Friday GCC Update

I haven’t been blogging much lately, at least partly because I’ve been having fun hacking on GCC. Mark pointed out, though, that I should blog regularly about my progress so people know what is happening.

I’ve got the basic compile server running. Recently I’ve been fixing bugs in it. I’m not seeing the mind-blowing 2x speedup I once was; I need to look into that a bit. This doesn’t matter, though, because the real benefits will come from the next step, which is incremental code generation.

This week, to get away from the bugs a bit, I made GCC’s garbage collector thread-aware. Following the implementation methodology known as “Biting Off More Than You Can Chew”, I also dove in to making the whole front end work multi-threaded. So far this has yielded an evil-looking patch that marks a couple hundred global variables with __thread.

My current plan is to try to merge what I’ve got during the next Stage 1. My thinking is, the current code provides benefits, even if it not every planned benefit. It would be better to merge as frequently as possible — not just for testing but also because smaller patches are simpler to understand, and an early merge would get other GCC maintainers used to the new stuff.

Actually… why don’t I just post my road-map here

  1. Fix bugs. Make it bootstrap again.
  2. Clean up the hacks I put in. Implement the things I skipped (anti-dependencies, maybe semantic dependencies, fix PCH).
  3. Test on bigger programs.
  4. Make sure --enable-intermodule bootstrap works. Measure performance improvement.
  5. Stage 1 merge.

At this point there are multiple options for what to do next. I’m not sure what order I will tackle them — as the thread experiment shows, I’m prone to following what looks fun, in the absence of other constraints.

  1. Incremental code generation. May require linker changes.
  2. C++ front end. (I’m thinking we should make the front ends into shared libraries that gcc will dlopen.)
  3. Finish multi-threading work (if I don’t do this next week).
  4. If there isn’t one yet, finish incremental linker.

After this comes other fun stuff, like adding a way to query the server for information about your program. I’m thinking http…

I’ve also gotten interested in other aspects of GCC’s C front end. For example, it is not ideal for some kinds of static analysis because it folds too early. It might be fun to fix this.

One Comment

  • Mark is right!!!
    Keep it up!

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