On Thu, 18 May 2023 09:50:13 GMT, Chang Peng <d...@openjdk.org> wrote:
>> 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_vect... > > Chang Peng has updated the pull request incrementally with one additional > commit since the last revision: > > Update benchmark to avoid potential optimization Marked as reviewed by aph (Reviewer). src/hotspot/cpu/aarch64/aarch64_vector_ad.m4 line 3825: > 3823: %} > 3824: > 3825: // Combined rule for VectorStoreMask + VectorMaskTrueCount when the > vector element type is not T_BYTE. Suggestion: // Combined rule for VectorMaskTrueCount (VectorStoreMask) when the vector element type is not T_BYTE. Using `+` is unnecessarily confusing, as is swapping the operands. ------------- PR Review: https://git.openjdk.org/jdk/pull/13974#pullrequestreview-1443414797 PR Review Comment: https://git.openjdk.org/jdk/pull/13974#discussion_r1205210387
