RFR: 8357554: Enable vectorization of Bool -> CMove with different type size (on riscv)

[Hamlin Li]

On Tue, 3 Jun 2025 13:50:07 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Thanks for the information!
>> I'll hold off these prs until integer CMove vectorization is fully supported.
>> 
>> At first, I also just planned to implement the CMoveF/D on riscv and let it automatically vectorized based on current C2 implementation.
>> But, I found some performance regression in the cases of some type combination (please check the `table 1` below), the reason is that for some type combination cmoveF/D can not be vectorized, because of the type size check in `SuperWord::is_velt_basic_type_compatible_use_def`, on the other hand scalar implementation of CMoveF/D on riscv explode the generated code after loop unroll (because of the complicated implmentation on riscv). These 2 reasons will lead to the performance regression in some cases.
>> 
>> table 1
>> <google-sheets-html-origin style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0); font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;">
>> Can be vectorized? | CMoveF | CMoveD
>> -- | -- | --
>> CmpI | V | X
>> CmpU | V | X
>> CmpL | X | V
>> CmpUL | X | V
>> CmpF | V | X
>> CmpD | X | V
>> CmpN | V | X
>> CmpP | X | V
>> 
>> </google-sheets-html-origin>
>
> Yes, getting this all right and with optimal performance is tricky... @jaskarth is working on https://github.com/openjdk/jdk/pull/23413, which will make changes to `SuperWord::is_velt_basic_type_compatible_use_def` ... so  we also will have to see how this plays together...

Yes, it is.
Thank you for discussion!

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PR Review Comment: https://git.openjdk.org/jdk/pull/25336#discussion_r2123908890