re PR tree-optimization/86835 (Bogus "is used uninitialized" warning with -ffast-math)

	PR tree-optimization/86835
	* tree-ssa-math-opts.c (insert_reciprocals): Even when inserting
	new_stmt after def_gsi, make sure to insert new_square_stmt after
	that stmt, not 2 stmts before it.

	* gcc.dg/pr86835.c: New test.

From-SVN: r263487

gcc/ChangeLog

+2018-08-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/86835
+	* tree-ssa-math-opts.c (insert_reciprocals): Even when inserting
+	new_stmt after def_gsi, make sure to insert new_square_stmt after
+	that stmt, not 2 stmts before it.
+
 2018-08-10  Alexander Monakov  <amonakov@ispras.ru>
 
 	PR target/82418

gcc/testsuite/ChangeLog

+2018-08-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/86835
+	* gcc.dg/pr86835.c: New test.
+
 2018-08-10  Janus Weil  <janus@gcc.gnu.org>
 
 	PR fortran/57160

gcc/testsuite/gcc.dg/pr86835.c

+/* PR tree-optimization/86835 */
+/* { dg-do run } */
+/* { dg-options "-O2 -ffast-math -Wuninitialized" } */
+
+__attribute__((noipa)) void
+foo (int n, double *x, double *y)
+{		/* { dg-bogus "is used uninitialized in this function" "" { target *-*-* } 0 } */
+  int i;
+  double b = y[4];
+  for (i = 0; i < n; ++i)
+    y[3] += __builtin_sin (x[i] / b);
+  y[0] /= b;
+  y[1] /= b * b;
+  y[2] /= b;
+}
+
+int
+main ()
+{
+  double y[] = { 16.0, 64.0, 128.0, 0.0, 2.0 };
+  foo (0, y, y);
+  if (__builtin_fabs (y[0] - 8.0) > 0.0001
+      || __builtin_fabs (y[1] - 16.0) > 0.0001
+      || __builtin_fabs (y[2] - 64.0) > 0.0001
+      || y[3] != 0.0
+      || y[4] != 2.0)
+    __builtin_abort ();
+  return 0;
+}

gcc/tree-ssa-math-opts.c

@@ -422,6 +422,8 @@ insert_reciprocals (gimple_stmt_iterator *def_gsi, struct occurrence *occ,
 	    gsi_next (&gsi);
 
 	  gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
+	  if (should_insert_square_recip)
+	    gsi_insert_before (&gsi, new_square_stmt, GSI_SAME_STMT);
 	}
       else if (def_gsi && occ->bb == def_gsi->bb)
 	{
@@ -429,21 +431,19 @@ insert_reciprocals (gimple_stmt_iterator *def_gsi, struct occurrence *occ,
 	     never happen if the definition statement can throw, because in
 	     that case the sole successor of the statement's basic block will
 	     dominate all the uses as well.  */
-	  gsi = *def_gsi;
 	  gsi_insert_after (def_gsi, new_stmt, GSI_NEW_STMT);
+	  if (should_insert_square_recip)
+	    gsi_insert_after (def_gsi, new_square_stmt, GSI_NEW_STMT);
 	}
       else
 	{
 	  /* Case 3: insert in a basic block not containing defs/uses.  */
 	  gsi = gsi_after_labels (occ->bb);
 	  gsi_insert_before (&gsi, new_stmt, GSI_SAME_STMT);
+	  if (should_insert_square_recip)
+	    gsi_insert_before (&gsi, new_square_stmt, GSI_SAME_STMT);
 	}
 
-      /* Regardless of which case the reciprocal as inserted in,
-	 we insert the square immediately after the reciprocal.  */
-      if (should_insert_square_recip)
-	gsi_insert_before (&gsi, new_square_stmt, GSI_SAME_STMT);
-
       reciprocal_stats.rdivs_inserted++;
 
       occ->recip_def_stmt = new_stmt;