RFR: 8318509: x86 count_positives intrinsic broken for -XX:AVX3Threshold=0

[Jatin Bhateja]

On Thu, 19 Oct 2023 17:25:18 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp line 3888:
>> 
>>> 3886:       mov64(tmp3_aliased, 0xFFFFFFFFFFFFFFFF);
>>> 3887:       shlxq(tmp3_aliased, tmp3_aliased, tmp1);
>>> 3888:       notq(tmp3_aliased);
>> 
>> We can replace these two instructions with BZHI under BMI2 check.
>
> We probably shouldn't do incremental enhancements in this PR. For code enhancements to make much sense we also need a plan to refactor this so that this AVX-512 version can be enabled in production modes (when/if it makes sense).

sounds good.,

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PR Review Comment: https://git.openjdk.org/jdk/pull/16267#discussion_r1368569718