Hi rnk, rsmith, rjmccall,

This add support for the C++11 feature, thread_local global variables.
The ABI Clang implements is an improvement of the MSVC ABI.  Sadly,
further improvements could be made but not without sacrificing ABI
compatibility.

The feature is implemented as follows:
- All thread_local initialization routines are pointed to from the
  .CRT$XDU section.
- All non-weak thread_local variables have their initialization routines
  call from a single function instead of getting their own .CRT$XDU
  section entry.  This is done to open up optimization opportunities to
  the compiler.
- All weak thread_local variables have their own .CRT$XDU section entry.
  This entry is in a COMDAT with the global variable it is initializing;
  this ensures that we will initialize the global exactly once.
- Destructors are registered in the initialization function using
  __tlregdtor.

http://reviews.llvm.org/D5597

Files:
  lib/CodeGen/CGCXXABI.cpp
  lib/CodeGen/CGCXXABI.h
  lib/CodeGen/CGDeclCXX.cpp
  lib/CodeGen/CodeGenFunction.h
  lib/CodeGen/CodeGenModule.h
  lib/CodeGen/ItaniumCXXABI.cpp
  lib/CodeGen/MicrosoftCXXABI.cpp
  test/CodeGenCXX/ms-thread_local.cpp
Index: lib/CodeGen/CGCXXABI.cpp
===================================================================
--- lib/CodeGen/CGCXXABI.cpp
+++ lib/CodeGen/CGCXXABI.cpp
@@ -310,18 +310,6 @@
   return nullptr;
 }
 
-void CGCXXABI::EmitThreadLocalInitFuncs(
-    ArrayRef<std::pair<const VarDecl *, llvm::GlobalVariable *> > Decls,
-    llvm::Function *InitFunc) {
-}
-
-LValue CGCXXABI::EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF,
-                                              const VarDecl *VD,
-                                              QualType LValType) {
-  ErrorUnsupportedABI(CGF, "odr-use of thread_local global");
-  return LValue();
-}
-
 bool CGCXXABI::NeedsVTTParameter(GlobalDecl GD) {
   return false;
 }
Index: lib/CodeGen/CGCXXABI.h
===================================================================
--- lib/CodeGen/CGCXXABI.h
+++ lib/CodeGen/CGCXXABI.h
@@ -446,6 +446,9 @@
   /// Return whether the given global decl needs a VTT parameter.
   virtual bool NeedsVTTParameter(GlobalDecl GD);
 
+  /// Return whether the __tls_init function require a guard variable.
+  virtual bool requiresTLSGuard() const = 0;
+
 protected:
   /// Returns the extra size required in order to store the array
   /// cookie for the given type.  Assumes that an array cookie is
@@ -499,15 +502,18 @@
   ///        initialization or non-trivial destruction for thread_local
   ///        variables, a function to perform the initialization. Otherwise, 0.
   virtual void EmitThreadLocalInitFuncs(
-      ArrayRef<std::pair<const VarDecl *, llvm::GlobalVariable *> > Decls,
-      llvm::Function *InitFunc);
+      CodeGenModule &CGM,
+      ArrayRef<std::pair<const VarDecl *, llvm::GlobalVariable *>>
+          CXXThreadLocals,
+      ArrayRef<llvm::Function *> CXXThreadLocalInits,
+      ArrayRef<llvm::GlobalVariable *> CXXThreadLocalInitVars) = 0;
 
   /// Emit a reference to a non-local thread_local variable (including
   /// triggering the initialization of all thread_local variables in its
   /// translation unit).
   virtual LValue EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF,
                                               const VarDecl *VD,
-                                              QualType LValType);
+                                              QualType LValType) = 0;
 
   /// Emit a single constructor/destructor with the given type from a C++
   /// constructor Decl.
Index: lib/CodeGen/CGDeclCXX.cpp
===================================================================
--- lib/CodeGen/CGDeclCXX.cpp
+++ lib/CodeGen/CGDeclCXX.cpp
@@ -155,26 +155,19 @@
   EmitStoreOfScalar(RV.getScalarVal(), DeclPtr, false, Alignment, T);
 }
 
-static llvm::Function *
-CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
-                                   llvm::FunctionType *ty,
-                                   const Twine &name,
-                                   bool TLS = false);
-
 /// Create a stub function, suitable for being passed to atexit,
 /// which passes the given address to the given destructor function.
-static llvm::Constant *createAtExitStub(CodeGenModule &CGM, const VarDecl &VD,
-                                        llvm::Constant *dtor,
-                                        llvm::Constant *addr) {
+llvm::Constant *CodeGenFunction::createAtExitStub(const VarDecl &VD,
+                                                  llvm::Constant *dtor,
+                                                  llvm::Constant *addr) {
   // Get the destructor function type, void(*)(void).
   llvm::FunctionType *ty = llvm::FunctionType::get(CGM.VoidTy, false);
   SmallString<256> FnName;
   {
     llvm::raw_svector_ostream Out(FnName);
     CGM.getCXXABI().getMangleContext().mangleDynamicAtExitDestructor(&VD, Out);
   }
-  llvm::Function *fn =
-      CreateGlobalInitOrDestructFunction(CGM, ty, FnName.str());
+  llvm::Function *fn = CGM.CreateGlobalInitOrDestructFunction(ty, FnName.str());
 
   CodeGenFunction CGF(CGM);
 
@@ -198,7 +191,7 @@
                                                    llvm::Constant *dtor,
                                                    llvm::Constant *addr) {
   // Create a function which calls the destructor.
-  llvm::Constant *dtorStub = createAtExitStub(CGM, VD, dtor, addr);
+  llvm::Constant *dtorStub = createAtExitStub(VD, dtor, addr);
 
   // extern "C" int atexit(void (*f)(void));
   llvm::FunctionType *atexitTy =
@@ -226,31 +219,29 @@
   CGM.getCXXABI().EmitGuardedInit(*this, D, DeclPtr, PerformInit);
 }
 
-static llvm::Function *
-CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
-                                   llvm::FunctionType *FTy,
-                                   const Twine &Name, bool TLS) {
+llvm::Function *
+CodeGenModule::CreateGlobalInitOrDestructFunction(llvm::FunctionType *FTy,
+                                                  const Twine &Name, bool TLS) {
   llvm::Function *Fn =
     llvm::Function::Create(FTy, llvm::GlobalValue::InternalLinkage,
-                           Name, &CGM.getModule());
-  if (!CGM.getLangOpts().AppleKext && !TLS) {
+                           Name, &getModule());
+  if (!getLangOpts().AppleKext && !TLS) {
     // Set the section if needed.
-    if (const char *Section = 
-          CGM.getTarget().getStaticInitSectionSpecifier())
+    if (const char *Section = getTarget().getStaticInitSectionSpecifier())
       Fn->setSection(Section);
   }
 
-  Fn->setCallingConv(CGM.getRuntimeCC());
+  Fn->setCallingConv(getRuntimeCC());
 
-  if (!CGM.getLangOpts().Exceptions)
+  if (!getLangOpts().Exceptions)
     Fn->setDoesNotThrow();
 
-  if (!CGM.getSanitizerBlacklist().isIn(*Fn)) {
-    if (CGM.getLangOpts().Sanitize.Address)
+  if (!getSanitizerBlacklist().isIn(*Fn)) {
+    if (getLangOpts().Sanitize.Address)
       Fn->addFnAttr(llvm::Attribute::SanitizeAddress);
-    if (CGM.getLangOpts().Sanitize.Thread)
+    if (getLangOpts().Sanitize.Thread)
       Fn->addFnAttr(llvm::Attribute::SanitizeThread);
-    if (CGM.getLangOpts().Sanitize.Memory)
+    if (getLangOpts().Sanitize.Memory)
       Fn->addFnAttr(llvm::Attribute::SanitizeMemory);
   }
 
@@ -295,8 +286,7 @@
   }
 
   // Create a variable initialization function.
-  llvm::Function *Fn =
-      CreateGlobalInitOrDestructFunction(*this, FTy, FnName.str());
+  llvm::Function *Fn = CreateGlobalInitOrDestructFunction(FTy, FnName.str());
 
   auto *ISA = D->getAttr<InitSegAttr>();
   CodeGenFunction(*this).GenerateCXXGlobalVarDeclInitFunc(Fn, D, Addr,
@@ -312,6 +302,7 @@
     // FIXME: We only need to register one __cxa_thread_atexit function for the
     // entire TU.
     CXXThreadLocalInits.push_back(Fn);
+    CXXThreadLocalInitVars.push_back(Addr);
   } else if (PerformInit && ISA) {
     EmitPointerToInitFunc(D, Addr, Fn, ISA);
     DelayedCXXInitPosition.erase(D);
@@ -354,23 +345,11 @@
 }
 
 void CodeGenModule::EmitCXXThreadLocalInitFunc() {
-  llvm::Function *InitFn = nullptr;
-  if (!CXXThreadLocalInits.empty()) {
-    // Generate a guarded initialization function.
-    llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
-    InitFn = CreateGlobalInitOrDestructFunction(*this, FTy, "__tls_init",
-                                                /*TLS*/ true);
-    llvm::GlobalVariable *Guard = new llvm::GlobalVariable(
-        getModule(), Int8Ty, false, llvm::GlobalVariable::InternalLinkage,
-        llvm::ConstantInt::get(Int8Ty, 0), "__tls_guard");
-    Guard->setThreadLocal(true);
-    CodeGenFunction(*this)
-        .GenerateCXXGlobalInitFunc(InitFn, CXXThreadLocalInits, Guard);
-  }
-
-  getCXXABI().EmitThreadLocalInitFuncs(CXXThreadLocals, InitFn);
+  getCXXABI().EmitThreadLocalInitFuncs(
+      *this, CXXThreadLocals, CXXThreadLocalInits, CXXThreadLocalInitVars);
 
   CXXThreadLocalInits.clear();
+  CXXThreadLocalInitVars.clear();
   CXXThreadLocals.clear();
 }
 
@@ -387,7 +366,7 @@
 
   // Create our global initialization function.
   if (!PrioritizedCXXGlobalInits.empty()) {
-    SmallVector<llvm::Constant*, 8> LocalCXXGlobalInits;
+    SmallVector<llvm::Function *, 8> LocalCXXGlobalInits;
     llvm::array_pod_sort(PrioritizedCXXGlobalInits.begin(), 
                          PrioritizedCXXGlobalInits.end());
     // Iterate over "chunks" of ctors with same priority and emit each chunk
@@ -406,10 +385,9 @@
       std::string PrioritySuffix = llvm::utostr(Priority);
       // Priority is always <= 65535 (enforced by sema).
       PrioritySuffix = std::string(6-PrioritySuffix.size(), '0')+PrioritySuffix;
-      llvm::Function *Fn = 
-        CreateGlobalInitOrDestructFunction(*this, FTy,
-                                           "_GLOBAL__I_" + PrioritySuffix);
-      
+      llvm::Function *Fn = CreateGlobalInitOrDestructFunction(
+          FTy, "_GLOBAL__I_" + PrioritySuffix);
+
       for (; I < PrioE; ++I)
         LocalCXXGlobalInits.push_back(I->second);
 
@@ -437,7 +415,7 @@
   }
 
   llvm::Function *Fn = CreateGlobalInitOrDestructFunction(
-      *this, FTy, llvm::Twine("_GLOBAL__sub_I_", FileName));
+      FTy, llvm::Twine("_GLOBAL__sub_I_", FileName));
 
   CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn, CXXGlobalInits);
   AddGlobalCtor(Fn);
@@ -453,8 +431,7 @@
   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
 
   // Create our global destructor function.
-  llvm::Function *Fn =
-    CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__D_a");
+  llvm::Function *Fn = CreateGlobalInitOrDestructFunction(FTy, "_GLOBAL__D_a");
 
   CodeGenFunction(*this).GenerateCXXGlobalDtorsFunc(Fn, CXXGlobalDtors);
   AddGlobalDtor(Fn);
@@ -488,7 +465,7 @@
 
 void
 CodeGenFunction::GenerateCXXGlobalInitFunc(llvm::Function *Fn,
-                                           ArrayRef<llvm::Constant *> Decls,
+                                           ArrayRef<llvm::Function *> Decls,
                                            llvm::GlobalVariable *Guard) {
   {
     ArtificialLocation AL(*this, Builder);
@@ -575,8 +552,8 @@
   const CGFunctionInfo &FI = CGM.getTypes().arrangeFreeFunctionDeclaration(
       getContext().VoidTy, args, FunctionType::ExtInfo(), /*variadic=*/false);
   llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(FI);
-  llvm::Function *fn = 
-    CreateGlobalInitOrDestructFunction(CGM, FTy, "__cxx_global_array_dtor");
+  llvm::Function *fn =
+      CGM.CreateGlobalInitOrDestructFunction(FTy, "__cxx_global_array_dtor");
 
   StartFunction(VD, getContext().VoidTy, fn, FI, args);
 
Index: lib/CodeGen/CodeGenFunction.h
===================================================================
--- lib/CodeGen/CodeGenFunction.h
+++ lib/CodeGen/CodeGenFunction.h
@@ -2485,6 +2485,9 @@
   void EmitCXXGlobalVarDeclInit(const VarDecl &D, llvm::Constant *DeclPtr,
                                 bool PerformInit);
 
+  llvm::Constant *createAtExitStub(const VarDecl &VD, llvm::Constant *Dtor,
+                                   llvm::Constant *Addr);
+
   /// Call atexit() with a function that passes the given argument to
   /// the given function.
   void registerGlobalDtorWithAtExit(const VarDecl &D, llvm::Constant *fn,
@@ -2501,7 +2504,7 @@
   /// GenerateCXXGlobalInitFunc - Generates code for initializing global
   /// variables.
   void GenerateCXXGlobalInitFunc(llvm::Function *Fn,
-                                 ArrayRef<llvm::Constant *> Decls,
+                                 ArrayRef<llvm::Function *> CXXThreadLocals,
                                  llvm::GlobalVariable *Guard = nullptr);
 
   /// GenerateCXXGlobalDtorsFunc - Generates code for destroying global
Index: lib/CodeGen/CodeGenModule.h
===================================================================
--- lib/CodeGen/CodeGenModule.h
+++ lib/CodeGen/CodeGenModule.h
@@ -387,10 +387,11 @@
 
   /// \brief thread_local variables with initializers that need to run
   /// before any thread_local variable in this TU is odr-used.
-  std::vector<llvm::Constant*> CXXThreadLocalInits;
+  std::vector<llvm::Function *> CXXThreadLocalInits;
+  std::vector<llvm::GlobalVariable *> CXXThreadLocalInitVars;
 
   /// Global variables with initializers that need to run before main.
-  std::vector<llvm::Constant*> CXXGlobalInits;
+  std::vector<llvm::Function *> CXXGlobalInits;
 
   /// When a C++ decl with an initializer is deferred, null is
   /// appended to CXXGlobalInits, and the index of that null is placed
@@ -683,6 +684,10 @@
   CreateOrReplaceCXXRuntimeVariable(StringRef Name, llvm::Type *Ty,
                                     llvm::GlobalValue::LinkageTypes Linkage);
 
+  llvm::Function *CreateGlobalInitOrDestructFunction(llvm::FunctionType *ty,
+                                                     const Twine &name,
+                                                     bool TLS = false);
+
   /// Return the address space of the underlying global variable for D, as
   /// determined by its declaration. Normally this is the same as the address
   /// space of D's type, but in CUDA, address spaces are associated with
Index: lib/CodeGen/ItaniumCXXABI.cpp
===================================================================
--- lib/CodeGen/ItaniumCXXABI.cpp
+++ lib/CodeGen/ItaniumCXXABI.cpp
@@ -234,11 +234,16 @@
   void registerGlobalDtor(CodeGenFunction &CGF, const VarDecl &D,
                           llvm::Constant *dtor, llvm::Constant *addr) override;
 
+  virtual bool requiresTLSGuard() const override { return true; }
+
   llvm::Function *getOrCreateThreadLocalWrapper(const VarDecl *VD,
                                                 llvm::Value *Val);
   void EmitThreadLocalInitFuncs(
-      ArrayRef<std::pair<const VarDecl *, llvm::GlobalVariable *> > Decls,
-      llvm::Function *InitFunc) override;
+      CodeGenModule &CGM,
+      ArrayRef<std::pair<const VarDecl *, llvm::GlobalVariable *>>
+          CXXThreadLocals,
+      ArrayRef<llvm::Function *> CXXThreadLocalInits,
+      ArrayRef<llvm::GlobalVariable *> CXXThreadLocalInitVars) override;
   LValue EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF, const VarDecl *VD,
                                       QualType LValType) override;
 
@@ -1897,11 +1902,28 @@
 }
 
 void ItaniumCXXABI::EmitThreadLocalInitFuncs(
-    ArrayRef<std::pair<const VarDecl *, llvm::GlobalVariable *> > Decls,
-    llvm::Function *InitFunc) {
-  for (unsigned I = 0, N = Decls.size(); I != N; ++I) {
-    const VarDecl *VD = Decls[I].first;
-    llvm::GlobalVariable *Var = Decls[I].second;
+    CodeGenModule &CGM,
+    ArrayRef<std::pair<const VarDecl *, llvm::GlobalVariable *>>
+        CXXThreadLocals, ArrayRef<llvm::Function *> CXXThreadLocalInits,
+    ArrayRef<llvm::GlobalVariable *> CXXThreadLocalInitVars) {
+  llvm::Function *InitFunc = nullptr;
+  if (!CXXThreadLocalInits.empty()) {
+    // Generate a guarded initialization function.
+    llvm::FunctionType *FTy =
+        llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
+    InitFunc = CGM.CreateGlobalInitOrDestructFunction(FTy, "__tls_init",
+                                                      /*TLS=*/true);
+    llvm::GlobalVariable *Guard = new llvm::GlobalVariable(
+        CGM.getModule(), CGM.Int8Ty, /*isConstant=*/false,
+        llvm::GlobalVariable::InternalLinkage,
+        llvm::ConstantInt::get(CGM.Int8Ty, 0), "__tls_guard");
+    Guard->setThreadLocal(true);
+    CodeGenFunction(CGM)
+        .GenerateCXXGlobalInitFunc(InitFunc, CXXThreadLocalInits, Guard);
+  }
+  for (unsigned I = 0, N = CXXThreadLocals.size(); I != N; ++I) {
+    const VarDecl *VD = CXXThreadLocals[I].first;
+    llvm::GlobalVariable *Var = CXXThreadLocals[I].second;
 
     // Some targets require that all access to thread local variables go through
     // the thread wrapper.  This means that we cannot attempt to create a thread
Index: lib/CodeGen/MicrosoftCXXABI.cpp
===================================================================
--- lib/CodeGen/MicrosoftCXXABI.cpp
+++ lib/CodeGen/MicrosoftCXXABI.cpp
@@ -255,9 +255,23 @@
   llvm::Value *performReturnAdjustment(CodeGenFunction &CGF, llvm::Value *Ret,
                                        const ReturnAdjustment &RA) override;
 
+  void EmitThreadLocalInitFuncs(
+      CodeGenModule &CGM,
+      ArrayRef<std::pair<const VarDecl *, llvm::GlobalVariable *>>
+          CXXThreadLocals,
+      ArrayRef<llvm::Function *> CXXThreadLocalInits,
+      ArrayRef<llvm::GlobalVariable *> CXXThreadLocalInitVars) override;
+
+  LValue EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF, const VarDecl *VD,
+                                      QualType LValType) override;
+
   void EmitGuardedInit(CodeGenFunction &CGF, const VarDecl &D,
                        llvm::GlobalVariable *DeclPtr,
                        bool PerformInit) override;
+  void registerGlobalDtor(CodeGenFunction &CGF, const VarDecl &D,
+                          llvm::Constant *Dtor, llvm::Constant *Addr) override;
+
+  virtual bool requiresTLSGuard() const override { return false; }
 
   // ==== Notes on array cookies =========
   //
@@ -1711,6 +1725,104 @@
                                                 cookieSize.getQuantity());
 }
 
+static void emitGlobalDtorWithTLRegDtor(CodeGenFunction &CGF, const VarDecl &VD,
+                                        llvm::Constant *Dtor,
+                                        llvm::Constant *Addr) {
+  // Create a function which calls the destructor.
+  llvm::Constant *DtorStub = CGF.createAtExitStub(VD, Dtor, Addr);
+
+  // extern "C" int __tlregdtor(void (*f)(void));
+  llvm::FunctionType *TLRegDtorTy = llvm::FunctionType::get(
+      CGF.IntTy, DtorStub->getType(), /*IsVarArg=*/false);
+
+  llvm::Constant *TLRegDtor =
+      CGF.CGM.CreateRuntimeFunction(TLRegDtorTy, "__tlregdtor");
+  if (llvm::Function *TLRegDtorFn = dyn_cast<llvm::Function>(TLRegDtor))
+    TLRegDtorFn->setDoesNotThrow();
+
+  CGF.EmitNounwindRuntimeCall(TLRegDtor, DtorStub);
+}
+
+void MicrosoftCXXABI::registerGlobalDtor(CodeGenFunction &CGF, const VarDecl &D,
+                                         llvm::Constant *Dtor,
+                                         llvm::Constant *Addr) {
+  if (D.getTLSKind())
+    return emitGlobalDtorWithTLRegDtor(CGF, D, Dtor, Addr);
+
+  // The default behavior is to use atexit.
+  CGF.registerGlobalDtorWithAtExit(D, Dtor, Addr);
+}
+
+void MicrosoftCXXABI::EmitThreadLocalInitFuncs(
+    CodeGenModule &CGM,
+    ArrayRef<std::pair<const VarDecl *, llvm::GlobalVariable *>>
+        CXXThreadLocals,
+    ArrayRef<llvm::Function *> CXXThreadLocalInits,
+    ArrayRef<llvm::GlobalVariable *> CXXThreadLocalInitVars) {
+  // This will create a GV in the .CRT$XDU section.  It will point to our
+  // initialization function.  The CRT will call all of these function
+  // pointers at start-up time and, eventually, at thread-creation time.
+  auto AddToXDU = [&CGM](llvm::Function *InitFunc) {
+    llvm::GlobalVariable *InitFuncPtr = new llvm::GlobalVariable(
+        CGM.getModule(), InitFunc->getType(), /*IsConstant=*/true,
+        llvm::GlobalVariable::InternalLinkage, InitFunc,
+        Twine(InitFunc->getName(), "$initializer$"));
+    InitFuncPtr->setSection(".CRT$XDU");
+    // This variable has discardable linkage, we have to add it to @llvm.used to
+    // ensure it won't get discarded.
+    CGM.addUsedGlobal(InitFuncPtr);
+    return InitFuncPtr;
+  };
+
+  llvm::FunctionType *FTy =
+      llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
+
+  std::vector<llvm::Function *> NondiscardableInits;
+  for (size_t I = 0, E = CXXThreadLocalInitVars.size(); I != E; ++I) {
+    llvm::GlobalVariable *GV = CXXThreadLocalInitVars[I];
+    llvm::Function *F = CXXThreadLocalInits[I];
+
+    // If the GV is already in a comdat group, then we have to join it.
+    llvm::Comdat *C = GV->getComdat();
+
+    // LinkOnce and Weak linkage are lowered down to a single-member comdat
+    // group.
+    // Make an explicit group so we can join it.
+    if (!C && (GV->hasWeakLinkage() || GV->hasLinkOnceLinkage())) {
+      C = CGM.getModule().getOrInsertComdat(GV->getName());
+      GV->setComdat(C);
+      AddToXDU(F)->setComdat(C);
+    } else {
+      NondiscardableInits.push_back(F);
+    }
+  }
+
+  if (!NondiscardableInits.empty()) {
+    llvm::Function *InitFunc =
+        CGM.CreateGlobalInitOrDestructFunction(FTy, "__tls_init",
+                                               /*TLS=*/true);
+    CodeGenFunction(CGM)
+        .GenerateCXXGlobalInitFunc(InitFunc, NondiscardableInits);
+
+    AddToXDU(InitFunc);
+  }
+}
+
+LValue MicrosoftCXXABI::EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF,
+                                                     const VarDecl *VD,
+                                                     QualType LValType) {
+  QualType T = VD->getType();
+  llvm::Type *Ty = CGF.getTypes().ConvertTypeForMem(T);
+  llvm::Value *Val = CGF.CGM.GetAddrOfGlobalVar(VD, Ty);
+
+  LValue LV;
+  if (VD->getType()->isReferenceType())
+    LV = CGF.MakeNaturalAlignAddrLValue(Val, LValType);
+  else
+    LV = CGF.MakeAddrLValue(Val, LValType, CGF.getContext().getDeclAlign(VD));
+  return LV;
+}
+
 void MicrosoftCXXABI::EmitGuardedInit(CodeGenFunction &CGF, const VarDecl &D,
                                       llvm::GlobalVariable *GV,
                                       bool PerformInit) {
Index: test/CodeGenCXX/ms-thread_local.cpp
===================================================================
--- /dev/null
+++ test/CodeGenCXX/ms-thread_local.cpp
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -emit-llvm -o - | FileCheck %s
+
+struct A {
+  A();
+  ~A();
+};
+
+// CHECK-DAG: $"\01??$a@X@@3UA@@A" = comdat any
+// CHECK-DAG: @"\01??$a@X@@3UA@@A" = linkonce_odr thread_local global %struct.A zeroinitializer, comdat $"\01??$a@X@@3UA@@A"
+// CHECK-DAG: @"\01??__E?$a@X@@YAXXZ$initializer$" = internal constant void ()* @"\01??__E?$a@X@@YAXXZ", section ".CRT$XDU", comdat $"\01??$a@X@@3UA@@A"
+template <typename T>
+thread_local A a = A();
+
+// CHECK-DAG: @"\01?b@@3UA@@A" = thread_local global %struct.A zeroinitializer, align 1
+// CHECK-DAG: @"__tls_init$initializer$" = internal constant void ()* @__tls_init, section ".CRT$XDU"
+thread_local A b;
+
+void f() {
+  (void)a<void>;
+  (void)b;
+}
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