durin VS imp

So I think I may be one of the few people in the world who has actually implemented a GC using LLVM's statepoint infrastructure. It's poorly documented and there are some gotchas, but I'd say it's definitely usable, and it works with basically any collector design, including moving collectors (I'm using Immix) and has no runtime bookkeeping overhead and allows LLVM to optimize the code without worrying about GC, which is nice. It's actually gotten a bit better with LLVM 13, too. If you're curious what a LLVM-based GC looks like, mine is in this folder. Of course, if you just want some sort of GC, you can also just link it with Boehm which is quite easy and has pretty good performance - this is what e.g. Crystal does, although they're talking about switching.

I also fixed lots of bugs in the GC and backend, so it should be a lot more stable now.

Recently, I've been working on adding garbage collection to Pika. I've successfully written an Immix-based garbage collector that works with the LLVM GC support infrastructure, and I'm currently working on integrating the GC with Pika, or really Durin, the dependently-typed intermediate representation that Pika compiles to. Because types are passed around at runtime, objects of unknown type and size can be stored unboxed in polymorphic data structures; but that makes keeping track of type information for heap allocations somewhat harder, because type information needs to be allocated and constructed at runtime in some cases. It's an interesting design problem, because you want constructing type information to be fast; but the GC will run much more often, so maximizing tracing speed by avoiding e.g. indirection in type information is important; and you also want to construct as much type information as possible at compile time and embed it as constants.

In August I finished the module system for Imp. I’ve been designing Imp from the start to support the programmer’s confidence in their code, and the module system is no different. Imp is based on the JVM so each file eventually becomes one (or more) classes but that’s abstracted away from the user. This sub’s Discord has been so helpful for asking people about these concepts and for opinions on my design decisions.

I've had good luck with ANTLR4 and ObjWeb ASM for my JVM language Imp https://github.com/mh15/imp