re PR rtl-optimization/25600 (unsigned>>31?-1:0 should be optimized to int>>31)

	PR middle-end/25600
	* fold-const.c (fold_binary): Fold (X >> C) != 0 into X < 0 when
	C is one less than the width of X (and related transformations).
	* simplify_rtx.c (simplify_unary_operation_1): Transform 
	(neg (lt x 0)) into either (ashiftrt X C) or (lshiftrt X C)
	depending on STORE_FLAG_VALUE, were C is one less then the
	width of X.

From-SVN: r111226

gcc/ChangeLog

+2006-02-17  Roger Sayle  <roger@eyesopen.com>
+
+	PR middle-end/25600
+	* fold-const.c (fold_binary): Fold (X >> C) != 0 into X < 0 when
+	C is one less than the width of X (and related transformations).
+	* simplify_rtx.c (simplify_unary_operation_1): Transform 
+	(neg (lt x 0)) into either (ashiftrt X C) or (lshiftrt X C)
+	depending on STORE_FLAG_VALUE, were C is one less then the
+	width of X.
+
 2006-02-17  Daniel Berlin  <dberlin@dberlin.org>
 
 	Fix PR tree-optimization/26341

gcc/fold-const.c

@@ -10042,6 +10042,30 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1)
 	    return t1;
 	}
 
+      /* Fold (X >> C) != 0 into X < 0 if C is one less than the width
+	 of X.  Similarly fold (X >> C) == 0 into X >= 0.  */
+      if ((code == EQ_EXPR || code == NE_EXPR)
+	  && integer_zerop (arg1)
+	  && TREE_CODE (arg0) == RSHIFT_EXPR
+	  && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST)
+	{
+	  tree arg00 = TREE_OPERAND (arg0, 0);
+	  tree arg01 = TREE_OPERAND (arg0, 1);
+	  tree itype = TREE_TYPE (arg00);
+	  if (TREE_INT_CST_HIGH (arg01) == 0
+	      && TREE_INT_CST_LOW (arg01)
+		 == (unsigned HOST_WIDE_INT) (TYPE_PRECISION (itype) - 1))
+	    {
+	      if (TYPE_UNSIGNED (itype))
+		{
+		  itype = lang_hooks.types.signed_type (itype);
+		  arg00 = fold_convert (itype, arg00);
+		}
+	      return fold_build2 (code == EQ_EXPR ? GE_EXPR : LT_EXPR,
+				  type, arg00, build_int_cst (itype, 0));
+	    }
+	}
+
       if ((code == EQ_EXPR || code == NE_EXPR)
 	  && integer_zerop (arg1)
 	  && tree_expr_nonzero_p (arg0))

gcc/simplify-rtx.c

@@ -584,6 +584,19 @@ simplify_unary_operation_1 (enum rtx_code code, enum machine_mode mode, rtx op)
 	  && XEXP (op, 1) == const1_rtx
 	  && nonzero_bits (XEXP (op, 0), mode) == 1)
 	return plus_constant (XEXP (op, 0), -1);
+
+      /* (neg (lt x 0)) is (ashiftrt X C) if STORE_FLAG_VALUE is 1.  */
+      /* (neg (lt x 0)) is (lshiftrt X C) if STORE_FLAG_VALUE is -1.  */
+      if (GET_CODE (op) == LT
+	  && XEXP (op, 1) == const0_rtx)
+	{
+	  if (STORE_FLAG_VALUE == 1)
+	    return simplify_gen_binary (ASHIFTRT, mode, XEXP (op, 0),
+					GEN_INT (GET_MODE_BITSIZE (mode) - 1));
+	  else if (STORE_FLAG_VALUE == -1)
+	    return simplify_gen_binary (LSHIFTRT, mode, XEXP (op, 0),
+					GEN_INT (GET_MODE_BITSIZE (mode) - 1));
+	}
       break;
 
     case TRUNCATE: