Revert [NFC] Better encapsulation of llvm::Optional Storage

llvm-svn: 354240

include/llvm/ADT/Optional.h

@@ -29,89 +29,83 @@ namespace llvm {
 class raw_ostream;
 
 namespace optional_detail {
-
-struct in_place_t {};
-
 /// Storage for any type.
-template <typename T, bool = is_trivially_copyable<T>::value>
-class OptionalStorage {
-  union {
-    char empty;
-    T value;
-  };
-  bool hasVal;
+template <typename T, bool = is_trivially_copyable<T>::value> struct OptionalStorage {
+  AlignedCharArrayUnion<T> storage;
+  bool hasVal = false;
+
+  OptionalStorage() = default;
+
+  OptionalStorage(const T &y) : hasVal(true) { new (storage.buffer) T(y); }
+  OptionalStorage(const OptionalStorage &O) : hasVal(O.hasVal) {
+    if (hasVal)
+      new (storage.buffer) T(*O.getPointer());
+  }
+  OptionalStorage(T &&y) : hasVal(true) {
+    new (storage.buffer) T(std::forward<T>(y));
+  }
+  OptionalStorage(OptionalStorage &&O) : hasVal(O.hasVal) {
+    if (O.hasVal) {
+      new (storage.buffer) T(std::move(*O.getPointer()));
+    }
+  }
+
+  OptionalStorage &operator=(T &&y) {
+    if (hasVal)
+      *getPointer() = std::move(y);
+    else {
+      new (storage.buffer) T(std::move(y));
+      hasVal = true;
+    }
+    return *this;
+  }
+  OptionalStorage &operator=(OptionalStorage &&O) {
+    if (!O.hasVal)
+      reset();
+    else {
+      *this = std::move(*O.getPointer());
+    }
+    return *this;
+  }
+
+  // FIXME: these assignments (& the equivalent const T&/const Optional& ctors)
+  // could be made more efficient by passing by value, possibly unifying them
+  // with the rvalue versions above - but this could place a different set of
+  // requirements (notably: the existence of a default ctor) when implemented
+  // in that way. Careful SFINAE to avoid such pitfalls would be required.
+  OptionalStorage &operator=(const T &y) {
+    if (hasVal)
+      *getPointer() = y;
+    else {
+      new (storage.buffer) T(y);
+      hasVal = true;
+    }
+    return *this;
+  }
+  OptionalStorage &operator=(const OptionalStorage &O) {
+    if (!O.hasVal)
+      reset();
+    else
+      *this = *O.getPointer();
+    return *this;
+  }
 
-public:
   ~OptionalStorage() { reset(); }
 
-  OptionalStorage() noexcept : empty(), hasVal(false) {}
-
-  OptionalStorage(OptionalStorage const &other) : OptionalStorage() {
-    if (other.hasValue()) {
-      emplace(other.value);
-    }
-  }
-  OptionalStorage(OptionalStorage &&other) : OptionalStorage() {
-    if (other.hasValue()) {
-      emplace(std::move(other.value));
-    }
-  }
-
-  template <class... Args>
-  explicit OptionalStorage(in_place_t, Args &&... args)
-      : value(std::forward<Args>(args)...), hasVal(true) {}
-
-  void reset() noexcept {
+  void reset() {
     if (hasVal) {
-      value.~T();
+      (*getPointer()).~T();
       hasVal = false;
     }
   }
 
-  bool hasValue() const noexcept { return hasVal; }
-
-  T &getValue() LLVM_LVALUE_FUNCTION noexcept {
+  T *getPointer() {
     assert(hasVal);
-    return value;
+    return reinterpret_cast<T *>(storage.buffer);
   }
-  T const &getValue() const LLVM_LVALUE_FUNCTION noexcept {
+  const T *getPointer() const {
     assert(hasVal);
-    return value;
-  }
-#if LLVM_HAS_RVALUE_REFERENCE_THIS
-  T &&getValue() && noexcept {
-    assert(hasVal);
-    return std::move(value);
-  }
-#endif
-
-  template <class... Args> void emplace(Args &&... args) {
-    reset();
-    ::new ((void *)std::addressof(value)) T(std::forward<Args>(args)...);
-    hasVal = true;
-  }
-
-  OptionalStorage &operator=(T const &y) {
-    return (*this) = OptionalStorage(in_place_t{}, y);
-  }
-  OptionalStorage &operator=(T &&y) {
-    return (*this) = OptionalStorage(in_place_t{}, std::move(y));
-  }
-
-  OptionalStorage &operator=(OptionalStorage const &other) {
-    if (other.hasValue())
-      emplace(other.getValue());
-    else
-      reset();
-    return *this;
-  }
-
-  OptionalStorage &operator=(OptionalStorage &&other) {
-    if (other.hasValue())
-      emplace(std::move(other.getValue()));
-    else
-      reset();
-    return *this;
+    return reinterpret_cast<const T *>(storage.buffer);
   }
 };
 
@@ -126,10 +120,10 @@ public:
   constexpr Optional() {}
   constexpr Optional(NoneType) {}
 
-  Optional(const T &y) : Storage(optional_detail::in_place_t{}, y) {}
+  Optional(const T &y) : Storage(y) {}
   Optional(const Optional &O) = default;
 
-  Optional(T &&y) : Storage(optional_detail::in_place_t{}, std::move(y)) {}
+  Optional(T &&y) : Storage(std::forward<T>(y)) {}
   Optional(Optional &&O) = default;
 
   Optional &operator=(T &&y) {
@@ -140,7 +134,9 @@ public:
 
   /// Create a new object by constructing it in place with the given arguments.
   template <typename... ArgTypes> void emplace(ArgTypes &&... Args) {
-    Storage.emplace(std::forward<ArgTypes>(Args)...);
+    reset();
+    Storage.hasVal = true;
+    new (getPointer()) T(std::forward<ArgTypes>(Args)...);
   }
 
   static inline Optional create(const T *y) {
@@ -155,17 +151,23 @@ public:
 
   void reset() { Storage.reset(); }
 
-  const T *getPointer() const { return &Storage.getValue(); }
-  T *getPointer() { return &Storage.getValue(); }
-  const T &getValue() const LLVM_LVALUE_FUNCTION { return Storage.getValue(); }
-  T &getValue() LLVM_LVALUE_FUNCTION { return Storage.getValue(); }
+  const T *getPointer() const {
+    assert(Storage.hasVal);
+    return reinterpret_cast<const T *>(Storage.storage.buffer);
+  }
+  T *getPointer() {
+    assert(Storage.hasVal);
+    return reinterpret_cast<T *>(Storage.storage.buffer);
+  }
+  const T &getValue() const LLVM_LVALUE_FUNCTION { return *getPointer(); }
+  T &getValue() LLVM_LVALUE_FUNCTION { return *getPointer(); }
 
-  explicit operator bool() const { return hasValue(); }
-  bool hasValue() const { return Storage.hasValue(); }
+  explicit operator bool() const { return Storage.hasVal; }
+  bool hasValue() const { return Storage.hasVal; }
   const T *operator->() const { return getPointer(); }
   T *operator->() { return getPointer(); }
-  const T &operator*() const LLVM_LVALUE_FUNCTION { return getValue(); }
-  T &operator*() LLVM_LVALUE_FUNCTION { return getValue(); }
+  const T &operator*() const LLVM_LVALUE_FUNCTION { return *getPointer(); }
+  T &operator*() LLVM_LVALUE_FUNCTION { return *getPointer(); }
 
   template <typename U>
   constexpr T getValueOr(U &&value) const LLVM_LVALUE_FUNCTION {
@@ -173,8 +175,8 @@ public:
   }
 
 #if LLVM_HAS_RVALUE_REFERENCE_THIS
-  T &&getValue() && { return std::move(Storage.getValue()); }
-  T &&operator*() && { return std::move(Storage.getValue()); }
+  T &&getValue() && { return std::move(*getPointer()); }
+  T &&operator*() && { return std::move(*getPointer()); }
 
   template <typename U>
   T getValueOr(U &&value) && {