[Commited] Constant fold (x | 5) != 0

[Roger Sayle]

I've committed the following minor improvement to GCC's constant folding
to mainline.  This patch adds three additional cases to the middle-end's
predicates that are used for simplifying conditional expressions.

[1] The expression "A & B" is nonnegative, if A or B is nonnegative.
[2] The expression "A | B" is nonnegative, if A and B are nonnegative.
[3] The expression "A | B" is nonzero, if A is nonzero or B is nonzero.

Although the expression "(x | 5) != 0" is currently optimized away at
the RTL-level, supporting this transformation in "fold" makes it available
to tree-ssa's optimizers.

The following patch was tested on i686-pc-linux-gnu with a complete "make
bootstrap", all languages except treelang, and regression tested with a
top-level "make -k check" with no new failures.


2004-03-23  Roger Sayle  <roger@eyesopen.com>

	* fold-const.c (tree_expr_nonnegative_p): A&B is nonnegative when
	A is nonnegative or B is nonnegative.  Similarly A|B is nonnegative
	when both A and B are nonnegative.
	(tree_expr_nonzero_p): A|B is nonzero when A is nonzero or B is
	nonzero.


Index: fold-const.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fold-const.c,v
retrieving revision 1.355
diff -c -3 -p -r1.355 fold-const.c
*** fold-const.c	21 Mar 2004 18:09:17 -0000	1.355
--- fold-const.c	22 Mar 2004 02:07:08 -0000
*************** tree_expr_nonnegative_p (tree t)
*** 8722,8727 ****
--- 8722,8734 ----
        return tree_expr_nonnegative_p (TREE_OPERAND (t, 0))
  	     && tree_expr_nonnegative_p (TREE_OPERAND (t, 1));

+     case BIT_AND_EXPR:
+       return tree_expr_nonnegative_p (TREE_OPERAND (t, 1))
+ 	     || tree_expr_nonnegative_p (TREE_OPERAND (t, 0));
+     case BIT_IOR_EXPR:
+       return tree_expr_nonnegative_p (TREE_OPERAND (t, 0))
+ 	     && tree_expr_nonnegative_p (TREE_OPERAND (t, 1));
+
      case NOP_EXPR:
        {
  	tree inner_type = TREE_TYPE (TREE_OPERAND (t, 0));
*************** tree_expr_nonzero_p (tree t)
*** 8959,8964 ****
--- 8966,8975 ----
      case SAVE_EXPR:
      case NON_LVALUE_EXPR:
        return tree_expr_nonzero_p (TREE_OPERAND (t, 0));
+
+     case BIT_IOR_EXPR:
+       return tree_expr_nonzero_p (TREE_OPERAND (t, 1))
+ 	     || tree_expr_nonzero_p (TREE_OPERAND (t, 0));

      default:
        break;

Roger
--
Roger Sayle,                         E-mail: roger@eyesopen.com
OpenEye Scientific Software,         WWW: http://www.eyesopen.com/
Suite 1107, 3600 Cerrillos Road,     Tel: (+1) 505-473-7385
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