LLVM  15.0.0git
EpochTracker.h
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1 //===- llvm/ADT/EpochTracker.h - ADT epoch tracking --------------*- C++ -*-==//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 ///
9 /// \file
10 /// This file defines the DebugEpochBase and DebugEpochBase::HandleBase classes.
11 /// These can be used to write iterators that are fail-fast when LLVM is built
12 /// with asserts enabled.
13 ///
14 //===----------------------------------------------------------------------===//
15 
16 #ifndef LLVM_ADT_EPOCHTRACKER_H
17 #define LLVM_ADT_EPOCHTRACKER_H
18 
19 #include "llvm/Config/abi-breaking.h"
20 
21 #include <cstdint>
22 
23 namespace llvm {
24 
25 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
26 
27 /// A base class for data structure classes wishing to make iterators
28 /// ("handles") pointing into themselves fail-fast. When building without
29 /// asserts, this class is empty and does nothing.
30 ///
31 /// DebugEpochBase does not by itself track handles pointing into itself. The
32 /// expectation is that routines touching the handles will poll on
33 /// isHandleInSync at appropriate points to assert that the handle they're using
34 /// is still valid.
35 ///
36 class DebugEpochBase {
37  uint64_t Epoch = 0;
38 
39 public:
40  DebugEpochBase() = default;
41 
42  /// Calling incrementEpoch invalidates all handles pointing into the
43  /// calling instance.
44  void incrementEpoch() { ++Epoch; }
45 
46  /// The destructor calls incrementEpoch to make use-after-free bugs
47  /// more likely to crash deterministically.
48  ~DebugEpochBase() { incrementEpoch(); }
49 
50  /// A base class for iterator classes ("handles") that wish to poll for
51  /// iterator invalidating modifications in the underlying data structure.
52  /// When LLVM is built without asserts, this class is empty and does nothing.
53  ///
54  /// HandleBase does not track the parent data structure by itself. It expects
55  /// the routines modifying the data structure to call incrementEpoch when they
56  /// make an iterator-invalidating modification.
57  ///
58  class HandleBase {
59  const uint64_t *EpochAddress;
60  uint64_t EpochAtCreation;
61 
62  public:
63  HandleBase() : EpochAddress(nullptr), EpochAtCreation(UINT64_MAX) {}
64 
65  explicit HandleBase(const DebugEpochBase *Parent)
66  : EpochAddress(&Parent->Epoch), EpochAtCreation(Parent->Epoch) {}
67 
68  /// Returns true if the DebugEpochBase this Handle is linked to has
69  /// not called incrementEpoch on itself since the creation of this
70  /// HandleBase instance.
71  bool isHandleInSync() const { return *EpochAddress == EpochAtCreation; }
72 
73  /// Returns a pointer to the epoch word stored in the data structure
74  /// this handle points into. Can be used to check if two iterators point
75  /// into the same data structure.
76  const void *getEpochAddress() const { return EpochAddress; }
77  };
78 };
79 
80 #else
81 
83 public:
84  void incrementEpoch() {}
85 
86  class HandleBase {
87  public:
88  HandleBase() = default;
89  explicit HandleBase(const DebugEpochBase *) {}
90  bool isHandleInSync() const { return true; }
91  const void *getEpochAddress() const { return nullptr; }
92  };
93 };
94 
95 #endif // LLVM_ENABLE_ABI_BREAKING_CHECKS
96 
97 } // namespace llvm
98 
99 #endif
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:17
llvm::DebugEpochBase::HandleBase::HandleBase
HandleBase()=default
UINT64_MAX
#define UINT64_MAX
Definition: DataTypes.h:77
llvm::DebugEpochBase::HandleBase::HandleBase
HandleBase(const DebugEpochBase *)
Definition: EpochTracker.h:89
uint64_t
llvm::DebugEpochBase::HandleBase::isHandleInSync
bool isHandleInSync() const
Definition: EpochTracker.h:90
llvm::DebugEpochBase::HandleBase::getEpochAddress
const void * getEpochAddress() const
Definition: EpochTracker.h:91
llvm::DebugEpochBase
Definition: EpochTracker.h:82
llvm::DebugEpochBase::incrementEpoch
void incrementEpoch()
Definition: EpochTracker.h:84
llvm::DebugEpochBase::HandleBase
Definition: EpochTracker.h:86