RFR: 8303401: Add a Vector API equalsIgnoreCase micro benchmark [v4]

[Eirik Bjorsnos]

On Wed, 1 Mar 2023 06:34:20 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

>> This PR suggests we add a vectorized equalsIgnoreCase benchmark to the set of benchmarks in `org.openjdk.bench.jdk.incubator.vector`. This benchmark serves as an example of how vectorization can be useful also in the area of text processing. It takes advantage of the fact that ASCII and Latin-1 were designed to optimize case-twiddling operations.
>> 
>> The code came about during the work on #12632, where vectorization was deemed out of scope.
>> 
>> Benchmark results:
>> 
>> 
>> Benchmark                             (size)  Mode  Cnt     Score   Error  Units
>> EqualsIgnoreCaseBenchmark.scalar          16  avgt   15    20.671 ± 0.718  ns/op
>> EqualsIgnoreCaseBenchmark.scalar          32  avgt   15    46.155 ± 3.258  ns/op
>> EqualsIgnoreCaseBenchmark.scalar          64  avgt   15    68.248 ± 1.767  ns/op
>> EqualsIgnoreCaseBenchmark.scalar         128  avgt   15   148.948 ± 0.890  ns/op
>> EqualsIgnoreCaseBenchmark.scalar        1024  avgt   15  1090.708 ± 7.540  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized      16  avgt   15    21.872 ± 0.232  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized      32  avgt   15    11.378 ± 0.097  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized      64  avgt   15    13.703 ± 0.135  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized     128  avgt   15    21.632 ± 0.735  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized    1024  avgt   15   105.509 ± 7.493  ns/op
>
> Eirik Bjorsnos has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Adjust whitespace as suggested in review
>  - Replace Blackhold.consume with return values

I realized that the `equal.allTrue()` condition is checked early in the loop, so there is no need to include the `equal` in the `equalsIgnoreCase` towards the end the loop. Removing it also gives a small performance improvement:

Before:


Benchmark                             (size)  Mode  Cnt    Score   Error  Units
EqualsIgnoreCaseBenchmark.vectorized    1024  avgt   15  123.753 ± 1.405  ns/op


After:


Benchmark                             (size)  Mode  Cnt    Score   Error  Units
EqualsIgnoreCaseBenchmark.vectorized    1024  avgt   15  118.578 ± 1.960  ns/op

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PR: https://git.openjdk.org/jdk/pull/12790