RFR: 8305189: C2 failed "assert(_outcnt==1) failed: not unique" [v2]

[Roland Westrelin]

On Mon, 15 May 2023 13:39:12 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> I see the following failure with `TestMissingMulLOptimization` from JDK-8299546 and `-XX:StressLongCountedLoop=2000000`:

What happens here is that a counted loop ends up in an infinite loop. So the `IdealLoopTree` tree object is unreachable from the root loop (for this round of loop opts as a `NeverBranch` is added so the `IdealLoopTree`  should become reachable again at next pass of loop opts). So the new logic removes an opaque node for a loop that still exists. I suppose it's rare and mostly harmless and I tweaked the assert to cover that corner case.

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PR Comment: https://git.openjdk.org/jdk/pull/13901#issuecomment-1557431091