2023-02-07  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108692
	* tree-vect-patterns.cc (vect_widened_op_tree): If rhs_code is
	widened_code which is different from code, don't call
	vect_look_through_possible_promotion but instead just check op is
	SSA_NAME with integral type for which vect_is_simple_use is true
	and call set_op on this_unprom.

	* gcc.dg/pr108692.c: New test.

--- gcc/tree-vect-patterns.cc.jj	2023-01-02 09:32:45.635949342 +0100
+++ gcc/tree-vect-patterns.cc	2023-02-07 15:27:33.214608837 +0100
@@ -601,7 +601,25 @@ vect_widened_op_tree (vec_info *vinfo, s
 	  if (shift_p && i == 1)
 	    return 0;
 
-	  if (!vect_look_through_possible_promotion (vinfo, op, this_unprom))
+	  if (rhs_code != code)
+	    {
+	      /* If rhs_code is widened_code, don't look through further
+		 possible promotions, there is a promotion already embedded
+		 in the WIDEN_*_EXPR.  */
+	      if (TREE_CODE (op) != SSA_NAME
+		  || !INTEGRAL_TYPE_P (TREE_TYPE (op)))
+		return 0;
+
+	      stmt_vec_info def_stmt_info;
+	      gimple *def_stmt;
+	      vect_def_type dt;
+	      if (!vect_is_simple_use (op, vinfo, &dt, &def_stmt_info,
+				       &def_stmt))
+		return 0;
+	      this_unprom->set_op (op, dt, NULL);
+	    }
+	  else if (!vect_look_through_possible_promotion (vinfo, op,
+							  this_unprom))
 	    return 0;
 
 	  if (TYPE_PRECISION (this_unprom->type) == TYPE_PRECISION (type))
--- gcc/testsuite/gcc.dg/pr108692.c.jj	2023-02-07 15:47:20.329076264 +0100
+++ gcc/testsuite/gcc.dg/pr108692.c	2023-02-07 15:46:15.623031983 +0100
@@ -0,0 +1,31 @@
+/* PR tree-optimization/108692 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-vectorize" } */
+
+__attribute__((noipa)) int
+foo (signed char *x, signed char *y, int n)
+{
+  int i, r = 0;
+  signed char a, b;
+  for (i = 0; i < n; i++)
+    {
+      a = x[i];
+      b = y[i];
+      int c = (unsigned char) a - (unsigned char) b;
+      r = r + (c < 0 ? -c : c);
+    }
+  return r;
+}
+
+int
+main ()
+{
+  signed char x[64] = {}, y[64] = {};
+  if (__CHAR_BIT__ != 8 || __SIZEOF_INT__ != 4)
+    return 0;
+  x[32] = -128;
+  y[32] = 1;
+  if (foo (x, y, 64) != 127)
+    __builtin_abort ();
+  return 0;
+}