RFR: 8316361: C2: assert(!failure) failed: Missed optimization opportunity in PhaseIterGVN with -XX:VerifyIterativeGVN=10

[Christian Hagedorn]

On Fri, 22 Sep 2023 10:47:00 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> This seems to be related to [JDK-8298176](https://bugs.openjdk.org/browse/JDK-8298176) / https://github.com/openjdk/jdk20/pull/65
> This change allows `OpaqueZeroTripGuard -> CmpI` to fold in some cases. We have also added code to notify the `CmpI` during IGVN, so it can potentially change its type/constant fold:
> https://github.com/openjdk/jdk/blob/a0a09d56ba4fc6133b423ad29d86fc99dd6dc19b/src/hotspot/share/opto/phaseX.cpp#L1681-L1687
> 
> However, when we hack the input to the `opaq` node, we must call `_igvn.add_users_to_worklist` to trigger this notification. I added this missing part.
> 
> Running Tier1-6 and stress testing...

Looks good!

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Marked as reviewed by chagedorn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/15886#pullrequestreview-1641841641