Index: clang/include/clang/AST/NonTrivialTypeVisitor.h
===================================================================
--- clang/include/clang/AST/NonTrivialTypeVisitor.h
+++ clang/include/clang/AST/NonTrivialTypeVisitor.h
@@ -1,4 +1,4 @@
-//===-- NonTrivialTypeVisitor.h - Visitor for non-trivial Types *- C++ --*-===//
+//===-- NonTrivialTypeVisitor.h - Visitor for non-trivial Types -*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
Index: clang/lib/CodeGen/CGNonTrivialStruct.cpp
===================================================================
--- clang/lib/CodeGen/CGNonTrivialStruct.cpp
+++ clang/lib/CodeGen/CGNonTrivialStruct.cpp
@@ -254,6 +254,10 @@
 
   void visitVolatileTrivial(QualType FT, const FieldDecl *FD,
                             CharUnits CurStructOffset) {
+    // Zero-length bit-fields don't need to be copied/assigned.
+    if (FD && FD->isZeroLengthBitField(this->Ctx))
+      return;
+
     // Because volatile fields can be bit-fields and are individually copied,
     // their offset and width are in bits.
     uint64_t OffsetInBits =
@@ -543,6 +547,10 @@
                             std::array<Address, 2> Addrs) {
     LValue DstLV, SrcLV;
     if (FD) {
+      // No need to copy zero-length bit-fields.
+      if (FD->isZeroLengthBitField(this->CGF->getContext()))
+        return;
+
       QualType RT = QualType(FD->getParent()->getTypeForDecl(), 0);
       llvm::PointerType *PtrTy = this->CGF->ConvertType(RT)->getPointerTo();
       Address DstAddr = this->getAddrWithOffset(Addrs[DstIdx], Offset);
Index: clang/test/CodeGenObjC/strong-in-c-struct.m
===================================================================
--- clang/test/CodeGenObjC/strong-in-c-struct.m
+++ clang/test/CodeGenObjC/strong-in-c-struct.m
@@ -887,4 +887,17 @@
   func(0);
 }
 
+struct ZeroBitfield {
+  int : 0;
+  id strong;
+};
+
+
+// CHECK: define linkonce_odr hidden void @__default_constructor_8_sv0
+// CHECK: define linkonce_odr hidden void @__copy_assignment_8_8_sv0
+void test_zero_bitfield() {
+  struct ZeroBitfield volatile a, b;
+  a = b;
+}
+
 #endif /* USESTRUCT */