On Wed, Nov 28, 2012 at 11:30:32AM +0100, Richard Biener wrote: > > Note that I don't think that non-GC is inherently better than GC. In fact, > using a GC leads to easier maintainable code. The fact that we are more > memory hungry than necessary (and also maybe consume more compile-time > than necessary) is because our GC isn't exactly using technology known > for 25 years (generational and copying collection come to my mind).
I definitely agree with that. And FWIW, MELT (http://gcc-melt.org/ has since its beginning a generational copying garbage collector above ggc+gengtype, so that is definitely doable. I would wish that GCC systematically used a generational copying GC scheme. However, this requires that the GCC community agree with that goal (and apparently, most - or some - people want on the contrary to get rid of GC). FWIW, C++ may help in having a manageable copying GC inside GCC, provided every GCC contributor agree with it. (The hard point is that garbage collection deals with a global -non-modular- property of the GCC program -liveness of data-, so it is not feasible to introduce a generational copying GC progressively or incrementally). What a precise copying generational GC needs to know is all the local (and global) variables containing GC-managed pointer data. The important word is *all*, and that means that everyone should agree to use it. We could for instance have a template for every garbage collector local pointer, and declare everywhere locals like gclocal<tree> pt1, pt2; gclocal<gimple> pg; we could also have them handled by a preprocessor (à la gengtype) and make that something like GCLOCAL(tree pt1, pt2); GCLOCAL(gimple pg); Introducing a copying generational scheme would involve perhaps a bigger effort than the vec.h transition, because a lot of GCC source files would have to be somehow modified. (there is an economical & social issue here: who is brave enough to spend time to work on that? Few people could take the risk to experiment that if an agreement on GC cannot be reached) Regards. -- Basile STARYNKEVITCH http://starynkevitch.net/Basile/ email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359 8, rue de la Faiencerie, 92340 Bourg La Reine, France *** opinions {are only mines, sont seulement les miennes} ***
