diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index fe4213bd8c7..7e1ab3c3f18 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2004-10-18  Pat Haugen  <pthaugen@us.ibm.com>
+
+	* simplify-rtx.c (mode_signbit_p): Externalize function...
+	* rtl.h (mode_signbit_p): ... to here.
+	* combine.c (simplify_shift_const): Recognize PLUS signbit as
+	canonical form of XOR signbit and move to outer op.
+
 2004-10-18  Diego Novillo  <dnovillo@redhat.com>
 
 	* tree-cfg.c (bsi_for_stmt): Rename from stmt_for_bsi.
diff --git a/gcc/combine.c b/gcc/combine.c
index 559ee153136..98efe3eb147 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -9022,6 +9022,26 @@ simplify_shift_const (rtx x, enum rtx_code code,
 	      varop = XEXP (varop, 0);
 	      continue;
 	    }
+
+	  /* Check for 'PLUS signbit', which is the canonical form of 'XOR
+	     signbit', and attempt to change the PLUS to an XOR and move it to
+	     the outer operation as is done above in the AND/IOR/XOR case
+	     leg for shift(logical). See details in logical handling above
+	     for reasoning in doing so. */
+	  if (code == LSHIFTRT
+	      && GET_CODE (XEXP (varop, 1)) == CONST_INT
+	      && mode_signbit_p (result_mode, XEXP (varop, 1))
+	      && (new = simplify_binary_operation (code, result_mode,
+						   XEXP (varop, 1),
+						   GEN_INT (count))) != 0
+	      && GET_CODE (new) == CONST_INT
+	      && merge_outer_ops (&outer_op, &outer_const, XOR,
+				  INTVAL (new), result_mode, &complement_p))
+	    {
+	      varop = XEXP (varop, 0);
+	      continue;
+	    }
+
 	  break;
 
 	case MINUS:
diff --git a/gcc/rtl.h b/gcc/rtl.h
index 3ebf4aa7a17..ca2a0174ae5 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -1570,6 +1570,7 @@ extern rtx simplify_gen_subreg (enum machine_mode, rtx, enum machine_mode,
 extern rtx simplify_replace_rtx (rtx, rtx, rtx);
 extern rtx simplify_rtx (rtx);
 extern rtx avoid_constant_pool_reference (rtx);
+extern bool mode_signbit_p (enum machine_mode, rtx);
 
 /* In regclass.c  */
 extern enum machine_mode choose_hard_reg_mode (unsigned int, unsigned int,
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index 7236bbfc064..4af468a40ca 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -50,7 +50,6 @@ Software Foundation, 59 Temple Place - Suite 330, Boston, MA
  ((((HOST_WIDE_INT) low) < 0) ? ((HOST_WIDE_INT) -1) : ((HOST_WIDE_INT) 0))
 
 static rtx neg_const_int (enum machine_mode, rtx);
-static bool mode_signbit_p (enum machine_mode, rtx);
 static int simplify_plus_minus_op_data_cmp (const void *, const void *);
 static rtx simplify_plus_minus (enum rtx_code, enum machine_mode, rtx,
 				rtx, int);
@@ -72,7 +71,7 @@ neg_const_int (enum machine_mode mode, rtx i)
 /* Test whether expression, X, is an immediate constant that represents
    the most significant bit of machine mode MODE.  */
 
-static bool
+bool
 mode_signbit_p (enum machine_mode mode, rtx x)
 {
   unsigned HOST_WIDE_INT val;