Index: clang/lib/CodeGen/ItaniumCXXABI.cpp
===================================================================
--- clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -2546,6 +2546,12 @@
       llvm::Function::Create(FnTy, getThreadLocalWrapperLinkage(VD, CGM),
                              WrapperName.str(), &CGM.getModule());
 
+  // On Windows, we need to make the weak/linkonce wrapper comdat to
+  // actually handle multiple TUs defining the same wrapper.
+  if (CGM.getTriple().isOSWindows() && CGM.supportsCOMDAT() &&
+      Wrapper->isWeakForLinker())
+    Wrapper->setComdat(CGM.getModule().getOrInsertComdat(Wrapper->getName()));
+
   CGM.SetLLVMFunctionAttributes(GlobalDecl(), FI, Wrapper);
 
   // Always resolve references to the wrapper at link time.
Index: clang/test/CodeGenCXX/tls-init-funcs.cpp
===================================================================
--- clang/test/CodeGenCXX/tls-init-funcs.cpp
+++ clang/test/CodeGenCXX/tls-init-funcs.cpp
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -triple x86_64-apple-macosx10.8 -std=c++1y -S -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-windows-gnu -std=c++1y -S -emit-llvm %s -o - | FileCheck %s --check-prefix=MINGW
 
 // CHECK: @a = internal thread_local global
 // CHECK: @_Z2vtIiE = linkonce_odr thread_local global i32 5
@@ -10,6 +11,9 @@
 // CHECK-DAG: define weak_odr hidden cxx_fast_tlscc i32* @_ZTW2vtIvE()
 // CHECK-DAG: define {{.*}} @_ZTW1a
 
+// MINGW-DAG: define weak_odr hidden i32* @_ZTW2vtIiE() {{.*}} comdat
+// MINGW-DAG: define weak_odr hidden i32* @_ZTW2vtIvE() {{.*}} comdat
+
 struct A {
   ~A();
 };