Fix ia64 gdb miscompilation reported by Kevin Buettner.

	* combine.c (force_to_mode, case LSHIFTRT): Check that shift shift
	plus mask size is smaller or equal to the mode size.

From-SVN: r33157

gcc/ChangeLog

+Fri Apr 14 16:09:02 2000  Jim Wilson  <wilson@cygnus.com>
+
+	* combine.c (force_to_mode, case LSHIFTRT): Check that shift shift
+	plus mask size is smaller or equal to the mode size.
+
 Fri Apr 14 18:07:30 2000  Richard Kenner  <kenner@vlsi1.ultra.nyu.edu>
 
 	* print-rtl.c (print_rtx, case NOTE): Don't blow up if NOTE_BASIC_BLOCK

gcc/combine.c

@@ -6935,10 +6935,17 @@ force_to_mode (x, mode, mask, reg, just_select)
 
       if (GET_CODE (x) == LSHIFTRT
 	  && GET_CODE (XEXP (x, 1)) == CONST_INT
+	  /* The shift puts one of the sign bit copies in the least significant
+	     bit.  */
 	  && ((INTVAL (XEXP (x, 1))
 	       + num_sign_bit_copies (XEXP (x, 0), GET_MODE (XEXP (x, 0))))
 	      >= GET_MODE_BITSIZE (GET_MODE (x)))
 	  && exact_log2 (mask + 1) >= 0
+	  /* Number of bits left after the shift must be more than the mask
+	     needs.  */
+	  && ((INTVAL (XEXP (x, 1)) + exact_log2 (mask + 1))
+	      <= GET_MODE_BITSIZE (GET_MODE (x)))
+	  /* Must be more sign bit copies than the mask needs.  */
 	  && ((int) num_sign_bit_copies (XEXP (x, 0), GET_MODE (XEXP (x, 0)))
 	      >= exact_log2 (mask + 1)))
 	x = gen_binary (LSHIFTRT, GET_MODE (x), XEXP (x, 0),