debugging loop pass

[ZhuDexin]

 I am debugging  the cc1's loop optimization pass with GDB ,   and want
 to construct some rtx listes based on the loop opimization  algorithm
 because I  want  to track most paths in it to understand cc1 better.
 It is not easy , since some  previous  optimizating pass such as
 jump-opt and cse-opt have changed the original rtxs . Someone can give
 some method , to easily construct a input,  or some sources to cover this?
 
Regards

Justin Zhu