Can I compile code from multiple languages together with LLVM?

Question

Can I write a program in two different languages and compile them together in one LLVM executable?

For example, part of my program is in C++, and part of it is in D.

Answer 1

Not in the general case. Only if the languages are ABI-compatible. This is true for C and C++ to a very limited degree (extern "C" code from the C++ side), and much less so for other languages.