Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -2213,7 +2213,10 @@
 
       // A dllimport variable never acts like a constant, unless we're
       // evaluating a value for use only in name mangling.
-      if (!isForManglingOnly(Kind) && Var->hasAttr<DLLImportAttr>())
+      if (Info.getLangOpts().C99 && !isForManglingOnly(Kind) &&
+              Var->hasAttr<DLLImportAttr>() ||
+          Info.getLangOpts().CPlusPlus && !isForManglingOnly(Kind) &&
+              Var->hasAttr<DLLExportAttr>())
         // FIXME: Diagnostic!
         return false;
     }
Index: clang/test/CodeGenCXX/PR19955.cpp
===================================================================
--- clang/test/CodeGenCXX/PR19955.cpp
+++ clang/test/CodeGenCXX/PR19955.cpp
@@ -6,20 +6,16 @@
 
 extern int *varp;
 int *varp = &var;
-// CHECK-DAG: @"?varp@@3PAHA" = dso_local global i32* null
-// X64-DAG: @"?varp@@3PEAHEA" = dso_local global i32* null
+// CHECK-DAG: @"?var@@3HA" = external dllimport global i32
+// CHECK-DAG: @"?varp@@3PAHA" = dso_local global i32* @"?var@@3HA"
+// X64-DAG: @"?var@@3HA" = external dllimport global i32, align 4
+// X64-DAG: @"?varp@@3PEAHEA" = dso_local global i32* @"?var@@3HA"
 
 extern void (*funp)();
 void (*funp)() = &fun;
 // CHECK-DAG: @"?funp@@3P6AXXZA" = dso_local global void ()* null
 // X64-DAG: @"?funp@@3P6AXXZEA" = dso_local global void ()* null
 
-// CHECK-LABEL: @"??__Evarp@@YAXXZ"
-// CHECK-DAG: store i32* @"?var@@3HA", i32** @"?varp@@3PAHA"
-
-// X64-LABEL: @"??__Evarp@@YAXXZ"
-// X64-DAG: store i32* @"?var@@3HA", i32** @"?varp@@3PEAHEA"
-
 // CHECK-LABEL: @"??__Efunp@@YAXXZ"()
 // CHECK-DAG: store void ()* @"?fun@@YAXXZ", void ()** @"?funp@@3P6AXXZA"
 
Index: clang/test/CodeGenCXX/dllimport.cpp
===================================================================
--- clang/test/CodeGenCXX/dllimport.cpp
+++ clang/test/CodeGenCXX/dllimport.cpp
@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -disable-noundef-analysis -triple i686-windows-msvc   -fno-rtti -fno-threadsafe-statics -fms-extensions -emit-llvm -std=c++1y -O0 -o - %s -DMSABI -w | FileCheck --check-prefix=MSC --check-prefix=M32 %s
-// RUN: %clang_cc1 -disable-noundef-analysis -triple x86_64-windows-msvc -fno-rtti -fno-threadsafe-statics -fms-extensions -emit-llvm -std=c++1y -O0 -o - %s -DMSABI -w | FileCheck --check-prefix=MSC --check-prefix=M64 %s
+// RUN: %clang_cc1 -disable-noundef-analysis -triple x86_64-windows-msvc -fno-rtti -fno-threadsafe-statics -fms-extensions -emit-llvm -std=c++1y -O0 -o - %s -DMSABI -w | FileCheck --check-prefix=MSC64 --check-prefix=M64 %s
 // RUN: %clang_cc1 -disable-noundef-analysis -triple i686-windows-gnu    -fno-rtti -fno-threadsafe-statics -fms-extensions -emit-llvm -std=c++1y -O0 -o - %s         -w | FileCheck --check-prefix=GNU --check-prefix=G32 %s
 // RUN: %clang_cc1 -disable-noundef-analysis -triple x86_64-windows-gnu  -fno-rtti -fno-threadsafe-statics -fms-extensions -emit-llvm -std=c++1y -O0 -o - %s         -w | FileCheck --check-prefix=GNU %s
 // RUN: %clang_cc1 -disable-noundef-analysis -triple i686-windows-msvc   -fno-rtti -fno-threadsafe-statics -fms-extensions -fms-compatibility-version=18.00 -emit-llvm -std=c++1y -O1 -disable-llvm-passes -o - %s -DMSABI -w | FileCheck --check-prefix=MO1 --check-prefix=M18 %s
@@ -39,30 +39,34 @@
 
 // Import declaration.
 // MSC-DAG: @"?ExternGlobalDecl@@3HA" = external dllimport global i32
+// MSC64-DAG: @"?ExternGlobalDecl@@3HA" = external dllimport global i32
 // GNU-DAG: @ExternGlobalDecl            = external dllimport global i32
 __declspec(dllimport) extern int ExternGlobalDecl;
 USEVAR(ExternGlobalDecl)
 
 // dllimport implies a declaration.
 // MSC-DAG: @"?GlobalDecl@@3HA" = external dllimport global i32
+// MSC64-DAG: @"?GlobalDecl@@3HA" = external dllimport global i32
 // GNU-DAG: @GlobalDecl            = external dllimport global i32
 __declspec(dllimport) int GlobalDecl;
 USEVAR(GlobalDecl)
 
 // Redeclarations
 // MSC-DAG: @"?GlobalRedecl1@@3HA" = external dllimport global i32
+// MSC64-DAG: @"?GlobalRedecl1@@3HA" = external dllimport global i32
 // GNU-DAG: @GlobalRedecl1            = external dllimport global i32
 __declspec(dllimport) extern int GlobalRedecl1;
 __declspec(dllimport) extern int GlobalRedecl1;
 USEVAR(GlobalRedecl1)
 
 // MSC-DAG: @"?GlobalRedecl2a@@3HA" = external dllimport global i32
+// MSC64-DAG: @"?GlobalRedecl2a@@3HA" = external dllimport global i32
 // GNU-DAG: @GlobalRedecl2a            = external dllimport global i32
 __declspec(dllimport) int GlobalRedecl2a;
 __declspec(dllimport) int GlobalRedecl2a;
 USEVAR(GlobalRedecl2a)
 
-// M32-DAG: @"?GlobalRedecl2b@@3PAHA"   = external dllimport global i32*
+// MSC-DAG: @"?GlobalRedecl2b@@3PAHA"   = external dllimport global i32*
 // M64-DAG: @"?GlobalRedecl2b@@3PEAHEA" = external dllimport global i32*
 // GNU-DAG: @GlobalRedecl2b                = external dllimport global i32*
 int *__attribute__((dllimport)) GlobalRedecl2b;
@@ -98,8 +102,8 @@
 USE(inlineStaticLocalsFunc);
 
 // The address of a dllimport global cannot be used in constant initialization.
-// M32-DAG: @"?arr@?1??initializationFunc@@YAPAHXZ@4QBQAHB" = internal global [1 x i32*] zeroinitializer
-// GNU-DAG: @_ZZ18initializationFuncvE3arr = internal global [1 x i32*] zeroinitializer
+// M32-DAG: @"?arr@?1??initializationFunc@@YAPAHXZ@4QBQAHB" = internal constant [1 x i32*] [i32* @"?ExternGlobalDecl@@3HA"]
+// GNU-DAG: @_ZZ18initializationFuncvE3arr = internal constant [1 x i32*] [i32* @ExternGlobalDecl]
 int *initializationFunc() {
   static int *const arr[] = {&ExternGlobalDecl};
   return arr[0];
Index: clang/test/SemaCXX/PR19955.cpp
===================================================================
--- clang/test/SemaCXX/PR19955.cpp
+++ clang/test/SemaCXX/PR19955.cpp
@@ -2,7 +2,7 @@
 // RUN: %clang_cc1 -triple i686-mingw32 -verify -std=c++11 %s
 
 extern int __attribute__((dllimport)) var;
-constexpr int *varp = &var; // expected-error {{must be initialized by a constant expression}}
+constexpr int *varp = &var;
 
 extern __attribute__((dllimport)) void fun();
 constexpr void (*funp)(void) = &fun; // expected-error {{must be initialized by a constant expression}}
Index: clang/test/SemaCXX/dllimport-constexpr.cpp
===================================================================
--- clang/test/SemaCXX/dllimport-constexpr.cpp
+++ clang/test/SemaCXX/dllimport-constexpr.cpp
@@ -40,7 +40,6 @@
 // constexpr initialization doesn't work for dllimport things.
 // expected-error@+1{{must be initialized by a constant expression}}
 constexpr void (*constexpr_import_func)() = &imported_func;
-// expected-error@+1{{must be initialized by a constant expression}}
 constexpr int *constexpr_import_int = &imported_int;
 // expected-error@+1{{must be initialized by a constant expression}}
 constexpr void (Foo::*constexpr_memptr)() = &Foo::imported_method;
@@ -60,3 +59,8 @@
   // expected-note@+1 {{requested here}}
   StaticConstexpr<imported_func>::g_fp();
 }
+
+void foo() {
+  extern int __declspec(dllimport) dll_import_int;
+  constexpr int& dll_import_constexpr_ref = dll_import_int;
+}