RFR: 8290964: C2 compilation fails with assert "non-reduction loop contains reduction nodes"

[Christian Hagedorn]

On Mon, 3 Oct 2022 13:41:07 GMT, Roberto Castañeda Lozano <rcastanedalo at openjdk.org> wrote:

> This changeset removes the [reduction information consistency assertion](https://github.com/openjdk/jdk/blob/46633e644a8ab94ceb75803bd40739214f8a60e8/src/hotspot/share/opto/superword.cpp#L2458-L2459) in `SuperWord::output()`, which has proven to report too many false positives (inconsistencies that do not lead to miscompilation) since its introduction by [JDK-8279622](https://bugs.openjdk.org/browse/JDK-8279622), despite the efforts to reduce the false positive rate in [JDK-8286177](https://bugs.openjdk.org/browse/JDK-8286177). During the time the assertion has been enabled in our internal CI system, no true positive case (reported inconsistencies actually leading to a miscompilation or a crash) has been observed.
> 
> An alternative solution would be to wait for [JDK-8287087](https://bugs.openjdk.org/browse/JDK-8287087) (work in progress), which proposes a refactoring of the reduction analysis logic that eliminates by construction the need for this assertion. This changeset proposes removing the assertion earlier, to reduce noise in test environments.
> 
> #### Testing
> 
> - hs-tier1 (windows-x64, linux-x64, linux-aarch64, and macosx-x64).

That makes sense, looks good!

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Marked as reviewed by chagedorn (Reviewer).

PR: https://git.openjdk.org/jdk/pull/10535