On Nov 16, 2007 11:43 PM, Steven Bosscher <[EMAIL PROTECTED]> wrote: > Hello, > > The amount of duplicate work done on RTL is sometimes really amazing, > especially since the merge of the dataflow branch. Some of the people > who have worked on the dataflow branch had hoped that other developers > would help with the follow-up actions to actually *use* all the > information that, for example, the df-scan problem collects. > > 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? > > Attached is an example of the cleanups I would have liked to see > during stage 2 of GCC 4.3. The patch is not finished, but it gives > you an idea of what is possible. The patch avoids computation of > redundant information by making gcse use the df-scan information, > instead of computing everything for itself. In theory, this saves > memory and it reduces the number of passes over all RTX'en in memory. > So, if finished, this should give compile time improvements and a > slightly smaller memory footprint. > > Question is, whether this kind of rather large changes is acceptable > for stage 3 or not. Me, I call it a "regression fix" if it reduces > compile time. But I will not work on it now (or ask help from others) > if it is a priori not acceptable for stage 3. > > Thus, thoughts please! :-)
I think we should be able to rely on DF enough to make mostly mechanical changes like this ok for stage3. I don't know where we are in terms of compile-time compared to 4.2 or 4.1, but certainly if you go back further compile-time is always a "regression". Thanks, Richard.
