RFR: 8318218: RISC-V: C2 CompressBits [v2]

[Ludovic Henry]

On Fri, 3 Nov 2023 12:17:39 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> Hi,
>> Can you review the change to add intrinsic for CompressBits for Long & Integer?
>> Thanks!
>> 
>> ## Test
>> pass jtreg test:
>> test/jdk/java/lang/CompressExpand*.java
>
> Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove the new vm option, using Matcher::match_rule_supported instead; move code to riscv_v.ad and C2_MacroAssembler

src/hotspot/cpu/riscv/riscv.ad line 1897:

> 1895: 
> 1896:     case Op_CompressBits:
> 1897:       return UseRVV && (MaxVectorSize >= 16);

Isn't it guaranteed that `MaxVectorSize >= 16` if `UseRVV` is true?

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PR Review Comment: https://git.openjdk.org/jdk/pull/16481#discussion_r1382702413