Question about doloop_end pattern

Hello,
I tried to use doloop_end pattern to reduce loop overhead for our target
processor, which features a dedicated loop instruction.  Somehow even a
simple loop just cannot pass the test of doloop_condition_get, which
requires following canonical pattern.

  /* The canonical doloop pattern we expect has one of the following
     forms:

     1)  (parallel [(set (pc) (if_then_else (condition)
	  			            (label_ref (label))
				            (pc)))
	             (set (reg) (plus (reg) (const_int -1)))
	             (additional clobbers and uses)])

     The branch must be the first entry of the parallel (also required
     by jump.c), and the second entry of the parallel must be a set of
     the loop counter register.  Some targets (IA-64) wrap the set of
     the loop counter in an if_then_else too.

     2)  (set (reg) (plus (reg) (const_int -1))
         (set (pc) (if_then_else (reg != 0)
	                         (label_ref (label))
			         (pc))).  */

Here is a simple function I used, it should meet all doloop optimization
requirements.
void Unroll( short s, int * restrict b_inout, int *restrict out, int N)
{
        int i;