C compile time

[Richard Guenther]

>> It would be nice if some of the inlining issues got sorted out for 3.4,
>> and -Winline became deterministic again.
>
>For 3.4, we could consider going back to the "bottom-up" inlining
>strategy.  That might be better than what we have now, even though it's
>inherently quadratic.  Implementing bottom-up inlining wouldn't be
>terribly hard; all the same tree-inlining machinery would work.
>
>One of the things we seem to forget in all the inlining discussion is
>that inlining has never worked well.  In fact, one of the big
>motivations in going to function-at-a-time was to try to fix all the
>lameness in the RTL inliner!  On many large C++ programs, the 2.95 era
>compilers would simply exhaust all memory trying to do inlining...
>
>I'm pretty convinced that there's no easy fix, unfortunately.

I think at least with a callgraph available we can do better. Also
implementing more user hints (like __attribute__((leafify))) correctly
needs a callgraph due to our function deffering stuff.

Richard.