Prepare wpiutil for merge into allwpilib.

wpiutil/src/main/native/include/llvm/EpochTracker.h

@@ -0,0 +1,97 @@
+//===- llvm/ADT/EpochTracker.h - ADT epoch tracking --------------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the DebugEpochBase and DebugEpochBase::HandleBase classes.
+// These can be used to write iterators that are fail-fast when LLVM is built
+// with asserts enabled.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_EPOCH_TRACKER_H
+#define LLVM_ADT_EPOCH_TRACKER_H
+
+#include <cstdint>
+
+namespace llvm {
+
+#ifdef NDEBUG //ifndef LLVM_ENABLE_ABI_BREAKING_CHECKS
+
+class DebugEpochBase {
+public:
+  void incrementEpoch() {}
+
+  class HandleBase {
+  public:
+    HandleBase() = default;
+    explicit HandleBase(const DebugEpochBase *) {}
+    bool isHandleInSync() const { return true; }
+    const void *getEpochAddress() const { return nullptr; }
+  };
+};
+
+#else
+
+/// \brief A base class for data structure classes wishing to make iterators
+/// ("handles") pointing into themselves fail-fast.  When building without
+/// asserts, this class is empty and does nothing.
+///
+/// DebugEpochBase does not by itself track handles pointing into itself.  The
+/// expectation is that routines touching the handles will poll on
+/// isHandleInSync at appropriate points to assert that the handle they're using
+/// is still valid.
+///
+class DebugEpochBase {
+  uint64_t Epoch;
+
+public:
+  DebugEpochBase() : Epoch(0) {}
+
+  /// \brief Calling incrementEpoch invalidates all handles pointing into the
+  /// calling instance.
+  void incrementEpoch() { ++Epoch; }
+
+  /// \brief The destructor calls incrementEpoch to make use-after-free bugs
+  /// more likely to crash deterministically.
+  ~DebugEpochBase() { incrementEpoch(); }
+
+  /// \brief A base class for iterator classes ("handles") that wish to poll for
+  /// iterator invalidating modifications in the underlying data structure.
+  /// When LLVM is built without asserts, this class is empty and does nothing.
+  ///
+  /// HandleBase does not track the parent data structure by itself.  It expects
+  /// the routines modifying the data structure to call incrementEpoch when they
+  /// make an iterator-invalidating modification.
+  ///
+  class HandleBase {
+    const uint64_t *EpochAddress;
+    uint64_t EpochAtCreation;
+
+  public:
+    HandleBase() : EpochAddress(nullptr), EpochAtCreation(UINT64_MAX) {}
+
+    explicit HandleBase(const DebugEpochBase *Parent)
+        : EpochAddress(&Parent->Epoch), EpochAtCreation(Parent->Epoch) {}
+
+    /// \brief Returns true if the DebugEpochBase this Handle is linked to has
+    /// not called incrementEpoch on itself since the creation of this
+    /// HandleBase instance.
+    bool isHandleInSync() const { return *EpochAddress == EpochAtCreation; }
+
+    /// \brief Returns a pointer to the epoch word stored in the data structure
+    /// this handle points into.  Can be used to check if two iterators point
+    /// into the same data structure.
+    const void *getEpochAddress() const { return EpochAddress; }
+  };
+};
+
+#endif // LLVM_ENABLE_ABI_BREAKING_CHECKS
+
+} // namespace llvm
+
+#endif