RFR: 8298920: Improve microbenchmark build times [v2]

[Jan Lahoda]

> Currently incremental builds for the microbenchmarks may take notable amount of time, like:
> 
> $ touch test/micro/org/openjdk/bench/java/io/BlackholedOutputStream.java; time make test TEST=jaxp:tier1
> Building target 'test' in configuration 'linux-x86_64-server-release'
> Compiling up to 656 files for BUILD_JDK_MICROBENCHMARK
> Running Indify on microbenchmark classes
> [snip]
> ==============================
> Test summary
> ==============================
>    TEST                                              TOTAL  PASS  FAIL ERROR
>    jtreg:test/jaxp:tier1                                 0     0     0     0
> ==============================
> TEST SUCCESS
> 
> Finished building target 'test' in configuration 'linux-x86_64-server-release'
> 
> real    0m37,581s
> user    2m4,747s
> sys     0m7,223s
> 
> 
> The microbenchmark compilation is not using the `Depend` plugin that avoids recompilation of other files if the change files only contain minor changes (i.e. non-API changes). The patch here proposes to enhance the build to use the `Depend` plugin. The change that enables that is `CREATE_API_DIGEST := true,`, but since both the `Depend` plugin and JMH framework needs to be added to the classpath the patch re-organizes the code a little to properly augment the classpath.
> 
> With this patch, a build similar to the above might be:
> 
> $ touch test/micro/org/openjdk/bench/java/io/BlackholedOutputStream.java; time make test TEST=jaxp:tier1
> Building target 'test' in configuration 'linux-x86_64-server-release'
> Compiling up to 656 files for BUILD_JDK_MICROBENCHMARK
> Running Indify on microbenchmark classes
> [snip]
> ==============================
> Test summary
> ==============================
>    TEST                                              TOTAL  PASS  FAIL ERROR
>    jtreg:test/jaxp:tier1                                 0     0     0     0
> ==============================
> TEST SUCCESS
> 
> Finished building target 'test' in configuration 'linux-x86_64-server-release'
> 
> real    0m7,505s
> user    0m14,128s
> sys     0m3,158s

Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:

  Fixing classpath for incremental microbenchmark build.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20616/files
  - new: https://git.openjdk.org/jdk/pull/20616/files/3f6875cb..f21c2b76

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20616&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20616&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20616.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20616/head:pull/20616

PR: https://git.openjdk.org/jdk/pull/20616