On Wed, 28 Jan 2026 01:49:52 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 incrementally with one additional
> commit since the last revision:
>
> Add clearer comments to VectorMaskCastIdentityTest.java
test/hotspot/jtreg/compiler/vectorapi/VectorStoreMaskIdentityTest.java line 288:
> 286: @IR(counts = { IRNode.VECTOR_LOAD_MASK, "= 0",
> 287: IRNode.VECTOR_STORE_MASK, "= 0",
> 288: IRNode.VECTOR_MASK_CAST, "= 0" },
Can we also check `IRNode.LOAD_VECTOR` to make sure these APIs are intrinsified
successfully, and the nodes are eliminated by `VectorStoreMask::Identity()` ?
Because if these APIs are not intrinsified due to some reasons, above IRs do
not exist as well.
test/hotspot/jtreg/compiler/vectorapi/VectorStoreMaskIdentityTest.java line 289:
> 287: IRNode.VECTOR_STORE_MASK, "= 0",
> 288: IRNode.VECTOR_MASK_CAST, "= 0" },
> 289: applyIfCPUFeatureOr = { "asimd", "true", "avx2", "true" },
This might not affect the result because it has `applyIf = { "MaxVectorSize",
"> 16" }` check additionally. But it will more accurate if:
Suggestion:
applyIfCPUFeatureOr = { "sve", "true", "avx2", "true" },
because the max vector size for neon is 16-byte.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2753114650
PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2753117731
