On Mon, 10 Nov 2025, Victor Do Nascimento wrote:
> The iteration count profitability check is irrelevant for uncounted
> loops given that, even at runtime, the number of iterations is unknown
> at the start of loop execution.
>
> Likewise, the test for skipping the vectorized version of the loop is
> based on whether the number of iterations that will be run for the
> loop and whether it is smaller than the vectorization factor. As this
> is undetermined, the check can never be run for uncounted loops.
>
> Consequently, we skip these checks.
>
> gcc/ChangeLog:
>
> * tree-vect-loop-manip.cc (vect_loop_versioning): skip
> profitability check for uncounted loops.
> * tree-vect-loop-manip.cc (vect_do_peeling): Disable vector
> loop skip checking.
> ---
> gcc/tree-vect-loop-manip.cc | 17 ++++++++++-------
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
> index 18a5059251b..640735388fe 100644
> --- a/gcc/tree-vect-loop-manip.cc
> +++ b/gcc/tree-vect-loop-manip.cc
> @@ -3293,11 +3293,13 @@ vect_do_peeling (loop_vec_info loop_vinfo, tree
> niters, tree nitersm1,
> because we have asserted that there are enough scalar iterations to
> enter
> the main loop, so this skip is not necessary. When we are versioning
> then
> we only add such a skip if we have chosen to vectorize the epilogue. */
> - bool skip_vector = (LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
> - ? maybe_lt (LOOP_VINFO_INT_NITERS (loop_vinfo),
> - bound_prolog + bound_epilog)
> - : (!LOOP_VINFO_USE_VERSIONING_WITHOUT_PEELING (loop_vinfo)
> - || vect_epilogues));
> + bool skip_vector = false;
> + if (!uncounted_p)
> + skip_vector = (LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
> + ? maybe_lt (LOOP_VINFO_INT_NITERS (loop_vinfo),
> + bound_prolog + bound_epilog)
> + : (!LOOP_VINFO_USE_VERSIONING_WITHOUT_PEELING (loop_vinfo)
> + || vect_epilogues));
>
> /* Epilog loop must be executed if the number of iterations for epilog
> loop is known at compile time, otherwise we need to add a check at
> @@ -4157,13 +4159,14 @@ vect_loop_versioning (loop_vec_info loop_vinfo,
> tree version_simd_if_cond
> = LOOP_REQUIRES_VERSIONING_FOR_SIMD_IF_COND (loop_vinfo);
> unsigned th = LOOP_VINFO_COST_MODEL_THRESHOLD (loop_vinfo);
> + bool uncounted_p = LOOP_VINFO_NITERS_UNCOUNTED_P (loop_vinfo);
>
> if (vect_apply_runtime_profitability_check_p (loop_vinfo)
> - && !ordered_p (th, versioning_threshold))
> + && !ordered_p (th, versioning_threshold) && !uncounted_p)
can you test !uncounted_p first, before calling
vect_apply_runtime_profitability_check_p?
Otherwise OK.
Richard.
> cond_expr = fold_build2 (GE_EXPR, boolean_type_node, scalar_loop_iters,
> build_int_cst (TREE_TYPE (scalar_loop_iters),
> th - 1));
> - if (maybe_ne (versioning_threshold, 0U))
> + if (!uncounted_p && maybe_ne (versioning_threshold, 0U))
> {
> tree expr = fold_build2 (GE_EXPR, boolean_type_node, scalar_loop_iters,
> build_int_cst (TREE_TYPE (scalar_loop_iters),
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
