[LLVMdev] CLR or C++/CLI interface to IR building API

[Gordon Henriksen]

On Aug 12, 2008, at 19:38, Scott Graham wrote:

> Our front end is written in a CLR language, and we're currently  
> interacting with the middle/back-end by writing out .ll files. This  
> was convenient to get started with, but they're getting to a "huge  
> and unwieldy" stage now.

Yup. This is in the FAQ now: http://llvm.org/docs/FAQ.html#langirgen

> I was wondering if anyone's attempted writing proxy/wrapper C++/CLI  
> classes so that the IR API can be used directly from managed  
> languages.


LLVM has C bindings which you should be able to P/Invoke  
straightforwardly. A rational managed API could be built atop these.  
Visit include/llvm-c in the source tree. These were specifically  
designed for use via FFIs like P/Invoke.

Several bindings have been built atop the C bindings (Ocaml, Haskell,  
D, and Python that I know of), but only the Ocaml ones are on trunk.  
We would welcome additional bindings into mainline if you are inclined  
to contribute.

These bindings are not 100% complete, but your usage case has the best  
coverage.

> Any tips/pointers/code/stories of horrible failure?


I would advise against the Managed C++ route. In my experience, the  
pointy edges of the unmanaged environment (no GC, no memory safety)  
compound the pointy edges of the managed environment (finalization,  
asynchronous exceptions)—the end result is the worst of both worlds.

I wouldn't really advise trying to P/Invoke LLVM's C++ APIs directly,  
either.

There is a recurring 'first/next/prev/last' pattern in the bindings.  
It allows efficiently implementing values similar to Module::iterator,  
Function::iterator, et al. The Ocaml bindings include a functional  
interpretation of this pattern. Each language seems to have a  
different idiom for handling iteration.

— Gordon