[Bug c++/50734] const and pure attributes don't have the effect as in C

["joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50734

--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-10-15 15:47:27 UTC ---
On Sat, 15 Oct 2011, rguenth at gcc dot gnu.org wrote:

> This is because f can throw, you need to mark it nothrow as well in C++.
> Whether something throws or accesses global memory is orthogonal.
> Works with -fno-exceptions.

I don't see the difference here from C.  In C, f might exit the program or 
call longjmp (if you allow such functions to throw, I'd have thought they 
could also not-return in other ways) - but if it does, the exit status, or 
where it longjmps do, will only depend on the global state visible to f, 
meaning that it will do so on the first time through the loop.  The same 
reasoning that it's safe to hoist the call out of the loop in C - the loop 
is guaranteed to call f at least once with the same state as if it is 
called before the loop - should apply in C++; throwing from a hoisted call 
could not be distinguished by a catcher from throwing from the first call 
in the loop.