It turns out that linkers (at least, the Darwin linker) don't necessarily

do the right thing with mixed-visibility symbols, so disable the visibility
optimization where that's possible, i.e. with template classes (since it's
possible that an arbitrary template might be subject to an explicit
instantiation elsewhere).  447.dealII actually does this.

I've put the code under an option that's currently not hooked up to anything.

llvm-svn: 110374

clang/include/clang/Frontend/CodeGenOptions.h

@@ -46,7 +46,12 @@ public:
                                   /// internal state before optimizations are
                                   /// done.
   unsigned DisableRedZone    : 1; /// Set when -mno-red-zone is enabled.
+  unsigned EmitDeclMetadata  : 1; /// Emit special metadata indicating what Decl*
+                                  /// various IR entities came from.  Only useful
+                                  /// when running CodeGen as a subroutine.
   unsigned FunctionSections  : 1; /// Set when -ffunction-sections is enabled
+  unsigned EmitWeakTemplatesHidden : 1;  /// Emit weak vtables and typeinfo for
+                                  /// template classes with hidden visibility
   unsigned InstrumentFunctions : 1; /// Set when -finstrument-functions is enabled
   unsigned MergeAllConstants : 1; /// Merge identical constants.
   unsigned NoCommon          : 1; /// Set when -fno-common or C++ is enabled.
@@ -67,9 +72,6 @@ public:
   unsigned UnwindTables      : 1; /// Emit unwind tables.
   unsigned VerifyModule      : 1; /// Control whether the module should be run
                                   /// through the LLVM Verifier.
-  unsigned EmitDeclMetadata  : 1; /// Emit special metadata indicating what Decl*
-                                  /// various IR entities came from.  Only useful
-                                  /// when running CodeGen as a subroutine.
 
   /// The code model to use (-mcmodel).
   std::string CodeModel;
@@ -108,7 +110,9 @@ public:
     DisableFPElim = 0;
     DisableLLVMOpts = 0;
     DisableRedZone = 0;
+    EmitDeclMetadata = 0;
     FunctionSections = 0;
+    EmitWeakTemplatesHidden = 0;
     MergeAllConstants = 1;
     NoCommon = 0;
     NoImplicitFloat = 0;
@@ -125,7 +129,6 @@ public:
     UnrollLoops = 0;
     UnwindTables = 0;
     VerifyModule = 1;
-    EmitDeclMetadata = 0;
 
     Inlining = NoInlining;
     RelocationModel = "pic";

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;
   }
 

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;
   }
 

clang/test/CodeGenCXX/mangle-subst-std.cpp

@@ -3,13 +3,13 @@
 // Check mangling of Vtables, VTTs, and construction vtables that
 // involve standard substitutions.
 
-// CHECK: @_ZTVSd = weak_odr hidden constant 
+// CHECK: @_ZTVSd = weak_odr constant 
 // CHECK: @_ZTCSd0_Si = internal constant 
 // CHECK: @_ZTCSd16_So = internal constant
 // CHECK: @_ZTTSd = weak_odr constant
-// CHECK: @_ZTVSo = weak_odr hidden constant
+// CHECK: @_ZTVSo = weak_odr constant
 // CHECK: @_ZTTSo = weak_odr constant
-// CHECK: @_ZTVSi = weak_odr hidden constant
+// CHECK: @_ZTVSi = weak_odr constant
 // CHECK: @_ZTTSi = weak_odr constant
 namespace std {
   struct A { A(); };

clang/test/CodeGenCXX/rtti-linkage.cpp

@@ -14,7 +14,7 @@
 // CHECK: _ZTI1A = weak_odr hidden constant
 // CHECK: _ZTI1B = constant
 // CHECK: _ZTI1C = internal constant
-// CHECK: _ZTI1TILj0EE = weak_odr hidden constant
+// CHECK: _ZTI1TILj0EE = weak_odr constant
 // CHECK: _ZTI1TILj1EE = weak_odr constant
 // CHECK: _ZTI1TILj2EE = external constant
 // CHECK: _ZTIA10_i = weak_odr hidden constant

clang/test/CodeGenCXX/virt-template-vtable.cpp

@@ -19,4 +19,4 @@ template class A<short>;
 // CHECK: @_ZTV1B = weak_odr hidden constant
 // CHECK: @_ZTV1AIlE = weak_odr constant
 // CHECK: @_ZTV1AIsE = weak_odr constant
-// CHECK: @_ZTV1AIiE = weak_odr hidden constant
+// CHECK: @_ZTV1AIiE = weak_odr constant

clang/test/CodeGenCXX/vtable-linkage.cpp

@@ -137,10 +137,10 @@ void use_F() {
 // CHECK-7: @_ZTI1EIlE = weak_odr constant
 
 // F<long> is an implicit template instantiation with no key function,
-// so its vtable should have weak_odr linkage and hidden visibility.
-// CHECK-8: @_ZTV1FIlE = weak_odr hidden constant
+// so its vtable should have weak_odr linkage.
+// CHECK-8: @_ZTV1FIlE = weak_odr constant
 // CHECK-8: @_ZTS1FIlE = weak_odr constant
-// CHECK-8: @_ZTI1FIlE = weak_odr hidden constant
+// CHECK-8: @_ZTI1FIlE = weak_odr constant
 
 // F<int> is an explicit template instantiation declaration without a
 // key function, so its vtable should have external linkage.
@@ -164,10 +164,10 @@ void use_F() {
 // CHECK-12: @_ZTIN12_GLOBAL__N_11AE = internal constant
 
 // F<char> is an explicit specialization without a key function, so
-// its vtable should have weak_odr linkage and hidden visibility.
-// CHECK-13: @_ZTV1FIcE = weak_odr hidden constant
+// its vtable should have weak_odr linkage.
+// CHECK-13: @_ZTV1FIcE = weak_odr constant
 // CHECK-13: @_ZTS1FIcE = weak_odr constant
-// CHECK-13: @_ZTI1FIcE = weak_odr hidden constant
+// CHECK-13: @_ZTI1FIcE = weak_odr constant
 
 // RUN: FileCheck --check-prefix=CHECK-G %s < %t
 //