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

[Vladimir Ivanov]

On Tue, 16 Mar 2021 19:08:58 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> 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.

But then RA has to allocate a k-register irrespective of whether AVX512 is supported or not, doesn't it?

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