RFR: 8262355: Support for AVX-512 opmask register allocation. [v3]

[Jatin Bhateja]

On Mon, 29 Mar 2021 06:18:45 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8262355: Creating a new ideal type TypeVectMask for mask generating nodes.
>
> src/hotspot/share/opto/type.hpp line 856:
> 
>> 854: };
>> 855: 
>> 856: class TypeVectMask : public TypeVect {
> 
> Hi, recently we found an issue that some optimizations cannot work well for the floating point VectorMask due to the different element type for different APIs (see: https://github.com/openjdk/jdk/pull/3238).  It might need more consideration for the `hash()/eq()` method `TypeVectMask` especially for SVE.  I guess the current implementation works well for AVX-512? If so, maybe we can have a separate patch to fix it in future once the main mask support codes are merged.

Hi, bitwise operation involving VectorMask nodes (i.e. the nodes with type TypeVectMask) works over predicate registers. Since for x86 opmask register representation is consistent for all primitive types, it may not be a problem. For SVE a different instruction pattern for masks of floating types may suffice.  Yes, we can do refinements in subsequent patches.

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