+//===- 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 "llvm/Config/llvm-config.h"
+
+#include <cstdint>
+
+namespace llvm {
+
+#ifndef LLVM_ENABLE_ABI_BREAKING_CHECKS
+
+class DebugEpochBase {
+public:
+ void incrementEpoch() {}
+
+ class HandleBase {
+ public:
+ HandleBase() {}
+ 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
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