RFR: 8262355: Support for AVX-512 opmask register allocation. [v14]

[Vladimir Ivanov]

On Tue, 23 Mar 2021 07:25:33 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: Extending Type::isa_vect and Type::is_vect routines to TypeVectMask since its a valid vector type.
>
> src/hotspot/share/opto/type.cpp line 2524:
> 
>> 2522:   if (!t->isa_vectmask()) {
>> 2523:     return false;
>> 2524:   }
> 
> Maybe TypeVect::eq/hash also need to have such check?

No need in the check (neither in `TypeVect` nor in `TypeVectMask`): `Type::eq()` relies on `Type::cmp()` to ensure all casts succeed and `Type::cmp()` compares `Type::_base` which differ for vectors and masks (`Vector[SDXYZA]` vs `VectorM`). 

Nevertheless, it can be turned into an assert to stress the invariant.

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