c++/9393: [3.2/3.3/3.4 regression] Anonymous namespaces and compiling the same file twice

[bangerth at ticam dot utexas dot edu]

>Number:         9393
>Category:       c++
>Synopsis:       [3.2/3.3/3.4 regression] Anonymous namespaces and compiling the same file twice
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jan 21 23:06:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     Wolfgang Bangerth
>Release:        unknown-1.0
>Organization:
>Environment:
gcc 3.4
>Description:
Hm, this counters what anonymous namespaces are all about:
if I have the following file, and compile it twice (once
with D defined, once without), then I get a linker error
that elements of the anonymous namespaces are defined twice:
------------------------
namespace {
  struct S {
      void f();
  };
  void S::f () {}
}

#if D
  void foo () { S s; }
#else
  int main () { S s; }
#endif
--------------------------
With present 3.4 CVS, I get the following:

g/a> /home/bangerth/bin/gcc-3.4-pre/bin/c++ -c x.cc -DD -o x1.o
g/a> /home/bangerth/bin/gcc-3.4-pre/bin/c++ -c x.cc -o x2.o
g/a> /home/bangerth/bin/gcc-3.4-pre/bin/c++ x?.o -o a.out
x2.o: In function `(anonymous namespace)::S::f()':
x2.o(.text+0x0): multiple definition of `(anonymous namespace)::S::f()'
x1.o(.text+0x0): first defined here
collect2: ld returned 1 exit status


On the other hand, it worked with 2.95:

g/a> c++ -c x.cc -DD -o x1.o
g/a> c++ -c x.cc -o x2.o
g/a> c++ x?.o -o a.out
g/a>

It also works with 3.0.4, but is already broken on the
3.2 branch. In any case, it's a regression. Too bad,
anonymous namespaces are a useful feature...

When digging a little deeper, it is of course clear what
happens: until 3.0.4, the name of a symbol from an anonymous
namespace differs when the file is compiled twice (even with
the exact same flags). This is no longer the case since
3.2.2. A simpler testcase is thus the following: take
---------------------
namespace {
  int i;
}
---------------------
and compile it twice and look at the symbol names. I get

g/a> /home/bangerth/bin/gcc-3.0.4/bin/c++ -c x.cc -o x2.o
g/a> nm x2.o
00000000 B _ZN21_GLOBAL__N_x.ccc18R7c1iE

g/a> /home/bangerth/bin/gcc-3.0.4/bin/c++ -c x.cc -o x2.o
g/a> nm x2.o
00000000 B _ZN21_GLOBAL__N_x.ccQqZgxc1iE

which is different, but

g/a> /home/bangerth/bin/gcc-3.4-pre/bin/c++ -c x.cc -o x2.o
g/a> nm x2.o
00000000 B _ZN21_GLOBAL__N_x.ccI4JKib1iE

g/a> /home/bangerth/bin/gcc-3.4-pre/bin/c++ -c x.cc -o x2.o
g/a> nm x2.o
00000000 B _ZN21_GLOBAL__N_x.ccI4JKib1iE

which is the same twice.

W.
>How-To-Repeat:

>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: