Why is static initialization order STILL unspecified?

Question

Doesn't a compiler have all the information it needs to generate a dependency tree of all globals and create a well defined and correct initialization order for them? I realize you could write a cyclic dependency with globals - make only that case undefined behavior - and the compiler could warn and maybe error about it.

Usually the reason for this sort of thing is that it would be burdensome to compiler makers or cause compilation to slow significantly. I have no metrics or evidence that indicates either of these wouldn't be true in this case, but my inclination is that neither would be true.

Answer 1

Hm, imagine the following setup, which is perfectly valid C++, but tricky to analyze:

// TU #1

bool c = coin();

// TU #2

extern bool c;
extern int b;
int a = c ? b : 10;

// TU #3

extern bool c;
extern int a;
int b = c ? 20 : a;

It is clear that TU #1 needs to be initialized first, but then what? The standard solution with references-to-statics allows you to write this code correctly with standard C++, but solving this by fixing the global initialization order seems tricky.