RFR: 8319879: Stress mode to randomize incremental inlining decision

[Jatin Bhateja]

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

src/hotspot/share/opto/doCall.cpp line 188:

> 186:     if (!call_does_dispatch) {
> 187:       InlineTree* ilt = InlineTree::find_subtree_from_root(this->ilt(), jvms->caller(), jvms->method());
> 188:       bool should_delay = AlwaysIncrementalInline || (StressIncrementalInlining && (C->random() % 2) == 0);

Any specific reason to keep vector, string , boxing call generators out of scope, I understand that lazy intrinsification gives constants to seep in the graph and enable meeting closed world compilation constraints, but this is a stress testing option,  an eager failed intrinsification will take the control flow to [line# 214](https://github.com/openjdk/jdk/pull/16597/files#diff-3193ffb06a457828099ec450d72afd32942635de23191d70ec3bf3f349ca45feL214) , but only if we randomize creating LateInlineCallGenerators for these APIs.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16597#discussion_r1392099524