re PR middle-end/55863 (Fails to fold (i + 2) - (i + 1) to 1)

2013-01-04  Richard Biener  <rguenther@suse.de>

	PR middle-end/55863
	* fold-const.c (split_tree): Undo -X - 1 to ~X folding for
	reassociation.

	* gcc.dg/fold-reassoc-2.c: New testcase.

From-SVN: r194899

gcc/ChangeLog

+2013-01-04  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/55863
+	* fold-const.c (split_tree): Undo -X - 1 to ~X folding for
+	reassociation.
+
 2013-01-03  John David Anglin  <dave.anglin@nrc-cnrc.gc.ca>
 
 	PR target/53789

gcc/fold-const.c

@@ -821,6 +821,13 @@ split_tree (tree in, enum tree_code code, tree *conp, tree *litp,
       if (neg_var_p)
 	var = negate_expr (var);
     }
+  else if (TREE_CODE (in) == BIT_NOT_EXPR
+	   && code == PLUS_EXPR)
+    {
+      /* -X - 1 is folded to ~X, undo that here.  */
+      *minus_litp = build_one_cst (TREE_TYPE (in));
+      var = negate_expr (TREE_OPERAND (in, 0));
+    }
   else if (TREE_CONSTANT (in))
     *conp = in;
   else

gcc/testsuite/ChangeLog

+2013-01-04  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/55863
+	* gcc.dg/fold-reassoc-2.c: New testcase.
+
 2013-01-04  Tobias Burnus  <burnus@net-b.de>
 
 	PR fortran/55763

gcc/testsuite/gcc.dg/fold-reassoc-2.c

+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-original" } */
+
+int foo (int i)
+{
+  return (i + 2) - (i + 1);
+}
+int bar (int i)
+{
+  return (i + 2) + ~i;
+}
+
+/* { dg-final { scan-tree-dump "return 1;" "original" } } */
+/* { dg-final { cleanup-tree-dump "original" } } */