Different compilers produce different binaries, different compiler settings result in different binaries. The reality is that the source code is just an input,

Different compilers produce different binaries, different compiler settings result in different binaries. The reality is that the source code is just an input, and even if it's correct or sensible, the control flow in the produced binary is the only truth on a system. An example is when e.g. zeroing out a buffer containing secrets after usage, this overwrite is stripped by the compiler.