[Bug c++/18267] New: external linkage of functions declared in an anonymous namespace

[Bug c++/18267] New: external linkage of functions declared in an anonymous namespace

[TazForEver at dlfp dot org]

Here are 3 functions and a dummy main:

--begin--
int one() { return 1; }

static int two() { return 2; }

namespace
{
  int three() { return 3; }
}

int main()
{
  return one() + two() + three();
}
--end--

i was expecting that g++ handled two() and three() the same way, that
is to say generated object-code with internal linkage.
 
But g++ doesn't. three() has external linkage, just like one(). TCPPPL
says that an anonymous namespace is a namespace with a unique
name. Fine. Then why g++ does not optimize this ?  The previous
program returns 6. g++ outputs a definition for three(), but it is
obvious that two() and three() definitions are no longer needed
because they've been inlined. That's why g++ doesn't output a
definition for two(). In the end, i get a never-used definition of
three() ...

Thanks

>>> LC_ALL=C g++-3.4 -v
Reading specs from /usr/lib/gcc/powerpc-linux/3.4.2/specs
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,pascal,objc,ada --prefix=/usr
--libexecdir=/usr/lib --with-gxx-include-dir=/usr/include/c++/3.4
--enable-shared --with-system-zlib --enable-nls --without-included-gettext
--program-suffix=-3.4 --enable-__cxa_atexit --enable-libstdcxx-allocator=mt
--enable-clocale=gnu --enable-libstdcxx-debug --enable-java-gc=boehm
--enable-java-awt=gtk --disable-multilib --disable-multilib powerpc-linux
Thread model: posix
gcc version 3.4.2 (Debian 3.4.2-3)

-- 
           Summary: external linkage of functions declared in an anonymous
                    namespace
           Product: gcc
           Version: 3.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: TazForEver at dlfp dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-01 19:05 -------
The main reason IIRC for this is because C++ and export templates (even though we don't implement 
export yet).

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-11-01 23:52 -------
Names declared in anonymous namespaces do not get internal linkage by default. 
In fact, they can be used as template non-type arguments (names with internal 
linkage cannot be used in such contexts).

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[TazForEver at dlfp dot org]

------- Additional Comments From TazForEver at dlfp dot org  2004-11-02 00:10 -------
of course. but if they are not ? they should be optimize, no ?
if g++ inlines three(), why does it remove three() global definition if it's
never used ?

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-11-02 00:19 -------
GCC is not allowed to remove the definition of a function with external 
linkage. The fact that nobody will be able to call it because it is in an 
anonymous namespace it is irrelevant.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[TazForEver at dlfp dot org]

------- Additional Comments From TazForEver at dlfp dot org  2004-11-02 00:48 -------
i understand your point of view though i'm not happy with g++ behaviour. A
function with external linkage that can't be called seems like an oxymoron to
me. This makes my library very big. i had to mark a lot of functions inline to
get the behaviour i expect. But it is hard to manage. I have lo live with it.

Thanks for your explanation.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-11-02 01:22 -------
It is not exactly a G++ choice. This is what the ISO/ANSI C++ International 
Standard mandates. I suggest you to post a mail to the newsgroup 
comp.lang.c++.moderated or to comp.std.c++ to enquire an explanation for the 
rationale.

Also, notice you can try compiling your code with -ffunction-sections to let 
the linker drop the unused functions from the final executable. But remember 
that this option might regress the code performance a bit on x86 because it 
forces the compiler to generate slower code for each function call.

Alternatively, why don't you simply use "static"?

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-11-02 01:53 -------
This point has been discussed in a number of PRs already. I maintain 
my position that gcc could invoke the as-if rule to give these functions 
internal linkage if they aren't taken as template parameters. Since 
there is no user-visible effect, this is well within the allowed range, 
and it would save us from a good number of the problems we've had over 
time with mangling of symbol names in anonymous namespaces. 
 
W. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[TazForEver at dlfp dot org]

------- Additional Comments From TazForEver at dlfp dot org  2004-11-02 09:21 -------
>> Alternatively, why don't you simply use "static"?

because everybody tells me that 'static' is deprecated in favor of 'namespace{}'

>> gcc could invoke the as-if rule to give these functions internal linkage

this sounds great.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-11-02 11:55 -------
(In reply to comment #7)

> This point has been discussed in a number of PRs already. I maintain 
> my position that gcc could invoke the as-if rule to give these functions 
> internal linkage if they aren't taken as template parameters. Since 
> there is no user-visible effect, this is well within the allowed range, 
> and it would save us from a good number of the problems we've had over 
> time with mangling of symbol names in anonymous namespaces. 

I don't think it would solve the problem about mangling because the 
function/classes in anonymous namespaces can still be used as template 
arguments, so they could end up being mangled.

But it is an interesting point of view.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267

[Bug c++/18267] external linkage of functions declared in an anonymous namespace

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-11-02 16:10 -------
I don't want to have these symbols not mangled (they need indeed be 
mangled and randomized), the problem is that the randomness is sometimes 
not enough. See PR 9393 for a case that would have been solved with 
making symbols have internal linkage. 
 
W. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18267