No compiler warnings for uninitialized std::atomic

Question

Earlier today I stumbled over addition on std::atomic<double> not adding up to non-atomic counterpart, which turned out to be due to a std::atomic<double> being left uninitialized (see also What's the default value for a std::atomic?). What caught my attention, though, was that my compiler did not warn me about the fact that the std::atomic<double> was uninitialized. Consider:

#include <iostream>
#include <atomic>

int main()
{
  std::atomic<double> d;
  double e;

  std::cout << d << " " << e << std::endl;
}

Neither clang 3.8 nor GCC 6.2 appear to be able to produce a warning for d being uninitialized. See live at coliru: I used -Wall -pedantic -Wextra, but got no warning both with and without -O2. Of course a warning about e not being initialized is typically produced. _{(Interestingly, gcc does not actually produce any warning when -O2 is enabled.)}

Of course I cannot expect the compiler to warn me about these things; but this case left me wondering:

• Is there a particular reason why this situation is not (currently) detected/reported by the compilers in question?
• …or even (I would assume this to be unlikely): Is it impossible in general, for some reason, to detect/report the missing initialization in the specific case of std::atomic<T> where T has no default constructor?
• or, maybe, is there just another command-line switch I am missing which would make the compiler produce the warning?

Answer 1

Why: Unfortunately we have no way of knowing. Perhaps nobody who contributes to gcc development bothered to do it yet or thought it was worth it.

Impossible to detect? Not technically, I suppose. But it would have to be a special case, otherwise you'd introduce loads of warnings for a not uncommon case of declaring vars of struct and class types with no explicitly defined default constructors without initializer lists or whatever.

Worth it to add a special case? Probably, but that's a matter of opinion, and convincing somebody to implement it in gcc.

Command line switches? Not really, although -Weffc++ might get you something. I have not tried it. You could also try running it through valgrind, maybe that will report something. Also have not tried.