When generating `MethodHandle`-based concatenation expressions in `StringConcatFactory` we can reduce the number of classes generated at runtime by creating small batches of prependers and mixers before binding them into the root expression tree.
Improvements on one-off tests are modest, while the improvement on bootstrapping stress tests can be substantial ([MixedStringCombinations.java](https://gist.github.com/cl4es/08fb581dece3a73e89bfa52337bc4248)): | Build | # classes | Runtime | | ----------- | ----------------- | --------------- | | Baseline | 31119 | 2.942s | | Patch | 16208 | 1.958s | An earlier version of this patch saw a regression in the `StringConcatFactoryBootstraps` microbenchmark. After some refactoring along with the optimizations in #8881 and #8923 that is no longer the case, and allocation pressure is down slightly compared to the baseline on such a repeat-the-same-bootstrap stress test: Baseline: Benchmark Mode Cnt Score Error Units SCFB.makeConcatWithConstants avgt 5 2170.039 ? 117.441 ns/op SCFB.makeConcatWithConstants:?gc.alloc.rate.norm avgt 5 3538.020 ? 4.558 B/op This patch: Benchmark Mode Cnt Score Error Units SCFB.makeConcatWithConstants avgt 5 2144.807 ? 162.685 ns/op SCFB.makeConcatWithConstants:?gc.alloc.rate.norm avgt 5 3184.943 ? 4.495 B/op ------------- Commit messages: - Revert change to HelloClasslist (doesn't affect generation) - Reduce allocation adding in mixers by extracting constant arg lists and caching double arg mixers - De-CHM the prepender and mixer caches - Reduce allocations: Extract constant argument lists, cache base form for two-arg prependers - Refactor, reduce allocations - Merge branch 'master' into scf_chunked - Improve chunking further - Fix mis-merged change - Experiment: Chunk prependers and mixers to reduce number of rebinds and generated LF classes Changes: https://git.openjdk.java.net/jdk/pull/8855/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8855&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8287522 Stats: 390 lines in 2 files changed: 232 ins; 99 del; 59 mod Patch: https://git.openjdk.java.net/jdk/pull/8855.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/8855/head:pull/8855 PR: https://git.openjdk.java.net/jdk/pull/8855
