309 lines
9.2 KiB
C
309 lines
9.2 KiB
C
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//==- llvm/ADT/IntrusiveRefCntPtr.h - Smart Refcounting Pointer --*- C++ -*-==//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the RefCountedBase, ThreadSafeRefCountedBase, and
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// IntrusiveRefCntPtr classes.
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//
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// IntrusiveRefCntPtr is a smart pointer to an object which maintains a
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// reference count. (ThreadSafe)RefCountedBase is a mixin class that adds a
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// refcount member variable and methods for updating the refcount. An object
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// that inherits from (ThreadSafe)RefCountedBase deletes itself when its
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// refcount hits zero.
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//
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// For example:
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//
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// class MyClass : public RefCountedBase<MyClass> {};
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//
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// void foo() {
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// // Constructing an IntrusiveRefCntPtr increases the pointee's refcount by
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// // 1 (from 0 in this case).
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// IntrusiveRefCntPtr<MyClass> Ptr1(new MyClass());
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//
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// // Copying an IntrusiveRefCntPtr increases the pointee's refcount by 1.
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// IntrusiveRefCntPtr<MyClass> Ptr2(Ptr1);
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//
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// // Constructing an IntrusiveRefCntPtr has no effect on the object's
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// // refcount. After a move, the moved-from pointer is null.
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// IntrusiveRefCntPtr<MyClass> Ptr3(std::move(Ptr1));
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// assert(Ptr1 == nullptr);
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//
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// // Clearing an IntrusiveRefCntPtr decreases the pointee's refcount by 1.
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// Ptr2.reset();
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//
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// // The object deletes itself when we return from the function, because
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// // Ptr3's destructor decrements its refcount to 0.
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// }
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//
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// You can use IntrusiveRefCntPtr with isa<T>(), dyn_cast<T>(), etc.:
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//
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// IntrusiveRefCntPtr<MyClass> Ptr(new MyClass());
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// OtherClass *Other = dyn_cast<OtherClass>(Ptr); // Ptr.get() not required
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//
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// IntrusiveRefCntPtr works with any class that
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//
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// - inherits from (ThreadSafe)RefCountedBase,
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// - has Retain() and Release() methods, or
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// - specializes IntrusiveRefCntPtrInfo.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ADT_INTRUSIVEREFCNTPTR_H
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#define LLVM_ADT_INTRUSIVEREFCNTPTR_H
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#include <atomic>
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#include <cassert>
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#include <cstddef>
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#include <memory>
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namespace llvm {
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/// A CRTP mixin class that adds reference counting to a type.
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///
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/// The lifetime of an object which inherits from RefCountedBase is managed by
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/// calls to Release() and Retain(), which increment and decrement the object's
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/// refcount, respectively. When a Release() call decrements the refcount to 0,
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/// the object deletes itself.
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template <class Derived> class RefCountedBase {
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mutable unsigned RefCount = 0;
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protected:
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RefCountedBase() = default;
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RefCountedBase(const RefCountedBase &) {}
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RefCountedBase &operator=(const RefCountedBase &) = delete;
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#ifndef NDEBUG
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~RefCountedBase() {
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assert(RefCount == 0 &&
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"Destruction occured when there are still references to this.");
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}
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#else
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// Default the destructor in release builds, A trivial destructor may enable
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// better codegen.
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~RefCountedBase() = default;
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#endif
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public:
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void Retain() const { ++RefCount; }
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void Release() const {
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assert(RefCount > 0 && "Reference count is already zero.");
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if (--RefCount == 0)
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delete static_cast<const Derived *>(this);
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}
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};
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/// A thread-safe version of \c RefCountedBase.
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template <class Derived> class ThreadSafeRefCountedBase {
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mutable std::atomic<int> RefCount{0};
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protected:
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ThreadSafeRefCountedBase() = default;
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ThreadSafeRefCountedBase(const ThreadSafeRefCountedBase &) {}
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ThreadSafeRefCountedBase &
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operator=(const ThreadSafeRefCountedBase &) = delete;
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#ifndef NDEBUG
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~ThreadSafeRefCountedBase() {
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assert(RefCount == 0 &&
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"Destruction occured when there are still references to this.");
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}
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#else
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// Default the destructor in release builds, A trivial destructor may enable
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// better codegen.
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~ThreadSafeRefCountedBase() = default;
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#endif
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public:
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void Retain() const { RefCount.fetch_add(1, std::memory_order_relaxed); }
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void Release() const {
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int NewRefCount = RefCount.fetch_sub(1, std::memory_order_acq_rel) - 1;
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assert(NewRefCount >= 0 && "Reference count was already zero.");
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if (NewRefCount == 0)
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delete static_cast<const Derived *>(this);
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}
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};
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/// Class you can specialize to provide custom retain/release functionality for
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/// a type.
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///
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/// Usually specializing this class is not necessary, as IntrusiveRefCntPtr
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/// works with any type which defines Retain() and Release() functions -- you
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/// can define those functions yourself if RefCountedBase doesn't work for you.
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///
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/// One case when you might want to specialize this type is if you have
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/// - Foo.h defines type Foo and includes Bar.h, and
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/// - Bar.h uses IntrusiveRefCntPtr<Foo> in inline functions.
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///
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/// Because Foo.h includes Bar.h, Bar.h can't include Foo.h in order to pull in
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/// the declaration of Foo. Without the declaration of Foo, normally Bar.h
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/// wouldn't be able to use IntrusiveRefCntPtr<Foo>, which wants to call
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/// T::Retain and T::Release.
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///
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/// To resolve this, Bar.h could include a third header, FooFwd.h, which
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/// forward-declares Foo and specializes IntrusiveRefCntPtrInfo<Foo>. Then
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/// Bar.h could use IntrusiveRefCntPtr<Foo>, although it still couldn't call any
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/// functions on Foo itself, because Foo would be an incomplete type.
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template <typename T> struct IntrusiveRefCntPtrInfo {
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static void retain(T *obj) { obj->Retain(); }
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static void release(T *obj) { obj->Release(); }
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};
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/// A smart pointer to a reference-counted object that inherits from
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/// RefCountedBase or ThreadSafeRefCountedBase.
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///
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/// This class increments its pointee's reference count when it is created, and
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/// decrements its refcount when it's destroyed (or is changed to point to a
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/// different object).
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template <typename T> class IntrusiveRefCntPtr {
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T *Obj = nullptr;
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public:
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using element_type = T;
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explicit IntrusiveRefCntPtr() = default;
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IntrusiveRefCntPtr(T *obj) : Obj(obj) { retain(); }
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IntrusiveRefCntPtr(const IntrusiveRefCntPtr &S) : Obj(S.Obj) { retain(); }
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IntrusiveRefCntPtr(IntrusiveRefCntPtr &&S) : Obj(S.Obj) { S.Obj = nullptr; }
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template <class X>
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IntrusiveRefCntPtr(IntrusiveRefCntPtr<X> &&S) : Obj(S.get()) {
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S.Obj = nullptr;
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}
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template <class X>
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IntrusiveRefCntPtr(std::unique_ptr<X> S) : Obj(S.release()) {
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retain();
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}
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template <class X>
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IntrusiveRefCntPtr(const IntrusiveRefCntPtr<X> &S) : Obj(S.get()) {
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retain();
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}
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~IntrusiveRefCntPtr() { release(); }
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IntrusiveRefCntPtr &operator=(IntrusiveRefCntPtr S) {
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swap(S);
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return *this;
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}
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T &operator*() const { return *Obj; }
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T *operator->() const { return Obj; }
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T *get() const { return Obj; }
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explicit operator bool() const { return Obj; }
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void swap(IntrusiveRefCntPtr &other) {
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T *tmp = other.Obj;
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other.Obj = Obj;
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Obj = tmp;
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}
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void reset() {
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release();
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Obj = nullptr;
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}
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void resetWithoutRelease() { Obj = nullptr; }
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private:
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void retain() {
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if (Obj)
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IntrusiveRefCntPtrInfo<T>::retain(Obj);
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}
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void release() {
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if (Obj)
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IntrusiveRefCntPtrInfo<T>::release(Obj);
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}
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template <typename X> friend class IntrusiveRefCntPtr;
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};
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template <class T, class U>
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inline bool operator==(const IntrusiveRefCntPtr<T> &A,
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const IntrusiveRefCntPtr<U> &B) {
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return A.get() == B.get();
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}
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template <class T, class U>
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inline bool operator!=(const IntrusiveRefCntPtr<T> &A,
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const IntrusiveRefCntPtr<U> &B) {
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return A.get() != B.get();
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}
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template <class T, class U>
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inline bool operator==(const IntrusiveRefCntPtr<T> &A, U *B) {
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return A.get() == B;
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}
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template <class T, class U>
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inline bool operator!=(const IntrusiveRefCntPtr<T> &A, U *B) {
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return A.get() != B;
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}
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template <class T, class U>
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inline bool operator==(T *A, const IntrusiveRefCntPtr<U> &B) {
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return A == B.get();
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}
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template <class T, class U>
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inline bool operator!=(T *A, const IntrusiveRefCntPtr<U> &B) {
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return A != B.get();
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}
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template <class T>
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bool operator==(std::nullptr_t A, const IntrusiveRefCntPtr<T> &B) {
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return !B;
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}
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template <class T>
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bool operator==(const IntrusiveRefCntPtr<T> &A, std::nullptr_t B) {
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return B == A;
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}
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template <class T>
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bool operator!=(std::nullptr_t A, const IntrusiveRefCntPtr<T> &B) {
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return !(A == B);
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}
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template <class T>
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bool operator!=(const IntrusiveRefCntPtr<T> &A, std::nullptr_t B) {
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return !(A == B);
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}
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// Make IntrusiveRefCntPtr work with dyn_cast, isa, and the other idioms from
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// Casting.h.
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template <typename From> struct simplify_type;
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template <class T> struct simplify_type<IntrusiveRefCntPtr<T>> {
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using SimpleType = T *;
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static SimpleType getSimplifiedValue(IntrusiveRefCntPtr<T> &Val) {
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return Val.get();
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}
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};
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template <class T> struct simplify_type<const IntrusiveRefCntPtr<T>> {
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using SimpleType = /*const*/ T *;
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static SimpleType getSimplifiedValue(const IntrusiveRefCntPtr<T> &Val) {
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return Val.get();
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}
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};
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/// Factory function for creating intrusive ref counted pointers.
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template <typename T, typename... Args>
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IntrusiveRefCntPtr<T> makeIntrusiveRefCnt(Args &&...A) {
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return IntrusiveRefCntPtr<T>(new T(std::forward<Args>(A)...));
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}
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} // end namespace llvm
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#endif // LLVM_ADT_INTRUSIVEREFCNTPTR_H
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