Kozlov]

On Fri, 19 Feb 2021 01:23:04 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> The slice and unslice intrinsics for 256-bit byte/short vectors can be implemented for x86 platforms supporting AVX2 using a sequence of instructions.
>> 
>> JBS: https://bugs.openjdk.java.net/browse/JDK-8261542
>> 
>> The PerfSliceOrigin.java jmh test attached to the JBS shows the following performance on AVX2 platform.
>> 
>> Before:
>> Benchmark                                 (size)   Mode  Cnt   Score   Error   Units
>> PerfSliceOrigin.vectorSliceOrigin           1024  thrpt    5  18.887 ± 1.128  ops/ms
>> PerfSliceOrigin.vectorSliceUnsliceOrigin    1024  thrpt    5   9.374 ± 0.370  ops/ms
>> 
>> After:
>> Benchmark                                 (size)   Mode  Cnt      Score     Error   Units
>> PerfSliceOrigin.vectorSliceOrigin           1024  thrpt    5  13861.420 ±  19.071  ops/ms
>> PerfSliceOrigin.vectorSliceUnsliceOrigin    1024  thrpt    5   7895.199 ± 142.580  ops/ms
>
> Sandhya Viswanathan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   corrected assert

src/hotspot/cpu/x86/x86.ad line 1695:

> 1693:       if(vlen == 2) {
> 1694:         return false; // Implementation limitation due to how shuffle is loaded
> 1695:       } else if (size_in_bits == 256 && UseAVX < 2) {

Should this be >= 256?

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PR: https://git.openjdk.java.net/jdk/pull/2520