On Wed, Jul 5, 2023 at 8:44 AM Hao Liu OS via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
>
> If a loop is unrolled by n times during vectoriation, two steps are used to
> calculate the induction variable:
> - The small step for the unrolled ith-copy: vec_1 = vec_iv + (VF/n * Step)
> - The large step for the whole loop: vec_loop = vec_iv + (VF * Step)
>
> This patch calculates an extra vec_n to replace vec_loop:
> vec_n = vec_prev + (VF/n * S) = vec_iv + (VF/n * S) * n = vec_loop.
>
> So that we can save the large step register and related operations.
OK. It would be nice to avoid the dead stmts created earlier though.
Thanks,
Richard.
> gcc/ChangeLog:
>
> PR tree-optimization/110449
> * tree-vect-loop.cc (vectorizable_induction): use vec_n to replace
> vec_loop for the unrolled loop.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/aarch64/pr110449.c: New testcase.
> ---
> gcc/testsuite/gcc.target/aarch64/pr110449.c | 40 +++++++++++++++++++++
> gcc/tree-vect-loop.cc | 21 +++++++++--
> 2 files changed, 58 insertions(+), 3 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/aarch64/pr110449.c
>
> diff --git a/gcc/testsuite/gcc.target/aarch64/pr110449.c
> b/gcc/testsuite/gcc.target/aarch64/pr110449.c
> new file mode 100644
> index 00000000000..bb3b6dcfe08
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/pr110449.c
> @@ -0,0 +1,40 @@
> +/* { dg-do compile } */
> +/* { dg-options "-Ofast -mcpu=neoverse-n2 --param
> aarch64-vect-unroll-limit=2" } */
> +/* { dg-final { scan-assembler-not "8.0e\\+0" } } */
> +
> +/* Calcualte the vectorized induction with smaller step for an unrolled loop.
> +
> + before (suggested_unroll_factor=2):
> + fmov s30, 8.0e+0
> + fmov s31, 4.0e+0
> + dup v27.4s, v30.s[0]
> + dup v28.4s, v31.s[0]
> + .L6:
> + mov v30.16b, v31.16b
> + fadd v31.4s, v31.4s, v27.4s
> + fadd v29.4s, v30.4s, v28.4s
> + stp q30, q29, [x0]
> + add x0, x0, 32
> + cmp x1, x0
> + bne .L6
> +
> + after:
> + fmov s31, 4.0e+0
> + dup v29.4s, v31.s[0]
> + .L6:
> + fadd v30.4s, v31.4s, v29.4s
> + stp q31, q30, [x0]
> + add x0, x0, 32
> + fadd v31.4s, v29.4s, v30.4s
> + cmp x0, x1
> + bne .L6 */
> +
> +void
> +foo2 (float *arr, float freq, float step)
> +{
> + for (int i = 0; i < 1024; i++)
> + {
> + arr[i] = freq;
> + freq += step;
> + }
> +}
> diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> index 3b46c58a8d8..706ecbffd0c 100644
> --- a/gcc/tree-vect-loop.cc
> +++ b/gcc/tree-vect-loop.cc
> @@ -10114,7 +10114,7 @@ vectorizable_induction (loop_vec_info loop_vinfo,
> new_vec, step_vectype, NULL);
>
> vec_def = induc_def;
> - for (i = 1; i < ncopies; i++)
> + for (i = 1; i < ncopies + 1; i++)
> {
> /* vec_i = vec_prev + vec_step */
> gimple_seq stmts = NULL;
> @@ -10124,8 +10124,23 @@ vectorizable_induction (loop_vec_info loop_vinfo,
> vec_def = gimple_convert (&stmts, vectype, vec_def);
>
> gsi_insert_seq_before (&si, stmts, GSI_SAME_STMT);
> - new_stmt = SSA_NAME_DEF_STMT (vec_def);
> - STMT_VINFO_VEC_STMTS (stmt_info).safe_push (new_stmt);
> + if (i < ncopies)
> + {
> + new_stmt = SSA_NAME_DEF_STMT (vec_def);
> + STMT_VINFO_VEC_STMTS (stmt_info).safe_push (new_stmt);
> + }
> + else
> + {
> + /* vec_1 = vec_iv + (VF/n * S)
> + vec_2 = vec_1 + (VF/n * S)
> + ...
> + vec_n = vec_prev + (VF/n * S) = vec_iv + VF * S = vec_loop
> +
> + vec_n is used as vec_loop to save the large step register and
> + related operations. */
> + add_phi_arg (induction_phi, vec_def, loop_latch_edge (iv_loop),
> + UNKNOWN_LOCATION);
> + }
> }
> }
>
> --
> 2.34.1
