RFR: 8262355: Support for AVX-512 opmask register allocation. [v8]

[Jatin Bhateja]

On Tue, 16 Mar 2021 13:08:04 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8262355: Removing object re-materialization handling for mask-generating nodes during de-opt, it will be added separately.
>
> src/hotspot/cpu/x86/x86_64.ad line 10922:
> 
>> 10920: // =======================================================================
>> 10921: // fast clearing of an array
>> 10922: instruct rep_stos(rcx_RegL cnt, rdi_RegP base, regD tmp, kReg ktmp, rax_RegI zero,
> 
> I'm curious how it works w/o AVX512 considering`rep_stos` and others are not AVX512-specific AD instructions.

Instructions using kReg temp are all guarded by UseAVX > 2 checks. Thus they are never JITed.

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PR: https://git.openjdk.java.net/jdk/pull/2768