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

[Emanuel Peter]

On Fri, 31 Jan 2025 06:17:30 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/vectorization/TestPopulateIndex.java line 117:
> 
>> 115: 
>> 116:     @Test
>> 117:     // Currently disabled due to sum-under-mask optimization.
> 
> Suggestion:
> 
>     // Does not vectorize: due to sum-under-mask optimization.
>     // (i+0) & 7, (i+1) & 7 ... (i+8) & 7 ....  -> PopulateIndex
>     // becomes
>     // (i+0) & 7, (i+1) & 7 ... (i+0) & 7 .... -> pattern broken
>     // See JDK-8349128.

@mernst-github Did you drop the `// See JDK-8349128.` on purpose?

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PR Review Comment: https://git.openjdk.org/jdk/pull/22856#discussion_r1936826982