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

llvm-svn: 319446

1 files changed, 165 insertions, 1 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index d4c94368e68..c16882a7e67 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/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.