RFR: 8346664: C2: Optimize mask check with constant offset [v8]

[Matthias Ernst]

On Thu, 30 Jan 2025 12:33:16 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> Why don't you try tweaking the IR rules until they pass on your machine.

Done. This affected three scenarios int/long 3d 3d2 and 3e, and only under -XX:-AlignVector. I have no insight why that is, my changes (split each scenario) only reflect what I observed. Also, 3e's setup says it should actually never vectorize; this needs special attention, something must be off.

> * I'm ok with disabling the IR rules in `TestPopulateIndex.java` for `exprWithIndex1`.
> * But create another IR test with `i | 7` instead of `i & 7`, which should still vectorize and pass with IR rules, as it does not trigger your optimization.

Done, I verified that it compiles/checks, but IR tests @require something I don't seem to have.

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PR Comment: https://git.openjdk.org/jdk/pull/22856#issuecomment-2624699193