Depends on the definition of "linking". Having multiple source files each compiled to LLVM bitcode and not re-doing this if another file changes is fine. Turning the bitcode to native code is where traditionally the compiler back-end, assembler and linker are involved, and these are steps you want to re-do to enable global optimization (e.g. inlining functions from another source file, followed by dead code elimitation -- these two steps give you no-cost "runtime" parameter checks, for example). The traditional 3-step split is just becoming cumbersome there, and linker relaxation is treating that symptom.