[Bug preprocessor/7263] __extension__ keyword doesn't suppress warning on LL or ULL constants

["tromey at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #12 from tromey at gcc dot gnu dot org  2008-08-10 22:17 -------
> I am not sure how that will work. How do you specify a different value of
> system_header for a single location? My understanding is that sysp is for a
> whole line_map, so you cannot just change its value for a single location.

My understanding is that the problem is that we have a define in a system
header, like this from comment #8:

#define _Complex_I 1.0iF

But then we use this macro in user code, and get a warning, because we
lose track of the system-header-ness.  Right now c_lex_with_flags calls
cpp_get_token_with_location.  This function returns two locations for tokens
coming from a macro expansion: the original location of the token, and also
the location of the start of the expansion.  Current we throw away the
former and just use the latter.  But, we could be smarter about using
the former location as well.

I think there is another PR (maybe more) where this same idea would make sense.

This would need some work to handle the token pasting case.

> We could handle this for each error but that is not ideal either. This would be
> trivial if tokens expanded from macros carried two locations around but I guess
> that is too expensive, isn't it?

I think it would be interesting to encode the macro expansion and
token pasting history into a location, the same way we encode the include
history.  I don't know how expensive this would be.  If it is not too bad
it would let us emit much nicer error messages in otherwise confusing
macro-expansion cases.  (In fact this would be my preferred implementation
approach ... but it is much harder than just looking at the already-known
second location.)

I hope this makes sense and that I'm not missing something :)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7263