On 2 October 2015 at 22:07, Aaron Ballman <aa...@aaronballman.com> wrote:
> On Fri, Oct 2, 2015 at 4:01 PM, mats petersson <m...@planetcatfish.com>
> wrote:
> > Since "varargs" often involve some kind of special passing mechanisms
> [I've
> > seen implementations that build data block and pass a pointer to that,
> > rather than passing on the stack, for example], or additional code in the
> > recipient function, I would say that `f2()` does not mean `f2(...)`.
>
> I kind of wondered if that was the case. If that's reality, perhaps we
> may want to consider naming it FunctionDecl::hasVarArgs() or something
> that specifies the difference is in whether we need to care about
> packaging up the argument list so it can be used with va_start() and
> friends?
>
My understanding of the meaning of `isVariadic` is indeed "needs to use
va_* to get arguments".
I believe it's technically valid to do something like:
void f2();
....
f2(42);
....
voif f2(int x)
{
... use x ...
}
and no special code should be required. Of course, the results of changing
`f2(42);` int `f2(4.2);` or `f2("foo");` and retaining the `int x`
parameter will lead to undefined behaviour, and compiler can do anything it
likes with that... :)
--
Mats
>
> ~Aaron
>
> >
> > --
> > Mats
> >
> > On 2 October 2015 at 20:16, Aaron Ballman via cfe-commits
> > <cfe-commits@lists.llvm.org> wrote:
> >>
> >> Given the following two function declarations:
> >>
> >> void f1(...);
> >> void f2();
> >>
> >> It makes sense to me that isVariadic() returns true for f1 in both C
> >> and C++. It makes sense to me that isVariadic() returns false for f2
> >> in C++. I am confused as to why it returns false instead of true for
> >> C, however.
> >>
> >> In C11, 6.7.6.3p9 states: If the list terminates with an ellipsis (,
> >> ...), no information about the number or types of the parameters after
> >> the comma is supplied.
> >>
> >> p14 states, in part: "The empty list in a function declarator that is
> >> not part of a definition of that function specifies that no
> >> information about the number or types of the parameters is supplied."
> >>
> >> It seems to me that for function *declarations* (not definitions),
> >> isVariadic() should return true for f2 in C. Is there a reason it
> >> doesn't currently behave that way, or is this a bug?
> >>
> >> I ask because I was writing an AST matcher for isVariadic() for an
> >> in-progress checker, but the checker was failing to catch that f2 was
> >> a variadic function. I am not certain whether
> >> FunctionDecl::isVariadic() should be changed, whether the AST matcher
> >> isVariadic() should be smarter about C code, or whether the checker
> >> itself needs to be smarter about this particular behavior in C code.
> >> My gut reaction is that FunctionDecl::isVariadic() has a bug, but from
> >> looking at code elsewhere, everything seems to assume isVariadic()
> >> implies the ellipsis, which makes me think I just need to make my
> >> checker smarter.
> >>
> >> Thanks!
> >>
> >> ~Aaron
> >> _______________________________________________
> >> cfe-commits mailing list
> >> cfe-commits@lists.llvm.org
> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
> >
> >
>
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