RFR: 8320448: Accelerate IndexOf using AVX2 [v38]

[Scott Gibbons]

On Fri, 24 May 2024 20:12:07 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Scott Gibbons has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Test clarifications
>
> test/jdk/java/lang/StringBuffer/IndexOf.java line 28:
> 
>> 26:  * @summary Test indexOf and lastIndexOf
>> 27:  * @run main/othervm IndexOf
>> 28:  * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -Xcomp -XX:-TieredCompilation -XX:UseAVX=2 -XX:+UnlockDiagnosticVMOptions -XX:+EnableX86ECoreOpts IndexOf
> 
> I suggest to split it into 2 subtest jobs and use `@requires vm.cpu.features ~= ".*avx2.*"` for second which specified `-XX:UseAVX=2`.
> See `compiler/loopopts/superword/TestDependencyOffsets.java` for example.

Right.  Done.  Also added `@requires vm.compiler2.enabled` since my stub is only valid with C2.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16753#discussion_r1613985672