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Re: Phase 1 of gcc-in-cxx now complete
- From: Ian Lance Taylor <iant at google dot com>
- To: Matt <matt at use dot net>
- Cc: gcc at gcc dot gnu dot org
- Date: Fri, 26 Jun 2009 17:55:21 -0700
- Subject: Re: Phase 1 of gcc-in-cxx now complete
- References: <Pine.NEB.firstname.lastname@example.org>
Matt <email@example.com> writes:
>> * Develop some trial patches which require C++, e.g., convert VEC to
> Do you have any ideas for the easiest starting points? Is there
> anywhere that is decently self-contained, or will if have to be a big
Thanks for your interest.
I think the one I mentioned--converting VEC to std::vector--is a good
starting point. This is the interface in vec.h.
Another easy starting point would be converting uses of htab_t to type
safe C++ hash tables, e.g., std::tr1:;unordered_map. Here portability
suggests the ability to switch to different hash table implementations;
see gold/gold.h in the GNU binutils for one way to approach that.
Another easy starting point is finding calls to qsort and converting
them to std::sort, which typically leads to code which is larger but
Longer term, we know that memory usage is an issue in gcc. In the old
obstack days, we had a range of obstacks with different lifespans, so we
could create RTL with a temporary lifetime which was given a longer
lifetime when needed. We got away from that because we spent far too
much time chasing bugs in which RTL should have been saved to a longer
lifetime but wasn't. However, that model should permit us to run with
significantly less memory, which would translate to less compile time.
I think we might be able to do it by implementing a custom allocator,
such as a pool allocator which permits allocating different sizes of
memory, and never frees memory. Then the tree class could take an
allocator as a template parameter. Then we would provide convertors
which copied the tree class to a different allocation style. Then, for
example, fold-const.c could use a temporary pool which lived only for
the length of the call to fold. If it returned a new value, the
convertor would force a copy out of the temporary pool. If this works
out, we can use type safety to enforce memory discipline, use
significantly less memory during compilation, and take a big step toward
getting rid of the garbage collector.