Tart status update

Monday, October 25, 2010
I've been working pretty hard on Tart the last few weeks. I've been focused on several areas:

DWARF debugging - There's not much progress in this area, despite my best efforts. Lately I've been attacking the problem from a different direction, which is to produce a reproducible test case that doesn't require the entire Tart infrastructure to be present. Unfortunately, doing this requires fixing a bunch of minor issues which would not otherwise be high priority. For example, the Tart linker fails unless optimization is enabled, due to a bug in the LLVM lowering pass for garbage collection intrinsics. Unfortunately, I need an unoptimized test case if I want to get the LLVM experts to help me with my problem. So I have to fix the second problem in order to even start working on the first.

Garbage Collection - The stack crawler is completely working now. The next step is to write a very simple test collector and a test for it.

One issue that concerns me is that I want Tart to be able to support pluggable collectors like Java does. Java has the ability to specify a collector when you launch the program - in other words, the selection of collection algorithm can be deferred until the program begins execution. In order to do this, I'd need some sort of plugin or loadable module system, something I haven't even begun to think about.

The best I can do for the moment is to make the collector algorithm a link-time decision, that is to have different static link libraries for different collectors.

Reflection - I've been working hard on the new reflection system, the one that uses compressed metadata to describe all of the various classes and methods in a module. Right now the compiler emits the metadata for both the old and new systems, which makes the resulting object files much larger than I would like them. Unfortunately, the new system isn't yet up to the task of replacing the old system. For example, the "execute by name" feature - which is used by the unit test framework - isn't ready yet.

I've also been plagued by a number of strange anomalies. CMake has been acting weird lately - a build rule that was working fine for several months suddenly stopped working. I didn't notice at first since the bug only manifests on a clean build. Although CMake is a great tool, there are certain kinds of build rules which really ought to be simple, but which are nearly impossible to do without truly ugly and non-intuitive work-arounds. For example, it's nearly impossible to define an add_custom_command() rule which has a dependency on a build product which was produced in a different directory.

Sigh...it seems like the last 3-4 months has been spent dealing with low-level details of LLVM, DWARF, and so on - I've spent virtually no time thinking about the Tart language per se, which is what I really want to be working on.

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