The Nuanti compiler is described as a portable C++/CLI compiler built atop LLVM/Clang. While it's not too widely known, the compiler itself is a few years old and has evolved into a self-hosting toolchain for porting applications to run on Mono, SilverLight, Mac OS X, and Linux.
From the blog post of one of the Nuanti developers describing this work, "There are two codegen modes: (1) fully managed .NET bytecode, and (2) native optimized machine code with hooks into the Mono runtime for invocations. There’s some flexibility to mix and match the two. Sometimes it’s handy to call into an existing managed library from your C++ application and this use case is simple as adding an import header and calling the methods you need. No bindings or wrappers, and if using a runtime like Mono the stack is garbage collected behind the scenes."
The developer, Alp Toker, mentions there's a CIL back-end using the LLVM code generation infrastructure to "generate native-looking SDK-quality assemblies out of all kinds of unmanaged code." The compiler also goes beyond the ECMA-372 specification with support for dynamic types from C# 4.0, LINQ from C++, express trees, and DLR syntax trees. The Nuanti compiler is also self-hosting.
The Nuanti C++/CLI compiler was presented yesterday at the European LLVM Developers' Conference so hopefully soon we will get the slides on the presentation and/or a video.
Meanwhile, at the end of March the big Mono 2.11 was released.