machine ir transformation

Hi
   I would like to add transformation - mostly peephole- after
register allocation that make use of def-use information. Would it be
possible to make use of the dag codebase to help do that ?

thanks for any pointers
shrey

On rereading i thought I probably wasnt very clear.

to restate, I was wondering if I can use the selection dag
infrastructure to build def use information. I am looking to use
information such as def-use within a basic block, is the register
used outside the basic block and load/store dependencies.

Any thoughts on doing it before register allocation?

I will appreciate any ideas !
shrey