Explain how bitcode works

https://jonasdevlieghere.com/embedded-bitcode/ Bitcode is the intermediate representation used by the LLVM compiler and contains all the information required to recompile an application. Having the bitcode present, in addition to machine code, Apple can further optimize applications by compiling and linking specifically for the user's target device. This is one approach to app thinning, which aims to achieve smaller binaries and therefore more free space on your iDevice. It will most likely replace Apple's current approach, where a developer uploads a fat binary to the App Store, which contains machine code for each target architecture.