Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -13890,6 +13890,9 @@
       // FIXME: Consider replacing the initializer with a ConstantExpr.
     } else if (var->isConstexpr()) {
       SourceLocation DiagLoc = var->getLocation();
+      if (IsGlobal || (!IsGlobal && Notes.size() != 0))
+        Diag(DiagLoc, diag::err_constexpr_var_requires_const_init)
+            << var << Init->getSourceRange();
       // If the note doesn't add any useful information other than a source
       // location, fold it into the primary diagnostic.
       if (Notes.size() == 1 && Notes[0].second.getDiagID() ==
@@ -13897,8 +13900,6 @@
         DiagLoc = Notes[0].first;
         Notes.clear();
       }
-      Diag(DiagLoc, diag::err_constexpr_var_requires_const_init)
-          << var << Init->getSourceRange();
       for (unsigned I = 0, N = Notes.size(); I != N; ++I)
         Diag(Notes[I].first, Notes[I].second);
     } else if (GlobalStorage && var->hasAttr<ConstInitAttr>()) {
Index: clang/test/CodeGenCXX/PR19955.cpp
===================================================================
--- clang/test/CodeGenCXX/PR19955.cpp
+++ clang/test/CodeGenCXX/PR19955.cpp
@@ -14,9 +14,6 @@
 // CHECK-DAG: @"?funp@@3P6AXXZA" = dso_local global ptr null
 // X64-DAG: @"?funp@@3P6AXXZEA" = dso_local global ptr null
 
-// CHECK-LABEL: @"??__Evarp@@YAXXZ"
-// CHECK-DAG: store ptr @"?var@@3HA", ptr @"?varp@@3PAHA"
-
 // X64-LABEL: @"??__Evarp@@YAXXZ"
 // X64-DAG: store ptr @"?var@@3HA", ptr @"?varp@@3PEAHEA"
 
Index: clang/test/CodeGenCXX/dllimport.cpp
===================================================================
--- clang/test/CodeGenCXX/dllimport.cpp
+++ clang/test/CodeGenCXX/dllimport.cpp
@@ -769,6 +769,7 @@
   USEVAR(D<42>::y);
   // MSC-DAG: @"?x@?$D@$0CK@@PR19933@@2HA" = external dllimport global i32
   // MSC-DAG: @"?y@?$D@$0CK@@PR19933@@2HA" = external dllimport global i32
+  // MSC-DAG: @"?val@@3HA" = external dllimport global i32
 }
 
 namespace PR21355 {
@@ -1026,3 +1027,11 @@
 void baz() { U<int> u; u.foo(); } // No diagnostic.
 
 }
+
+void assigndllimport () {
+  // MSC-DAG: define dso_local void @"?assigndllimport@@YAXXZ"()
+  // MSC-DAG: %[[VAL_REF:.*]] = alloca ptr
+  // MSC-DAG-NEXT: store ptr @"?val@@3HA", ptr %[[VAL_REF]]
+  extern int _declspec(dllimport) val;
+  constexpr int& val_ref = val;
+}
Index: clang/test/SemaCXX/constant-expression-cxx11.cpp
===================================================================
--- clang/test/SemaCXX/constant-expression-cxx11.cpp
+++ clang/test/SemaCXX/constant-expression-cxx11.cpp
@@ -1594,8 +1594,8 @@
 
   void f(int k) { // expected-note {{here}}
     int arr[k]; // expected-warning {{C99}} expected-note {{function parameter 'k'}}
-    constexpr int n = 1 +
-        sizeof(arr) // expected-error {{constant expression}}
+    constexpr int n = 1 + // expected-error{{constexpr variable 'n' must be initialized by a constant expression}}
+        sizeof(arr)
         * 3;
   }
 }
Index: clang/test/SemaCXX/dllimport-constexpr.cpp
===================================================================
--- clang/test/SemaCXX/dllimport-constexpr.cpp
+++ clang/test/SemaCXX/dllimport-constexpr.cpp
@@ -60,3 +60,12 @@
   // expected-note@+1 {{requested here}}
   StaticConstexpr<imported_func>::g_fp();
 }
+
+extern int __declspec(dllimport) val;
+// expected-error@+1{{constexpr variable 'val_ref' must be initialized by a constant expression}}
+constexpr int& val_ref = val;
+
+void AssignDllImportToConst () {
+  extern int _declspec(dllimport) val;
+  constexpr int& val_ref = val;
+}