re PR tree-optimization/64322 (More optimize opportunity for constant folding)

	PR tree-optimization/64322
	* tree-vrp.c (extract_range_from_binary_expr_1): Attempt to derive
	range for RSHIFT_EXPR even if vr0 range is not VR_RANGE or is symbolic.

	* gcc.dg/tree-ssa/vrp95.c: New test.

From-SVN: r218812

gcc/ChangeLog

+2014-12-17  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/64322
+	* tree-vrp.c (extract_range_from_binary_expr_1): Attempt to derive
+	range for RSHIFT_EXPR even if vr0 range is not VR_RANGE or is symbolic.
+
 2014-12-17  Tobias Burnus  <burnus@net-b.de>
 
 	PR fortran/54687

gcc/testsuite/ChangeLog

 2014-12-17  Jakub Jelinek  <jakub@redhat.com>
 
+	PR tree-optimization/64322
+	* gcc.dg/tree-ssa/vrp95.c: New test.
+
 	PR sanitizer/64289
 	* c-c++-common/ubsan/pr64289.c: New test.
 

gcc/testsuite/gcc.dg/tree-ssa/vrp95.c

+/* PR tree-optimization/64322 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-vrp1" } */
+
+extern void link_error ();
+extern void required_check ();
+
+long long int
+foo (long long int x)
+{
+  x >>= sizeof (long long int) * __CHAR_BIT__ - 1;
+  if (x != 0 && x != -1)
+    link_error ();
+  return x;
+}
+
+unsigned long long int
+bar (unsigned long long int x)
+{
+  x >>= sizeof (long long int) * __CHAR_BIT__ - 1;
+  if (x != 0 && x != 1)
+    link_error ();
+  return x;
+}
+
+long long int
+baz (long long int x)
+{
+  x = (x >> sizeof (long long int) * __CHAR_BIT__ - 1) << 1;
+  x = x / 0x100000000LL;
+  if (x != 0)
+    link_error ();
+  return x;
+}
+
+unsigned long long int
+range (unsigned long long int x, int y)
+{
+  y &= 3;
+  x >>= sizeof (long long int) * __CHAR_BIT__ - 1 - y;
+  if (x > 15)
+    link_error ();
+  if (x == 15)
+    required_check ();
+  return x;
+}
+
+/* { dg-final { scan-tree-dump-not "link_error" "vrp1" } } */
+/* { dg-final { scan-tree-dump "required_check" "vrp1" } } */
+/* { dg-final { cleanup-tree-dump "vrp1" } } */

gcc/tree-vrp.c

@@ -2434,6 +2434,7 @@ extract_range_from_binary_expr_1 (value_range_t *vr,
       && code != MAX_EXPR
       && code != PLUS_EXPR
       && code != MINUS_EXPR
+      && code != RSHIFT_EXPR
       && (vr0.type == VR_VARYING
 	  || vr1.type == VR_VARYING
 	  || vr0.type != vr1.type
@@ -2948,6 +2949,15 @@ extract_range_from_binary_expr_1 (value_range_t *vr,
 	{
 	  if (code == RSHIFT_EXPR)
 	    {
+	      /* Even if vr0 is VARYING or otherwise not usable, we can derive
+		 useful ranges just from the shift count.  E.g.
+		 x >> 63 for signed 64-bit x is always [-1, 0].  */
+	      if (vr0.type != VR_RANGE || symbolic_range_p (&vr0))
+		{
+		  vr0.type = type = VR_RANGE;
+		  vr0.min = vrp_val_min (expr_type);
+		  vr0.max = vrp_val_max (expr_type);
+		}
 	      extract_range_from_multiplicative_op_1 (vr, code, &vr0, &vr1);
 	      return;
 	    }