RFR: 8346664: C2: Optimize mask check with constant offset [v12]

[Emanuel Peter]

On Fri, 31 Jan 2025 06:28:03 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Matthias Ernst has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   "should never vectorize" only holds for long[] input.
>
> test/hotspot/jtreg/compiler/loopopts/superword/TestEquivalentInvariants.java line 880:
> 
>> 878:         applyIfCPUFeatureOr = {"sse4.1", "true", "asimd", "true"})
>> 879:     // Would be nice if it vectorized.
>> 880:     // Fails because of control flow. Somehow the "offsetPlain" check (checks for alignment) is not folded away.
> 
> Suggestion:
> 
>     // With AlignVector (strict alignment requirements): we cannot prove that the invariants are alignable -> no vectorization.

Check where else this applies too now ;)

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PR Review Comment: https://git.openjdk.org/jdk/pull/22856#discussion_r1936743851