The LLVM inlining behavior is left over from C. Different compilation units won't inline. The LLVM and its Gold linker actually allow their input to be LLVM-By

The LLVM inlining behavior is left over from C. Different compilation units won't inline. The LLVM and its Gold linker actually allow their input to be LLVM-Byte Code not just obj files. The advantage is cross language and cross module optimization. As it works today with the right make file one can link Rust/C/C++ and mutually inline/optimize across language barriers.