https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126516
--- Comment #6 from Josef Melcr <jmelcr at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #5)
> I'll note the change will aggressively prefer SSE vectorization width,
> irrespective of the cost of the operations leading up to the fold-left
> reduction.
>
> Also (but unlikely here), for slp_inst_kind_reduc_group we only
> actually implement fold-left reductions for SLP_TREE_LANES == 1
> unless there's no actual fold-left reduction to be performed
> (VF == 1). Meaning, slp_inst_kind_reduc_group with VF == 1
> is free, which isn't reflected in the change. But unlikely to be
> the issue here.
>
> So you might want to check whether the following fixes the regression:
>
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index dcfe4531f11..b2a96820ad3 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -27212,7 +27212,7 @@ ix86_vector_costs::finish_cost (const vector_costs
> *scalar_costs)
> {
> unsigned int vf = vect_vf_for_cost (loop_vinfo);
> for (auto inst : LOOP_VINFO_SLP_INSTANCES (loop_vinfo))
> - if ((SLP_INSTANCE_KIND (inst) == slp_inst_kind_reduc_group
> + if (((SLP_INSTANCE_KIND (inst) == slp_inst_kind_reduc_group && vf !=
> 1)
> || SLP_INSTANCE_KIND (inst) == slp_inst_kind_reduc_chain)
> && (vect_reduc_type (loop_vinfo, SLP_INSTANCE_TREE (inst))
> == FOLD_LEFT_REDUCTION))
It does not unfortunately :/
