https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65345
--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot
com> ---
Or e.g.
_Atomic int i = 5;
int j = sizeof (i + 1);
which is valid code not involving _Generic. And, similarly:
_Atomic int i = 5;
int j = sizeof (i = 0);
or
_Atomic int i = 5;
int j = sizeof (++i);
or
_Atomic int i = 5;
int j = sizeof (i--);
This at first suggests (but see below) that the special-case handling of
atomics on lvalue-to-rvalue conversion, and on assignment / increment /
decrement / any other cases where creation of temporaries is involved,
should be disabled when at file scope - either the expression in question
is in a context such as sizeof or _Generic where its side effects do not
occur so the special handling is not needed, or an error will occur for
the expression being non-constant even without the special handling.
Much the same applies at function prototype scope, e.g.:
_Atomic int i = 5;
void f (int a[i + 1]);
(where [i + 1] means the same as [*]). But in the case of
_Atomic int i = 5;
void f (int a[i = 1]) {}
you have a valid program, where the atomic assignment must be executed on
function entry (see the pending_sizes handling in c-decl.c). So to handle
such cases, maybe the special handling of atomics needs to be partly
deferred, so that parsing "i = 1" generates some tree for atomic
assignment and the temporaries only get added at gimplification time.
