Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -4184,18 +4184,27 @@
 
   CallStackFrame Frame(Info, CallLoc, Callee, This, ArgValues.data());
 
+  const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Callee);
+  bool IsCopyOrMove = MD && MD->isCopyAssignmentOperator();
+  IsCopyOrMove |= MD && MD->isMoveAssignmentOperator();
+
+  // We support explicit constructor calls as an MS extension. These can be
+  // constexpr by C++11 rules.
+  auto CD = dyn_cast_or_null<CXXConstructorDecl>(MD);
+  IsCopyOrMove |= CD && CD->isCopyConstructor();
+  IsCopyOrMove |= CD && CD->isMoveConstructor();
+
   // For a trivial copy or move assignment, perform an APValue copy. This is
   // essential for unions, where the operations performed by the assignment
   // operator cannot be represented as statements.
   //
   // Skip this for non-union classes with no fields; in that case, the defaulted
   // copy/move does not actually read the object.
-  const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Callee);
-  if (MD && MD->isDefaulted() &&
+  if (MD && MD->isDefaulted() && IsCopyOrMove &&
       (MD->getParent()->isUnion() ||
        (MD->isTrivial() && hasFields(MD->getParent())))) {
-    assert(This &&
-           (MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator()));
+    assert(This);
+
     LValue RHS;
     RHS.setFrom(Info.Ctx, ArgValues[0]);
     APValue RHSValue;
Index: clang/test/CodeGenCXX/constructor-direct-call.cpp
===================================================================
--- clang/test/CodeGenCXX/constructor-direct-call.cpp
+++ clang/test/CodeGenCXX/constructor-direct-call.cpp
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -triple i686-pc-mingw32 -fms-extensions -Wmicrosoft %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple i686-pc-mingw32 -fms-extensions -Wmicrosoft %s -emit-llvm -o - -std=gnu++11| FileCheck %s
 
 class Test1 {
 public: