My favorite example of this lack of follow-through is gcse.c. It computes reg-def chains and monotonic insn IDs. Guess what df-scan provides?
This is great. I did that for combine and CSE, but I didn't know GCSE as well. From the description from my first read I like this patch, and I think you are the person that has studied GCSE more so I trust it a lot. (Most of this could be done in postreload GCSE too, by the way).
Paolo
