[Mono-list] C++/CLI compiler

[Karsten Pedersen]

Awesome work!

I have been looking for something like this for a long time.

If we can get it working on Linux (Or preferably FreeBSD), I am very committed to testing it out and reporting issues. My compiler development skills are pretty much non-existent but I am happy to help where I can.

Out of interest, can the compiler generate a pure .NET output (similar to cl /clr:safe)?

Best regards,

Karsten

From: ripzonetriton at gmail.com
Date: Sun, 9 Dec 2012 04:36:26 +0000
To: mono-list at lists.ximian.com
Subject: [Mono-list] C++/CLI compiler

Hi.


So I've been working for a bit on a C++/CLI compiler and I think it's came along enough that it makes sense to announce it.




I started it because of the need to interop with existing C/C++ native code. I first tried extending Cxxi for a bit, but found some problems that cannot be solved with the approach of generating IL code at runtime. So I tried Microsoft's implementation C++/CLI and found it is a pretty nice extension of C++ that makes it play nice on .NET and started implementing. Since there is nothing like it for Mono (at least publicly), I started working on a new implementation of it above the Clang and LLVM platforms.




The frontend (Clang) was extended to support the Ecma 372 (C++/CLI standard) additions to the type system, expressions and declarations, like handles, tracking references, CLI arrays, CLI properties and CLI generics. It then uses Cecil to import the metadata from DLLs that are introduced in the translation unit via #using.




LLVM was also extended with a CIL backend based on the old MSIL LLVM backend. The old backend had some problems and had to be updated to compile with the new LLVM interfaces. It also only generated IL code from native code and had no support for calling .NET types. I later found out LLVM is not really that suited to an higher-level assembly language like IL so I also had to modify and extend Clang's IR gen to send some bits as metadata (LLVM does not have signedness support on its integer types, for instance). The backend at the moment generates ILasm text code that is assembled externally, but long term I'd really like to emit IL directly via Cecil.




Here are some use cases where it might be useful: 1. Calling .NET libraries from native C++ (via calls to the Mono runtime for invocations)

 2. Compiling existing C++ code to CIL code (of course you can also call .NET code in this case)

 3. Introducing new .NET types via pure CIL C++ code 4. Calling native libraries from .NET types (seamless interop)




At the moment only use case 2. is implemented and fully functional, though I am starting to work on the other use cases. 1. is especially important for bootstrapping on Linux (see below).


Implemented CLI features:

 + Handles + Ref classes

 + Value classes + Properties

 + Indexers + Generics

 + Arrays + Parameter arrays (variadics)

 + Attributes (WIP)


Missing CLI features: - Exceptions

 - Delegates - Events

 - Static Constructors


So you can that there are still quite a bit of things left to implement and some that are implemented need some love:


 - Diagnostics and error handling needs a bit of work to be robust. It has not been tested that much yet.




 - The generated code is really crap at the moment, LLVM is not that well suited to generate code for stack machines, but there are papers out there with stack optimization strategies that can be implemented to improve on this front.


 - The compiler still has a bit of a bootstrapping problem, as it uses the existing MS C++/CLI to bootstrap. I don't expect this to be a big problem, since once Mono code-gen mode is added you will be able to call existing .NET libraries from native code (instead of generating IL) and it should work well on Linux too.




 - It needs a linker to be able to compile multiple C++ translation units into just one .NET DLL. The strategy here is not fully clear to me, but I was thinking on using the newly-developed LLVM linker (lld) to do it, since it seems the best way forward. Another option would be trying to use il-repack.




Somebody interested in helping out? Or maybe in sponsoring some features? There is a lot of work left to do :)


Code is up at https://github.com/tritao/clang. There is still quite a bit of code left to commit so don't try to compile it yet. The rest of the code should be up in a day or two, along with instructions on how to compile it.


-- 
João Matos


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