Lehua Ding <lehua.d...@rivai.ai> writes:
> V3 change: Address Richard's comments.
>
> Hi,
>
> This patch adds support that tries to fold `MIN (poly, poly)` to
> a constant. Consider the following C Code:
>
> ```
> void foo2 (int* restrict a, int* restrict b, int n)
> {
> for (int i = 0; i < 3; i += 1)
> a[i] += b[i];
> }
> ```
>
> Before this patch:
>
> ```
> void foo2 (int * restrict a, int * restrict b, int n)
> {
> vector([4,4]) int vect__7.27;
> vector([4,4]) int vect__6.26;
> vector([4,4]) int vect__4.23;
> unsigned long _32;
>
> <bb 2> [local count: 268435456]:
> _32 = MIN_EXPR <3, POLY_INT_CST [4, 4]>;
> vect__4.23_20 = .MASK_LEN_LOAD (a_11(D), 32B, { -1, ... }, _32, 0);
> vect__6.26_15 = .MASK_LEN_LOAD (b_12(D), 32B, { -1, ... }, _32, 0);
> vect__7.27_9 = vect__6.26_15 + vect__4.23_20;
> .MASK_LEN_STORE (a_11(D), 32B, { -1, ... }, _32, 0, vect__7.27_9); [tail
> call]
> return;
>
> }
> ```
>
> After this patch:
>
> ```
> void foo2 (int * restrict a, int * restrict b, int n)
> {
> vector([4,4]) int vect__7.27;
> vector([4,4]) int vect__6.26;
> vector([4,4]) int vect__4.23;
>
> <bb 2> [local count: 268435456]:
> vect__4.23_20 = .MASK_LEN_LOAD (a_11(D), 32B, { -1, ... }, 3, 0);
> vect__6.26_15 = .MASK_LEN_LOAD (b_12(D), 32B, { -1, ... }, 3, 0);
> vect__7.27_9 = vect__6.26_15 + vect__4.23_20;
> .MASK_LEN_STORE (a_11(D), 32B, { -1, ... }, 3, 0, vect__7.27_9); [tail call]
> return;
>
> }
> ```
>
> For RISC-V RVV, csrr and branch instructions can be reduced:
>
> Before this patch:
>
> ```
> foo2:
> csrr a4,vlenb
> srli a4,a4,2
> li a5,3
> bleu a5,a4,.L5
> mv a5,a4
> .L5:
> vsetvli zero,a5,e32,m1,ta,ma
> ...
> ```
>
> After this patch.
>
> ```
> foo2:
> vsetivli zero,3,e32,m1,ta,ma
> ...
> ```
>
> Best,
> Lehua
>
> gcc/ChangeLog:
>
> * fold-const.cc (can_min_p): New function.
> (poly_int_binop): Try fold MIN_EXPR.
OK, thanks.
Richard
> gcc/testsuite/ChangeLog:
>
> * gcc.target/riscv/rvv/autovec/vls/div-1.c: Adjust.
> * gcc.target/riscv/rvv/autovec/vls/shift-3.c: Adjust.
> * gcc.target/riscv/rvv/autovec/fold-min-poly.c: New test.
>
> ---
> gcc/fold-const.cc | 24 +++++++++++++++++++
> .../riscv/rvv/autovec/fold-min-poly.c | 24 +++++++++++++++++++
> .../gcc.target/riscv/rvv/autovec/vls/div-1.c | 2 +-
> .../riscv/rvv/autovec/vls/shift-3.c | 2 +-
> 4 files changed, 50 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/fold-min-poly.c
>
> diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
> index 1da498a3152..d19b4666c65 100644
> --- a/gcc/fold-const.cc
> +++ b/gcc/fold-const.cc
> @@ -1213,6 +1213,25 @@ wide_int_binop (wide_int &res,
> return true;
> }
>
> +/* Returns true if we know who is smaller or equal, ARG1 or ARG2, and set the
> + min value to RES. */
> +bool
> +can_min_p (const_tree arg1, const_tree arg2, poly_wide_int &res)
> +{
> + if (known_le (wi::to_poly_widest (arg1), wi::to_poly_widest (arg2)))
> + {
> + res = wi::to_poly_wide (arg1);
> + return true;
> + }
> + else if (known_le (wi::to_poly_widest (arg2), wi::to_poly_widest (arg1)))
> + {
> + res = wi::to_poly_wide (arg2);
> + return true;
> + }
> +
> + return false;
> +}
> +
> /* Combine two poly int's ARG1 and ARG2 under operation CODE to
> produce a new constant in RES. Return FALSE if we don't know how
> to evaluate CODE at compile-time. */
> @@ -1261,6 +1280,11 @@ poly_int_binop (poly_wide_int &res, enum tree_code
> code,
> return false;
> break;
>
> + case MIN_EXPR:
> + if (!can_min_p (arg1, arg2, res))
> + return false;
> + break;
> +
> default:
> return false;
> }
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/fold-min-poly.c
> b/gcc/testsuite/gcc.target/riscv/rvv/autovec/fold-min-poly.c
> new file mode 100644
> index 00000000000..de4c472c76e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/fold-min-poly.c
> @@ -0,0 +1,24 @@
> +/* { dg-do compile } */
> +/* { dg-options " -march=rv64gcv_zvl128b -mabi=lp64d -O3 --param
> riscv-autovec-preference=scalable --param riscv-autovec-lmul=m1
> -fno-vect-cost-model" } */
> +
> +void foo1 (int* restrict a, int* restrict b, int n)
> +{
> + for (int i = 0; i < 4; i += 1)
> + a[i] += b[i];
> +}
> +
> +void foo2 (int* restrict a, int* restrict b, int n)
> +{
> + for (int i = 0; i < 3; i += 1)
> + a[i] += b[i];
> +}
> +
> +void foo3 (int* restrict a, int* restrict b, int n)
> +{
> + for (int i = 0; i < 5; i += 1)
> + a[i] += b[i];
> +}
> +
> +/* { dg-final { scan-assembler-not {\tcsrr\t} } } */
> +/* { dg-final { scan-assembler {\tvsetivli\tzero,4,e32,m1,t[au],m[au]} } } */
> +/* { dg-final { scan-assembler {\tvsetivli\tzero,3,e32,m1,t[au],m[au]} } } */
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/vls/div-1.c
> b/gcc/testsuite/gcc.target/riscv/rvv/autovec/vls/div-1.c
> index f3388a86e38..40224c69458 100644
> --- a/gcc/testsuite/gcc.target/riscv/rvv/autovec/vls/div-1.c
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/vls/div-1.c
> @@ -55,4 +55,4 @@ DEF_OP_VV (div, 512, int64_t, /)
>
> /* { dg-final { scan-assembler-times
> {vdivu?\.vv\s+v[0-9]+,\s*v[0-9]+,\s*v[0-9]+} 42 } } */
> /* TODO: Ideally, we should make sure there is no "csrr vlenb". However, we
> still have 'csrr vlenb' for some cases since we don't support VLS mode
> conversion which are needed by division. */
> -/* { dg-final { scan-assembler-times {csrr} 19 } } */
> +/* { dg-final { scan-assembler-not {csrr} } } */
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/vls/shift-3.c
> b/gcc/testsuite/gcc.target/riscv/rvv/autovec/vls/shift-3.c
> index 98822b15657..b34a349949b 100644
> --- a/gcc/testsuite/gcc.target/riscv/rvv/autovec/vls/shift-3.c
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/vls/shift-3.c
> @@ -55,4 +55,4 @@ DEF_OP_VV (shift, 512, int64_t, <<)
>
> /* { dg-final { scan-assembler-times
> {vsll\.vv\s+v[0-9]+,\s*v[0-9]+,\s*v[0-9]+} 41 } } */
> /* TODO: Ideally, we should make sure there is no "csrr vlenb". However, we
> still have 'csrr vlenb' for some cases since we don't support VLS mode
> conversion which are needed by division. */
> -/* { dg-final { scan-assembler-times {csrr} 18 } } */
> +/* { dg-final { scan-assembler-not {csrr} } } */
