[vectorIntrinsics] RFR: RFC: Vector API masking support proposal for Arm SVE [v3]

[Xiaohong Gong]

On Mon, 15 Mar 2021 02:17:53 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/aarch64_sve.ad line 377:
>> 
>>> 375: instruct vmask2vector(vReg dst, pRegGov pg) %{
>>> 376:   predicate(UseSVE > 0);
>>> 377:   match(Set dst (MaskToVector pg));
>> 
>> We already have VectorLoadMask and VectorStoreMask nodes which have same semantics as Mask2Vector and Vector2Mask operation. Can you please elaborate the need for these new nodes.
>
> Thanks for your comment about this. `VectorLoadMask` and `VectorStoreMask` are vector nodes that have the `TypeVect` type, while `Vector2Mask` is a mask node that have the `TypeVMask` type.  For SVE, the two new added nodes are used for conversions between vector register and predicate register, e.g. `Mask2Vector` for `predicate -> vector` and `Vector2Mask` for `vector -> predicate`. Yes, it seems `VectorLoadMask` and `VectorStoreMask` can match the same requirements like what have been done in the AVX-512 patch. However, in our whole proposal, we defined different IRs to separate vector and mask operations. I think the main conflict is the IR part for mask. And it's better to get a final solution to the different operations together for SVE and AVX-512.

Note that `MaskToVector` can be used for API `VectorMask.toVector()` in future which is implemented with `blend` currently.

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

PR: https://git.openjdk.java.net/panama-vector/pull/40