Programmers have an ideal obvious translation of C programs to machine instructions in their head, but there's no spec for that.
It creates impossible expectations for the compilers. My recent favorite paradox is: in clang's optimizer comparing addresses of two variables always gives false, because they're obviously separate entities (the hardcoded assumption allows optimizing out the comparison, and doesn't stop variables from being in registers).
But then clang is expected to avoid redundant memcpys and remove useless copies, so the same memory location can be reused instead of copying, and then two variables on the stack can end up having the same address, contradicting the previous hardcoded result. You get a different result of the same expression depending on order of optimizations. Clang won't remove this paradox, because there are programs and benchmarks that rely on both of these.
It creates impossible expectations for the compilers. My recent favorite paradox is: in clang's optimizer comparing addresses of two variables always gives false, because they're obviously separate entities (the hardcoded assumption allows optimizing out the comparison, and doesn't stop variables from being in registers).
But then clang is expected to avoid redundant memcpys and remove useless copies, so the same memory location can be reused instead of copying, and then two variables on the stack can end up having the same address, contradicting the previous hardcoded result. You get a different result of the same expression depending on order of optimizations. Clang won't remove this paradox, because there are programs and benchmarks that rely on both of these.