> In Vector API Java level, vector mask is represented as a boolean array with > 0x00/0x01 (8 bits of each element) as values, aka in-memory format. When it > is loaded into vector register, e.g. Neon, the in-memory format will be > converted to in-register format with 0/-1 value for each lane (lane width > aligned to its type) by VectorLoadMask [1] operation, and convert back to > in-memory format by VectorStoreMask[2]. In Neon, a typical VectorStoreMask > operation will first narrow given vector registers by xtn insn [3] into byte > element type, and then do a vector negate to convert to 0x00/0x01 value for > each element. > > For most of the vector mask operations, the input mask is in-register format. > And a vector mask also works in-register format all through the compilation. > But for some operations like VectorMask.trueCount()[4] which counts the > elements of true value, the expected input mask is in-memory format. So a > VectorStoreMask is generated to convert the mask from in-register format to > in-memory format before those operations. > > However, for trueCount() these xtn instructions in VectorStoreMask can be > saved, since the narrowing operations will not influence the number of active > lane (value of 0x01) of its input. > > This patch adds an optimized rule `VectorMaskTrueCount (VectorStoreMask > mask)` to save the unnecessary narrowing operations. > > For example, > > > var m = VectorMask.fromArray(IntVector.SPECIES_PREFERRED, ba, 0); > m.not().trueCount(); > > > will produce following assembly on a Neon machine before this patch: > > > ... > mvn v16.16b, v16.16b // VectorMask.not() > xtn v16.4h, v16.4s > xtn v16.8b, v16.8h > neg v16.8b, v16.8b // VectorStoreMask > addv b17, v16.8b > umov w0, v17.b[0] // VectorMask.trueCount() > ... > > > After this patch: > > > ... > mvn v16.16b, v16.16b // VectorMask.not() > addv s17, v16.4s > smov x0, v17.b[0] > neg x0, x0 // Optimized VectorMask.trueCount() > ... > > > In this case, we can save two xtn insns. > > Performance: > > Benchmark Before After Unit > testInt 723.822 ± 1.029 1182.375 ± 12.363 ops/ms > testLong 632.154 ± 0.197 1382.74 ± 2.188 ops/ms > testShort 788.665 ± 1.852 1152.38 ± 3.77 ops/ms > > [1]: > https://github.com/openjdk/jdk/blob/e1e758a7b43c29840296d337bd2f0213ab0ca3c9/src/hotspot/cpu/aarch64/aarch64_vector.ad#L4740 > [2]: https://github.com/openjdk/jdk/b...
Chang Peng has updated the pull request incrementally with one additional commit since the last revision: Update benchmark to avoid potential optimization ------------- Changes: - all: https://git.openjdk.org/jdk/pull/13974/files - new: https://git.openjdk.org/jdk/pull/13974/files/49e35b63..567f69a2 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=13974&range=02 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13974&range=01-02 Stats: 20 lines in 4 files changed: 0 ins; 5 del; 15 mod Patch: https://git.openjdk.org/jdk/pull/13974.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/13974/head:pull/13974 PR: https://git.openjdk.org/jdk/pull/13974
