RFR: 8342095: Add autovectorizer support for subword vector casts [v15]

[Emanuel Peter]

On Fri, 23 Jan 2026 08:59:41 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> test/hotspot/jtreg/compiler/vectorization/TestRotateByteAndShortVector.java line 122:
>> 
>>> 120:     @IR(counts = { IRNode.LOAD_VECTOR_B, IRNode.VECTOR_SIZE + "min(max_int, max_byte)", "> 0",
>>> 121:                    IRNode.ROTATE_LEFT_V, "> 0" },
>>> 122:         applyIfCPUFeature = {"avx512f", "true"})
>> 
>> We could also improve things here, right? Or is there a reason why we need to cast from and to int?
>> 
>> Do you agree that we should file an RFE to track this?
>
> Can you add the current issue/bug/RFE number to all the files JTREG `@bug` annotations, please :)

Filed:
[JDK-8376179](https://bugs.openjdk.org/browse/JDK-8376179): C2 SuperWord: improve subword vectorization, avoid cast to-and-from int

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PR Review Comment: https://git.openjdk.org/jdk/pull/23413#discussion_r2720385001