[cfe-commits] r148158 - in /cfe/trunk: lib/Sema/SemaDecl.cpp lib/Sema/SemaExpr.cpp lib/Serialization/ASTWriterDecl.cpp test/SemaCXX/linkage.cpp

[Chandler Carruth]

On Sat, Jan 14, 2012 at 4:29 PM, Eli Friedman <eli.friedman at gmail.com>wrote:

> [On Sat, Jan 14, 2012 at 4:14 PM, Chandler Carruth <chandlerc at google.com>
> wrote:
> > On Fri, Jan 13, 2012 at 9:16 PM, Eli Friedman <eli.friedman at gmail.com>
> > wrote:
> >>
> >> On Fri, Jan 13, 2012 at 7:22 PM, Matt Beaumont-Gay <
> matthewbg at google.com>
> >> wrote:
> >> > Hi Eli,
> >> >
> >> > On Fri, Jan 13, 2012 at 15:41, Eli Friedman <eli.friedman at gmail.com>
> >> > wrote:
> >> >> Modified: cfe/trunk/test/SemaCXX/linkage.cpp
> >> >> URL:
> >> >>
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/linkage.cpp?rev=148158&r1=148157&r2=148158&view=diff
> >> >>
> >> >>
> ==============================================================================
> >> >> --- cfe/trunk/test/SemaCXX/linkage.cpp (original)
> >> >> +++ cfe/trunk/test/SemaCXX/linkage.cpp Fri Jan 13 17:41:25 2012
> >> >> @@ -76,13 +76,15 @@
> >> >>     struct X {
> >> >>       int f() {
> >> >>         extern int g();
> >> >> -        extern int a;
> >> >> +        // FIXME: We don't compute the correct linkage for this
> >> >> variable
> >> >> +        // at the moment
> >> >> +        // extern int a;
> >> >
> >> > Are you planning on addressing this FIXME soon? We have some code
> >> > which looks roughly like this, and now Clang is producing a warning
> >> > "variable 'a' has internal linkage but is not defined".
> >>
> >> Per the C++11 rules, this variable clearly has internal linkage, but
> >> the C++98 rules aren't very clear, and I'm not sure what the
> >> gcc-compatible rules are.  If you can point me to some description, I
> >> can implement it.
> >
> >
> > I'm not sure what C++11 rules you're referring to (I just haven't read
> that
> > part of the standard), but these definitely don't actually have internal
> > linkage... Both Clang and GCC give them external linkage and C mangling.
> > This is true even in C++11 mode, both with GCC and Clang in my tests...
> So
> > this warning looks like a false positive.
>
> Oh, wait, nevermind, I was misreading the standard.  It's just that
> our code for this stuff appears a bit circular because our
> linkage-computation code distinguishes between UniqueExternal and
> External, while the standard doesn't.


Yea, I'm trying to remember how this works... the linkage is
UniqueExternal, but it still gets code-genned w/ C mangling and picked up
correctly from another TU... I think I'm actually partially responsible for
this working, but I'll have to dig more. It's not yet clear whether the
warnings implementation needs to change or whether we're computing the
wrong linkage kind and just patching it up later....
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