Re: Undefined references to `std::locale::id::_S_highwater'

[Michael Elizabeth Chastain <chastain at cygnus dot com>]

I narrowed down the problem:

. I ran libstdc++-v3/src/locale.cc through the preprocessor and boiled
  it down to a fifty line test program.

. I date-searched gcc down to a single patch.

My platform is native Red Hat Linux 7.  I am using gcc-3_0-branch, but I
think the same code is in mainline.  The bug happens when I compile with
"g++ -O2 -S"; it does not happen with "g++ -S".

The problem with the test program is that g++ does not emit a definition
for the static class variable std::locale::id::_S_highwater, or for
the simpler static class variable foo::i.  The variables are "static"
in the sense of being class-static, but they do have external linkage.

This problem affects a file in libstdc++ and causes unresolved externals
for std::locale:id::_S_highwater with the latest g++'s.

Michael Elizabeth Chastain
<chastain@redhat.com>
"love without fear"

===

// compile with g++ -O2 -S
// look for the definition of std::locale::id::_S_highwater
// look for the definition of foo::i

// this part comes from libstdc++-v3/src/locale.cc

typedef unsigned int size_t;

namespace std
{
  using ::size_t;
}

namespace std
{
  class locale;
  class locale
  {
    class id;
  };
  class locale::id
  {
    private:
      static size_t _S_highwater;
  };
}

namespace std
{
  size_t locale::id::_S_highwater;
}

// this is a very simple example

class foo
{
  public:
    static int i;
};

int foo::i;

===

Output of "g++ -O2 -S y1.cc" with a compiler from "2001-03-22 14:40:00 UTC".
This output is good:

	.file	"y1.cc"
	.version	"01.01"
gcc2_compiled.:
	.comm	_ZNSt6locale2id12_S_highwaterE,4,4
	.comm	_ZN3foo1iE,4,4
	.ident	"GCC: (GNU) 3.0 20010322 (prerelease)"

Output of "g++ -O2 -S y1.cc" with a compiler from "2001-03-22 14:49:00 UTC".
This output is bad:

	.file	"y1.cc"
	.version	"01.01"
gcc2_compiled.:
	.ident	"GCC: (GNU) 3.0 20010322 (prerelease)"

===

diff -u -r -N -x CVS 2001-03-22-14.40.00/source/gcc/ChangeLog 2001-03-22-14.49.00/source/gcc/ChangeLog
--- 2001-03-22-14.40.00/source/gcc/ChangeLog	Thu Mar 22 06:55:30 2001
+++ 2001-03-22-14.49.00/source/gcc/ChangeLog	Thu Mar 22 09:46:52 2001
@@ -1,3 +1,8 @@
+2001-03-22  Jason Merrill  <jason@redhat.com>
+
+	* toplev.c (wrapup_global_declarations): Don't emit DECL_COMDAT
+	variables unless necessary, either.
+
 2001-03-22  Joseph S. Myers  <jsm28@cam.ac.uk>
 
 	* gcc.texi: Remove more obsolete documentation of bugs and
diff -u -r -N -x CVS 2001-03-22-14.40.00/source/gcc/toplev.c 2001-03-22-14.49.00/source/gcc/toplev.c
--- 2001-03-22-14.40.00/source/gcc/toplev.c	Wed Mar 14 13:26:32 2001
+++ 2001-03-22-14.49.00/source/gcc/toplev.c	Thu Mar 22 09:47:00 2001
@@ -1975,8 +1975,8 @@
 	     defined in a main file, as opposed to an include file.  */
 
 	  if (TREE_CODE (decl) == VAR_DECL && TREE_STATIC (decl)
-	      && (! TREE_READONLY (decl)
-		  || TREE_PUBLIC (decl)
+	      && (((! TREE_READONLY (decl) || TREE_PUBLIC (decl))
+		   && !DECL_COMDAT (decl))
 		  || (!optimize
 		      && flag_keep_static_consts
 		      && !DECL_ARTIFICIAL (decl))