[gcc r17-5611] Make match.pd single_use track a single use stmt

[Richard Biener via Gcc-cvs]

https://gcc.gnu.org/g:1396d6015c968b69a3c45fe3ae4c3bd623ba4594

commit r17-5611-g1396d6015c968b69a3c45fe3ae4c3bd623ba4594
Author: Richard Biener <rguent...@suse.de>
Date:   Tue Oct 20 15:09:17 2026 +0200

    Make match.pd single_use track a single use stmt
    
    The following adjusts single_use to instead of a single actual use
    tracks whether all uses are within a single statement.  This is to
    make the existing
    
    (simplify
     (vec_perm (view_convert?@0 (vec_perm@1 @2 @3 VECTOR_CST@4)) @0 
VECTOR_CST@5)
    ...
           /* If the new VEC_PERM_EXPR can't be handled but both
              original VEC_PERM_EXPRs can, punt.
              If one or both of the original VEC_PERM_EXPRs can't be
              handled and the new one can't be either, don't increase
              number of VEC_PERM_EXPRs that can't be handled.  */
           if (can_vec_perm_const_p (perm_mode, op2_mode, new_sel, false)
               || (single_use (@0)
                   ? (!can_vec_perm_const_p (inner_mode, op2_mode, sel4, true)
                      || !can_vec_perm_const_p (result_mode, vc_mode, sel5, 
true))
                   : !can_vec_perm_const_p (result_mode, vc_mode, sel5, true)))
             new_vcst = vec_perm_indices_to_tree (TREE_TYPE (@5), new_sel);
    
    work as expected where @0 has two uses in the single-vector permute.
    
            * gimple-match-head.cc (single_use): Track single use stmt.

Diff:
---
 gcc/gimple-match-head.cc | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/gcc/gimple-match-head.cc b/gcc/gimple-match-head.cc
index b2f26c71fc9c..c6a0c74eabb7 100644
--- a/gcc/gimple-match-head.cc
+++ b/gcc/gimple-match-head.cc
@@ -91,7 +91,7 @@ types_match (tree t1, tree t2, tree t3)
   return types_match (t1, t2) && types_match (t2, t3);
 }
 
-/* Return if T has a single use.  For GIMPLE, we also allow any
+/* Return if T has uses in a single stmt.  For GIMPLE, we also allow any
    non-SSA_NAME (ie constants) and zero uses to cope with uses
    that aren't linked up yet.  */
 
@@ -107,14 +107,14 @@ single_use (const_tree t)
   /* Inline return has_zero_uses (t) || has_single_use (t);  */
   const ssa_use_operand_t *const head = &(SSA_NAME_IMM_USE_NODE (t));
   const ssa_use_operand_t *ptr;
-  bool single = false;
+  gimple *single = NULL;
 
   for (ptr = head->next; ptr != head; ptr = ptr->next)
-    if (USE_STMT(ptr) && !is_gimple_debug (USE_STMT (ptr)))
+    if (USE_STMT (ptr) && !is_gimple_debug (USE_STMT (ptr)))
       {
-        if (single)
+       if (single && single != USE_STMT (ptr))
           return false;
-       single = true;
+       single = USE_STMT (ptr);
       }
   return true;
 }