RFR: 8303401: Add a Vector API equalsIgnoreCase micro benchmark [v7]

[Paul Sandoz]

On Wed, 1 Mar 2023 14:28:55 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    21.575 ± 0.365  ns/op
>> EqualsIgnoreCaseBenchmark.scalar          32  avgt   15    43.199 ± 2.786  ns/op
>> EqualsIgnoreCaseBenchmark.scalar          64  avgt   15    71.389 ± 0.891  ns/op
>> EqualsIgnoreCaseBenchmark.scalar         128  avgt   15   146.827 ± 1.115  ns/op
>> EqualsIgnoreCaseBenchmark.scalar        1024  avgt   15  1062.759 ± 9.331  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized      16  avgt   15    21.483 ± 0.121  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized      32  avgt   15    10.538 ± 0.125  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized      64  avgt   15    13.182 ± 0.177  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized     128  avgt   15    19.192 ± 0.421  ns/op
>> EqualsIgnoreCaseBenchmark.vectorized    1024  avgt   15    92.521 ± 3.494  ns/op
>
> Eirik Bjorsnos has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use GT, LT, EQ operations since they seem to outperform GE, LE, NE.

Benchmark looks good.

I think you need to look at the generated code and perf data to get more insight into the differences you are observing.

Sometimes array alignment can add variance to the results (which may not be the case here), and to rule that out i sometimes run vector tests with the HotSpot option `-XX:ObjectAlignmentInBytes` e.g. `-XX:ObjectAlignmentInBytes=32`.

test/micro/org/openjdk/bench/jdk/incubator/vector/EqualsIgnoreCaseBenchmark.java line 111:

> 109:                     .or(letter.and(upperA.eq(upperB)));
> 110: 
> 111:             if(equalsIgnoreCase.allTrue()) {

Suggestion:

            if (equalsIgnoreCase.allTrue()) {

-------------

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