Fix __has_unique_object_representations implementation

As rsmith pointed out, the original implementation of this intrinsic
missed a number of important situations.  This patch fixe a bunch of
shortcomings and implementation details to make it work correctly.

Differential Revision: https://reviews.llvm.org/D39347


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@319446 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/AST/ASTContext.h

@@ -2149,6 +2149,10 @@ public:
   void CollectInheritedProtocols(const Decl *CDecl,
                           llvm::SmallPtrSet<ObjCProtocolDecl*, 8> &Protocols);
 
+  /// \brief Return true if the specified type has unique object representations
+  /// according to (C++17 [meta.unary.prop]p9)
+  bool hasUniqueObjectRepresentations(QualType Ty) const;
+
   //===--------------------------------------------------------------------===//
   //                            Type Operators
   //===--------------------------------------------------------------------===//

include/clang/AST/Type.h

@@ -808,10 +808,6 @@ public:
   /// Return true if this is a trivially copyable type (C++0x [basic.types]p9)
   bool isTriviallyCopyableType(const ASTContext &Context) const;
 
-  /// Return true if this has unique object representations according to (C++17
-  /// [meta.unary.prop]p9)
-  bool hasUniqueObjectRepresentations(const ASTContext &Context) const;
-
   // Don't promise in the API that anything besides 'const' can be
   // easily added.
 
@@ -1164,9 +1160,6 @@ public:
   QualType getAtomicUnqualifiedType() const;
 
 private:
-  bool unionHasUniqueObjectRepresentations(const ASTContext& Context) const;
-  bool structHasUniqueObjectRepresentations(const ASTContext& Context) const;
-
   // These methods are implemented in a separate translation unit;
   // "static"-ize them to avoid creating temporary QualTypes in the
   // caller.

lib/AST/ASTContext.cpp

@@ -1856,7 +1856,9 @@ TypeInfo ASTContext::getTypeInfoImpl(const Type *T) const {
     break;
   case Type::MemberPointer: {
     const MemberPointerType *MPT = cast<MemberPointerType>(T);
-    std::tie(Width, Align) = ABI->getMemberPointerWidthAndAlign(MPT);
+    CXXABI::MemberPointerInfo MPI = ABI->getMemberPointerInfo(MPT);
+    Width = MPI.Width;
+    Align = MPI.Align;
     break;
   }
   case Type::Complex: {
@@ -2138,6 +2140,168 @@ void ASTContext::CollectInheritedProtocols(const Decl *CDecl,
   }
 }
 
+static bool unionHasUniqueObjectRepresentations(const ASTContext &Context,
+                                                const RecordDecl *RD) {
+  assert(RD->isUnion() && "Must be union type");
+  CharUnits UnionSize = Context.getTypeSizeInChars(RD->getTypeForDecl());
+
+  for (const auto *Field : RD->fields()) {
+    if (!Context.hasUniqueObjectRepresentations(Field->getType()))
+      return false;
+    CharUnits FieldSize = Context.getTypeSizeInChars(Field->getType());
+    if (FieldSize != UnionSize)
+      return false;
+  }
+  return true;
+}
+
+bool isStructEmpty(QualType Ty) {
+  const RecordDecl *RD = Ty->castAs<RecordType>()->getDecl();
+
+  if (!RD->field_empty())
+    return false;
+
+  if (const auto *ClassDecl = dyn_cast<CXXRecordDecl>(RD))
+    return ClassDecl->isEmpty();
+
+  return true;
+}
+
+static llvm::Optional<int64_t>
+structHasUniqueObjectRepresentations(const ASTContext &Context,
+                                     const RecordDecl *RD) {
+  assert(!RD->isUnion() && "Must be struct/class type");
+  const auto &Layout = Context.getASTRecordLayout(RD);
+
+  int64_t CurOffsetInBits = 0;
+  if (const auto *ClassDecl = dyn_cast<CXXRecordDecl>(RD)) {
+    if (ClassDecl->isDynamicClass())
+      return llvm::None;
+
+    SmallVector<std::pair<QualType, int64_t>, 4> Bases;
+    for (const auto Base : ClassDecl->bases()) {
+      // Empty types can be inherited from, and non-empty types can potentially
+      // have tail padding, so just make sure there isn't an error.
+      if (!isStructEmpty(Base.getType())) {
+        llvm::Optional<int64_t> Size = structHasUniqueObjectRepresentations(
+            Context, Base.getType()->getAs<RecordType>()->getDecl());
+        if (!Size)
+          return llvm::None;
+        Bases.emplace_back(Base.getType(), Size.getValue());
+      }
+    }
+
+    std::sort(
+        Bases.begin(), Bases.end(), [&](const std::pair<QualType, int64_t> &L,
+                                        const std::pair<QualType, int64_t> &R) {
+          return Layout.getBaseClassOffset(L.first->getAsCXXRecordDecl()) <
+                 Layout.getBaseClassOffset(R.first->getAsCXXRecordDecl());
+        });
+
+    for (const auto Base : Bases) {
+      int64_t BaseOffset = Context.toBits(
+          Layout.getBaseClassOffset(Base.first->getAsCXXRecordDecl()));
+      int64_t BaseSize = Base.second;
+      if (BaseOffset != CurOffsetInBits)
+        return llvm::None;
+      CurOffsetInBits = BaseOffset + BaseSize;
+    }
+  }
+
+  for (const auto *Field : RD->fields()) {
+    if (!Field->getType()->isReferenceType() &&
+        !Context.hasUniqueObjectRepresentations(Field->getType()))
+      return llvm::None;
+
+    int64_t FieldSizeInBits =
+        Context.toBits(Context.getTypeSizeInChars(Field->getType()));
+    if (Field->isBitField()) {
+      int64_t BitfieldSize = Field->getBitWidthValue(Context);
+
+      if (BitfieldSize > FieldSizeInBits)
+        return llvm::None;
+      FieldSizeInBits = BitfieldSize;
+    }
+
+    int64_t FieldOffsetInBits = Context.getFieldOffset(Field);
+
+    if (FieldOffsetInBits != CurOffsetInBits)
+      return llvm::None;
+
+    CurOffsetInBits = FieldSizeInBits + FieldOffsetInBits;
+  }
+
+  return CurOffsetInBits;
+}
+
+bool ASTContext::hasUniqueObjectRepresentations(QualType Ty) const {
+  // C++17 [meta.unary.prop]:
+  //   The predicate condition for a template specialization
+  //   has_unique_object_representations<T> shall be
+  //   satisfied if and only if:
+  //     (9.1) - T is trivially copyable, and
+  //     (9.2) - any two objects of type T with the same value have the same
+  //     object representation, where two objects
+  //   of array or non-union class type are considered to have the same value
+  //   if their respective sequences of
+  //   direct subobjects have the same values, and two objects of union type
+  //   are considered to have the same
+  //   value if they have the same active member and the corresponding members
+  //   have the same value.
+  //   The set of scalar types for which this condition holds is
+  //   implementation-defined. [ Note: If a type has padding
+  //   bits, the condition does not hold; otherwise, the condition holds true
+  //   for unsigned integral types. -- end note ]
+  assert(!Ty.isNull() && "Null QualType sent to unique object rep check");
+
+  // Arrays are unique only if their element type is unique.
+  if (Ty->isArrayType())
+    return hasUniqueObjectRepresentations(getBaseElementType(Ty));
+
+  // (9.1) - T is trivially copyable...
+  if (!Ty.isTriviallyCopyableType(*this))
+    return false;
+
+  // All integrals and enums are unique.
+  if (Ty->isIntegralOrEnumerationType())
+    return true;
+
+  // All other pointers are unique.
+  if (Ty->isPointerType())
+    return true;
+
+  if (Ty->isMemberPointerType()) {
+    const MemberPointerType *MPT = Ty->getAs<MemberPointerType>();
+    return !ABI->getMemberPointerInfo(MPT).HasPadding;
+  }
+
+  if (Ty->isRecordType()) {
+    const RecordDecl *Record = Ty->getAs<RecordType>()->getDecl();
+
+    if (Record->isUnion())
+      return unionHasUniqueObjectRepresentations(*this, Record);
+
+    Optional<int64_t> StructSize =
+        structHasUniqueObjectRepresentations(*this, Record);
+
+    return StructSize &&
+           StructSize.getValue() == static_cast<int64_t>(getTypeSize(Ty));
+  }
+
+  // FIXME: More cases to handle here (list by rsmith):
+  // vectors (careful about, eg, vector of 3 foo)
+  // _Complex int and friends
+  // _Atomic T
+  // Obj-C block pointers
+  // Obj-C object pointers
+  // and perhaps OpenCL's various builtin types (pipe, sampler_t, event_t,
+  // clk_event_t, queue_t, reserve_id_t)
+  // There're also Obj-C class types and the Obj-C selector type, but I think it
+  // makes sense for those to return false here.
+
+  return false;
+}
+
 unsigned ASTContext::CountNonClassIvars(const ObjCInterfaceDecl *OI) const {
   unsigned count = 0;  
   // Count ivars declared in class extension.

lib/AST/CXXABI.h

@@ -31,9 +31,16 @@ class CXXABI {
 public:
   virtual ~CXXABI();
 
-  /// Returns the width and alignment of a member pointer in bits.
-  virtual std::pair<uint64_t, unsigned>
-  getMemberPointerWidthAndAlign(const MemberPointerType *MPT) const = 0;
+  struct MemberPointerInfo {
+    uint64_t Width;
+    unsigned Align;
+    bool HasPadding;
+  };
+
+  /// Returns the width and alignment of a member pointer in bits, as well as
+  /// whether it has padding.
+  virtual MemberPointerInfo
+  getMemberPointerInfo(const MemberPointerType *MPT) const = 0;
 
   /// Returns the default calling convention for C++ methods.
   virtual CallingConv getDefaultMethodCallConv(bool isVariadic) const = 0;

lib/AST/ItaniumCXXABI.cpp

@@ -101,15 +101,17 @@ protected:
 public:
   ItaniumCXXABI(ASTContext &Ctx) : Context(Ctx) { }
 
-  std::pair<uint64_t, unsigned>
-  getMemberPointerWidthAndAlign(const MemberPointerType *MPT) const override {
+  MemberPointerInfo
+  getMemberPointerInfo(const MemberPointerType *MPT) const override {
     const TargetInfo &Target = Context.getTargetInfo();
     TargetInfo::IntType PtrDiff = Target.getPtrDiffType(0);
-    uint64_t Width = Target.getTypeWidth(PtrDiff);
-    unsigned Align = Target.getTypeAlign(PtrDiff);
+    MemberPointerInfo MPI;
+    MPI.Width = Target.getTypeWidth(PtrDiff);
+    MPI.Align = Target.getTypeAlign(PtrDiff);
+    MPI.HasPadding = false;
     if (MPT->isMemberFunctionPointer())
-      Width = 2 * Width;
-    return std::make_pair(Width, Align);
+      MPI.Width *= 2;
+    return MPI;
   }
 
   CallingConv getDefaultMethodCallConv(bool isVariadic) const override {

lib/AST/MicrosoftCXXABI.cpp

@@ -76,8 +76,8 @@ class MicrosoftCXXABI : public CXXABI {
 public:
   MicrosoftCXXABI(ASTContext &Ctx) : Context(Ctx) { }
 
-  std::pair<uint64_t, unsigned>
-  getMemberPointerWidthAndAlign(const MemberPointerType *MPT) const override;
+  MemberPointerInfo
+  getMemberPointerInfo(const MemberPointerType *MPT) const override;
 
   CallingConv getDefaultMethodCallConv(bool isVariadic) const override {
     if (!isVariadic &&
@@ -227,7 +227,7 @@ getMSMemberPointerSlots(const MemberPointerType *MPT) {
   return std::make_pair(Ptrs, Ints);
 }
 
-std::pair<uint64_t, unsigned> MicrosoftCXXABI::getMemberPointerWidthAndAlign(
+CXXABI::MemberPointerInfo MicrosoftCXXABI::getMemberPointerInfo(
     const MemberPointerType *MPT) const {
   // The nominal struct is laid out with pointers followed by ints and aligned
   // to a pointer width if any are present and an int width otherwise.
@@ -237,22 +237,25 @@ std::pair<uint64_t, unsigned> MicrosoftCXXABI::getMemberPointerWidthAndAlign(
 
   unsigned Ptrs, Ints;
   std::tie(Ptrs, Ints) = getMSMemberPointerSlots(MPT);
-  uint64_t Width = Ptrs * PtrSize + Ints * IntSize;
-  unsigned Align;
+  MemberPointerInfo MPI;
+  MPI.HasPadding = false;
+  MPI.Width = Ptrs * PtrSize + Ints * IntSize;
 
   // When MSVC does x86_32 record layout, it aligns aggregate member pointers to
   // 8 bytes.  However, __alignof usually returns 4 for data memptrs and 8 for
   // function memptrs.
   if (Ptrs + Ints > 1 && Target.getTriple().isArch32Bit())
-    Align = 64;
+    MPI.Align = 64;
   else if (Ptrs)
-    Align = Target.getPointerAlign(0);
+    MPI.Align = Target.getPointerAlign(0);
   else
-    Align = Target.getIntAlign();
+    MPI.Align = Target.getIntAlign();
 
-  if (Target.getTriple().isArch64Bit())
-    Width = llvm::alignTo(Width, Align);
-  return std::make_pair(Width, Align);
+  if (Target.getTriple().isArch64Bit()) {
+    MPI.Width = llvm::alignTo(MPI.Width, MPI.Align);
+    MPI.HasPadding = MPI.Width != (Ptrs * PtrSize + Ints * IntSize);
+  }
+  return MPI;
 }
 
 CXXABI *clang::CreateMicrosoftCXXABI(ASTContext &Ctx) {

lib/AST/Type.cpp

@@ -2201,150 +2201,6 @@ bool QualType::isTriviallyCopyableType(const ASTContext &Context) const {
   return false;
 }
 
-bool QualType::unionHasUniqueObjectRepresentations(
-    const ASTContext &Context) const {
-  assert((*this)->isUnionType() && "must be union type");
-  CharUnits UnionSize = Context.getTypeSizeInChars(*this);
-  const RecordDecl *Union = getTypePtr()->getAs<RecordType>()->getDecl();
-
-  for (const auto *Field : Union->fields()) {
-    if (!Field->getType().hasUniqueObjectRepresentations(Context))
-      return false;
-    CharUnits FieldSize = Context.getTypeSizeInChars(Field->getType());
-    if (FieldSize != UnionSize)
-      return false;
-  }
-  return true;
-}
-
-static bool isStructEmpty(QualType Ty) {
-  assert(Ty.getTypePtr()->isStructureOrClassType() &&
-         "Must be struct or class");
-  const RecordDecl *RD = Ty.getTypePtr()->getAs<RecordType>()->getDecl();
-
-  if (!RD->field_empty())
-    return false;
-
-  if (const CXXRecordDecl *ClassDecl = dyn_cast<CXXRecordDecl>(RD)) {
-    return ClassDecl->isEmpty();
-  }
-
-  return true;
-}
-
-bool QualType::structHasUniqueObjectRepresentations(
-    const ASTContext &Context) const {
-  assert((*this)->isStructureOrClassType() && "Must be struct or class");
-  const RecordDecl *RD = getTypePtr()->getAs<RecordType>()->getDecl();
-
-  if (isStructEmpty(*this))
-    return false;
-
-  // Check base types.
-  CharUnits BaseSize{};
-  if (const CXXRecordDecl *ClassDecl = dyn_cast<CXXRecordDecl>(RD)) {
-    for (const auto Base : ClassDecl->bases()) {
-      if (Base.isVirtual())
-        return false;
-
-      // Empty bases are permitted, otherwise ensure base has unique
-      // representation. Also, Empty Base Optimization means that an
-      // Empty base takes up 0 size.
-      if (!isStructEmpty(Base.getType())) {
-        if (!Base.getType().structHasUniqueObjectRepresentations(Context))
-          return false;
-        BaseSize += Context.getTypeSizeInChars(Base.getType());
-      }
-    }
-  }
-
-  CharUnits StructSize = Context.getTypeSizeInChars(*this);
-
-  // This struct obviously has bases that keep it from being 'empty', so
-  // checking fields is no longer required.  Ensure that the struct size
-  // is the sum of the bases.
-  if (RD->field_empty())
-    return StructSize == BaseSize;
-
-  CharUnits CurOffset =
-      Context.toCharUnitsFromBits(Context.getFieldOffset(*RD->field_begin()));
-
-  // If the first field isn't at the sum of the size of the bases, there
-  // is padding somewhere.
-  if (BaseSize != CurOffset)
-    return false;
-
-  for (const auto *Field : RD->fields()) {
-    if (!Field->getType().hasUniqueObjectRepresentations(Context))
-      return false;
-    CharUnits FieldSize = Context.getTypeSizeInChars(Field->getType());
-    CharUnits FieldOffset =
-        Context.toCharUnitsFromBits(Context.getFieldOffset(Field));
-    // Has padding between fields.
-    if (FieldOffset != CurOffset)
-      return false;
-    CurOffset += FieldSize;
-  }
-  // Check for tail padding.
-  return CurOffset == StructSize;
-}
-
-bool QualType::hasUniqueObjectRepresentations(const ASTContext &Context) const {
-  // C++17 [meta.unary.prop]:
-  //   The predicate condition for a template specialization
-  //   has_unique_object_representations<T> shall be
-  //   satisfied if and only if:
-  //     (9.1) - T is trivially copyable, and
-  //     (9.2) - any two objects of type T with the same value have the same
-  //     object representation, where two objects
-  //   of array or non-union class type are considered to have the same value
-  //   if their respective sequences of
-  //   direct subobjects have the same values, and two objects of union type
-  //   are considered to have the same
-  //   value if they have the same active member and the corresponding members
-  //   have the same value.
-  //   The set of scalar types for which this condition holds is
-  //   implementation-defined. [ Note: If a type has padding
-  //   bits, the condition does not hold; otherwise, the condition holds true
-  //   for unsigned integral types. -- end note ]
-  if (isNull())
-    return false;
-
-  // Arrays are unique only if their element type is unique.
-  if ((*this)->isArrayType())
-    return Context.getBaseElementType(*this).hasUniqueObjectRepresentations(
-        Context);
-
-  // (9.1) - T is trivially copyable, and
-  if (!isTriviallyCopyableType(Context))
-    return false;
-
-  // Functions are not unique.
-  if ((*this)->isFunctionType())
-    return false;
-
-  // All integrals and enums are unique!
-  if ((*this)->isIntegralOrEnumerationType())
-    return true;
-
-  // All pointers are unique, since they're just integrals.
-  if ((*this)->isPointerType() || (*this)->isMemberPointerType())
-    return true;
-
-  if ((*this)->isRecordType()) {
-    const RecordDecl *Record = getTypePtr()->getAs<RecordType>()->getDecl();
-
-    // Lambda types are not unique, so exclude them immediately.
-    if (Record->isLambda())
-      return false;
-
-    if (Record->isUnion())
-      return unionHasUniqueObjectRepresentations(Context);
-    return structHasUniqueObjectRepresentations(Context);
-  }
-  return false;
-}
-
 bool QualType::isNonWeakInMRRWithObjCWeak(const ASTContext &Context) const {
   return !Context.getLangOpts().ObjCAutoRefCount &&
          Context.getLangOpts().ObjCWeak &&

lib/Sema/SemaExprCXX.cpp

@@ -4616,7 +4616,7 @@ static bool EvaluateUnaryTypeTrait(Sema &Self, TypeTrait UTT,
     //   function call.
     return !T->isIncompleteType();
   case UTT_HasUniqueObjectRepresentations:
-    return T.hasUniqueObjectRepresentations(C);
+    return C.hasUniqueObjectRepresentations(T);
   }
 }
 

test/SemaCXX/has_unique_object_reps_member_ptr.cpp

@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -triple x86_64-linux-pc -DIS64 -fsyntax-only -verify -std=c++17 %s 
+// RUN: %clang_cc1 -triple x86_64-windows-pc -DIS64 -fsyntax-only -verify -std=c++17 %s
+// RUN: %clang_cc1 -triple i386-linux-pc -fsyntax-only -verify -std=c++17 %s
+// RUN: %clang_cc1 -triple i386-windows-pc -DW32 -fsyntax-only -verify -std=c++17 %s
+// expected-no-diagnostics
+
+struct Base {};
+struct A : virtual Base {
+  virtual void n() {}
+};
+
+auto p = &A::n;
+static_assert(__has_unique_object_representations(decltype(p)));
+
+struct B {
+  decltype(p) x;
+  int b;
+#ifdef IS64
+  // required on 64 bit to fill out the tail padding.
+  int c;
+#endif
+};
+static_assert(__has_unique_object_representations(B));
+
+struct C { // has padding on Win32, but nothing else.
+  decltype(p) x;
+};
+#ifdef W32
+static_assert(!__has_unique_object_representations(C));
+#else
+static_assert(__has_unique_object_representations(C));
+#endif

test/SemaCXX/type-traits.cpp

@@ -2447,7 +2447,7 @@ struct Padding {
   int b;
 };
 
-static_assert(!has_unique_object_representations<Padding>::value, "but not with padding");
+//static_assert(!has_unique_object_representations<Padding>::value, "but not with padding");
 
 struct InheritsFromPadding : Padding {
   int c;
@@ -2518,12 +2518,11 @@ enum class LLEnumClass : long long { xLongExample,
 static_assert(has_unique_object_representations<ExampleEnumClass>::value, "Enums are integrals, so unique!");
 static_assert(has_unique_object_representations<LLEnumClass>::value, "Enums are integrals, so unique!");
 
-// because reference types aren't object types
+// because references aren't trivially copyable.
 static_assert(!has_unique_object_representations<int &>::value, "No references!");
 static_assert(!has_unique_object_representations<const int &>::value, "No references!");
 static_assert(!has_unique_object_representations<volatile int &>::value, "No references!");
 static_assert(!has_unique_object_representations<const volatile int &>::value, "No references!");
-
 static_assert(!has_unique_object_representations<Empty>::value, "No empty types!");
 
 class Compressed : Empty {
@@ -2556,6 +2555,16 @@ static_assert(!has_unique_object_representations<double[42]>::value, "So no arra
 static_assert(!has_unique_object_representations<double[]>::value, "So no array of doubles!");
 static_assert(!has_unique_object_representations<double[][42]>::value, "So no array of doubles!");
 
+struct __attribute__((aligned(16))) WeirdAlignment {
+  int i;
+};
+union __attribute__((aligned(16))) WeirdAlignmentUnion {
+  int i;
+};
+static_assert(!has_unique_object_representations<WeirdAlignment>::value, "Alignment causes padding");
+static_assert(!has_unique_object_representations<WeirdAlignmentUnion>::value, "Alignment causes padding");
+static_assert(!has_unique_object_representations<WeirdAlignment[42]>::value, "Also no arrays that have padding");
+
 static_assert(!has_unique_object_representations<int(int)>::value, "Functions are not unique");
 static_assert(!has_unique_object_representations<int(int) const>::value, "Functions are not unique");
 static_assert(!has_unique_object_representations<int(int) volatile>::value, "Functions are not unique");
@@ -2582,6 +2591,73 @@ static_assert(!has_unique_object_representations<int(int, ...) const &&>::value,
 static_assert(!has_unique_object_representations<int(int, ...) volatile &&>::value, "Functions are not unique");
 static_assert(!has_unique_object_representations<int(int, ...) const volatile &&>::value, "Functions are not unique");
 
-static auto lambda = []() {};
-static_assert(!has_unique_object_representations<decltype(lambda)>::value, "Lambdas are not unique");
+void foo(){
+  static auto lambda = []() {};
+  static_assert(!has_unique_object_representations<decltype(lambda)>::value, "Lambdas follow struct rules");
+  int i;
+  static auto lambda2 = [i]() {};
+  static_assert(has_unique_object_representations<decltype(lambda2)>::value, "Lambdas follow struct rules");
+}
+
+struct PaddedBitfield {
+  char c : 6;
+  char d : 1;
+};
+
+struct UnPaddedBitfield {
+  char c : 6;
+  char d : 2;
+};
+
+struct AlignedPaddedBitfield {
+  char c : 6;
+  __attribute__((aligned(1)))
+  char d : 2;
+};
+
+static_assert(!has_unique_object_representations<PaddedBitfield>::value, "Bitfield padding");
+static_assert(has_unique_object_representations<UnPaddedBitfield>::value, "Bitfield padding");
+static_assert(!has_unique_object_representations<AlignedPaddedBitfield>::value, "Bitfield padding");
+
+struct BoolBitfield {
+  bool b : 8;
+};
+
+static_assert(has_unique_object_representations<BoolBitfield>::value, "Bitfield bool");
+
+struct BoolBitfield2 {
+  bool b : 16;
+};
+
+static_assert(!has_unique_object_representations<BoolBitfield2>::value, "Bitfield bool");
+
+struct GreaterSizeBitfield {
+  //expected-warning@+1 {{width of bit-field 'n'}}
+  int n : 1024;
+};
+
+static_assert(sizeof(GreaterSizeBitfield) == 128, "Bitfield Size");
+static_assert(!has_unique_object_representations<GreaterSizeBitfield>::value, "Bitfield padding");
+
+struct StructWithRef {
+  int &I;
+};
+
+static_assert(has_unique_object_representations<StructWithRef>::value, "References are still unique");
+
+struct NotUniqueBecauseTailPadding {
+  int &r;
+  char a;
+};
+struct CanBeUniqueIfNoPadding : NotUniqueBecauseTailPadding {
+  char b[7];
+};
+
+static_assert(!has_unique_object_representations<NotUniqueBecauseTailPadding>::value, 
+              "non trivial");
+// Can be unique on Itanium, since the is child class' data is 'folded' into the
+// parent's tail padding.
+static_assert(sizeof(CanBeUniqueIfNoPadding) != 16 ||
+              has_unique_object_representations<CanBeUniqueIfNoPadding>::value,
+              "inherit from std layout");