Hi,
> -----Original Message-----
> From: Pengxuan Zheng <quic_pzh...@quicinc.com>
> Sent: Friday, June 14, 2024 12:57 AM
> To: gcc-patches@gcc.gnu.org
> Cc: Pengxuan Zheng <quic_pzh...@quicinc.com>
> Subject: [PATCH v3] aarch64: Add vector popcount besides QImode [PR113859]
>
> This patch improves GCC’s vectorization of __builtin_popcount for aarch64
> target
> by adding popcount patterns for vector modes besides QImode, i.e., HImode,
> SImode and DImode.
>
> With this patch, we now generate the following for V8HI:
> cnt v1.16b, v.16b
> uaddlp v2.8h, v1.16b
>
> For V4HI, we generate:
> cnt v1.8b, v.8b
> uaddlp v2.4h, v1.8b
>
> For V4SI, we generate:
> cnt v1.16b, v.16b
> uaddlp v2.8h, v1.16b
> uaddlp v3.4s, v2.8h
>
> For V2SI, we generate:
> cnt v1.8b, v.8b
> uaddlp v2.4h, v1.8b
> uaddlp v3.2s, v2.4h
>
> For V2DI, we generate:
> cnt v1.16b, v.16b
> uaddlp v2.8h, v1.16b
> uaddlp v3.4s, v2.8h
> uaddlp v4.2d, v3.4s
Nice patch! We can do better for these sequences though. Would you instead
consider using udot with a 0 accumulator and 1 multiplicatent.
Essentially
movi v0.16b, #0
movi v1.16b, #1
cnt v3.16b, v2.16b
udot v0.4s, v3.16b, v1.16b
this has 1 instruction less on the critical path so should be half the latency
of the uaddlp variants.
For the DI case you'll still need a final uaddlp.
Cheers,
Tamar
>
> PR target/113859
>
> gcc/ChangeLog:
>
> * config/aarch64/aarch64-simd.md (aarch64_<su>addlp<mode>):
> Rename to...
> (@aarch64_<su>addlp<mode>): ... This.
> (popcount<mode>2): New define_expand.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/aarch64/popcnt-vec.c: New test.
>
> Signed-off-by: Pengxuan Zheng <quic_pzh...@quicinc.com>
> ---
> gcc/config/aarch64/aarch64-simd.md | 28 +++++++-
> gcc/testsuite/gcc.target/aarch64/popcnt-vec.c | 69 +++++++++++++++++++
> 2 files changed, 96 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.target/aarch64/popcnt-vec.c
>
> diff --git a/gcc/config/aarch64/aarch64-simd.md b/gcc/config/aarch64/aarch64-
> simd.md
> index 0bb39091a38..ee73e13534b 100644
> --- a/gcc/config/aarch64/aarch64-simd.md
> +++ b/gcc/config/aarch64/aarch64-simd.md
> @@ -3461,7 +3461,7 @@ (define_insn
> "*aarch64_<su>addlv<VDQV_L:mode>_ze<GPI:mode>"
> [(set_attr "type" "neon_reduc_add<VDQV_L:q>")]
> )
>
> -(define_expand "aarch64_<su>addlp<mode>"
> +(define_expand "@aarch64_<su>addlp<mode>"
> [(set (match_operand:<VDBLW> 0 "register_operand")
> (plus:<VDBLW>
> (vec_select:<VDBLW>
> @@ -3517,6 +3517,32 @@ (define_insn "popcount<mode>2<vczle><vczbe>"
> [(set_attr "type" "neon_cnt<q>")]
> )
>
> +(define_expand "popcount<mode>2"
> + [(set (match_operand:VDQHSD 0 "register_operand")
> + (popcount:VDQHSD (match_operand:VDQHSD 1 "register_operand")))]
> + "TARGET_SIMD"
> + {
> + /* Generate a byte popcount. */
> + machine_mode mode = <bitsize> == 64 ? V8QImode : V16QImode;
> + rtx tmp = gen_reg_rtx (mode);
> + auto icode = optab_handler (popcount_optab, mode);
> + emit_insn (GEN_FCN (icode) (tmp, gen_lowpart (mode, operands[1])));
> +
> + /* Use a sequence of UADDLPs to accumulate the counts. Each step doubles
> + the element size and halves the number of elements. */
> + do
> + {
> + auto icode = code_for_aarch64_addlp (ZERO_EXTEND, GET_MODE (tmp));
> + mode = insn_data[icode].operand[0].mode;
> + rtx dest = mode == <MODE>mode ? operands[0] : gen_reg_rtx (mode);
> + emit_insn (GEN_FCN (icode) (dest, tmp));
> + tmp = dest;
> + }
> + while (mode != <MODE>mode);
> + DONE;
> + }
> +)
> +
> ;; 'across lanes' max and min ops.
>
> ;; Template for outputting a scalar, so we can create __builtins which can be
> diff --git a/gcc/testsuite/gcc.target/aarch64/popcnt-vec.c
> b/gcc/testsuite/gcc.target/aarch64/popcnt-vec.c
> new file mode 100644
> index 00000000000..0c4926d7ca8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/popcnt-vec.c
> @@ -0,0 +1,69 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fno-vect-cost-model" } */
> +
> +/* This function should produce cnt v.16b. */
> +void
> +bar (unsigned char *__restrict b, unsigned char *__restrict d)
> +{
> + for (int i = 0; i < 1024; i++)
> + d[i] = __builtin_popcount (b[i]);
> +}
> +
> +/* This function should produce cnt v.16b and uaddlp (Add Long Pairwise). */
> +void
> +bar1 (unsigned short *__restrict b, unsigned short *__restrict d)
> +{
> + for (int i = 0; i < 1024; i++)
> + d[i] = __builtin_popcount (b[i]);
> +}
> +
> +/* This function should produce cnt v.16b and 2 uaddlp (Add Long Pairwise).
> */
> +void
> +bar2 (unsigned int *__restrict b, unsigned int *__restrict d)
> +{
> + for (int i = 0; i < 1024; i++)
> + d[i] = __builtin_popcount (b[i]);
> +}
> +
> +/* This function should produce cnt v.16b and 3 uaddlp (Add Long Pairwise).
> */
> +void
> +bar3 (unsigned long long *__restrict b, unsigned long long *__restrict d)
> +{
> + for (int i = 0; i < 1024; i++)
> + d[i] = __builtin_popcountll (b[i]);
> +}
> +
> +/* SLP
> + This function should produce cnt v.8b and uaddlp (Add Long Pairwise). */
> +void
> +bar4 (unsigned short *__restrict b, unsigned short *__restrict d)
> +{
> + d[0] = __builtin_popcount (b[0]);
> + d[1] = __builtin_popcount (b[1]);
> + d[2] = __builtin_popcount (b[2]);
> + d[3] = __builtin_popcount (b[3]);
> +}
> +
> +/* SLP
> + This function should produce cnt v.8b and 2 uaddlp (Add Long Pairwise). */
> +void
> +bar5 (unsigned int *__restrict b, unsigned int *__restrict d)
> +{
> + d[0] = __builtin_popcount (b[0]);
> + d[1] = __builtin_popcount (b[1]);
> +}
> +
> +/* SLP
> + This function should produce cnt v.16b and 3 uaddlp (Add Long Pairwise).
> */
> +void
> +bar6 (unsigned long long *__restrict b, unsigned long long *__restrict d)
> +{
> + d[0] = __builtin_popcountll (b[0]);
> + d[1] = __builtin_popcountll (b[1]);
> +}
> +
> +/* { dg-final { scan-assembler-not {\tbl\tpopcount} } } */
> +/* { dg-final { scan-assembler-times {cnt\t} 7 } } */
> +/* { dg-final { scan-assembler-times {uaddlp\t} 12 } } */
> +/* { dg-final { scan-assembler-times {ldr\tq} 5 } } */
> +/* { dg-final { scan-assembler-times {ldr\td} 2 } } */
> --
> 2.17.1
