title: How to tell if `constexpr` is evaluated at compile time (without manual inspection)
body: <p>Is there a standard way to find out what the compiler does to <code>constexpr</code> functions?</p>
  
  <p>(Side note: For debug, every constexpr function is deferred to runtime by default. Why is this sensible? Is there a way to influence this?)</p>
  
  <p>For release it depends on the context. Obviously, for small test settings you can easily inspect the generated machine code, but this cannot be the way to go for a real project.</p>
  
  <p>My current 'workaround' (VC++) is to break somewhere, go to my constexpr function and (try to) inspect the disassembly. If none is there, I conclude that it was all done at compile time.
  But it is not 100% reliable this way. (Optimization, etc.)
  Only the other way around is certain: If I do find disassembly (and can even break there), I know that it was NOT done at compile time. </p>