On Fri, Oct 19, 2012 at 10:26:58AM +0200, Richard Biener wrote:
> On Thu, Oct 18, 2012 at 10:33 PM, Basile Starynkevitch
> <bas...@starynkevitch.net> wrote:
> > Hello
> >
> > I'm coding in MELT the ex06/ of https://github.com/bstarynk/melt-examples/
> > which should typecheck calls to variadic functions json_pack & json_unpack
> > from http://www.digip.org/jansson (a JSON library in C).
> >
> > I'm working on a MELT pass on Gimple/SSA after phiopt (maybe that place is
> > wrong?)
> >
> > I don't understand well how to check that a given Gimple argument is a
> > string.
> > I was thinking of using useless_type_conversion_p or types_compatible_p on
> > the TREE_TYPE of some POINTER_TYPE with char_type_node, but it seems to not
> > work as I would expect
> >
> > How would you (in C++ or C for a 4.6) code such a test (that argument 2 of
> > some GIMPLE_CALL is a string, ie. a char* in C parlance)?
>
> You would look at the function signature of the function called, not at its
> argument. The argument can be a void * and still be a "string" (well, a
> pointer
> to a string). GIMPLE doesn't care about the actual type pointed to.
GCC is using the syntactic type of the argument for printf. The following code
void f (char *s)
{ printf ("%s\n", (void *) s); }
gives when compiled with gcc -Wall
f.c:4:1: warning: format ‘%s’ expects argument of type ‘char *’, but argument
2 has type ‘void *’ [-Wformat]
and we are in the case where the argument is a string casted to (void*); I
don't want to give more clever warnings.
So I don't follow you. I want to typecheck (at least in the common simple
cases) the calls to that variadic function.
I don't care that much about its signature.
To be concrete, <jansson.h> declares
json_t *json_pack(const char *fmt, ...);
and the documentation
http://www.digip.org/jansson/doc/2.4/apiref.html#building-values
suggests that
/* Create the JSON integer 42 */
json_pack("i", 42);
/* Create the JSON array ["foo", "bar", true] */
json_pack("[ssb]", "foo", "bar", 1);
I just want to extend GCC (thru a MELT extension, but that could be a GCC
plugin in C++) to detect
incorrect calls like
json_pack("i", /*that should be an int:*/ 3.14);
or
json_pack("[ss]", "foo", /* that should be a string*/ 3
/*and the arity is wrong an argument is missing*/);
I believe I should use
extern bool useless_type_conversion_p (tree, tree);
from gcc/gimple.h (it is funny that function is in gimple.h, I would expected
it to be in tree.h)
with one of the argument being char_type_node
But I might have trouble in using it.
Thanks for reading. Regards.
--
Basile STARYNKEVITCH http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
8, rue de la Faiencerie, 92340 Bourg La Reine, France
*** opinions {are only mines, sont seulement les miennes} ***
