> Am 11.03.2025 um 16:44 schrieb Richard Sandiford <richard.sandif...@arm.com>:
>
> pr110625_[24].c started failing after r15-1329-gd66b820f392aa9a7,
> which switched to single def-use cycles for single-lane SLP.
> The problem is that we only costed one vector accumulator
> operation for an N-vector cycle.
>
> The problem seems to have been latent, and meant that we also
> only costed one FADDA for reduc_strict_4.c and reduc_strict_5.c,
> even though they need 4 and 6 FADDAs respectively.
>
> I'm not sure why:
>
> if ((double_reduc || reduction_type != TREE_CODE_REDUCTION)
> && ncopies > 1)
>
> was previously only necessary for non-SLP, but the patch preserves
> that for safety.
>
> Tested on aarch64-linux-gnu & x86_64-linux-gnu. OK to install?
Ok. I hope this ncopies stuff gets cleaned up in next stage1.
Richard
> Richard
>
>
> gcc/
> PR tree-optimization/116901
> * tree-vect-loop.cc (vectorizable_reduction): Set ncopies to
> SLP_TREE_NUMBER_OF_VEC_STMTS for SLP.
>
> gcc/testsuite/
> PR tree-optimization/116901
> * gcc.target/aarch64/sve/reduc_strict_4.c: Turn off costing.
> * gcc.target/aarch64/sve/reduc_strict_5.c: Likewise.
> ---
> .../gcc.target/aarch64/sve/reduc_strict_4.c | 2 +-
> .../gcc.target/aarch64/sve/reduc_strict_5.c | 2 +-
> gcc/tree-vect-loop.cc | 14 +++++++-------
> 3 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/reduc_strict_4.c
> b/gcc/testsuite/gcc.target/aarch64/sve/reduc_strict_4.c
> index 9a12edad42e..8dad5ee6016 100644
> --- a/gcc/testsuite/gcc.target/aarch64/sve/reduc_strict_4.c
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/reduc_strict_4.c
> @@ -1,5 +1,5 @@
> /* { dg-do compile } */
> -/* { dg-options "-O2 -ftree-vectorize" } */
> +/* { dg-options "-O2 -ftree-vectorize -fno-vect-cost-model" } */
>
> double mat[100][8];
>
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/reduc_strict_5.c
> b/gcc/testsuite/gcc.target/aarch64/sve/reduc_strict_5.c
> index 7c3068fe87a..9e117812d34 100644
> --- a/gcc/testsuite/gcc.target/aarch64/sve/reduc_strict_5.c
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/reduc_strict_5.c
> @@ -1,5 +1,5 @@
> /* { dg-do compile } */
> -/* { dg-options "-O2 -ftree-vectorize" } */
> +/* { dg-options "-O2 -ftree-vectorize -fno-vect-cost-model" } */
>
> double mat[100][12];
>
> diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> index 52533623cab..9413dcef702 100644
> --- a/gcc/tree-vect-loop.cc
> +++ b/gcc/tree-vect-loop.cc
> @@ -8180,7 +8180,7 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
> return false;
>
> if (slp_node)
> - ncopies = 1;
> + ncopies = SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node);
> else
> ncopies = vect_get_num_copies (loop_vinfo, vectype_in);
>
> @@ -8288,7 +8288,7 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
> || reduction_type == CONST_COND_REDUCTION
> || reduction_type == EXTRACT_LAST_REDUCTION)
> && slp_node
> - && SLP_TREE_NUMBER_OF_VEC_STMTS (slp_node) > 1)
> + && ncopies > 1)
> {
> if (dump_enabled_p ())
> dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> @@ -8297,6 +8297,7 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
> }
>
> if ((double_reduc || reduction_type != TREE_CODE_REDUCTION)
> + && !slp_node
> && ncopies > 1)
> {
> if (dump_enabled_p ())
> @@ -8523,11 +8524,10 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
> participating. When unrolling we want each unrolled iteration to have its
> own reduction accumulator since one of the main goals of unrolling a
> reduction is to reduce the aggregate loop-carried latency. */
> - if ((ncopies > 1
> - || (slp_node
> - && !REDUC_GROUP_FIRST_ELEMENT (stmt_info)
> - && SLP_TREE_LANES (slp_node) == 1
> - && vect_get_num_copies (loop_vinfo, vectype_in) > 1))
> + if (ncopies > 1
> + && (!slp_node
> + || (!REDUC_GROUP_FIRST_ELEMENT (stmt_info)
> + && SLP_TREE_LANES (slp_node) == 1))
> && (STMT_VINFO_RELEVANT (stmt_info) <= vect_used_only_live)
> && reduc_chain_length == 1
> && loop_vinfo->suggested_unroll_factor == 1)
> --
> 2.25.1
>
