2 files changed, 19 insertions, 16 deletions
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index cd34d03cd77..494176a9063 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -15,6 +15,7 @@
 #include "CodeGenFunction.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/RecordLayout.h"
+#include "clang/Frontend/CodeGenOptions.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/Support/Compiler.h"
@@ -2469,34 +2470,29 @@ static void setThunkVisibility(CodeGenModule &CGM, const CXXMethodDecl *MD,
   // emit its thunks with hidden visibility, since its thunks must be
   // emitted when the function is.
 
-  // This mostly follows CodeGenModule::setTypeVisibility.
+  // This follows CodeGenModule::setTypeVisibility; see the comments
+  // there for explanation.
 
   if ((Fn->getLinkage() != llvm::GlobalVariable::LinkOnceODRLinkage &&
        Fn->getLinkage() != llvm::GlobalVariable::WeakODRLinkage) ||
       Fn->getVisibility() != llvm::GlobalVariable::DefaultVisibility)
     return;
 
-  // Don't override an explicit visibility attribute.
   if (MD->hasAttr<VisibilityAttr>())
     return;
 
   switch (MD->getTemplateSpecializationKind()) {
-  // We have to disable the optimization if this is an EI definition
-  // because there might be EI declarations in other shared objects.
   case TSK_ExplicitInstantiationDefinition:
   case TSK_ExplicitInstantiationDeclaration:
     return;
 
-  // Every use of a non-template or explicitly-specialized class's
-  // type information has to emit it.
-  case TSK_ExplicitSpecialization:
   case TSK_Undeclared:
     break;
 
-  // Implicit instantiations can ignore the possibility of an
-  // explicit instantiation declaration because there necessarily
-  // must be an EI definition somewhere with default visibility.
+  case TSK_ExplicitSpecialization:
   case TSK_ImplicitInstantiation:
+    if (!CGM.getCodeGenOpts().EmitWeakTemplatesHidden)
+      return;
     break;
   }
 
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 63384025799..297aa4524e3 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -229,6 +229,9 @@ void CodeGenModule::setTypeVisibility(llvm::GlobalValue *GV,
   // This isn't possible if there might be unresolved references
   // elsewhere that rely on this symbol being visible.
 
+  // This should be kept roughly in sync with setThunkVisibility
+  // in CGVTables.cpp.
+
   // Preconditions.
   if (GV->getLinkage() != llvm::GlobalVariable::WeakODRLinkage ||
       GV->getVisibility() != llvm::GlobalVariable::DefaultVisibility)
@@ -245,16 +248,20 @@ void CodeGenModule::setTypeVisibility(llvm::GlobalValue *GV,
   case TSK_ExplicitInstantiationDeclaration:
     return;
 
-  // Every use of a non-template or explicitly-specialized class's
-  // type information has to emit it.
-  case TSK_ExplicitSpecialization:
+  // Every use of a non-template class's type information has to emit it.
   case TSK_Undeclared:
     break;
 
-  // Implicit instantiations can ignore the possibility of an
-  // explicit instantiation declaration because there necessarily
-  // must be an EI definition somewhere with default visibility.
+  // In theory, implicit instantiations can ignore the possibility of
+  // an explicit instantiation declaration because there necessarily
+  // must be an EI definition somewhere with default visibility.  In
+  // practice, it's possible to have an explicit instantiation for
+  // an arbitrary template class, and linkers aren't necessarily able
+  // to deal with mixed-visibility symbols.
+  case TSK_ExplicitSpecialization:
   case TSK_ImplicitInstantiation:
+    if (!CodeGenOpts.EmitWeakTemplatesHidden)
+      return;
     break;
   }