RFR: 8346475: RISC-V: Small improvement for MacroAssembler::ctzc_bit [v3]

[Hamlin Li]

On Wed, 18 Dec 2024 14:38:57 GMT, Fei Yang <fyang at openjdk.org> wrote:

>> Hi, please review this small improvement.
>> 
>> When `step` is 16, the `andi` instruction in the loop performs a bitwise AND with immediate mask value 0xFFFF. This will emit 3 instructions. It's effectively a zero extension operation and could be reduced to 1 or 2 instructions repectively depending on whether Zbb extension is available. And there is no difference when `step` is 8 with this change.
>> 
>> Testing: tier1 and gtest:all are clean on Premier-P550 SBC running Ubuntu-24.04.
>
> Fei Yang has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Review comments
>  - Review comments

Looks good, thanks for updating!

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Marked as reviewed by mli (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22800#pullrequestreview-2512097646