(num_sign_bit_copies): Properly handle case when MODE is narrower than that of X.

(num_sign_bit_copies): Properly handle case when MODE is narrower than that
of X.
(simplify_shift_const): Remove change of July 26.

From-SVN: r5110

gcc/combine.c

@@ -6687,6 +6687,11 @@ num_sign_bit_copies (x, mode)
 
   bitwidth = GET_MODE_BITSIZE (mode);
 
+  /* For a smaller object, just ignore the high bits. */
+  if (bitwidth < GET_MODE_BITSIZE (GET_MODE (x)))
+    return MAX (1, (num_sign_bit_copies (x, GET_MODE (x))
+		    - (GET_MODE_BITSIZE (GET_MODE (x)) - bitwidth)));
+     
   switch (code)
     {
     case REG:
@@ -7181,11 +7186,6 @@ simplify_shift_const (x, code, result_mode, varop, count)
       else if (count < 0)
 	abort ();
 
-      /* If we have replaced VAROP with something wider
-	 (such as, the SUBREG_REG), then this won't work;
-	 num_sign_bit_copies will give the wrong answer in that case.  */
-      if (shift_mode == GET_MODE (varop))
-	{
       /* An arithmetic right shift of a quantity known to be -1 or 0
 	 is a no-op.  */
       if (code == ASHIFTRT
@@ -7205,7 +7205,6 @@ simplify_shift_const (x, code, result_mode, varop, count)
 	  && (count + num_sign_bit_copies (varop, shift_mode)
 	      >= GET_MODE_BITSIZE (shift_mode)))
 	count = GET_MODE_BITSIZE (shift_mode) - 1;
-	}
 
       /* We simplify the tests below and elsewhere by converting
 	 ASHIFTRT to LSHIFTRT if we know the sign bit is clear.