RFR: 8262355: Support for AVX-512 opmask register allocation. [v12]

[Vladimir Ivanov]

On Fri, 19 Mar 2021 14:33:10 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

> On a second thought, we may enforce strict base type constraint (base >= VectorA && < base <= VectorZ) on TypeVect::isa_vect routine, but TypeVect::is_vect should be relaxed to include TypeVectorMask , considering TypeVectMask is a subclass of TypeVect and thus qualifies to be a vector type. It will simplify adding conditional checks across the code.

The assert ensures the safety of the cast. Since the range for `TypeVect::_base` includes `VectorM`, it doesn't make much sense to artificially strengthen the assert and exclude it until `TypeVectMask` is a subtype of `TypeVect`.

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