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.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@111226 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 479e8e8..9acf0ac 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+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

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 7413883..c77e7ba 100644 (file)
--- a/gcc/fold-const.c
+++ b/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))

diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 6f4f09b..8b1f6fd 100644 (file)
--- a/gcc/simplify-rtx.c
+++ b/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: