C requires a diagnostic if a static function is used but not defined in a
translation unit. The present implementation of this is a pedwarn in
check_global_declarations in toplev.c.
(a) Which language front ends use this pedwarn, rather than avoiding
getting that far with a translation unit using an undefined static
function?
(b) Is there any reason this shouldn't be a hard error rather than just a
pedwarn?
(c) This diagnostic is broken for C with -funit-at-a-time (implied by
-O2), ": Search converges between 2004-07-08-trunk (#482) and
2004-07-09-trunk (#483).". Test (should be diagnosed, now isn't at -O2):
static void f0(void);
void g0(void) { f0(); }
I would guess TREE_SYMBOL_REFERENCED is being tested too early for
unit-at-a-time mode; certainly it's the wrong way to implement this
diagnostic.
(d) It also has always been broken with regard to calls that are optimised
away; C90 and C99 are explicit that it is any use outside sizeof (sizeof
whose result is an integer constant, in C99) that is erroneous. For
example,
static void f1(void);
void g1(void) { if (0) { f1(); } }
should be diagnosed. Is there any reason this shouldn't be a hard error
as well?
I propose to fix this C90 issue (which was missing from my original C90
project proposal) in the front end, and there is nothing tricky about so
doing (flag all used static function decls, ignoring uses inside
__alignof__ and keeping lists inside sizeof/typeof so they can be flagged
afterwards if the result turns out nonconstant). It would however be
convenient to be able to get rid of the checks in toplev.c (or make them
internal_error if no errors have been given by the front end) by having
all front ends give proper errors, to avoid the need to do anything
special to avoid duplicate error messages.
(e) Consider the following C++ variation on the above program:
inline static void f1(void);
void g1(void) { if (0) { f1(); } }
Does "no diagnostic required" in C++03 [basic.def.odr] paragraph 3 apply
to the whole paragraph, or only to the sentence it appears in? That is,
is "An inline function shall be defined in every translation unit in which
it is used." a diagnosable rule?