re PR tree-optimization/68021 (ice in rewrite_use_nonlinear_expr with -O3)

	PR tree-optimization/68021
	* tree-ssa-loop-ivopts.c (get_computation_aff): Set ratio to 1 if
	when computing the value of biv cand by itself.

	gcc/testsuite/ChangeLog
	PR tree-optimization/68021
	* gcc.dg/tree-ssa/pr68021.c: New test.

From-SVN: r233269

gcc/ChangeLog

+2016-02-10  Bin Cheng  <bin.cheng@arm.com>
+
+	PR tree-optimization/68021
+	* tree-ssa-loop-ivopts.c (get_computation_aff): Set ratio to 1 if
+	when computing the value of biv cand by itself.
+
 2016-02-10  Wilco Dijkstra  <wdijkstr@arm.com>
 
 	* config/aarch64/aarch64.c (cortexa53_tunings): Enable AES fusion.

gcc/testsuite/ChangeLog

+2016-02-10  Bin Cheng  <bin.cheng@arm.com>
+
+	PR tree-optimization/68021
+	* gcc.dg/tree-ssa/pr68021.c: New test.
+
 2016-02-10  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/69726

gcc/testsuite/gcc.dg/tree-ssa/pr68021.c

+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+char a;
+void fn1 (char *p1, int p2, int p3)
+{
+  int i, x;
+  for (i = 0; i < 10; i++)
+    {
+      for (x = 0; x < p3; x++)
+	{
+	  *p1 = a;
+	  p1--;
+	}
+      p1 += p2;
+    }
+}

gcc/tree-ssa-loop-ivopts.c

@@ -3741,7 +3741,19 @@ get_computation_aff (struct loop *loop,
       var = fold_convert (uutype, var);
     }
 
-  if (!constant_multiple_of (ustep, cstep, &rat))
+  /* Ratio is 1 when computing the value of biv cand by itself.
+     We can't rely on constant_multiple_of in this case because the
+     use is created after the original biv is selected.  The call
+     could fail because of inconsistent fold behavior.  See PR68021
+     for more information.  */
+  if (cand->pos == IP_ORIGINAL && cand->incremented_at == use->stmt)
+    {
+      gcc_assert (is_gimple_assign (use->stmt));
+      gcc_assert (use->iv->ssa_name == cand->var_after);
+      gcc_assert (gimple_assign_lhs (use->stmt) == cand->var_after);
+      rat = 1;
+    }
+  else if (!constant_multiple_of (ustep, cstep, &rat))
     return false;
 
   /* In case both UBASE and CBASE are shortened to UUTYPE from some common