Rust has it's own (Free) LLVM fork, too. If the watchOS/iOS Bitcode format were Free, they could merge that into their own LLVM instead of having to support two

Rust has it's own (Free) LLVM fork, too. If the watchOS/iOS Bitcode format were Free, they could merge that into their own LLVM instead of having to support two slightly-different compiler backends. The GPL would legally require Apple to publish source code for all LLVM forks they make, if they accepted third-party contributions under GPL terms. It doesn't require them to upstream it anywhere, you just have to let someone else do it.