re PR rtl-optimization/3640 (small lost optimization of "x==0 || x==1")

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

From-SVN: r49096

gcc/ChangeLog

+2002-01-22  Roger Sayle  <roger@eyesopen.com>
+	    Richard Henderson  <rth@redhat.com>
+
+	PR opt/3640
+	* fold-const.c (fold): Optimize unsigned comparisons against
+	UINT_MAX (and similar unsigned constants).
+
 2002-01-22  Janis Johnson  <janis187@us.ibm.com>
 
 	* Makefile.in (loop.o): Depend on OPTABS_H.

gcc/fold-const.c

 /* 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.
+   1999, 2000, 2001, 2002 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -6753,6 +6753,31 @@ fold (expr)
 		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;
+                }
 	  }
       }