[llvm] r231125 - [ADT] fail-fast iterators for DenseMap
Sanjoy Das
sanjoy at playingwithpointers.com
Tue Mar 3 12:46:45 PST 2015
Author: sanjoy
Date: Tue Mar 3 14:46:45 2015
New Revision: 231125
URL: http://llvm.org/viewvc/llvm-project?rev=231125&view=rev
Log:
[ADT] fail-fast iterators for DenseMap
This patch was landed in r231035 and reverted because it was buggy.
This is fixed version of the same change.
Summary:
This patch is an attempt at making `DenseMapIterator`s "fail-fast".
Fail-fast iterators that have been invalidated due to insertion into
the host `DenseMap` deterministically trip an assert (in debug mode)
on access, instead of non-deterministically hitting memory corruption
issues.
Reviewers: dexonsmith, dberlin, ruiu, chandlerc
Reviewed By: chandlerc
Subscribers: yaron.keren, chandlerc, llvm-commits
Differential Revision: http://reviews.llvm.org/D7931
Added:
llvm/trunk/include/llvm/ADT/EpochTracker.h
Modified:
llvm/trunk/include/llvm/ADT/DenseMap.h
Modified: llvm/trunk/include/llvm/ADT/DenseMap.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/DenseMap.h?rev=231125&r1=231124&r2=231125&view=diff
==============================================================================
--- llvm/trunk/include/llvm/ADT/DenseMap.h (original)
+++ llvm/trunk/include/llvm/ADT/DenseMap.h Tue Mar 3 14:46:45 2015
@@ -15,6 +15,7 @@
#define LLVM_ADT_DENSEMAP_H
#include "llvm/ADT/DenseMapInfo.h"
+#include "llvm/ADT/EpochTracker.h"
#include "llvm/Support/AlignOf.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/MathExtras.h"
@@ -50,7 +51,7 @@ class DenseMapIterator;
template <typename DerivedT, typename KeyT, typename ValueT, typename KeyInfoT,
typename BucketT>
-class DenseMapBase {
+class DenseMapBase : public DebugEpochBase {
public:
typedef unsigned size_type;
typedef KeyT key_type;
@@ -62,16 +63,17 @@ public:
const_iterator;
inline iterator begin() {
// When the map is empty, avoid the overhead of AdvancePastEmptyBuckets().
- return empty() ? end() : iterator(getBuckets(), getBucketsEnd());
+ return empty() ? end() : iterator(getBuckets(), getBucketsEnd(), *this);
}
inline iterator end() {
- return iterator(getBucketsEnd(), getBucketsEnd(), true);
+ return iterator(getBucketsEnd(), getBucketsEnd(), *this, true);
}
inline const_iterator begin() const {
- return empty() ? end() : const_iterator(getBuckets(), getBucketsEnd());
+ return empty() ? end()
+ : const_iterator(getBuckets(), getBucketsEnd(), *this);
}
inline const_iterator end() const {
- return const_iterator(getBucketsEnd(), getBucketsEnd(), true);
+ return const_iterator(getBucketsEnd(), getBucketsEnd(), *this, true);
}
bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const {
@@ -81,11 +83,13 @@ public:
/// Grow the densemap so that it has at least Size buckets. Does not shrink
void resize(size_type Size) {
+ incrementEpoch();
if (Size > getNumBuckets())
grow(Size);
}
void clear() {
+ incrementEpoch();
if (getNumEntries() == 0 && getNumTombstones() == 0) return;
// If the capacity of the array is huge, and the # elements used is small,
@@ -118,13 +122,13 @@ public:
iterator find(const KeyT &Val) {
BucketT *TheBucket;
if (LookupBucketFor(Val, TheBucket))
- return iterator(TheBucket, getBucketsEnd(), true);
+ return iterator(TheBucket, getBucketsEnd(), *this, true);
return end();
}
const_iterator find(const KeyT &Val) const {
const BucketT *TheBucket;
if (LookupBucketFor(Val, TheBucket))
- return const_iterator(TheBucket, getBucketsEnd(), true);
+ return const_iterator(TheBucket, getBucketsEnd(), *this, true);
return end();
}
@@ -137,14 +141,14 @@ public:
iterator find_as(const LookupKeyT &Val) {
BucketT *TheBucket;
if (LookupBucketFor(Val, TheBucket))
- return iterator(TheBucket, getBucketsEnd(), true);
+ return iterator(TheBucket, getBucketsEnd(), *this, true);
return end();
}
template<class LookupKeyT>
const_iterator find_as(const LookupKeyT &Val) const {
const BucketT *TheBucket;
if (LookupBucketFor(Val, TheBucket))
- return const_iterator(TheBucket, getBucketsEnd(), true);
+ return const_iterator(TheBucket, getBucketsEnd(), *this, true);
return end();
}
@@ -163,12 +167,13 @@ public:
std::pair<iterator, bool> insert(const std::pair<KeyT, ValueT> &KV) {
BucketT *TheBucket;
if (LookupBucketFor(KV.first, TheBucket))
- return std::make_pair(iterator(TheBucket, getBucketsEnd(), true),
+ return std::make_pair(iterator(TheBucket, getBucketsEnd(), *this, true),
false); // Already in map.
// Otherwise, insert the new element.
TheBucket = InsertIntoBucket(KV.first, KV.second, TheBucket);
- return std::make_pair(iterator(TheBucket, getBucketsEnd(), true), true);
+ return std::make_pair(iterator(TheBucket, getBucketsEnd(), *this, true),
+ true);
}
// Inserts key,value pair into the map if the key isn't already in the map.
@@ -177,14 +182,15 @@ public:
std::pair<iterator, bool> insert(std::pair<KeyT, ValueT> &&KV) {
BucketT *TheBucket;
if (LookupBucketFor(KV.first, TheBucket))
- return std::make_pair(iterator(TheBucket, getBucketsEnd(), true),
+ return std::make_pair(iterator(TheBucket, getBucketsEnd(), *this, true),
false); // Already in map.
-
+
// Otherwise, insert the new element.
TheBucket = InsertIntoBucket(std::move(KV.first),
std::move(KV.second),
TheBucket);
- return std::make_pair(iterator(TheBucket, getBucketsEnd(), true), true);
+ return std::make_pair(iterator(TheBucket, getBucketsEnd(), *this, true),
+ true);
}
/// insert - Range insertion of pairs.
@@ -431,6 +437,8 @@ private:
}
BucketT *InsertIntoBucketImpl(const KeyT &Key, BucketT *TheBucket) {
+ incrementEpoch();
+
// If the load of the hash table is more than 3/4, or if fewer than 1/8 of
// the buckets are empty (meaning that many are filled with tombstones),
// grow the table.
@@ -987,9 +995,10 @@ private:
template <typename KeyT, typename ValueT, typename KeyInfoT, typename Bucket,
bool IsConst>
-class DenseMapIterator {
+class DenseMapIterator : DebugEpochBase::HandleBase {
typedef DenseMapIterator<KeyT, ValueT, KeyInfoT, Bucket, true> ConstIterator;
friend class DenseMapIterator<KeyT, ValueT, KeyInfoT, Bucket, true>;
+ friend class DenseMapIterator<KeyT, ValueT, KeyInfoT, Bucket, false>;
public:
typedef ptrdiff_t difference_type;
@@ -1003,8 +1012,10 @@ private:
public:
DenseMapIterator() : Ptr(nullptr), End(nullptr) {}
- DenseMapIterator(pointer Pos, pointer E, bool NoAdvance = false)
- : Ptr(Pos), End(E) {
+ DenseMapIterator(pointer Pos, pointer E, const DebugEpochBase &Epoch,
+ bool NoAdvance = false)
+ : DebugEpochBase::HandleBase(&Epoch), Ptr(Pos), End(E) {
+ assert(isHandleInSync() && "invalid construction!");
if (!NoAdvance) AdvancePastEmptyBuckets();
}
@@ -1015,28 +1026,40 @@ public:
typename = typename std::enable_if<!IsConstSrc && IsConst>::type>
DenseMapIterator(
const DenseMapIterator<KeyT, ValueT, KeyInfoT, Bucket, IsConstSrc> &I)
- : Ptr(I.Ptr), End(I.End) {}
+ : DebugEpochBase::HandleBase(I), Ptr(I.Ptr), End(I.End) {}
reference operator*() const {
+ assert(isHandleInSync() && "invalid iterator access!");
return *Ptr;
}
pointer operator->() const {
+ assert(isHandleInSync() && "invalid iterator access!");
return Ptr;
}
bool operator==(const ConstIterator &RHS) const {
- return Ptr == RHS.operator->();
+ assert((!Ptr || isHandleInSync()) && "handle not in sync!");
+ assert((!RHS.Ptr || RHS.isHandleInSync()) && "handle not in sync!");
+ assert(getEpochAddress() == RHS.getEpochAddress() &&
+ "comparing incomparable iterators!");
+ return Ptr == RHS.Ptr;
}
bool operator!=(const ConstIterator &RHS) const {
- return Ptr != RHS.operator->();
+ assert((!Ptr || isHandleInSync()) && "handle not in sync!");
+ assert((!RHS.Ptr || RHS.isHandleInSync()) && "handle not in sync!");
+ assert(getEpochAddress() == RHS.getEpochAddress() &&
+ "comparing incomparable iterators!");
+ return Ptr != RHS.Ptr;
}
inline DenseMapIterator& operator++() { // Preincrement
+ assert(isHandleInSync() && "invalid iterator access!");
++Ptr;
AdvancePastEmptyBuckets();
return *this;
}
DenseMapIterator operator++(int) { // Postincrement
+ assert(isHandleInSync() && "invalid iterator access!");
DenseMapIterator tmp = *this; ++*this; return tmp;
}
Added: llvm/trunk/include/llvm/ADT/EpochTracker.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/EpochTracker.h?rev=231125&view=auto
==============================================================================
--- llvm/trunk/include/llvm/ADT/EpochTracker.h (added)
+++ llvm/trunk/include/llvm/ADT/EpochTracker.h Tue Mar 3 14:46:45 2015
@@ -0,0 +1,95 @@
+//===- 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
+
+class DebugEpochBase {
+public:
+ void incrementEpoch() {}
+
+ class HandleBase {
+ public:
+ HandleBase() {}
+ explicit HandleBase(const DebugEpochBase *) {}
+ bool isHandleInSync() { return true; }
+ };
+};
+
+#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.
+ const uint64_t *getEpochAddress() const { return EpochAddress; }
+ };
+};
+
+#endif
+
+} // namespace llvm
+
+#endif
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