re PR tree-optimization/68911 (wrong code with -O1 -ftree-vrp)

	PR tree-optimization/68911
	* tree-vrp.c (adjust_range_with_scev): Check overflow in range
	information computed for expression "init + nit * step".

	gcc/testsuite/ChangeLog
	PR tree-optimization/68911
	* gcc.c-torture/execute/pr68911.c: New test.

From-SVN: r232286

gcc/ChangeLog

+2016-01-12  Bin Cheng  <bin.cheng@arm.com>
+
+	PR tree-optimization/68911
+	* tree-vrp.c (adjust_range_with_scev): Check overflow in range
+	information computed for expression "init + nit * step".
+
 2016-01-12  Sandra Loosemore <sandra@codesourcery.com>
 
 	* doc/invoke.texi (Invoking GCC): Copy-edit.  Incorporate information

gcc/testsuite/ChangeLog

+2016-01-12  Bin Cheng  <bin.cheng@arm.com>
+
+	PR tree-optimization/68911
+	* gcc.c-torture/execute/pr68911.c: New test.
+
 2016-01-12  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/68979

gcc/testsuite/gcc.c-torture/execute/pr68911.c

+extern void abort (void);
+
+char a;
+int b, c;
+short d;
+
+int main ()
+{
+  unsigned e = 2;
+  unsigned timeout = 0;
+
+  for (; c < 2; c++)
+    {
+      int f = ~e / 7;
+      if (f)
+	a = e = ~(b && d);
+      while (e < 94)
+	{
+	  e++;
+	  if (++timeout > 100)
+	    goto die;
+	}
+    }
+  return 0;
+die:
+  abort ();
+}

gcc/tree-vrp.c

@@ -4259,6 +4259,27 @@ adjust_range_with_scev (value_range *vr, struct loop *loop,
 	      /* Likewise if the addition did.  */
 	      if (maxvr.type == VR_RANGE)
 		{
+		  value_range initvr = VR_INITIALIZER;
+
+		  if (TREE_CODE (init) == SSA_NAME)
+		    initvr = *(get_value_range (init));
+		  else if (is_gimple_min_invariant (init))
+		    set_value_range_to_value (&initvr, init, NULL);
+		  else
+		    return;
+
+		  /* Check if init + nit * step overflows.  Though we checked
+		     scev {init, step}_loop doesn't wrap, it is not enough
+		     because the loop may exit immediately.  Overflow could
+		     happen in the plus expression in this case.  */
+		  if ((dir == EV_DIR_DECREASES
+		       && (is_negative_overflow_infinity (maxvr.min)
+			   || compare_values (maxvr.min, initvr.min) != -1))
+		      || (dir == EV_DIR_GROWS
+			  && (is_positive_overflow_infinity (maxvr.max)
+			      || compare_values (maxvr.max, initvr.max) != 1)))
+		    return;
+
 		  tmin = maxvr.min;
 		  tmax = maxvr.max;
 		}