DR1113: anonymous namespaces formally give their contents internal linkage.

This doesn't affect our code generation in any material way -- we already give
such declarations internal linkage from a codegen perspective -- but it has
some subtle effects on code validity.

We suppress the 'L' (internal linkage) marker for mangled names in anonymous
namespaces, because it is redundant (the information is already carried by the
namespace); this deviates from GCC's behavior if a variable or function in an
anonymous namespace is redundantly declared 'static' (where GCC does include
the 'L'), but GCC's behavior is incoherent because such a declaration can be
validly declared with or without the 'static'.

We still deviate from the standard in one regard here: extern "C" declarations
in anonymous namespaces are still granted external linkage. Changing those does
not appear to have been an intentional consequence of the standard change in
DR1113.

llvm-svn: 314037

1 files changed, 7 insertions, 1 deletions

diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index 5ce52171562..8c5ebd0113a 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -1287,9 +1287,15 @@ void CXXNameMangler::mangleUnqualifiedName(const NamedDecl *ND,
       //
       //   void test() { extern void foo(); }
       //   static void foo();
+      //
+      // Don't bother with the L marker for names in anonymous namespaces; the
+      // 12_GLOBAL__N_1 mangling is quite sufficient there, and this better
+      // matches GCC anyway, because GCC does not treat anonymous namespaces as
+      // implying internal linkage.
       if (ND && ND->getFormalLinkage() == InternalLinkage &&
           !ND->isExternallyVisible() &&
-          getEffectiveDeclContext(ND)->isFileContext())
+          getEffectiveDeclContext(ND)->isFileContext() &&
+          !ND->isInAnonymousNamespace())
         Out << 'L';
 
       auto *FD = dyn_cast<FunctionDecl>(ND);