[MS ABI] Explicit specialization of static data members are weak

Normally, explicit specializations are treated like strong external
definitions.  However, MSVC treats explicit specializations of static
data members as weak.  MSVC 2013's <regex> implementation has such an
explicit specialization which leads to clang emitting a strong
definition in each translation unit which includes it.  Tweak clang's
linkage calculation to give such entities GVA_StrongODR linkage instead.

This fixes PR24165.

llvm-svn: 242592

1 files changed, 5 insertions, 1 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index fb9630180dc..61bd1077941 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -8285,9 +8285,13 @@ static GVALinkage basicGVALinkageForVariable(const ASTContext &Context,
 
   switch (VD->getTemplateSpecializationKind()) {
   case TSK_Undeclared:
-  case TSK_ExplicitSpecialization:
     return GVA_StrongExternal;
 
+  case TSK_ExplicitSpecialization:
+    return Context.getLangOpts().MSVCCompat && VD->isStaticDataMember()
+               ? GVA_StrongODR
+               : GVA_StrongExternal;
+
   case TSK_ExplicitInstantiationDefinition:
     return GVA_StrongODR;