RFR: 8283187: C2: loop candidate for superword not always unrolled fully if superword fails [v2]

[Christian Hagedorn]

On Wed, 23 Mar 2022 07:36:20 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> This fixes the issue:
> 
> ```
> - * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI compiler.c2.irTests.TestSuperwordFailsUnrolling
> + * @run main/othervm -Xbootclasspath/a:. -DSkipWhiteBoxInstall=true -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI compiler.c2.irTests.TestSuperwordFailsUnrolling
> ```
> 
> @chhagedorn Maybe the IR verification framework could detect this automatically?

Yes, it would be good to extend the framework to handle this. I added this `-DSkipWhiteBoxInstall` flag at some point to prevent the problem above but was more of a quick fix. I will follow up with an RFE to make this better without the need to use `-DSkipWhiteBoxInstall`.

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PR: https://git.openjdk.java.net/jdk/pull/7822