[PATCH] Only emit .weak for externs that have weak attribute or pragma weak (PR c++/42608)

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

This got broken by a change for LTO, which moved queuing of decls into
weak_decls chain from declare_weak to assemble_external.  declare_weak is
called just for real weak attribute, pragma weak, darwin weak_import
or something in Ada and we only want .weak for externs in those cases,
not for DECL_WEAK set because of weakref attribute or C++ vague linkage.
The following patch fixes it by making sure the decl has weak attribute
(for weak attribute that's no change, just for #pragma weak or weak_import),
and only adding to weak_decls decls that have that attribute.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2010-01-09  Jakub Jelinek  <jakub@redhat.com>

	PR c++/42608
	* varasm.c (declare_weak): Add weak attribute to decl if it
	doesn't have one already.
	(assemble_external): Only add decls to weak_decls if they also
	have weak attribute.

	* g++.dg/template/instantiate11.C: New test.

--- gcc/varasm.c.jj	2009-11-09 16:38:29.000000000 +0100
+++ gcc/varasm.c	2010-01-08 13:30:12.000000000 +0100
@@ -2337,13 +2337,15 @@ assemble_external (tree decl ATTRIBUTE_U
   /* We want to output annotation for weak and external symbols at
      very last to check if they are references or not.  */
 
-  if (SUPPORTS_WEAK && DECL_WEAK (decl)
+  if (SUPPORTS_WEAK
+      && DECL_WEAK (decl)
       /* TREE_STATIC is a weird and abused creature which is not
 	 generally the right test for whether an entity has been
 	 locally emitted, inlined or otherwise not-really-extern, but
 	 for declarations that can be weak, it happens to be
 	 match.  */
       && !TREE_STATIC (decl)
+      && lookup_attribute ("weak", DECL_ATTRIBUTES (decl))
       && value_member (decl, weak_decls) == NULL_TREE)
     weak_decls = tree_cons (NULL, decl, weak_decls);
 
@@ -5227,6 +5229,9 @@ declare_weak (tree decl)
     warning (0, "weak declaration of %q+D not supported", decl);
 
   mark_weak (decl);
+  if (!lookup_attribute ("weak", DECL_ATTRIBUTES (decl)))
+    DECL_ATTRIBUTES (decl)
+      = tree_cons (get_identifier ("weak"), NULL, DECL_ATTRIBUTES (decl));
 }
 
 static void
--- gcc/testsuite/g++.dg/template/instantiate11.C.jj	2010-01-08 13:48:58.000000000 +0100
+++ gcc/testsuite/g++.dg/template/instantiate11.C	2010-01-08 14:18:44.000000000 +0100
@@ -0,0 +1,25 @@
+// PR c++/42608
+// { dg-do compile }
+
+template <class U, class V>
+struct A;
+
+template <class V>
+struct A<int, V>
+{
+  void f ();
+};
+
+template struct A<int, int>;
+
+int
+main ()
+{
+  A<int, int> a;
+  a.f ();
+  return 0;
+}
+
+// Make sure we get undefined reference error if
+// A<int, int>::f () isn't instantiated elsewhere.
+// { dg-final { scan-assembler-not "weak\[\n\t\]*_ZN1AIiiE1fEv" } }

	Jakub