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

[Emanuel Peter]

On Tue, 27 Jan 2026 03:06:32 GMT, Jasmine Karthikeyan <jkarthikeyan at openjdk.org> wrote:

>> Filed:
>> [JDK-8376179](https://bugs.openjdk.org/browse/JDK-8376179): C2 SuperWord: improve subword vectorization, avoid cast to-and-from int
>
> We wouldn't be able to remove the casts in this case because `CountLeadingZeros` [doesn't support truncation](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/superword.cpp#L2506), so the cast to and from int is required for correctness.

Ah ok, got it. Makes sense :)

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PR Review Comment: https://git.openjdk.org/jdk/pull/23413#discussion_r2730528557