RFR: 8370227: Migrate micros-javac benchmarks from jmh-jdk-microbenchmarks [v3]

[Adam Sotona]

On Wed, 22 Oct 2025 13:22:32 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> To improve and consolidate workflow this PR proposes moving micros-javac from https://github.com/openjdk/jmh-jdk-microbenchmarks into the main OpenJDK tree.
>> 
>> Most of jmh-jdk-microbenchmarks was effectively migrated in-tree as part of https://openjdk.org/jeps/230 
>> These javac benchmarks, however, were added after migration as a stop-gap solution: they rely on an antrun task to download a configurable set of JDK source files deemed problematic to integrate with the JDK build and the resulting benchmark jar is quite bulky (~52M), so unconditionally piling that on the test image built on every change seems unwise.
>> 
>> Proposal:
>> - The JMH benchmarks are moved over as-is along with a flattened and updated maven pom.xml into a new non-jtreg test root, `test/benchmarks/micros-javac`
>> - Any integration with the JDK build is deferred to a future enhancement. I.e., no integration with `make test` or equivalent of `make micros-javac` for now. Instead users of these benchmarks are encouraged to build the benchmarks by running `mvn install` in the `micros-javac` folder, similar to what you would do today in the jmh-jdk-microbenchmarks project.
>
> Claes Redestad has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Tabs not allowed
>  - Missing comma

Marked as reviewed by asotona (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/27917#pullrequestreview-3365813147