On Mon, 5 Jan 2026 08:14:10 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 12 commits: > > - Update copyright year to 2026 > - Merge branch 'master' into JDK-8370863-mask-cast-opt > - Convert the check condition for vector length into an assertion > > Also refined the tests. > - Refine code comments > - 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 > - ... and 2 more: https://git.openjdk.org/jdk/compare/6eaabed5...9c38a6d9 src/hotspot/share/opto/vectornode.cpp line 1063: > 1061: return n; > 1062: } > 1063: This has a clear parallel in `Node::uncast`. But there, we may recursively uncast. Your pattern: `(VectorStoreMask (VectorMaskCast* (VectorLoadMask x))) => (x)` We could also have a chain of casts here. Can you explain why you chose only to do a single step here? test/hotspot/jtreg/compiler/vectorapi/VectorMaskCastIdentityTest.java line 121: > 119: VectorMask<Integer> mInt128 = > mFloat128.cast(IntVector.SPECIES_128); > 120: return mInt128.not().trueCount(); > 121: } Why can't the casts be eliminated here? Can you please add a comment to the test? ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2730746738 PR Review Comment: https://git.openjdk.org/jdk/pull/28313#discussion_r2730754926
