On Fri, 12 Dec 2025 15:13:35 GMT, Emanuel Peter <[email protected]> wrote:
>> Eric Fang has updated the pull request with a new target base due to a merge
>> or a rebase. The pull request now contains eight commits:
>>
>> - Merge branch 'master' into JDK-8370863-mask-cast-opt
>> - Merge branch 'master' into JDK-8370863-mask-cast-opt
>> - Add MaxVectorSize IR test condition for VectorStoreMaskIdentityTest.java
>> - Refine the test code and comments
>> - Merge branch 'master' into JDK-8370863-mask-cast-opt
>> - Don't read and write the same memory in the JMH benchmarks
>> - Merge branch 'master' into JDK-8370863-mask-cast-opt
>> - 8370863: VectorAPI: Optimize the VectorMaskCast chain in specific patterns
>>
>> `VectorMaskCastNode` is used to cast a vector mask from one type to
>> another type. The cast may be generated by calling the vector API `cast`
>> or generated by the compiler. For example, some vector mask operations
>> like `trueCount` require the input mask to be integer types, so for
>> floating point type masks, the compiler will cast the mask to the
>> corresponding integer type mask automatically before doing the mask
>> operation. This kind of cast is very common.
>>
>> If the vector element size is not changed, the `VectorMaskCastNode`
>> don't generate code, otherwise code will be generated to extend or narrow
>> the mask. This IR node is not free no matter it generates code or not
>> because it may block some optimizations. For example:
>> 1. `(VectorStoremask (VectorMaskCast (VectorLoadMask x)))`
>> The middle `VectorMaskCast` prevented the following optimization:
>> `(VectorStoremask (VectorLoadMask x)) => (x)`
>> 2. `(VectorMaskToLong (VectorMaskCast (VectorLongToMask x)))`, which
>> blocks the optimization `(VectorMaskToLong (VectorLongToMask x)) => (x)`.
>>
>> In these IR patterns, the value of the input `x` is not changed, so we
>> can safely do the optimization. But if the input value is changed, we
>> can't eliminate the cast.
>>
>> The general idea of this PR is introducing an `uncast_mask` helper
>> function, which can be used to uncast a chain of `VectorMaskCastNode`,
>> like the existing `Node::uncast(bool)` function. The funtion returns
>> the first non `VectorMaskCastNode`.
>>
>> The intended use case is when the IR pattern to be optimized may
>> contain one or more consecutive `VectorMaskCastNode` and this does not
>> affect the correctness of the optimization. Then this function can be
>> called to eliminate the `VectorMaskCastNode` ch...
>
> src/hotspot/share/opto/vectornode.cpp line 1492:
>
>> 1490: // vector[n]{bool} => vector[n]{t} => vector[n]{bool}
>> 1491: Node* in1 = VectorNode::uncast_mask(in(1));
>> 1492: if (in1->Opcode() == Op_VectorLoadMask && length() ==
>> in1->as_Vector()->length()) {
>
> Can there be a mismatch with the length? Can you give me an example?
Hi @eme64 , I’d really appreciate hearing your thoughts on this when you have a
moment.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2644986216
