re PR tree-optimization/53355 (Autovectorization of a simple loop could be improved.)

2012-05-15  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/53355
	* tree-vrp.c (extract_range_from_binary_expr_1): Handle LSHIFT_EXPRs
	by constants.

	* gcc.dg/tree-ssa/vrp67.c: New testcase.

From-SVN: r187535

gcc/ChangeLog

+2012-05-15  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/53355
+	* tree-vrp.c (extract_range_from_binary_expr_1): Handle LSHIFT_EXPRs
+	by constants.
+
 2012-05-15  Tristan Gingold  <gingold@adacore.com>
 
       * tree-ssa-strlen.c (get_string_length): Convert lhs if needed.

gcc/testsuite/ChangeLog

+2012-05-15  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/53355
+	* gcc.dg/tree-ssa/vrp67.c: New testcase.
+
 2012-05-15  Bernhard Reutner-Fischer  <aldot@gcc.gnu.org>
 
 	* gfortran.dg/*.f90: Remove now redundant manual

gcc/testsuite/gcc.dg/tree-ssa/vrp67.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-vrp1" } */
+
+unsigned foo (unsigned i)
+{
+  if (i == 2)
+    {
+      i = i << 2;
+      if (i != 8)
+	link_error ();
+    }
+  return i;
+}
+unsigned bar (unsigned i)
+{
+  if (i == 1 << (sizeof (unsigned) * 8 - 1))
+    {
+      i = i << 1;
+      if (i != 0)
+	link_error ();
+    }
+  return i;
+}
+unsigned baz (unsigned i)
+{
+  i = i & 15;
+  if (i == 0)
+    return 0;
+  i = 1000 - i;
+  i >>= 1;
+  i <<= 1;
+  if (i == 0)
+    link_error ();
+  return i;
+}
+
+/* { dg-final { scan-tree-dump-times "Folding predicate" 3 "vrp1" } } */
+/* { dg-final { cleanup-tree-dump "vrp1" } } */

gcc/tree-vrp.c

@@ -2403,6 +2403,7 @@ extract_range_from_binary_expr_1 (value_range_t *vr,
       && code != ROUND_DIV_EXPR
       && code != TRUNC_MOD_EXPR
       && code != RSHIFT_EXPR
+      && code != LSHIFT_EXPR
       && code != MIN_EXPR
       && code != MAX_EXPR
       && code != BIT_AND_EXPR
@@ -2596,6 +2597,40 @@ extract_range_from_binary_expr_1 (value_range_t *vr,
       extract_range_from_multiplicative_op_1 (vr, code, &vr0, &vr1);
       return;
     }
+  else if (code == LSHIFT_EXPR)
+    {
+      /* If we have a LSHIFT_EXPR with any shift values outside [0..prec-1],
+	 then drop to VR_VARYING.  Outside of this range we get undefined
+	 behavior from the shift operation.  We cannot even trust
+	 SHIFT_COUNT_TRUNCATED at this stage, because that applies to rtl
+	 shifts, and the operation at the tree level may be widened.  */
+      if (vr1.type != VR_RANGE
+	  || !value_range_nonnegative_p (&vr1)
+	  || TREE_CODE (vr1.max) != INTEGER_CST
+	  || compare_tree_int (vr1.max, TYPE_PRECISION (expr_type) - 1) == 1)
+	{
+	  set_value_range_to_varying (vr);
+	  return;
+	}
+
+      /* We can map shifts by constants to MULT_EXPR handling.  */
+      if (range_int_cst_singleton_p (&vr1))
+	{
+	  value_range_t vr1p = { VR_RANGE, NULL_TREE, NULL_TREE, NULL };
+	  vr1p.min
+	    = double_int_to_tree (expr_type,
+				  double_int_lshift (double_int_one,
+						     TREE_INT_CST_LOW (vr1.min),
+						     TYPE_PRECISION (expr_type),
+						     false));
+	  vr1p.max = vr1p.min;
+	  extract_range_from_multiplicative_op_1 (vr, MULT_EXPR, &vr0, &vr1p);
+	  return;
+	}
+
+      set_value_range_to_varying (vr);
+      return;
+    }
   else if (code == TRUNC_DIV_EXPR
 	   || code == FLOOR_DIV_EXPR
 	   || code == CEIL_DIV_EXPR