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

[Ningsheng Jian]

On Thu, 18 Mar 2021 11:46:08 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> I am fine with current code. Since we don't have other SlotsPerRegVMask* yet, we will treat it as variable-sized slots for SVE, which is 1.
>
> Ok, maybe set `SlotsPerRegVMask = 2` unconditionally then?

Since SVE predicate reg size is 1 ~ 8 slots, I think 1 would be better here, which can save one mask bit and make bit mask handling easier (e.g. allocation on stack).

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