On Dec 2, 2013, at 10:26 PM, Jeff Law <l...@redhat.com> wrote: > On 11/27/13 17:13, Cesar Philippidis wrote: >> >> I looked into adding support for incremental DF scanning from df*.[ch] >> in combine but there are a couple of problems. First of all, combine >> does its own DF analysis. It does so because its usage falls under this >> category (df-core.c): >> >> c) If the pass modifies insns several times, this incremental >> updating may be expensive. >> >> Furthermore, combine's DF relies on the DF scanning to be deferred, so >> the DF_REF_DEF_COUNT values would be off. Eg, calls to SET_INSN_DELETED >> take place before it updates the notes for those insns. Also, combine >> has a tendency to undo its changes occasionally. > I think at this stage of the release cycle, converting combine to incremental > DF is probably a no-go. However, we should keep it in mind for the future -- > while hairy I'd really like to see that happen in the long term.
I think Kenny has some thoughts in this area. I'll cc him to ensure he sees it.