RFR: 8262355: Support for AVX-512 opmask register allocation. [v4]

[Jatin Bhateja]

On Wed, 10 Mar 2021 07:25:42 GMT, Ningsheng Jian <njian at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8262355: Some synthetic changes for cleanup.
>
> src/hotspot/share/opto/type.hpp line 859:
> 
>> 857: public:
>> 858:   friend class TypeVect;
>> 859:   TypeVectMask(const Type* elem, uint length) : TypeVect(VectorM, elem, length) {}
> 
> Any reason why TypeVectMask is a subclass of TypeVect? Do existing helper functions in TypeVect also work for TypeVectMask, e.g. xmeet.

For targets which do not support predicated registers, masks are propagated though vectors. Thus inheriting it seemed logical extension for mask type.

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