[PATCH] D23466: ADT: Remove UB in ilist (and use a circular linked list)
Duncan P. N. Exon Smith via llvm-commits
llvm-commits at lists.llvm.org
Fri Aug 12 17:23:00 PDT 2016
> On 2016-Aug-12, at 15:05, Justin Bogner <mail at justinbogner.com> wrote:
>
> "Duncan P. N. Exon Smith" <dexonsmith at apple.com> writes:
>> dexonsmith created this revision.
>> dexonsmith added reviewers: bogner, dblaikie, mehdi_amini.
>> dexonsmith added a subscriber: llvm-commits.
>>
>> This removes the undefined behaviour (UB) in ilist/ilist_node/etc.,
>> mainly by removing (gutting) the ilist_sentinel_traits customization
>> point and canonicalizing on a single, efficient memory layout.
>>
>> The new ilist is a doubly-linked circular list.
>> - ilist_node_base has two ilist_node_base*: Next and Prev. Size-of: two
>> pointers.
>> - ilist_node<T> (size-of: two pointers) is a type-safe wrapper around
>> ilist_node_base.
>> - ilist_iterator<T> (size-of: two pointers) operates on an
>> ilist_node<T>*, and downcasts to T* on dereference.
>> - ilist_sentinel<T> (size-of: two pointers) is a wrapper around
>> ilist_node<T> that has some extra API for list management.
>> - ilist<T> (size-of: two pointers) has an ilist_sentinel<T>, whose
>> address is returned for end().
>
> So, instead of a list that's hard to understand and that invokes UB,
> this is just a normal doubly linked list. LGTM.
Thanks for the review!
> A couple of minor comments on your comments below.
>
>> The new memory layout matches ilist_half_embedded_sentinel_traits<T>
>> exactly. The Head pointer that previously lived in ilist<T> is
>> effectively glued to the ilist_half_node<T> that lived in
>> ilist_half_embedded_sentinel_traits<T>, becoming the Next and Prev in
>> the ilist_sentinel_node<T>, respectively. sizeof(ilist<T>) is now the
>> size of two pointers, and there is never any additional storage for a
>> sentinel.
>>
>> This is a much simpler design for a doubly-linked list, removing most of
>> the corner cases of list manipulation (add, remove, etc.). In follow-up
>> commits, I intend to move as many algorithms as possible into a
>> non-templated base class (ilist_base) to reduce code size.
>>
>> Moreover, this fixes the UB in ilist_iterator/getNext/getPrev
>> operations. Previously, ilist_iterator<T> operated on a T*, even when
>> the sentinel was not of type T (i.e., ilist_embedded_sentinel_traits and
>> ilist_half_embedded_sentinel_traits). This added UB to all operations
>> involving end(). Now, ilist_iterator<T> operates on an ilist_node<T>*,
>> and only downcasts when the full type is guaranteed to be T*.
>>
>> What did we lose? There used to be a crash (in some configurations) on
>> ++end(). Curiously (via UB), ++end() would return begin() for users of
>> ilist_half_embedded_sentinel_traits<T>, but otherwise ++end() would
>> cause a nice dependable nullptr dereference, crashing instead of a
>> possible infinite loop. Options:
>> 1. Lose that behaviour.
>> 2. Have a template parameter to opt-in to a crash in asserts builds.
>> This requires stealing a bit from Prev.
>> 3. Have a template parameter to opt-in to a crash in all builds.
>>
>> IMO #1 is the best option (which is why I implemented it here). Most
>> users of ilist effectively had this behaviour anyway. #2 and #3 are
>> more complicated than they are worth.
>>
>> I added only a couple of unit tests to root out specific bugs I hit
>> during bring-up, but otherwise this is tested implicitly via the
>> extensive usage throughout LLVM.
>>
>> Planned follow-ups:
>> - Remove ilist_*sentinel_traits<T>. Here I've just gutted them to
>> prevent build failures in sub-projects. Once I stop referring to them
>> in sub-projects, I'll come back and delete them.
>> - Add ilist_base and move algorithms there.
>>
>> Eventually, there are other interesting directions:
>> - Remove ilist_traits::createNode, by deleting the remaining API that
>> creates nodes. Intrusive lists shouldn't be creating nodes
>> themselves.
>> - Remove ilist_traits::deleteNode, by (1) asserting that lists are empty
>> on destruction and (2) changing API that calls it to take a Deleter
>> functor (intrusive lists shouldn't be in the memory management
>> business).
>> - Reconfigure the remaining callback traits (addNodeToList, etc.) to be
>> higher-level, pulling out a simple_ilist<T> that is much easier to
>> read and understand.
>> - Allow tags (e.g., ilist_node<T,tag1> and ilist_node<T,tag2>) so that T
>> can be a member of multiple intrusive lists.
>>
>>
>> https://reviews.llvm.org/D23466
>>
>> Files:
>> include/llvm/ADT/ilist.h
>> include/llvm/ADT/ilist_node.h
>> unittests/ADT/ilistTest.cpp
>>
>> Index: unittests/ADT/ilistTest.cpp
>> ===================================================================
>> --- unittests/ADT/ilistTest.cpp
>> +++ unittests/ADT/ilistTest.cpp
>> @@ -96,4 +96,66 @@
>> EXPECT_EQ(6, List.back().Value);
>> }
>>
>> +struct NodeWithCallback : ilist_node<NodeWithCallback> {
>> + int Value = 0;
>> + bool IsInList = false;
>> +
>> + NodeWithCallback() = default;
>> + NodeWithCallback(int Value) : Value(Value) {}
>> + NodeWithCallback(const NodeWithCallback &) = delete;
>> +};
>> +
>> +} // end namespace
>> +
>> +namespace llvm {
>> +template <>
>> +struct ilist_traits<NodeWithCallback>
>> + : public ilist_node_traits<NodeWithCallback> {
>> + void addNodeToList(NodeWithCallback *N) { N->IsInList = true; }
>> + void removeNodeFromList(NodeWithCallback *N) { N->IsInList = false; }
>> +};
>> +} // end namespace llvm
>> +
>> +namespace {
>> +
>> +TEST(ilistTest, addNodeToList) {
>> + ilist<NodeWithCallback> L;
>> + NodeWithCallback N(7);
>> + ASSERT_FALSE(N.IsInList);
>> +
>> + L.insert(L.begin(), &N);
>> + ASSERT_EQ(1u, L.size());
>> + ASSERT_EQ(&N, &*L.begin());
>> + ASSERT_TRUE(N.IsInList);
>> +
>> + L.remove(&N);
>> + ASSERT_EQ(0u, L.size());
>> + ASSERT_FALSE(N.IsInList);
>> +}
>> +
>> +struct PrivateNode : private ilist_node<PrivateNode> {
>> + friend struct llvm::ilist_node_access;
>> +
>> + int Value = 0;
>> +
>> + PrivateNode() = default;
>> + PrivateNode(int Value) : Value(Value) {}
>> + PrivateNode(const PrivateNode &) = delete;
>> +};
>> +
>> +TEST(ilistTest, privateNode) {
>> + // Instantiate various APIs to be sure they're callable when ilist_node is
>> + // inherited privately.
>> + ilist<NodeWithCallback> L;
>> + NodeWithCallback N(7);
>> + L.insert(L.begin(), &N);
>> + ++L.begin();
>> + (void)*L.begin();
>> + (void)(L.begin() == L.end());
>> +
>> + ilist<NodeWithCallback> L2;
>> + L2.splice(L2.end(), L);
>> + L2.remove(&N);
>> }
>> +
>> +} // end namespace
>> Index: include/llvm/ADT/ilist_node.h
>> ===================================================================
>> --- include/llvm/ADT/ilist_node.h
>> +++ include/llvm/ADT/ilist_node.h
>> @@ -22,48 +22,57 @@
>> template <typename NodeTy> struct ilist_embedded_sentinel_traits;
>> template <typename NodeTy> struct ilist_half_embedded_sentinel_traits;
>>
>> -/// ilist_half_node - Base class that provides prev services for sentinels.
>> -///
>> -template<typename NodeTy>
>> -class ilist_half_node {
>> - friend struct ilist_traits<NodeTy>;
>> - friend struct ilist_half_embedded_sentinel_traits<NodeTy>;
>> - NodeTy *Prev;
>> -protected:
>> - NodeTy *getPrev() { return Prev; }
>> - const NodeTy *getPrev() const { return Prev; }
>> - void setPrev(NodeTy *P) { Prev = P; }
>> - ilist_half_node() : Prev(nullptr) {}
>> +/// Base class for ilist nodes.
>> +struct ilist_node_base {
>> + ilist_node_base *Prev = nullptr;
>> + ilist_node_base *Next = nullptr;
>> };
>>
>> struct ilist_node_access;
>> template <typename NodeTy> class ilist_iterator;
>> +template <typename NodeTy> class ilist_sentinel;
>>
>> -/// Base class that provides next/prev services for ilist nodes.
>> -template<typename NodeTy>
>> -class ilist_node : private ilist_half_node<NodeTy> {
>> +/// Templated wrapper class.
>> +template <typename NodeTy> class ilist_node : ilist_node_base {
>> friend struct ilist_node_access;
>> friend struct ilist_traits<NodeTy>;
>> friend struct ilist_half_embedded_sentinel_traits<NodeTy>;
>> friend struct ilist_embedded_sentinel_traits<NodeTy>;
>> - NodeTy *Next;
>> - NodeTy *getNext() { return Next; }
>> - const NodeTy *getNext() const { return Next; }
>> - void setNext(NodeTy *N) { Next = N; }
>> + friend class ilist_iterator<NodeTy>;
>> + friend class ilist_sentinel<NodeTy>;
>> +
>> protected:
>> - ilist_node() : Next(nullptr) {}
>> + ilist_node() = default;
>> +
>> +private:
>> + ilist_node *getPrev() { return static_cast<ilist_node *>(Prev); }
>> + ilist_node *getNext() { return static_cast<ilist_node *>(Next); }
>> +
>> + const ilist_node *getPrev() const { return static_cast<ilist_node *>(Prev); }
>> + const ilist_node *getNext() const { return static_cast<ilist_node *>(Next); }
>> +
>> + void setPrev(ilist_node *N) { Prev = N; }
>> + void setNext(ilist_node *N) { Next = N; }
>>
>> public:
>> - ilist_iterator<NodeTy> getIterator() {
>> - // FIXME: Stop downcasting to create the iterator (potential UB).
>> - return ilist_iterator<NodeTy>(static_cast<NodeTy *>(this));
>> - }
>> + ilist_iterator<NodeTy> getIterator() { return ilist_iterator<NodeTy>(*this); }
>> ilist_iterator<const NodeTy> getIterator() const {
>> - // FIXME: Stop downcasting to create the iterator (potential UB).
>> - return ilist_iterator<const NodeTy>(static_cast<const NodeTy *>(this));
>> + return ilist_iterator<const NodeTy>(*this);
>> }
>> };
>>
>> +template <typename NodeTy> class ilist_sentinel : public ilist_node<NodeTy> {
>> +public:
>> + ilist_sentinel() { reset(); }
>> +
>> + void reset() {
>> + this->setPrev(this);
>> + this->setNext(this);
>> + }
>> +
>> + bool empty() const { return this == this->getPrev(); }
>> +};
>> +
>> /// An ilist node that can access its parent list.
>> ///
>> /// Requires \c NodeTy to have \a getParent() to find the parent node, and the
>> Index: include/llvm/ADT/ilist.h
>> ===================================================================
>> --- include/llvm/ADT/ilist.h
>> +++ include/llvm/ADT/ilist.h
>> @@ -26,6 +26,7 @@
>> #ifndef LLVM_ADT_ILIST_H
>> #define LLVM_ADT_ILIST_H
>>
>> +#include "llvm/ADT/ilist_node.h"
>> #include "llvm/Support/Compiler.h"
>> #include <algorithm>
>> #include <cassert>
>> @@ -38,37 +39,42 @@
>> template<typename NodeTy, typename Traits> class iplist;
>> template<typename NodeTy> class ilist_iterator;
>>
>> -/// An access class for next/prev on ilist_nodes.
>> +/// An access class for ilist_node private API.
>> ///
>> /// This gives access to the private parts of ilist nodes. Nodes for an ilist
>> /// should friend this class if they inherit privately from ilist_node.
>> ///
>> -/// It's strongly discouraged to *use* this class outside of ilist
>> +/// It's strongly discouraged to *use* this class outside of the ilist
>> /// implementation.
>> struct ilist_node_access {
>> - template <typename NodeTy> static NodeTy *getPrev(NodeTy *N) {
>> + template <typename T> static ilist_node<T> *getNodePtr(T *N) { return N; }
>> + template <typename T> static const ilist_node<T> *getNodePtr(const T *N) {
>> + return N;
>> + }
>> +
>> + template <typename T> static ilist_node<T> *getPrev(ilist_node<T> *N) {
>> return N->getPrev();
>> }
>> - template <typename NodeTy> static NodeTy *getNext(NodeTy *N) {
>> + template <typename T> static ilist_node<T> *getNext(ilist_node<T> *N) {
>> return N->getNext();
>> }
>> - template <typename NodeTy> static const NodeTy *getPrev(const NodeTy *N) {
>> + template <typename T> static const ilist_node<T> *getPrev(const ilist_node<T> *N) {
>> return N->getPrev();
>> }
>> - template <typename NodeTy> static const NodeTy *getNext(const NodeTy *N) {
>> + template <typename T> static const ilist_node<T> *getNext(const ilist_node<T> *N) {
>> return N->getNext();
>> }
>>
>> - template <typename NodeTy> static void setPrev(NodeTy *N, NodeTy *Prev) {
>> + template <typename T> static void setPrev(ilist_node<T> *N, ilist_node<T> *Prev) {
>> N->setPrev(Prev);
>> }
>> - template <typename NodeTy> static void setNext(NodeTy *N, NodeTy *Next) {
>> + template <typename T> static void setNext(ilist_node<T> *N, ilist_node<T> *Next) {
>> N->setNext(Next);
>> }
>> - template <typename NodeTy> static void setPrev(NodeTy *N, std::nullptr_t) {
>> + template <typename T> static void setPrev(ilist_node<T> *N, std::nullptr_t) {
>> N->setPrev(nullptr);
>> }
>> - template <typename NodeTy> static void setNext(NodeTy *N, std::nullptr_t) {
>> + template <typename T> static void setNext(ilist_node<T> *N, std::nullptr_t) {
>> N->setNext(nullptr);
>> }
>> };
>> @@ -93,111 +99,31 @@
>> static const bool value = sizeof(hasGetNext<TraitsT>(nullptr)) == sizeof(Yes);
>> };
>>
>> -} // end namespace ilist_detail
>> -
>> -template<typename NodeTy>
>> -struct ilist_traits;
>> -
>> -/// ilist_sentinel_traits - A fragment for template traits for intrusive list
>> -/// that provides default sentinel implementations for common operations.
>> -///
>> -/// ilist_sentinel_traits implements a lazy dynamic sentinel allocation
>> -/// strategy. The sentinel is stored in the prev field of ilist's Head.
>> -///
>> -template<typename NodeTy>
>> -struct ilist_sentinel_traits {
>> - /// createSentinel - create the dynamic sentinel
>> - static NodeTy *createSentinel() { return new NodeTy(); }
>> -
>> - /// destroySentinel - deallocate the dynamic sentinel
>> - static void destroySentinel(NodeTy *N) { delete N; }
>> -
>> - /// provideInitialHead - when constructing an ilist, provide a starting
>> - /// value for its Head
>> - /// @return null node to indicate that it needs to be allocated later
>> - static NodeTy *provideInitialHead() { return nullptr; }
>> -
>> - /// ensureHead - make sure that Head is either already
>> - /// initialized or assigned a fresh sentinel
>> - /// @return the sentinel
>> - static NodeTy *ensureHead(NodeTy *&Head) {
>> - if (!Head) {
>> - Head = ilist_traits<NodeTy>::createSentinel();
>> - ilist_traits<NodeTy>::noteHead(Head, Head);
>> - ilist_node_access::setNext(Head, nullptr);
>> - return Head;
>> - }
>> - return ilist_node_access::getPrev(Head);
>> - }
>> -
>> - /// noteHead - stash the sentinel into its default location
>> - static void noteHead(NodeTy *NewHead, NodeTy *Sentinel) {
>> - ilist_node_access::setPrev(NewHead, Sentinel);
>> - }
>> -};
>> -
>> -template <typename NodeTy> class ilist_half_node;
>> -template <typename NodeTy> class ilist_node;
>> -
>> -/// Traits with an embedded ilist_node as a sentinel.
>> -template <typename NodeTy> struct ilist_embedded_sentinel_traits {
>> - /// Get hold of the node that marks the end of the list.
>> - ///
>> - /// FIXME: This downcast is UB. See llvm.org/PR26753.
>> - LLVM_NO_SANITIZE("object-size")
>> - NodeTy *createSentinel() const {
>> - // Since i(p)lists always publicly derive from their corresponding traits,
>> - // placing a data member in this class will augment the i(p)list. But since
>> - // the NodeTy is expected to be publicly derive from ilist_node<NodeTy>,
>> - // there is a legal viable downcast from it to NodeTy. We use this trick to
>> - // superimpose an i(p)list with a "ghostly" NodeTy, which becomes the
>> - // sentinel. Dereferencing the sentinel is forbidden (save the
>> - // ilist_node<NodeTy>), so no one will ever notice the superposition.
>> - return static_cast<NodeTy *>(&Sentinel);
>> - }
>> - static void destroySentinel(NodeTy *) {}
>> -
>> - NodeTy *provideInitialHead() const { return createSentinel(); }
>> - NodeTy *ensureHead(NodeTy *) const { return createSentinel(); }
>> - static void noteHead(NodeTy *, NodeTy *) {}
>> -
>> -private:
>> - mutable ilist_node<NodeTy> Sentinel;
>> -};
>> -
>> -/// Trait with an embedded ilist_half_node as a sentinel.
>> -template <typename NodeTy> struct ilist_half_embedded_sentinel_traits {
>> - /// Get hold of the node that marks the end of the list.
>> - ///
>> - /// FIXME: This downcast is UB. See llvm.org/PR26753.
>> - LLVM_NO_SANITIZE("object-size")
>> - NodeTy *createSentinel() const {
>> - // See comment in ilist_embedded_sentinel_traits::createSentinel().
>> - return static_cast<NodeTy *>(&Sentinel);
>> - }
>> - static void destroySentinel(NodeTy *) {}
>> +/// Type trait to check for a traits class that has a createSentinel member (as
>> +/// a canary for any of the ilist_sentinel_traits API).
>> +template <class TraitsT> struct HasCreateSentinel {
>> + typedef char Yes[1];
>> + typedef char No[2];
>> + template <size_t N> struct SFINAE {};
>>
>> - NodeTy *provideInitialHead() const { return createSentinel(); }
>> - NodeTy *ensureHead(NodeTy *) const { return createSentinel(); }
>> - static void noteHead(NodeTy *, NodeTy *) {}
>> + template <class U>
>> + static Yes &
>> + hasCreateSentinel(SFINAE<sizeof(make<U>().createSentinel())> * = 0);
>> + template <class U> static No &hasCreateSentinel(...);
>>
>> -private:
>> - mutable ilist_half_node<NodeTy> Sentinel;
>> + static const bool value =
>> + sizeof(hasCreateSentinel<TraitsT>(nullptr)) == sizeof(Yes);
>> };
>>
>> -/// Traits with an embedded full node as a sentinel.
>> -template <typename NodeTy> struct ilist_full_embedded_sentinel_traits {
>> - /// Get hold of the node that marks the end of the list.
>> - NodeTy *createSentinel() const { return &Sentinel; }
>> - static void destroySentinel(NodeTy *) {}
>> +} // end namespace ilist_detail
>>
>> - NodeTy *provideInitialHead() const { return createSentinel(); }
>> - NodeTy *ensureHead(NodeTy *) const { return createSentinel(); }
>> - static void noteHead(NodeTy *, NodeTy *) {}
>> +template <typename NodeTy> struct ilist_traits;
>>
>> -private:
>> - mutable NodeTy Sentinel;
>> -};
>> +// TODO: Delete these and their users.
>
> Probably worth finishing this sentence with "once all projects have
> stopped using them" or something like that.
Makes sense. Will do.
>> +template <typename NodeTy> struct ilist_sentinel_traits {};
>> +template <typename NodeTy> struct ilist_embedded_sentinel_traits {};
>> +template <typename NodeTy> struct ilist_half_embedded_sentinel_traits {};
>> +template <typename NodeTy> struct ilist_full_embedded_sentinel_traits {};
>>
>> /// ilist_node_traits - A fragment for template traits for intrusive list
>> /// that provides default node related operations.
>> @@ -219,8 +145,7 @@
>> /// for all common operations.
>> ///
>> template <typename NodeTy>
>> -struct ilist_default_traits : public ilist_sentinel_traits<NodeTy>,
>> - public ilist_node_traits<NodeTy> {};
>> +struct ilist_default_traits : public ilist_node_traits<NodeTy> {};
>>
>> // Template traits for intrusive list. By specializing this template class, you
>> // can change what next/prev fields are used to store the links...
>> @@ -263,38 +188,37 @@
>> typedef node_type &node_reference;
>>
>> private:
>> - pointer NodePtr;
>> + node_pointer NodePtr = nullptr;
>>
>> public:
>> /// Create from an ilist_node.
>> - explicit ilist_iterator(node_reference N)
>> - : NodePtr(static_cast<NodeTy *>(&N)) {}
>> + explicit ilist_iterator(node_reference N) : NodePtr(&N) {}
>>
>> explicit ilist_iterator(pointer NP) : NodePtr(NP) {}
>> explicit ilist_iterator(reference NR) : NodePtr(&NR) {}
>> - ilist_iterator() : NodePtr(nullptr) {}
>> + ilist_iterator() = default;
>>
>> // This is templated so that we can allow constructing a const iterator from
>> // a nonconst iterator...
>> template <class node_ty>
>> ilist_iterator(
>> const ilist_iterator<node_ty> &RHS,
>> typename std::enable_if<std::is_convertible<node_ty *, NodeTy *>::value,
>> void *>::type = nullptr)
>> - : NodePtr(RHS.getNodePtrUnchecked()) {}
>> + : NodePtr(RHS.getNodePtr()) {}
>>
>> // This is templated so that we can allow assigning to a const iterator from
>> // a nonconst iterator...
>> template <class node_ty>
>> const ilist_iterator &operator=(const ilist_iterator<node_ty> &RHS) {
>> - NodePtr = RHS.getNodePtrUnchecked();
>> + NodePtr = RHS.getNodePtr();
>> return *this;
>> }
>>
>> void reset(pointer NP) { NodePtr = NP; }
>>
>> // Accessors...
>> - reference operator*() const { return *NodePtr; }
>> + reference operator*() const { return static_cast<NodeTy &>(*getNodePtr()); }
>> pointer operator->() const { return &operator*(); }
>>
>> // Comparison operators
>> @@ -328,9 +252,6 @@
>>
>> /// Get the underlying ilist_node.
>> node_pointer getNodePtr() const { return static_cast<node_pointer>(NodePtr); }
>> -
>> - // Internal interface, do not use...
>> - pointer getNodePtrUnchecked() const { return NodePtr; }
>> };
>>
>> // Allow ilist_iterators to convert into pointers to a node automatically when
>> @@ -361,45 +282,23 @@
>> /// holds the next/prev pointers. The only state of the list itself is a single
>> /// pointer to the head of the list.
>> ///
>> -/// This list can be in one of three interesting states:
>> -/// 1. The list may be completely unconstructed. In this case, the head
>> -/// pointer is null. When in this form, any query for an iterator (e.g.
>> -/// begin() or end()) causes the list to transparently change to state #2.
>> -/// 2. The list may be empty, but contain a sentinel for the end iterator. This
>> -/// sentinel is created by the Traits::createSentinel method and is a link
>> -/// in the list. When the list is empty, the pointer in the iplist points
>> -/// to the sentinel. Once the sentinel is constructed, it
>> -/// is not destroyed until the list is.
>> -/// 3. The list may contain actual objects in it, which are stored as a doubly
>> -/// linked list of nodes. One invariant of the list is that the predecessor
>> -/// of the first node in the list always points to the last node in the list,
>> -/// and the successor pointer for the sentinel (which always stays at the
>> -/// end of the list) is always null.
>> -///
>> +/// This list has no particularly interesting states.
>
> While the diff is pretty amusing, I don't think we actually need to
> state this ;)
Right :).
>> template <typename NodeTy, typename Traits = ilist_traits<NodeTy>>
>> class iplist : public Traits, ilist_node_access {
>> + // TODO: Drop these assertions anytime after 4.1 is branched.
>> #if !defined(_MSC_VER)
>> // FIXME: This fails in MSVC, but it's worth keeping around to help
>> // non-Windows users root out bugs in their ilist_traits.
>> static_assert(!ilist_detail::HasGetNext<Traits, NodeTy>::value,
>> "ilist next and prev links are not customizable!");
>> + static_assert(!ilist_detail::HasCreateSentinel<Traits>::value,
>> + "ilist sentinel is not customizable!");
>> #endif
>>
>> - mutable NodeTy *Head;
>> + ilist_sentinel<NodeTy> Sentinel;
>>
>> - // Use the prev node pointer of 'head' as the tail pointer. This is really a
>> - // circularly linked list where we snip the 'next' link from the sentinel node
>> - // back to the first node in the list (to preserve assertions about going off
>> - // the end of the list).
>> - NodeTy *getTail() { return this->ensureHead(Head); }
>> - const NodeTy *getTail() const { return this->ensureHead(Head); }
>> - void setTail(NodeTy *N) const { this->noteHead(Head, N); }
>> -
>> - /// CreateLazySentinel - This method verifies whether the sentinel for the
>> - /// list has been created and lazily makes it if not.
>> - void CreateLazySentinel() const {
>> - this->ensureHead(Head);
>> - }
>> + typedef ilist_node<NodeTy> node_type;
>> + typedef const ilist_node<NodeTy> const_node_type;
>>
>> static bool op_less(NodeTy &L, NodeTy &R) { return L < R; }
>> static bool op_equal(NodeTy &L, NodeTy &R) { return L == R; }
>> @@ -422,30 +321,14 @@
>> typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
>> typedef std::reverse_iterator<iterator> reverse_iterator;
>>
>> - iplist() : Head(this->provideInitialHead()) {}
>> - ~iplist() {
>> - if (!Head) return;
>> - clear();
>> - Traits::destroySentinel(getTail());
>> - }
>> + iplist() = default;
>> + ~iplist() { clear(); }
>>
>> // Iterator creation methods.
>> - iterator begin() {
>> - CreateLazySentinel();
>> - return iterator(Head);
>> - }
>> - const_iterator begin() const {
>> - CreateLazySentinel();
>> - return const_iterator(Head);
>> - }
>> - iterator end() {
>> - CreateLazySentinel();
>> - return iterator(getTail());
>> - }
>> - const_iterator end() const {
>> - CreateLazySentinel();
>> - return const_iterator(getTail());
>> - }
>> + iterator begin() { return ++iterator(Sentinel); }
>> + const_iterator begin() const { return ++const_iterator(Sentinel); }
>> + iterator end() { return iterator(Sentinel); }
>> + const_iterator end() const { return const_iterator(Sentinel); }
>>
>> // reverse iterator creation methods.
>> reverse_iterator rbegin() { return reverse_iterator(end()); }
>> @@ -456,44 +339,39 @@
>>
>> // Miscellaneous inspection routines.
>> size_type max_size() const { return size_type(-1); }
>> - bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const {
>> - return !Head || Head == getTail();
>> - }
>> + bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const { return Sentinel.empty(); }
>>
>> // Front and back accessor functions...
>> reference front() {
>> assert(!empty() && "Called front() on empty list!");
>> - return *Head;
>> + return *begin();
>> }
>> const_reference front() const {
>> assert(!empty() && "Called front() on empty list!");
>> - return *Head;
>> + return *begin();
>> }
>> reference back() {
>> assert(!empty() && "Called back() on empty list!");
>> - return *this->getPrev(getTail());
>> + return *--end();
>> }
>> const_reference back() const {
>> assert(!empty() && "Called back() on empty list!");
>> - return *this->getPrev(getTail());
>> + return *--end();
>> }
>>
>> void swap(iplist &RHS) {
>> assert(0 && "Swap does not use list traits callback correctly yet!");
>> - std::swap(Head, RHS.Head);
>> + std::swap(Sentinel, RHS.Sentinel);
>> }
>>
>> iterator insert(iterator where, NodeTy *New) {
>> - NodeTy *CurNode = where.getNodePtrUnchecked();
>> - NodeTy *PrevNode = this->getPrev(CurNode);
>> - this->setNext(New, CurNode);
>> - this->setPrev(New, PrevNode);
>> -
>> - if (CurNode != Head) // Is PrevNode off the beginning of the list?
>> - this->setNext(PrevNode, New);
>> - else
>> - Head = New;
>> - this->setPrev(CurNode, New);
>> + node_type *NewN = this->getNodePtr(New);
>> + node_type *Next = where.getNodePtr();
>> + node_type *Prev = this->getPrev(Next);
>> + this->setNext(NewN, Next);
>> + this->setPrev(NewN, Prev);
>> + this->setNext(Prev, NewN);
>> + this->setPrev(Next, NewN);
>>
>> this->addNodeToList(New); // Notify traits that we added a node...
>> return iterator(New);
>> @@ -513,24 +391,22 @@
>> NodeTy *remove(iterator &IT) {
>> assert(IT != end() && "Cannot remove end of list!");
>> NodeTy *Node = &*IT;
>> - NodeTy *NextNode = this->getNext(Node);
>> - NodeTy *PrevNode = this->getPrev(Node);
>> + node_type *Base = this->getNodePtr(Node);
>> + node_type *Next = this->getNext(Base);
>> + node_type *Prev = this->getPrev(Base);
>>
>> - if (Node != Head) // Is PrevNode off the beginning of the list?
>> - this->setNext(PrevNode, NextNode);
>> - else
>> - Head = NextNode;
>> - this->setPrev(NextNode, PrevNode);
>> - IT.reset(NextNode);
>> + this->setNext(Prev, Next);
>> + this->setPrev(Next, Prev);
>> + IT = iterator(*Next);
>> this->removeNodeFromList(Node); // Notify traits that we removed a node...
>>
>> // Set the next/prev pointers of the current node to null. This isn't
>> // strictly required, but this catches errors where a node is removed from
>> // an ilist (and potentially deleted) with iterators still pointing at it.
>> // When those iterators are incremented or decremented, they will assert on
>> // the null next/prev pointer instead of "usually working".
>> - this->setNext(Node, nullptr);
>> - this->setPrev(Node, nullptr);
>> + this->setNext(Base, nullptr);
>> + this->setPrev(Base, nullptr);
>> return Node;
>> }
>>
>> @@ -556,62 +432,42 @@
>> ///
>> /// This should only be used immediately before freeing nodes in bulk to
>> /// avoid traversing the list and bringing all the nodes into cache.
>> - void clearAndLeakNodesUnsafely() {
>> - if (Head) {
>> - Head = getTail();
>> - this->setPrev(Head, Head);
>> - }
>> - }
>> + void clearAndLeakNodesUnsafely() { Sentinel.reset(); }
>>
>> private:
>> // transfer - The heart of the splice function. Move linked list nodes from
>> // [first, last) into position.
>> //
>> void transfer(iterator position, iplist &L2, iterator first, iterator last) {
>> assert(first != last && "Should be checked by callers");
>> // Position cannot be contained in the range to be transferred.
>> - // Check for the most common mistake.
>> assert(position != first &&
>> + // Check for the most common mistake.
>> "Insertion point can't be one of the transferred nodes");
>>
>> - if (position != last) {
>> - // Note: we have to be careful about the case when we move the first node
>> - // in the list. This node is the list sentinel node and we can't move it.
>> - NodeTy *ThisSentinel = getTail();
>> - setTail(nullptr);
>> - NodeTy *L2Sentinel = L2.getTail();
>> - L2.setTail(nullptr);
>> -
>> - // Remove [first, last) from its old position.
>> - NodeTy *First = &*first, *Prev = this->getPrev(First);
>> - NodeTy *Next = last.getNodePtrUnchecked(), *Last = this->getPrev(Next);
>> - if (Prev)
>> - this->setNext(Prev, Next);
>> - else
>> - L2.Head = Next;
>> - this->setPrev(Next, Prev);
>> -
>> - // Splice [first, last) into its new position.
>> - NodeTy *PosNext = position.getNodePtrUnchecked();
>> - NodeTy *PosPrev = this->getPrev(PosNext);
>> -
>> - // Fix head of list...
>> - if (PosPrev)
>> - this->setNext(PosPrev, First);
>> - else
>> - Head = First;
>> - this->setPrev(First, PosPrev);
>> -
>> - // Fix end of list...
>> - this->setNext(Last, PosNext);
>> - this->setPrev(PosNext, Last);
>> -
>> - this->transferNodesFromList(L2, iterator(First), iterator(PosNext));
>> -
>> - // Now that everything is set, restore the pointers to the list sentinels.
>> - L2.setTail(L2Sentinel);
>> - setTail(ThisSentinel);
>> - }
>> + if (position == last)
>> + return;
>> +
>> + // Get raw hooks to the first and final nodes being transferred.
>> + node_type *First = first.getNodePtr();
>> + node_type *Final = (--last).getNodePtr();
>> +
>> + // Detach from old list/position.
>> + node_type *Prev = this->getPrev(First);
>> + node_type *Next = this->getNext(Final);
>> + this->setNext(Prev, Next);
>> + this->setPrev(Next, Prev);
>> +
>> + // Splice [First, Final] into its new list/position.
>> + Next = position.getNodePtr();
>> + Prev = this->getPrev(Next);
>> + this->setNext(Final, Next);
>> + this->setPrev(First, Prev);
>> + this->setNext(Prev, First);
>> + this->setPrev(Next, Final);
>> +
>> + // Callback.
>> + this->transferNodesFromList(L2, iterator(*First), iterator(*Next));
>> }
>>
>> public:
>> @@ -621,7 +477,6 @@
>> //
>>
>> size_type LLVM_ATTRIBUTE_UNUSED_RESULT size() const {
>> - if (!Head) return 0; // Don't require construction of sentinel if empty.
>> return std::distance(begin(), end());
>> }
>>
>> @@ -631,7 +486,7 @@
>> return last;
>> }
>>
>> - void clear() { if (Head) erase(begin(), end()); }
>> + void clear() { erase(begin(), end()); }
>>
>> // Front and back inserters...
>> void push_front(NodeTy *val) { insert(begin(), val); }
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