Merge "Update prebuilt Clang to r353983." into p9.0HEADp9.0-backupp9.0

1 files changed, 243 insertions, 0 deletions

diff --git a/clang-r353983/include/llvm/ADT/fallible_iterator.h b/clang-r353983/include/llvm/ADT/fallible_iterator.h
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+//===--- fallible_iterator.h - Wrapper for fallible iterators ---*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_FALLIBLE_ITERATOR_H
+#define LLVM_ADT_FALLIBLE_ITERATOR_H
+
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/Support/Error.h"
+
+#include <type_traits>
+
+namespace llvm {
+
+/// A wrapper class for fallible iterators.
+///
+///   The fallible_iterator template wraps an underlying iterator-like class
+/// whose increment and decrement operations are replaced with fallible versions
+/// like:
+///
+///   @code{.cpp}
+///   Error inc();
+///   Error dec();
+///   @endcode
+///
+///   It produces an interface that is (mostly) compatible with a traditional
+/// c++ iterator, including ++ and -- operators that do not fail.
+///
+///   Instances of the wrapper are constructed with an instance of the
+/// underlying iterator and (for non-end iterators) a reference to an Error
+/// instance. If the underlying increment/decrement operations fail, the Error
+/// is returned via this reference, and the resulting iterator value set to an
+/// end-of-range sentinel value. This enables the following loop idiom:
+///
+///   @code{.cpp}
+///   class Archive { // E.g. Potentially malformed on-disk archive
+///   public:
+///     fallible_iterator<ArchiveChildItr> children_begin(Error &Err);
+///     fallible_iterator<ArchiveChildItr> children_end();
+///     iterator_range<fallible_iterator<ArchiveChildItr>>
+///     children(Error &Err) {
+///       return make_range(children_begin(Err), children_end());
+///     //...
+///   };
+///
+///   void walk(Archive &A) {
+///     Error Err = Error::success();
+///     for (auto &C : A.children(Err)) {
+///       // Loop body only entered when increment succeeds.
+///     }
+///     if (Err) {
+///       // handle error.
+///     }
+///   }
+///   @endcode
+///
+///   The wrapper marks the referenced Error as unchecked after each increment
+/// and/or decrement operation, and clears the unchecked flag when a non-end
+/// value is compared against end (since, by the increment invariant, not being
+/// an end value proves that there was no error, and is equivalent to checking
+/// that the Error is success). This allows early exits from the loop body
+/// without requiring redundant error checks.
+template <typename Underlying> class fallible_iterator {
+private:
+  template <typename T>
+  using enable_if_struct_deref_supported = std::enable_if<
+      !std::is_void<decltype(std::declval<T>().operator->())>::value,
+      decltype(std::declval<T>().operator->())>;
+
+public:
+  /// Construct a fallible iterator that *cannot* be used as an end-of-range
+  /// value.
+  ///
+  /// A value created by this method can be dereferenced, incremented,
+  /// decremented and compared, providing the underlying type supports it.
+  ///
+  /// The error that is passed in will be initially marked as checked, so if the
+  /// iterator is not used at all the Error need not be checked.
+  static fallible_iterator itr(Underlying I, Error &Err) {
+    (void)!!Err;
+    return fallible_iterator(std::move(I), &Err);
+  }
+
+  /// Construct a fallible iteratro that can be used as an end-of-range value.
+  ///
+  /// A value created by this method can be dereferenced (if the underlying
+  /// value points at a valid value) and compared, but not incremented or
+  /// decremented.
+  static fallible_iterator end(Underlying I) {
+    return fallible_iterator(std::move(I), nullptr);
+  }
+
+  /// Forward dereference to the underlying iterator.
+  auto operator*() -> decltype(*std::declval<Underlying>()) { return *I; }
+
+  /// Forward const dereference to the underlying iterator.
+  auto operator*() const -> decltype(*std::declval<const Underlying>()) {
+    return *I;
+  }
+
+  /// Forward structure dereference to the underlying iterator (if the
+  /// underlying iterator supports it).
+  template <typename T = Underlying>
+  typename enable_if_struct_deref_supported<T>::type operator->() {
+    return I.operator->();
+  }
+
+  /// Forward const structure dereference to the underlying iterator (if the
+  /// underlying iterator supports it).
+  template <typename T = Underlying>
+  typename enable_if_struct_deref_supported<const T>::type operator->() const {
+    return I.operator->();
+  }
+
+  /// Increment the fallible iterator.
+  ///
+  /// If the underlying 'inc' operation fails, this will set the Error value
+  /// and update this iterator value to point to end-of-range.
+  ///
+  /// The Error value is marked as needing checking, regardless of whether the
+  /// 'inc' operation succeeds or fails.
+  fallible_iterator &operator++() {
+    assert(getErrPtr() && "Cannot increment end iterator");
+    if (auto Err = I.inc())
+      handleError(std::move(Err));
+    else
+      resetCheckedFlag();
+    return *this;
+  }
+
+  /// Decrement the fallible iterator.
+  ///
+  /// If the underlying 'dec' operation fails, this will set the Error value
+  /// and update this iterator value to point to end-of-range.
+  ///
+  /// The Error value is marked as needing checking, regardless of whether the
+  /// 'dec' operation succeeds or fails.
+  fallible_iterator &operator--() {
+    assert(getErrPtr() && "Cannot decrement end iterator");
+    if (auto Err = I.dec())
+      handleError(std::move(Err));
+    else
+      resetCheckedFlag();
+    return *this;
+  }
+
+  /// Compare fallible iterators for equality.
+  ///
+  /// Returns true if both LHS and RHS are end-of-range values, or if both are
+  /// non-end-of-range values whose underlying iterator values compare equal.
+  ///
+  /// If this is a comparison between an end-of-range iterator and a
+  /// non-end-of-range iterator, then the Error (referenced by the
+  /// non-end-of-range value) is marked as checked: Since all
+  /// increment/decrement operations result in an end-of-range value, comparing
+  /// false against end-of-range is equivalent to checking that the Error value
+  /// is success. This flag management enables early returns from loop bodies
+  /// without redundant Error checks.
+  friend bool operator==(const fallible_iterator &LHS,
+                         const fallible_iterator &RHS) {
+    // If both iterators are in the end state they compare
+    // equal, regardless of whether either is valid.
+    if (LHS.isEnd() && RHS.isEnd())
+      return true;
+
+    assert(LHS.isValid() && RHS.isValid() &&
+           "Invalid iterators can only be compared against end");
+
+    bool Equal = LHS.I == RHS.I;
+
+    // If the iterators differ and this is a comparison against end then mark
+    // the Error as checked.
+    if (!Equal) {
+      if (LHS.isEnd())
+        (void)!!*RHS.getErrPtr();
+      else
+        (void)!!*LHS.getErrPtr();
+    }
+
+    return Equal;
+  }
+
+  /// Compare fallible iterators for inequality.
+  ///
+  /// See notes for operator==.
+  friend bool operator!=(const fallible_iterator &LHS,
+                         const fallible_iterator &RHS) {
+    return !(LHS == RHS);
+  }
+
+private:
+  fallible_iterator(Underlying I, Error *Err)
+      : I(std::move(I)), ErrState(Err, false) {}
+
+  Error *getErrPtr() const { return ErrState.getPointer(); }
+
+  bool isEnd() const { return getErrPtr() == nullptr; }
+
+  bool isValid() const { return !ErrState.getInt(); }
+
+  void handleError(Error Err) {
+    *getErrPtr() = std::move(Err);
+    ErrState.setPointer(nullptr);
+    ErrState.setInt(true);
+  }
+
+  void resetCheckedFlag() {
+    *getErrPtr() = Error::success();
+  }
+
+  Underlying I;
+  mutable PointerIntPair<Error *, 1> ErrState;
+};
+
+/// Convenience wrapper to make a fallible_iterator value from an instance
+/// of an underlying iterator and an Error reference.
+template <typename Underlying>
+fallible_iterator<Underlying> make_fallible_itr(Underlying I, Error &Err) {
+  return fallible_iterator<Underlying>::itr(std::move(I), Err);
+}
+
+/// Convenience wrapper to make a fallible_iterator end value from an instance
+/// of an underlying iterator.
+template <typename Underlying>
+fallible_iterator<Underlying> make_fallible_end(Underlying E) {
+  return fallible_iterator<Underlying>::end(std::move(E));
+}
+
+template <typename Underlying>
+iterator_range<fallible_iterator<Underlying>>
+make_fallible_range(Underlying I, Underlying E, Error &Err) {
+  return make_range(make_fallible_itr(std::move(I), Err),
+                    make_fallible_end(std::move(E)));
+}
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_FALLIBLE_ITERATOR_H