RFR: 8370863: VectorAPI: Optimize the VectorMaskCast chain in specific patterns [v6]

[Eric Fang]

On Mon, 15 Dec 2025 06:09:26 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Eric Fang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Refine code comments
>
> src/hotspot/share/opto/vectornode.cpp line 1062:
> 
>> 1060:     if (!in1->isa_Vector()) {
>> 1061:       break;
>> 1062:     }
> 
> Can you write a comment here, why you want to avoid handling masks of type TypeVectMask ?

Hi, @jatin-bhateja, I didn't quite understand what you meant. I'm not sure if you mistook `isa_Vector` for `isa_vectormask`. Checking `isa_Vector` here is to ensure that `in1` is a `VectorNode`, so that it calls the `as_Vector` function.

> src/hotspot/share/opto/vectornode.cpp line 1063:
> 
>> 1061:       break;
>> 1062:     }
>> 1063:     assert(n->as_Vector()->length() == in1->as_Vector()->length(), "vector length must match");
> 
> While assertions are good to add, but mask cast is a lanewise operation, i.e. length compatibility is implied, and adding an assertion for IR invariants is redundant.

My main concern here is that the requirement for `VectorMaskCastNode` to have the same length for both input and output might have been removed in the future. I'm not sure, but we do require the lengths to be the same here, so I added this assertion. @eme64  has a similar comment; see https://github.com/openjdk/jdk/pull/28313/changes#r2614577536. So, if you all think that the requirement for lane length in `VectorMaskCastNode` won't be removed, then we can delete this assertion and the condition below.

> test/hotspot/jtreg/compiler/vectorapi/VectorStoreMaskIdentityTest.java line 186:
> 
>> 184:         testThreeCastsKernel(IntVector.SPECIES_128, ShortVector.SPECIES_64, FloatVector.SPECIES_128, LongVector.SPECIES_256);
>> 185:         verifyResult(IntVector.SPECIES_128.length());
>> 186:     }
> 
> A nit, you can define final static species like S128, S64 pointing to fully qualified species, it will reduce the verbosity.

Make sense, I'll do the change in the next commit.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2618171442
PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2618189379
PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2618195582