RFR: 8324969: assert(false) failed: Non-balanced monitor enter/exit!

[Vladimir Kozlov]

On Wed, 7 Feb 2024 19:17:15 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> > > Doesn't this problem also go away if lock coarsening turns the two regions into a single region?
> > 
> > 
> > If that works that would probably be a more elegant solution. Could there be an invariant that a box always has a lock and an unlock?
> 
> Yes, this is good suggestion. Let me investigate how to implement it. It will allow to eliminate all lock/unlock nodes in nested combined region. The only concern for me is that I have to backport the fix into all releases and if it is too complex I would prefer to go with current "band-aid" fix and have separate RFE to implement this suggestion.

After looking on current code I think this will introduce more issues. In current state we have assumption that with `EliminateNestedLocks` flag ON we have only "one" Lock node per region. Depending when we start merging adjacent region it will break this  assumption.

But I share @eme64 concern that current fix may not work if coarsening eliminates an Unlock node on one of paths but left  Unlock nodes on other paths. The check will pass but we will have unbalanced lock/unlock on the first path.

I think I should just disable nested and not-escaped object lock eliminations if a coarsening elimination happens before it.

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PR Comment: https://git.openjdk.org/jdk/pull/17697#issuecomment-1932918813