RFR: 8262355: Support for AVX-512 opmask register allocation. [v20]

[Jatin Bhateja]

On Sun, 4 Apr 2021 03:30:58 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> In general looks better.
> But it seems you added new instructions into .ad files for ClearArray and String compare which was not in original changes and should not be.

Hi @vnkozlov ,

Thanks for reviewing the patch,  new instruction pattern hold a temporary opmask operand needed only for AVX512 flovour of instruction. 
Earleir same pattern was being used for non-AVX512 instruction which could have posed issues while accessing the encoding for these temporaries in emit routines  using as_KRegister()(as pointed by @iwanowww) which internally asserts is_KRegister() having UseAVX > 2 check.
We can look at opportunities to reducing redundancies around these new instruction pattern (if any) in subsiquent patches.

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