[vectorIntrinsics+mask] RFR: 8272971: Intrinsification of VectorMask.cast operation for all compatible vector species [v2]

[Ningsheng Jian]

On Mon, 30 Aug 2021 06:23:05 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

> Optimization handles casting operation b/w all compatible mask species i.e. having same vector lengths.
> And we see around 2X speedup over AVX512. IR fragment created for non-predicated targets uses existing VectorCast[B/S/I/L] nodes with appropriate insertion of VectorMaskCast for floating point types but they operate over regular vector operands, should be ok for AARCH64 NEON.
> Do you plan to extend the SVE backend to handle VectorMaskCast operations for various compatible species?

Yes. Currently we don't have different sized mask types conversion support for SVE backend. We can handle that in a follow-up patch. It's unfortunate that existing vector api cases cannot trigger this failure, but your JMH tests did hit that assertion of element size mismatch on SVE system.

> Alternatively as an interim solution I can add a target specific matcher routine Matcher::supports_predicate_reg_cast() and re-write above check as follows.
> 
> ```
>   if (is_mask && dst_type->isa_vectmask() && src_type->isa_vectmask() && !Matcher::supports_predicate_reg_cast()) {
>     return false; // elem size mismatch
>   }
> ```

I think you can also leave it to us to add the SVE backend code and simply fix (remove?) the assertion in https://github.com/openjdk/panama-vector/blob/vectorIntrinsics%2Bmask/src/hotspot/share/opto/vectornode.hpp#L1427

-------------

PR: https://git.openjdk.java.net/panama-vector/pull/113