[gcc r16-3598] Avoid costing vector stmts with count == 0

[Richard Biener]

https://gcc.gnu.org/g:2965a67c7ef34de74904b600a3e4a4cc858ea37b

commit r16-3598-g2965a67c7ef34de74904b600a3e4a4cc858ea37b
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Sep 5 11:55:50 2025 +0200

    Avoid costing vector stmts with count == 0
    
    This avoids confusing the backends.
    
            * tree-vect-slp.cc (vectorizable_bb_reduc_epilogue): Do not
            cost zero remaining scalar stmts.
            (vectorizable_slp_permutation): Do not cost zero actual
            permutations.
            * tree-vect-stmts.cc (vectorizable_load): Likewise.

Diff:
---
 gcc/tree-vect-slp.cc   | 7 ++++---
 gcc/tree-vect-stmts.cc | 5 +++--
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 6258a8eb53de..59bca1dfce7c 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -8701,8 +8701,9 @@ vectorizable_bb_reduc_epilogue (slp_instance instance,
 
   /* Since we replace all stmts of a possibly longer scalar reduction
      chain account for the extra scalar stmts for that.  */
-  record_stmt_cost (cost_vec, instance->remain_defs.length (), scalar_stmt,
-		    instance->root_stmts[0], 0, vect_body);
+  if (!instance->remain_defs.is_empty ())
+    record_stmt_cost (cost_vec, instance->remain_defs.length (), scalar_stmt,
+		      instance->root_stmts[0], 0, vect_body);
   return true;
 }
 
@@ -11370,7 +11371,7 @@ vectorizable_slp_permutation (vec_info *vinfo, gimple_stmt_iterator *gsi,
   if (nperms < 0)
     return false;
 
-  if (!gsi)
+  if (!gsi && nperms != 0)
     record_stmt_cost (cost_vec, nperms, vec_perm, node, vectype, 0, vect_body);
 
   return true;
diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index edc669ba3e47..9fcc2fd08498 100644
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -11387,8 +11387,9 @@ vectorizable_load (vec_info *vinfo,
 	{
 	  vect_transform_slp_perm_load (vinfo, slp_node, vNULL, nullptr, vf,
 					true, &n_perms, nullptr);
-	  inside_cost = record_stmt_cost (cost_vec, n_perms, vec_perm,
-					  slp_node, 0, vect_body);
+	  if (n_perms != 0)
+	    inside_cost = record_stmt_cost (cost_vec, n_perms, vec_perm,
+					    slp_node, 0, vect_body);
 	}
       else
 	{