combine.c (find_split_point): Don't turn a SIGN_EXTEND into a series of shifts if...

        * combine.c (find_split_point): Don't turn a SIGN_EXTEND into
        a series of shifts if either mode is a partial integer mode.

From-SVN: r13665

gcc/combine.c

@@ -2699,6 +2699,14 @@ find_split_point (loc, insn)
 
 	case SIGN_EXTEND:
 	  inner = XEXP (SET_SRC (x), 0);
+
+	  /* We can't optimize if either mode is a partial integer
+	     mode as we don't know how many bits are significant
+	     in those modes.  */
+	  if (GET_MODE_CLASS (GET_MODE (inner)) == MODE_PARTIAL_INT
+	      || GET_MODE_CLASS (GET_MODE (SET_SRC (x))) == MODE_PARTIAL_INT)
+	    break;
+
 	  pos = 0;
 	  len = GET_MODE_BITSIZE (GET_MODE (inner));
 	  unsignedp = 0;