Index: include/clang/AST/Decl.h
===================================================================
--- include/clang/AST/Decl.h
+++ include/clang/AST/Decl.h
@@ -693,7 +693,7 @@
     friend class ASTDeclReader;
 
     unsigned SClass : 3;
-    unsigned TSCSpec : 2;
+    unsigned TSCSpec : 3;
     unsigned InitStyle : 2;
 
     /// \brief Whether this variable is the exception variable in a C++ catch
@@ -725,7 +725,7 @@
     /// the type of this declaration with its previous declaration.
     unsigned PreviousDeclInSameBlockScope : 1;
   };
-  enum { NumVarDeclBits = 14 };
+  enum { NumVarDeclBits = 15 };
 
   friend class ASTDeclReader;
   friend class StmtIteratorBase;
@@ -754,7 +754,7 @@
     /// Otherwise, the number of function parameter scopes enclosing
     /// the function parameter scope in which this parameter was
     /// declared.
-    unsigned ScopeDepthOrObjCQuals : 7;
+    unsigned ScopeDepthOrObjCQuals : 6;
 
     /// The number of parameters preceding this parameter in the
     /// function parameter scope in which it was declared.
@@ -818,6 +818,7 @@
       return TLS_None;
     case TSCS___thread: // Fall through.
     case TSCS__Thread_local:
+    case TSCS___declspec_thread:
       return TLS_Static;
     case TSCS_thread_local:
       return TLS_Dynamic;
Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -1665,6 +1665,13 @@
   let Documentation = [Undocumented];
 }
 
+def Thread : InheritableAttr {
+  let Spellings = [Declspec<"thread">];
+  let LangOpts = [MicrosoftExt];
+  let Documentation = [Undocumented];
+  let Subjects = SubjectList<[Var]>;
+}
+
 def Win64 : IgnoredAttr {
   let Spellings = [Keyword<"__w64">];
   let LangOpts = [MicrosoftExt];
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -2081,6 +2081,9 @@
   "weak declaration cannot have internal linkage">;
 def err_attribute_selectany_non_extern_data : Error<
   "'selectany' can only be applied to data items with external linkage">;
+def err_multiple_thread_specifiers : Error<
+  "__declspec(thread) applied to variable declaration which already has a "
+  "thread specifier">;
 def err_attribute_dll_not_extern : Error<
   "%q0 must have external linkage when declared %q1">;
 def warn_attribute_invalid_on_definition : Warning<
Index: include/clang/Basic/Specifiers.h
===================================================================
--- include/clang/Basic/Specifiers.h
+++ include/clang/Basic/Specifiers.h
@@ -163,7 +163,9 @@
     TSCS_thread_local,
     /// C11 _Thread_local. Must be combined with either 'static' or 'extern'
     /// if used at block scope.
-    TSCS__Thread_local
+    TSCS__Thread_local,
+    /// __declspec(thread). Equivalent to GNU __thread.
+    TSCS___declspec_thread
   };
 
   /// \brief Storage classes.
Index: include/clang/Sema/DeclSpec.h
===================================================================
--- include/clang/Sema/DeclSpec.h
+++ include/clang/Sema/DeclSpec.h
@@ -232,6 +232,7 @@
   typedef ThreadStorageClassSpecifier TSCS;
   static const TSCS TSCS_unspecified = clang::TSCS_unspecified;
   static const TSCS TSCS___thread = clang::TSCS___thread;
+  static const TSCS TSCS___declspec_thread = clang::TSCS___declspec_thread;
   static const TSCS TSCS_thread_local = clang::TSCS_thread_local;
   static const TSCS TSCS__Thread_local = clang::TSCS__Thread_local;
 
Index: lib/AST/DeclPrinter.cpp
===================================================================
--- lib/AST/DeclPrinter.cpp
+++ lib/AST/DeclPrinter.cpp
@@ -655,6 +655,8 @@
     switch (D->getTSCSpec()) {
     case TSCS_unspecified:
       break;
+    case TSCS___declspec_thread:
+      break; // Nothing, the attribute printer will do it for us.
     case TSCS___thread:
       Out << "__thread ";
       break;
Index: lib/Sema/DeclSpec.cpp
===================================================================
--- lib/Sema/DeclSpec.cpp
+++ lib/Sema/DeclSpec.cpp
@@ -383,6 +383,7 @@
   switch (S) {
   case DeclSpec::TSCS_unspecified:   return "unspecified";
   case DeclSpec::TSCS___thread:      return "__thread";
+  case DeclSpec::TSCS___declspec_thread: return "__declspec(thread)";
   case DeclSpec::TSCS_thread_local:  return "thread_local";
   case DeclSpec::TSCS__Thread_local: return "_Thread_local";
   }
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -3697,6 +3697,18 @@
     D->addAttr(IA);
 }
 
+static void handleDeclspecThreadAttr(Sema &S, Decl *D,
+                                     const AttributeList &Attr) {
+  VarDecl *VD = cast<VarDecl>(D);
+  if (VD->getTSCSpec() != TSCS_unspecified) {
+    S.Diag(Attr.getLoc(), diag::err_multiple_thread_specifiers);
+    return;
+  }
+  D->addAttr(::new (S.Context) ThreadAttr(
+      Attr.getRange(), S.Context, Attr.getAttributeSpellingListIndex()));
+  VD->setTSCSpec(TSCS___declspec_thread);
+}
+
 static void handleARMInterruptAttr(Sema &S, Decl *D,
                                    const AttributeList &Attr) {
   // Check the attribute arguments.
@@ -4394,6 +4406,9 @@
   case AttributeList::AT_SelectAny:
     handleSimpleAttribute<SelectAnyAttr>(S, D, Attr);
     break;
+  case AttributeList::AT_Thread:
+    handleDeclspecThreadAttr(S, D, Attr);
+    break;
 
   // Thread safety attributes:
   case AttributeList::AT_AssertExclusiveLock:
Index: test/SemaCXX/declspec-thread.cpp
===================================================================
--- /dev/null
+++ test/SemaCXX/declspec-thread.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fms-extensions -verify %s
+
+__thread __declspec(thread) int a; // expected-error {{already has a thread specifier}}
+__declspec(thread) __thread int b; // expected-error {{already has a thread specifier}}
+__declspec(thread) int c(); // expected-warning {{only applies to variables}}
+__declspec(thread) int d;
+int foo();
+__declspec(thread) int e = foo(); // expected-error {{must be a constant expression}}