RFR: 8290034: Auto vectorize reverse bit operations.

[Vladimir Kozlov]

On Mon, 18 Jul 2022 08:01:09 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

> Summary of changes:
> - Intrinsify scalar bit reverse APIs to emit efficient instruction sequence for X86 targets with and w/o GFNI feature.
> - Handle auto-vectorization of Integer/Long.reverse bit operations.
> - Backend implementation for these were added with 4th incubation of VectorAPIs.
> 
> Following are performance number for newly added JMH mocro benchmarks:-
> 
> 
> No-GFNI(CLX):
> =============
> Baseline:
> Benchmark         (size)  Mode  Cnt  Score   Error  Units
> Integers.reverse     500  avgt    2  1.085          us/op
> Longs.reverse        500  avgt    2  1.236          us/op
> WithOpt:
> Benchmark         (size)  Mode  Cnt  Score   Error  Units
> Integers.reverse     500  avgt    2  0.104          us/op
> Longs.reverse        500  avgt    2  0.255          us/op
> 
> With-GFNI(ICX):
> ===============
> Baseline:
> Benchmark         (size)  Mode  Cnt  Score   Error  Units
> Integers.reverse     500  avgt    2  0.887          us/op
> Longs.reverse        500  avgt    2  1.095          us/op
> 
> Without:
> Benchmark         (size)  Mode  Cnt  Score   Error  Units
> Integers.reverse     500  avgt    2  0.037          us/op
> Longs.reverse        500  avgt    2  0.145          us/op
> 
> 
> Kindly review and share feedback.
> 
> Best Regards,
> Jatin

Looks good. I submitted testing.

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PR: https://git.openjdk.org/jdk/pull/9535