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

[Evgeny Astigeevich]

On Mon, 13 May 2024 13:03:26 GMT, Evgeny Astigeevich <eastigeevich at openjdk.org> wrote:

> Backout of [JDK-8309271](https://bugs.openjdk.org/browse/JDK-8309271) which has known bugs, possible bugs and performance issues. REDO work is tracked by [JDK-8331749](https://bugs.openjdk.org/browse/JDK-8331749).
> 
> 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.

There is no `PrintOptoAssembly` in output.
I use `lockCompilation()`/`unlockCompilation()` to simulate:
> A Java method with old directives might be in the compilation queue. A request to recompile it with new directives will be ignored.

I think using them we can also simulate, though it would not be easy to write a test:
> JIT compiler might be compiling a Java method with old directives. A request to recompile it with new directives will be ignored.

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PR Comment: https://git.openjdk.org/jdk/pull/19215#issuecomment-2108759073