I know that moving stack variables to the data section is in fact an optimization that is in use by commercial compilers. It works fine with function pointers.

I know that moving stack variables to the data section is in fact an optimization that is in use by commercial compilers. It works fine with function pointers. There are two possible answers to the problem of a compile-then-link workflow involving multiple object files. The first is that the optimization can be limited to within one file. Calls going between source files can sometimes limit the optimization opportunity because it may become impossible to prove that there is no mutual recursion. Functions that may be involved in recursion can not be optimized in this way. One might add a #pragma to override the compiler's determination of safety. The second possible answer is to have the link phase do the real compiling. The supposed compile phase just preprocesses and verifies syntax. Function pointers certainly liven things up. Suppose the function pointer of type *X is used to call a function of type X, which then exclusively calls functions of type Y. If we know that none of those type Y functions end up calling any type X functions, then that first-mentioned function of type X will not get more than one stack frame. It is thus safe to optimize with that assumption.