[Support] Port ErrorOr<T> from lld to C++03.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172991 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 373 insertions, 0 deletions

diff --git a/include/llvm/Support/Compiler.h b/include/llvm/Support/Compiler.h
index ebc1fadc14..2d49d4caf4 100644
--- a/include/llvm/Support/Compiler.h
+++ b/include/llvm/Support/Compiler.h
@@ -42,6 +42,33 @@
 #define LLVM_HAS_RVALUE_REFERENCE_THIS 0
 #endif
 
+/// \macro LLVM_HAS_CXX11_TYPETRAITS
+/// \brief Does the compiler have the C++11 type traits.
+///
+/// #include <type_traits>
+///
+/// * enable_if
+/// * {true,false}_type
+/// * is_constructible
+/// * etc...
+#if defined(__GXX_EXPERIMENTAL_CXX0X__) \
+    || (defined(_MSC_VER) && _MSC_VER >= 1600)
+#define LLVM_HAS_CXX11_TYPETRAITS 1
+#else
+#define LLVM_HAS_CXX11_TYPETRAITS 0
+#endif
+
+/// \macro LLVM_HAS_CXX11_STDLIB
+/// \brief Does the compiler have the C++11 standard library.
+///
+/// Implies LLVM_HAS_RVALUE_REFERENCES, LLVM_HAS_CXX11_TYPETRAITS
+#if defined(__GXX_EXPERIMENTAL_CXX0X__) \
+    || (defined(_MSC_VER) && _MSC_VER >= 1600)
+#define LLVM_HAS_CXX11_STDLIB 1
+#else
+#define LLVM_HAS_CXX11_STDLIB 0
+#endif
+
 /// llvm_move - Expands to ::std::move if the compiler supports
 /// r-value references; otherwise, expands to the argument.
 #if LLVM_HAS_RVALUE_REFERENCES
diff --git a/include/llvm/Support/ErrorOr.h b/include/llvm/Support/ErrorOr.h
new file mode 100644
index 0000000000..f74ff2166c
--- /dev/null
+++ b/include/llvm/Support/ErrorOr.h
@@ -0,0 +1,342 @@
+//===- llvm/Support/ErrorOr.h - Error Smart Pointer -----------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+///
+/// Provides ErrorOr<T> smart pointer.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_ERROR_OR_H
+#define LLVM_SUPPORT_ERROR_OR_H
+
+#include "llvm/Support/AlignOf.h"
+#include "llvm/Support/system_error.h"
+#include "llvm/Support/type_traits.h"
+
+#include <cassert>
+#if LLVM_HAS_CXX11_TYPETRAITS
+#include <type_traits>
+#endif
+
+namespace llvm {
+struct ErrorHolderBase {
+  error_code Error;
+  uint16_t RefCount;
+  bool HasUserData;
+
+  ErrorHolderBase() : RefCount(1) {}
+
+  void aquire() {
+    ++RefCount;
+  }
+
+  void release() {
+    if (--RefCount == 0)
+      delete this;
+  }
+
+protected:
+  virtual ~ErrorHolderBase() {}
+};
+
+template<class T>
+struct ErrorHolder : ErrorHolderBase {
+#if LLVM_HAS_RVALUE_REFERENCES
+  ErrorHolder(T &&UD) : UserData(llvm_move(UD)) {}
+#else
+  ErrorHolder(T &UD) : UserData(UD) {}
+#endif
+  T UserData;
+};
+
+template<class Tp> struct ErrorOrUserDataTraits : llvm::false_type {};
+
+#if LLVM_HAS_CXX11_TYPETRAITS && LLVM_HAS_RVALUE_REFERENCES
+template<class T, class V>
+typename std::enable_if< std::is_constructible<T, V>::value
+                       , typename std::remove_reference<V>::type>::type &&
+ moveIfMoveConstructible(V &Val) {
+  return std::move(Val);
+}
+
+template<class T, class V>
+typename std::enable_if< !std::is_constructible<T, V>::value
+                       , typename std::remove_reference<V>::type>::type &
+moveIfMoveConstructible(V &Val) {
+  return Val;
+}
+#else
+template<class T, class V>
+V &moveIfMoveConstructible(V &Val) {
+  return Val;
+}
+#endif
+
+/// \brief Stores a reference that can be changed.
+template <typename T>
+class ReferenceStorage {
+  T *Storage;
+
+public:
+  ReferenceStorage(T &Ref) : Storage(&Ref) {}
+
+  operator T &() const { return *Storage; }
+  T &get() const { return *Storage; }
+};
+
+/// \brief Represents either an error or a value T.
+///
+/// ErrorOr<T> is a pointer-like class that represents the result of an
+/// operation. The result is either an error, or a value of type T. This is
+/// designed to emulate the usage of returning a pointer where nullptr indicates
+/// failure. However instead of just knowing that the operation failed, we also
+/// have an error_code and optional user data that describes why it failed.
+///
+/// It is used like the following.
+/// \code
+///   ErrorOr<Buffer> getBuffer();
+///   void handleError(error_code ec);
+///
+///   auto buffer = getBuffer();
+///   if (!buffer)
+///     handleError(buffer);
+///   buffer->write("adena");
+/// \endcode
+///
+/// ErrorOr<T> also supports user defined data for specific error_codes. To use
+/// this feature you must first add a template specialization of
+/// ErrorOrUserDataTraits derived from std::true_type for your type in the lld
+/// namespace. This specialization must have a static error_code error()
+/// function that returns the error_code this data is used with.
+///
+/// getError<UserData>() may be called to get either the stored user data, or
+/// a default constructed UserData if none was stored.
+///
+/// Example:
+/// \code
+///   struct InvalidArgError {
+///     InvalidArgError() {}
+///     InvalidArgError(std::string S) : ArgName(S) {}
+///     std::string ArgName;
+///   };
+///
+///   namespace llvm {
+///   template<>
+///   struct ErrorOrUserDataTraits<InvalidArgError> : std::true_type {
+///     static error_code error() {
+///       return make_error_code(errc::invalid_argument);
+///     }
+///   };
+///   } // end namespace llvm
+///
+///   using namespace llvm;
+///
+///   ErrorOr<int> foo() {
+///     return InvalidArgError("adena");
+///   }
+///
+///   int main() {
+///     auto a = foo();
+///     if (!a && error_code(a) == errc::invalid_argument)
+///       llvm::errs() << a.getError<InvalidArgError>().ArgName << "\n";
+///   }
+/// \endcode
+///
+/// An implicit conversion to bool provides a way to check if there was an
+/// error. The unary * and -> operators provide pointer like access to the
+/// value. Accessing the value when there is an error has undefined behavior.
+///
+/// When T is a reference type the behaivor is slightly different. The reference
+/// is held in a std::reference_wrapper<std::remove_reference<T>::type>, and
+/// there is special handling to make operator -> work as if T was not a
+/// reference.
+///
+/// T cannot be a rvalue reference.
+template<class T>
+class ErrorOr {
+  static const bool isRef = is_reference<T>::value;
+  typedef ReferenceStorage<typename remove_reference<T>::type> wrap;
+
+public:
+  typedef typename
+    conditional< isRef
+               , wrap
+               , T
+               >::type storage_type;
+
+private:
+  typedef T &reference;
+  typedef typename remove_reference<T>::type *pointer;
+
+public:
+  ErrorOr() : IsValid(false) {}
+
+  ErrorOr(llvm::error_code EC) : HasError(true), IsValid(true) {
+    Error = new ErrorHolderBase;
+    Error->Error = EC;
+    Error->HasUserData = false;
+  }
+
+  template<class UserDataT>
+  ErrorOr(UserDataT UD, typename
+          enable_if_c<ErrorOrUserDataTraits<UserDataT>::value>::type* = 0)
+    : HasError(true), IsValid(true) {
+    Error = new ErrorHolder<UserDataT>(llvm_move(UD));
+    Error->Error = ErrorOrUserDataTraits<UserDataT>::error();
+    Error->HasUserData = true;
+  }
+
+  ErrorOr(T Val) : HasError(false), IsValid(true) {
+    new (get()) storage_type(moveIfMoveConstructible<storage_type>(Val));
+  }
+
+  ErrorOr(const ErrorOr &Other) : IsValid(false) {
+    // Construct an invalid ErrorOr if other is invalid.
+    if (!Other.IsValid)
+      return;
+    if (!Other.HasError) {
+      // Get the other value.
+      new (get()) storage_type(*Other.get());
+      HasError = false;
+    } else {
+      // Get other's error.
+      Error = Other.Error;
+      HasError = true;
+      Error->aquire();
+    }
+
+    IsValid = true;
+  }
+
+  ErrorOr &operator =(const ErrorOr &Other) {
+    if (this == &Other)
+      return *this;
+
+    this->~ErrorOr();
+    new (this) ErrorOr(Other);
+
+    return *this;
+  }
+
+#if LLVM_HAS_RVALUE_REFERENCES
+  ErrorOr(ErrorOr &&Other) : IsValid(false) {
+    // Construct an invalid ErrorOr if other is invalid.
+    if (!Other.IsValid)
+      return;
+    if (!Other.HasError) {
+      // Get the other value.
+      IsValid = true;
+      new (get()) storage_type(std::move(*Other.get()));
+      HasError = false;
+      // Tell other not to do any destruction.
+      Other.IsValid = false;
+    } else {
+      // Get other's error.
+      Error = Other.Error;
+      HasError = true;
+      // Tell other not to do any destruction.
+      Other.IsValid = false;
+    }
+
+    IsValid = true;
+  }
+
+  ErrorOr &operator =(ErrorOr &&Other) {
+    if (this == &Other)
+      return *this;
+
+    this->~ErrorOr();
+    new (this) ErrorOr(std::move(Other));
+
+    return *this;
+  }
+
+  ~ErrorOr() {
+    if (!IsValid)
+      return;
+    if (HasError)
+      Error->release();
+    else
+      get()->~storage_type();
+  }
+#endif
+
+  template<class ET>
+  ET getError() const {
+    assert(IsValid && "Cannot get the error of a default constructed ErrorOr!");
+    assert(HasError && "Cannot get an error if none exists!");
+    assert(ErrorOrUserDataTraits<ET>::error() == Error->Error &&
+           "Incorrect user error data type for error!");
+    if (!Error->HasUserData)
+      return ET();
+    return reinterpret_cast<const ErrorHolder<ET>*>(Error)->UserData;
+  }
+
+  typedef void (*unspecified_bool_type)();
+  static void unspecified_bool_true() {}
+
+  /// \brief Return false if there is an error.
+  operator unspecified_bool_type() const {
+    assert(IsValid && "Can't do anything on a default constructed ErrorOr!");
+    return HasError ? 0 : unspecified_bool_true;
+  }
+
+  operator llvm::error_code() const {
+    assert(IsValid && "Can't do anything on a default constructed ErrorOr!");
+    return HasError ? Error->Error : llvm::error_code::success();
+  }
+
+  pointer operator ->() {
+    return toPointer(get());
+  }
+
+  reference operator *() {
+    return *get();
+  }
+
+private:
+  pointer toPointer(pointer Val) {
+    return Val;
+  }
+
+  pointer toPointer(wrap *Val) {
+    return &Val->get();
+  }
+
+protected:
+  storage_type *get() {
+    assert(IsValid && "Can't do anything on a default constructed ErrorOr!");
+    assert(!HasError && "Cannot get value when an error exists!");
+    return reinterpret_cast<storage_type*>(TStorage.buffer);
+  }
+
+  const storage_type *get() const {
+    assert(IsValid && "Can't do anything on a default constructed ErrorOr!");
+    assert(!HasError && "Cannot get value when an error exists!");
+    return reinterpret_cast<const storage_type*>(TStorage.buffer);
+  }
+
+  union {
+    AlignedCharArrayUnion<storage_type> TStorage;
+    ErrorHolderBase *Error;
+  };
+  bool HasError : 1;
+  bool IsValid : 1;
+};
+
+template<class T, class E>
+typename enable_if_c<is_error_code_enum<E>::value ||
+                     is_error_condition_enum<E>::value, bool>::type
+operator ==(ErrorOr<T> &Err, E Code) {
+  return error_code(Err) == Code;
+}
+} // end namespace llvm
+
+#endif
diff --git a/include/llvm/Support/type_traits.h b/include/llvm/Support/type_traits.h
index f9306395fc..db43ccfece 100644
--- a/include/llvm/Support/type_traits.h
+++ b/include/llvm/Support/type_traits.h
@@ -145,6 +145,10 @@ template <typename T> struct is_pointer<T* const> : true_type {};
 template <typename T> struct is_pointer<T* volatile> : true_type {};
 template <typename T> struct is_pointer<T* const volatile> : true_type {};
 
+/// \brief Metafunction that determines wheather the given type is a reference.
+template <typename T> struct is_reference : false_type {};
+template <typename T> struct is_reference<T&> : true_type {};
+
 /// \brief Metafunction that determines whether the given type is either an
 /// integral type or an enumeration type.
 ///