On Fri, 12 Dec 2025 07:47:12 GMT, Eric Fang <[email protected]> wrote:
>> `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` chain.
>>
>> Current optimizations related to `VectorMaskCastNode` include:
>> 1. `(VectorMaskCast (VectorMaskCast x)) => (x)`, see JDK-8356760.
>> 2. `(XorV (VectorMaskCast (VectorMaskCmp src1 src2 cond)) (Replicate -1)) =>
>> (VectorMaskCast (VectorMaskCmp src1 src2 ncond))`, see JDK-8354242.
>>
>> This PR does the following optimizations:
>> 1. Extends the optimization pattern `(VectorMaskCast (VectorMaskCast x)) =>
>> (x)` as `(VectorMaskCast (VectorMaskCast ... (VectorMaskCast x))) => (x)`.
>> Because as long as types of the head and tail `VectorMaskCastNode` are
>> consistent, the optimization is correct.
>> 2. Supports a new optimization pattern `(VectorStoreMask (VectorMaskCast ...
>> (VectorLoadMask x))) => (x)`. Since the value before and after the pattern
>> is a boolean vect...
>
> 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` chain.
>
> Current optimizations related to `VectorMaskCastNode` include:
> 1. `(V...
Nice work! Thanks for working on this!
Just had a quick glance. Maybe I can do a full review next week.
src/hotspot/share/opto/vectornode.cpp line 1489:
> 1487: Node* VectorStoreMaskNode::Identity(PhaseGVN* phase) {
> 1488: // Identity transformation on boolean vectors.
> 1489: // VectorStoreMask (VectorMaskCast ... VectorLoadMask bv) elem_size
> ==> bv
Suggestion:
// VectorStoreMask (VectorMaskCast* VectorLoadMask bv) elem_size ==> bv
Would a regex star be more explicit about 0 or more repetitions?
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?
-------------
PR Review: https://git.openjdk.org/jdk/pull/28313#pullrequestreview-3572250876
PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2614574171
PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2614577536
