re PR middle-end/21082 (&a[b] - &a[c] is not folded to b - c)

2005-04-23  Richard Guenther  <rguenth@gcc.gnu.org>

	PR middle-end/21082
	* fold-const.c: Fold &a[i]-&a[j] to i-j.

	* g++.dg/tree-ssa/pr21082.C: New testcase.

From-SVN: r98636

gcc/ChangeLog

+2005-04-23  Richard Guenther  <rguenth@gcc.gnu.org>
+
+	PR middle-end/21082
+	* fold-const.c: Fold &a[i]-&a[j] to i-j.
+
 2005-04-23  Zdenek Dvorak  <dvorakz@suse.cz>
 
 	* tree-ssa-loop-niter.c (tree_simplify_using_condition): Expand simple

gcc/fold-const.c

@@ -7842,6 +7842,27 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
 	  return build_int_cst_type (type, diff);
       }
 
+      /* Fold &a[i] - &a[j] to i-j.  */
+      if (TREE_CODE (arg0) == ADDR_EXPR
+	  && TREE_CODE (TREE_OPERAND (arg0, 0)) == ARRAY_REF
+	  && TREE_CODE (arg1) == ADDR_EXPR
+	  && TREE_CODE (TREE_OPERAND (arg1, 0)) == ARRAY_REF)
+        {
+	  tree aref0 = TREE_OPERAND (arg0, 0);
+	  tree aref1 = TREE_OPERAND (arg1, 0);
+	  if (operand_equal_p (TREE_OPERAND (aref0, 0),
+			       TREE_OPERAND (aref1, 0), 0))
+	    {
+	      tree op0 = fold_convert (type, TREE_OPERAND (aref0, 1));
+	      tree op1 = fold_convert (type, TREE_OPERAND (aref1, 1));
+	      tree esz = array_ref_element_size (aref0);
+	      tree diff = build2 (MINUS_EXPR, type, op0, op1);
+	      return fold_build2 (MULT_EXPR, type, diff,
+			          fold_convert (type, esz));
+			          
+	    }
+	}
+
       /* Try replacing &a[i1] - c * i2 with &a[i1 - i2], if c is step
 	 of the array.  Loop optimizer sometimes produce this type of
 	 expressions.  */

gcc/testsuite/ChangeLog

+2005-04-23  Richard Guenther  <rguenth@gcc.gnu.org>
+
+	PR middle-end/21082
+	* g++.dg/tree-ssa/pr21082.C: New testcase.
+
 2005-04-23  Zdenek Dvorak  <dvorakz@suse.cz>
 
 	* gcc.dg/vect/vect-99.c: New test.

gcc/testsuite/g++.dg/tree-ssa/pr21082.C

+/* { dg-do link } */
+
+void link_error();
+
+int a[4];
+long b, c;
+
+int main()
+{
+	if (&a[b] - &a[c] != b - c)
+		link_error();
+	return 0;
+}