RFR: 8332111: [BACKOUT] A way to align already compiled methods with compiler directives

Evgeny Astigeevich eastigeevich at openjdk.org
Mon May 13 13:11:15 UTC 2024


Backout of [JDK-8309271](https://bugs.openjdk.org/browse/JDK-8309271) which has known bugs, possible bugs and performance issues.

Found bugs:
- When refreshing `CompilerDirectivesAddDCmd::execute` will call `DirectivesStack::hasMatchingDirectives(mh, true)` which only considers the compiler directive which is on the top of the directives stack. As more than one directive can be added, `CompilerDirectivesAddDCmd::execute` will not behave as expected.
- A Java method with old directives might be in the compilation queue. A request to recompile it with new directives will be ignored.

There are other concerns: bugs and performance issues.

Possible bugs:
- `has_matching_directives` might not be cleared. A nmethod might get into the unloading state before `CodeCache::recompile_marked_directives_matches`. If the nmethod has been used to mark a Java method and it is the only nmethod, there will be no nmethod in CodeCache to reach the Java method to clear the mark.
- A Java method might have been compiled with new directives before `CodeCache::recompile_marked_directives_matches`. `CodeCache::recompile_marked_directives_matches` will recompile it again.
- JIT compiler might be compiling a Java method with old directives. A request to recompile it with new directives will be ignored.

Performance issues:
- Usually directives are updated for a small number of Java methods. If CodeCache has thousands of nmethods, `CodeCache::recompile_marked_directives_matches` will be traversing nmethods most of which don't need recompilation.

The backout is not clean because of removal of `CompiledMethod`.

Tested with release and fastdebug builds: tier1  and tier2 passed.

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

Commit messages:
 - 8332111: [BACKOUT] A way to align already compiled methods with compiler directives

Changes: https://git.openjdk.org/jdk/pull/19215/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19215&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332111
  Stats: 380 lines in 15 files changed: 3 ins; 347 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/19215.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19215/head:pull/19215

PR: https://git.openjdk.org/jdk/pull/19215


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