RFR: 8319879: Stress mode to randomize incremental inlining decision

[Tobias Hartmann]

On Fri, 10 Nov 2023 09:12:19 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> We had quite a few C2 bugs in the past that only reproduced with a specific sequence of incremental inlining (for example, [JDK-8319764](https://bugs.openjdk.org/browse/JDK-8319764)). We should randomize the incremental inlining decision to trigger these code paths more frequently.
> 
> I did some testing with the flag enabled and I hit [JDK-8319764](https://bugs.openjdk.org/browse/JDK-8319764) and [JDK-8319889](https://bugs.openjdk.org/browse/JDK-8319889). I think it's still valuable to integrate this even if these bugs are not resolved yet.
> 
> Thanks,
> Tobias

Thanks for looking at this, Vladimir.

> I wish it was one flag - too much duplication. But I see why you separated them: to get randomness only if AlwaysIncrementalInline is not specified. If AlwaysIncrementalInline was tuple {false | true | random} it would solve this.

Right, a tuple would be better but then again we might want to merge all these stress flags into one flag at some point. For simplicity (and backport-ability), let's keep them separated for now and do a cleanup later. There's more to come, especially in the area of loop opts.

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PR Comment: https://git.openjdk.org/jdk/pull/16597#issuecomment-1809653648