3 files changed, 52 insertions, 20 deletions
diff --git a/clang/lib/AST/MicrosoftCXXABI.cpp b/clang/lib/AST/MicrosoftCXXABI.cpp
index 51308ea0c0f..575272d3573 100644
--- a/clang/lib/AST/MicrosoftCXXABI.cpp
+++ b/clang/lib/AST/MicrosoftCXXABI.cpp
@@ -55,6 +55,16 @@ public:
 unsigned MicrosoftCXXABI::getMemberPointerSize(const MemberPointerType *MPT) const {
   QualType Pointee = MPT->getPointeeType();
   CXXRecordDecl *RD = MPT->getClass()->getAsCXXRecordDecl();
+
+  if (RD->getTypeForDecl()->isIncompleteType()) {
+    if (RD->hasAttr<SingleInheritanceAttr>())
+      return 1;
+    else if (RD->hasAttr<MultipleInheritanceAttr>())
+      return 2;
+    else
+      return 3;
+  }
+
   if (RD->getNumVBases() > 0) {
     if (Pointee->isFunctionType())
       return 3;
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 50d11175995..bf1c14338db 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -4149,20 +4149,50 @@ static void handleUuidAttr(Sema &S, Decl *D, const AttributeList &Attr) {
     S.Diag(Attr.getLoc(), diag::warn_attribute_ignored) << "uuid";
 }
 
+static bool hasOtherInheritanceAttr(Decl *D, AttributeList::Kind Kind,
+    int& Existing) {
+  if (Kind != AttributeList::AT_SingleInheritance &&
+      D->hasAttr<SingleInheritanceAttr>()) {
+    Existing = 0;
+    return true;
+  }
+  else if (Kind != AttributeList::AT_MultipleInheritance &&
+      D->hasAttr<MultipleInheritanceAttr>()) {
+    Existing = 1;
+    return true;
+  }
+  else if (Kind != AttributeList::AT_VirtualInheritance &&
+      D->hasAttr<VirtualInheritanceAttr>()) {
+    Existing = 2;
+    return true;
+  }
+  return false;
+}
+
 static void handleInheritanceAttr(Sema &S, Decl *D, const AttributeList &Attr) {
-  if (S.LangOpts.MicrosoftExt) {
-    AttributeList::Kind Kind = Attr.getKind();
-    if (Kind == AttributeList::AT_SingleInheritance)
-      D->addAttr(
-          ::new (S.Context) SingleInheritanceAttr(Attr.getRange(), S.Context));
-    else if (Kind == AttributeList::AT_MultipleInheritance)
-      D->addAttr(
-          ::new (S.Context) MultipleInheritanceAttr(Attr.getRange(), S.Context));
-    else if (Kind == AttributeList::AT_VirtualInheritance)
-      D->addAttr(
-          ::new (S.Context) VirtualInheritanceAttr(Attr.getRange(), S.Context));
-  } else
+  if (!S.LangOpts.MicrosoftExt) {
     S.Diag(Attr.getLoc(), diag::warn_attribute_ignored) << Attr.getName();
+    return;
+  }
+
+  AttributeList::Kind Kind = Attr.getKind();
+
+  int Existing;
+  if (hasOtherInheritanceAttr(D->getCanonicalDecl(), Kind, Existing)) {
+      S.Diag(Attr.getLoc(), diag::warn_ms_inheritance_already_declared) << Existing;
+      return;
+  }
+
+  if (Kind == AttributeList::AT_SingleInheritance) {
+    D->addAttr(
+        ::new (S.Context) SingleInheritanceAttr(Attr.getRange(), S.Context));
+  } else if (Kind == AttributeList::AT_MultipleInheritance) {
+    D->addAttr(
+        ::new (S.Context) MultipleInheritanceAttr(Attr.getRange(), S.Context));
+  } else if (Kind == AttributeList::AT_VirtualInheritance) {
+    D->addAttr(
+        ::new (S.Context) VirtualInheritanceAttr(Attr.getRange(), S.Context));
+  }
 }
 
 static void handlePortabilityAttr(Sema &S, Decl *D, const AttributeList &Attr) {
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 82dccfa5f44..68cd5cdcf83 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -1583,14 +1583,6 @@ QualType Sema::BuildMemberPointerType(QualType T, QualType Class,
     return QualType();
   }
 
-  // In the Microsoft ABI, the class is allowed to be an incomplete
-  // type. In such cases, the compiler makes a worst-case assumption.
-  // We make no such assumption right now, so emit an error if the
-  // class isn't a complete type.
-  if (Context.getTargetInfo().getCXXABI() == CXXABI_Microsoft &&
-      RequireCompleteType(Loc, Class, diag::err_incomplete_type))
-    return QualType();
-
   return Context.getMemberPointerType(T, Class.getTypePtr());
 }