GCC 4.3 Hacking

I haven’t talked about the incremental compiler in a couple of weeks — first I was out of town, and then I was sick. And then yesterday, I put it off… I don’t want to be that way, but the truth is for the last couple of weeks I haven’t been working on this project much.

Instead, I’ve been doing a bit of work fixing bugs on the trunk, to help make it so that GCC 4.3 can be released in a timely way. I don’t really know much about most of GCC, though, so I’ve pretty much been working on only the bugs in parts I do know: more or less the C front end and the preprocessor.

Working on bugs this way is a humbling experience. Last week I think I fixed four bugs. Looking through the ChangeLog, I think Jakub fixed twenty. Hmm… I don’t even know how he can do that many bootstrap-and-check cycles in a week.

I also put a bit of work into making GCC emit better column number information — there’s some new location code that is more memory efficient (saves about 5%) and that enables column number output. Unfortunately the parsers and constant folders and debug output generators know nothing about columns; and fixing this is a big enough job that it won’t happen in 4.3.

The more I work on parts of GCC like this, the more I realize how awesome gcjx really was, if I may say so myself. GCC has several bad design decisions baked into things as basic as location handling. Sad. It will be a lot of work to clean this up… and when I look at GCC I think my eyes are bigger than my stomach. Or in other words, I need help.

I did do a little work on the incremental compiler, starting this week: I did a few cleanups to undo breakage I introduced earlier. My plan is to merge what I’ve got to the trunk during the next Stage 1. So, I’m cleaning up the little details I intentionally ignored during the experimentation phase.

My thinking behind the merge is that, first, the old compile server partly failed due to being on a branch too long, a mistake I don’t want to repeat; and second, even though this code does not do everything, it is reaching a good milestone, and at the very least it greatly speeds up --combine builds. I’ve heard that the Linux kernel uses combine; benchmarking this is on my to-do list.

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  • We do not yet have –combine support in mainline of the kernel.
    A few patches has been floating around but their status is unknow.


  • Ah, thanks. That explains why there aren’t many more bug reports about this.

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