Thanks Richard.
So you think increase scalar_to_vec cost is not the correct approach to fix
this case?
Or could you give me a suggestion to fix this case ?
Thanks.
juzhe.zh...@rivai.ai
From: Richard Biener
Date: 2024-01-11 17:18
To: Juzhe-Zhong
CC: gcc-patches; kito.cheng; kito.cheng; jeffreyalaw; rdapp.gcc
Subject: Re: [PATCH] RISC-V: Increase scalar_to_vec_cost from 1 to 3
On Thu, Jan 11, 2024 at 9:24 AM Juzhe-Zhong <juzhe.zh...@rivai.ai> wrote:
>
> This patch fixes the following inefficient vectorized codes:
>
> vsetvli a5,zero,e8,mf2,ta,ma
> li a2,17
> vid.v v1
> li a4,-32768
> vsetvli zero,zero,e16,m1,ta,ma
> addiw a4,a4,104
> vmv.v.i v3,15
> lui a1,%hi(a)
> li a0,19
> vsetvli zero,zero,e8,mf2,ta,ma
> vadd.vx v1,v1,a2
> sb a0,%lo(a)(a1)
> vsetvli zero,zero,e16,m1,ta,ma
> vzext.vf2 v2,v1
> vmv.v.x v1,a4
> vminu.vv v2,v2,v3
> vsrl.vv v1,v1,v2
> vslidedown.vi v1,v1,1
> vmv.x.s a0,v1
> snez a0,a0
> ret
>
> The reason is scalar_to_vec_cost is too low.
>
> Consider in VEC_SET, we always have a slide + scalar move instruction,
> scalar_to_vec_cost = 1 (current cost) is not reasonable.
scalar_to_vec is supposed to model a splat of GPR/FPR to a vector register.
We probably want to overhaul the cost classes, esp. vec_to_scalar, but of
course not now.
> I tried to set it as 2 but failed fix this case, that is, I need to
> set it as 3 to fix this case.
>
> No matter scalar move or slide instruction, I believe they are more costly
> than normal vector instructions (e.g. vadd.vv). So set it as 3 looks
> reasonable
> to me.
>
> After this patch:
>
> lui a5,%hi(a)
> li a4,19
> sb a4,%lo(a)(a5)
> li a0,0
> ret
>
> Tested on both RV32/RV64 no regression, Ok for trunk ?
>
> PR target/113281
>
> gcc/ChangeLog:
>
> * config/riscv/riscv.cc: Set scalar_to_vec_cost as 3.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/riscv/rvv/autovec/pr113209.c: Adapt test.
> * gcc.dg/vect/costmodel/riscv/rvv/pr113281-1.c: New test.
>
> ---
> gcc/config/riscv/riscv.cc | 4 ++--
> .../vect/costmodel/riscv/rvv/pr113281-1.c | 18 ++++++++++++++++++
> .../gcc.target/riscv/rvv/autovec/pr113209.c | 2 +-
> 3 files changed, 21 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/vect/costmodel/riscv/rvv/pr113281-1.c
>
> diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> index df9799d9c5e..bcfb3c15a39 100644
> --- a/gcc/config/riscv/riscv.cc
> +++ b/gcc/config/riscv/riscv.cc
> @@ -366,7 +366,7 @@ static const common_vector_cost rvv_vls_vector_cost = {
> 1, /* gather_load_cost */
> 1, /* scatter_store_cost */
> 1, /* vec_to_scalar_cost */
> - 1, /* scalar_to_vec_cost */
> + 3, /* scalar_to_vec_cost */
> 1, /* permute_cost */
> 1, /* align_load_cost */
> 1, /* align_store_cost */
> @@ -382,7 +382,7 @@ static const scalable_vector_cost rvv_vla_vector_cost = {
> 1, /* gather_load_cost */
> 1, /* scatter_store_cost */
> 1, /* vec_to_scalar_cost */
> - 1, /* scalar_to_vec_cost */
> + 3, /* scalar_to_vec_cost */
> 1, /* permute_cost */
> 1, /* align_load_cost */
> 1, /* align_store_cost */
> diff --git a/gcc/testsuite/gcc.dg/vect/costmodel/riscv/rvv/pr113281-1.c
> b/gcc/testsuite/gcc.dg/vect/costmodel/riscv/rvv/pr113281-1.c
> new file mode 100644
> index 00000000000..331cf961a1f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/costmodel/riscv/rvv/pr113281-1.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile } */
> +/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O3 -ftree-vectorize
> -fdump-tree-vect-details" } */
> +
> +unsigned char a;
> +
> +int main() {
> + short b = a = 0;
> + for (; a != 19; a++)
> + if (a)
> + b = 32872 >> a;
> +
> + if (b == 0)
> + return 0;
> + else
> + return 1;
> +}
> +
> +/* { dg-final { scan-tree-dump-times "vectorized 0 loops" 1 "vect" } } */
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr113209.c
> b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr113209.c
> index 081ee369394..70aae151000 100644
> --- a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr113209.c
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr113209.c
> @@ -1,5 +1,5 @@
> /* { dg-do compile } */
> -/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O3" } */
> +/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O3
> -fno-vect-cost-model" } */
>
> int b, c, d, f, i, a;
> int e[1] = {0};
> --
> 2.36.3
>
