On Tue, 12 Dec 2006, Christopher Li wrote: > > I am playing with the example.c. I am wondering why the parent > basic blocks need to generate first? They don't have to. But it generated nicer code, iirc, mainly because it did the storage allocation the natural way. In particular, if I recall correctly, it causes loops to have the storage for the _innermost_ loop to be done first. Notes off the top of my head, without actually looking at the code: because when you hit a loop, the "parent" set is actually both the entry and the BB that ha the loopback, so you actually end up going to the loopback thing, which goes to _its_ parents, etc etc, until you actually get back to the _top_ of the loop (and now the "generation" count triggers you to break the looping), so you end up doing the actual register allocation at tops of loops, but because you do this all recursively, and the inner loop will have _its_ parents point to the callback too, you generally tend to have started storage allocation at loop-tops. HOWEVER. There's a reason the thing is called "example.c". The reason is simply that it's stupid, idiotic, and not meant to be taken seriously. I also ended up just hackign things around randomly to make it output something that looked half-way sane, _and_ I ended up changign it to use the "unssa" pass by Luc, _and_ I'm border-line psychotic when it comes to compilers anyway. In other words, what I'm trying to say is that you shouldn't take anything I say too seriously, and that the "example.c" code wasn't really even meant to be serious. I always wanted somebody else to write the back-end, and held back as long as I could from writing example.c, and when I wrote it, it was more a case of desperately trying to find somebody interested in it, and having it as an example of how things _might_ work. So as far as I am concerned, the whole "example.c" is just total throw-away code. Go wild with it. Linus - To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
