[PATCH]: Constant fold comparisons against UINT_MAX

[Roger Sayle]

> Actually, you should be able to make use of TYPE_MAX_VALUE here.  Try
> 	else if (TREE_UNSIGNED (TREE_TYPE (arg1))
> 		 && tree_int_cst_equal (TYPE_MAX_VALUE (TREE_TYPE (arg1)),
> 					arg1))

Yep, that works and makes for a significantly shorter patch.  I've
tested this improved version with "make bootstrap" and "make -k check"
on i686-pc-linux-gnu with no new regressions.  I've also checked
that it solves PR opt/3640 by examining the output from "-da" and "-S".
I've taken the liberty of adding you as co-author, I hope that's OK.

Is this a suitable fix for mainline and to close PR opt/3640?


2002-01-21  Roger Sayle  <roger@eyesopen.com>
	    Richard Henderson  <rth@redhat.com>

	* fold-const.c (fold): Optimize unsigned comparisons against
	UINT_MAX (and similar unsigned constants). Fixes PR opt/3640.


*** gcc/gcc/fold-const.c	Sun Dec 16 21:19:08 2001
--- patch8b/gcc/fold-const.c	Mon Jan 21 21:04:26 2002
***************
*** 1,6 ****
  /* Fold a constant sub-tree into a single node for C-compiler
     Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
!    1999, 2000, 2001 Free Software Foundation, Inc.

  This file is part of GCC.

--- 1,6 ----
  /* Fold a constant sub-tree into a single node for C-compiler
     Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
!    1999, 2000, 2001, 2002 Free Software Foundation, Inc.

  This file is part of GCC.

*************** fold (expr)
*** 6753,6758 ****
--- 6753,6783 ----
  		default:
  		  break;
  		}
+
+             else if (TREE_UNSIGNED (TREE_TYPE (arg1))
+                      && tree_int_cst_equal (TYPE_MAX_VALUE (TREE_TYPE (arg1)),
+                                             arg1))
+               switch (TREE_CODE (t))
+                 {
+                 case GT_EXPR:
+                   return omit_one_operand (type,
+                                            convert (type, integer_zero_node),
+                                            arg0);
+                 case GE_EXPR:
+                   TREE_SET_CODE (t, EQ_EXPR);
+                   break;
+
+                 case LE_EXPR:
+                   return omit_one_operand (type,
+                                            convert (type, integer_one_node),
+                                            arg0);
+                 case LT_EXPR:
+                   TREE_SET_CODE (t, NE_EXPR);
+                   break;
+
+                 default:
+                   break;
+                 }
  	  }
        }


Roger
--
Roger Sayle,                         E-mail: roger@eyesopen.com
OpenEye Scientific Software,         WWW: http://www.eyesopen.com/
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