RFR: 8353600: RISC-V: compiler/vectorization/TestRotateByteAndShortVector.java is failing with Zvbb [v3]

[Fei Yang]

On Thu, 3 Apr 2025 13:49:05 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> Hi,
>> Can you help to review this patch?
>> 
>> Currently, the followign code is considered an RotateLeftV of byte by hotspot, but it's not a real rotate, as the `-shift` will 30, which makes `b >> -shift` zero, rather the value we expected.
>> 
>> int shift = 2;
>> byte b = 83;
>> byte res = (byte) (b << shift | b >> -shift); // res = 76
>> // but a real left rotate of 83 should be 77 ??
>> ``` 
>> 
>> So, the simple fix is to enable RotateLeftV only for  int and long, disable it for other types.
>> 
>> <del>A more rational fix should be change C2 to not convert code like ` (byte) (b << shift | b >> -shift)` to a RotateLeftV node, but it needs more investigation, and I'm not sure if it's feasible to do so, as currently no platform support RotateLeftV for non-int/long types.</del>
>> 
>> The vector instruction behaviour is different from java language spec, so seems there is no way to do it for now.
>> 
>> Thanks!
>
> Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:
> 
>   comment

LGTM. Thanks for fixing this!

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Marked as reviewed by fyang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24414#pullrequestreview-2745410453