Source/JavaScriptCore/runtime/InferredValue.h - WebKit - Git at Google

 /*
  * Copyright (C) 2015-2019 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #pragma once

 #include "JSScope.h"
 #include "VM.h"

 namespace JSC {

 template<typename JSCellType>
 class InferredValue {
     WTF_MAKE_NONCOPYABLE(InferredValue);
     WTF_MAKE_NONMOVABLE(InferredValue);
 public:
     // For the purpose of deciding whether or not to watch this variable, you only need
     // to inspect inferredValue(). If this returns something other than the empty
     // value, then it means that at all future safepoints, this watchpoint set will be
     // in one of these states:
     //
     //    IsWatched: in this case, the variable's value must still be the
     //        inferredValue.
     //
     //    IsInvalidated: in this case the variable's value may be anything but you'll
     //        either notice that it's invalidated and not install the watchpoint, or
     //        you will have been notified that the watchpoint was fired.
     JSCellType* inferredValue()
     {
         uintptr_t data = m_data;
         if (isFat(data))
             return fat(data)->inferredValue();
         return bitwise_cast<JSCellType*>(data & ValueMask);
     }

     explicit InferredValue()
         : m_data(encodeState(ClearWatchpoint))
     {
         ASSERT(inferredValue() == nullptr);
     }

     ~InferredValue()
     {
         if (isThin())
             return;
         freeFat();
     }

     // Fast way of getting the state, which only works from the main thread.
     WatchpointState stateOnJSThread() const
     {
         uintptr_t data = m_data;
         if (isFat(data))
             return fat(data)->stateOnJSThread();
         return decodeState(data);
     }

     // It is safe to call this from another thread. It may return a prior state,
     // but that should be fine since you should only perform actions based on the
     // state if you also add a watchpoint.
     WatchpointState state() const
     {
         WTF::loadLoadFence();
         uintptr_t data = m_data;
         WTF::loadLoadFence();
         if (isFat(data))
             return fat(data)->state();
         return decodeState(data);
     }

     // It is safe to call this from another thread. It may return false
     // even if the set actually had been invalidated, but that ought to happen
     // only in the case of races, and should be rare.
     bool hasBeenInvalidated() const
     {
         return state() == IsInvalidated;
     }

     // Like hasBeenInvalidated(), may be called from another thread.
     bool isStillValid() const
     {
         return !hasBeenInvalidated();
     }

     void add(Watchpoint*);

     void invalidate(VM& vm, const FireDetail& detail)
     {
         if (isFat())
             fat()->invalidate(vm, detail);
         else
             m_data = encodeState(IsInvalidated);
     }

     bool isBeingWatched() const
     {
         if (isFat())
             return fat()->isBeingWatched();
         return false;
     }

     void notifyWrite(VM& vm, JSCell* owner, JSCellType* value, const FireDetail& detail)
     {
         if (LIKELY(stateOnJSThread() == IsInvalidated))
             return;
         notifyWriteSlow(vm, owner, value, detail);
     }

     void notifyWrite(VM& vm, JSCell* owner, JSCellType* value, const char* reason)
     {
         if (LIKELY(stateOnJSThread() == IsInvalidated))
             return;
         notifyWriteSlow(vm, owner, value, reason);
     }

     void finalizeUnconditionally(VM&);

 private:
     class InferredValueWatchpointSet final : public WatchpointSet {
     public:
         InferredValueWatchpointSet(WatchpointState state, JSCellType* value)
             : WatchpointSet(state)
             , m_value(value)
         {
         }

         JSCellType* inferredValue() const { return m_value; }

         void invalidate(VM& vm, const FireDetail& detail)
         {
             m_value = nullptr;
             WatchpointSet::invalidate(vm, detail);
         }

         void notifyWriteSlow(VM&, JSCell* owner, JSCellType*, const FireDetail&);

     private:
         JSCellType* m_value;
     };

     static constexpr uintptr_t IsThinFlag        = 1;
     static constexpr uintptr_t StateMask         = 6;
     static constexpr uintptr_t StateShift        = 1;
     static constexpr uintptr_t ValueMask         = ~static_cast<uintptr_t>(IsThinFlag | StateMask);

     static bool isThin(uintptr_t data) { return data & IsThinFlag; }
     static bool isFat(uintptr_t data) { return !isThin(data); }

     static WatchpointState decodeState(uintptr_t data)
     {
         ASSERT(isThin(data));
         return static_cast<WatchpointState>((data & StateMask) >> StateShift);
     }

     static uintptr_t encodeState(WatchpointState state)
     {
         return (static_cast<uintptr_t>(state) << StateShift) | IsThinFlag;
     }

     bool isThin() const { return isThin(m_data); }
     bool isFat() const { return isFat(m_data); };

     static InferredValueWatchpointSet* fat(uintptr_t data)
     {
         return bitwise_cast<InferredValueWatchpointSet*>(data);
     }

     InferredValueWatchpointSet* fat()
     {
         ASSERT(isFat());
         return fat(m_data);
     }

     const InferredValueWatchpointSet* fat() const
     {
         ASSERT(isFat());
         return fat(m_data);
     }

     InferredValueWatchpointSet* inflate()
     {
         if (LIKELY(isFat()))
             return fat();
         return inflateSlow();
     }

     InferredValueWatchpointSet* inflateSlow();
     void freeFat();

     void notifyWriteSlow(VM&, JSCell* owner, JSCellType*, const FireDetail&);
     void notifyWriteSlow(VM&, JSCell* owner, JSCellType*, const char* reason);

     uintptr_t m_data;
 };

 template<typename JSCellType>
 void InferredValue<JSCellType>::InferredValueWatchpointSet::notifyWriteSlow(VM& vm, JSCell* owner, JSCellType* value, const FireDetail& detail)
 {
     switch (state()) {
     case ClearWatchpoint:
         m_value = value;
         vm.heap.writeBarrier(owner, value);
         startWatching();
         return;

     case IsWatched:
         ASSERT(!!m_value);
         if (m_value == value)
             return;
         invalidate(vm, detail);
         return;

     case IsInvalidated:
         ASSERT_NOT_REACHED();
         return;
     }

     ASSERT_NOT_REACHED();
 }

 template<typename JSCellType>
 void InferredValue<JSCellType>::notifyWriteSlow(VM& vm, JSCell* owner, JSCellType* value, const FireDetail& detail)
 {
     uintptr_t data = m_data;
     if (isFat(data)) {
         fat(data)->notifyWriteSlow(vm, owner, value, detail);
         return;
     }

     switch (state()) {
     case ClearWatchpoint:
         ASSERT(decodeState(m_data) != IsInvalidated);
         m_data = (bitwise_cast<uintptr_t>(value) & ValueMask) | encodeState(IsWatched);
         vm.heap.writeBarrier(owner, value);
         return;

     case IsWatched:
         ASSERT(!!inferredValue());
         if (inferredValue() == value)
             return;
         invalidate(vm, detail);
         return;

     case IsInvalidated:
         ASSERT_NOT_REACHED();
         return;
     }

     ASSERT_NOT_REACHED();
 }

 template<typename JSCellType>
 void InferredValue<JSCellType>::notifyWriteSlow(VM& vm, JSCell* owner, JSCellType* value, const char* reason)
 {
     notifyWriteSlow(vm, owner, value, StringFireDetail(reason));
 }

 template<typename JSCellType>
 void InferredValue<JSCellType>::add(Watchpoint* watchpoint)
 {
     inflate()->add(watchpoint);
 }

 template<typename JSCellType>
 auto InferredValue<JSCellType>::inflateSlow() -> InferredValueWatchpointSet*
 {
     ASSERT(isThin());
     ASSERT(!isCompilationThread());
     uintptr_t data = m_data;
     InferredValueWatchpointSet* fat = adoptRef(new InferredValueWatchpointSet(decodeState(m_data), bitwise_cast<JSCellType*>(data & ValueMask))).leakRef();
     WTF::storeStoreFence();
     m_data = bitwise_cast<uintptr_t>(fat);
     return fat;
 }

 template<typename JSCellType>
 void InferredValue<JSCellType>::freeFat()
 {
     ASSERT(isFat());
     fat()->deref();
 }

 } // namespace JSC
	/*
	* Copyright (C) 2015-2019 Apple Inc. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
	* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
	* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
	* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
	* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
	* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#pragma once

	#include "JSScope.h"
	#include "VM.h"

	namespace JSC {

	template<typename JSCellType>
	class InferredValue {
	WTF_MAKE_NONCOPYABLE(InferredValue);
	WTF_MAKE_NONMOVABLE(InferredValue);
	public:
	// For the purpose of deciding whether or not to watch this variable, you only need
	// to inspect inferredValue(). If this returns something other than the empty
	// value, then it means that at all future safepoints, this watchpoint set will be
	// in one of these states:
	//
	// IsWatched: in this case, the variable's value must still be the
	// inferredValue.
	//
	// IsInvalidated: in this case the variable's value may be anything but you'll
	// either notice that it's invalidated and not install the watchpoint, or
	// you will have been notified that the watchpoint was fired.
	JSCellType* inferredValue()
	{
	uintptr_t data = m_data;
	if (isFat(data))
	return fat(data)->inferredValue();
	return bitwise_cast<JSCellType*>(data & ValueMask);
	}

	explicit InferredValue()
	: m_data(encodeState(ClearWatchpoint))
	{
	ASSERT(inferredValue() == nullptr);
	}

	~InferredValue()
	{
	if (isThin())
	return;
	freeFat();
	}

	// Fast way of getting the state, which only works from the main thread.
	WatchpointState stateOnJSThread() const
	{
	uintptr_t data = m_data;
	if (isFat(data))
	return fat(data)->stateOnJSThread();
	return decodeState(data);
	}

	// It is safe to call this from another thread. It may return a prior state,
	// but that should be fine since you should only perform actions based on the
	// state if you also add a watchpoint.
	WatchpointState state() const
	{
	WTF::loadLoadFence();
	uintptr_t data = m_data;
	WTF::loadLoadFence();
	if (isFat(data))
	return fat(data)->state();
	return decodeState(data);
	}

	// It is safe to call this from another thread. It may return false
	// even if the set actually had been invalidated, but that ought to happen
	// only in the case of races, and should be rare.
	bool hasBeenInvalidated() const
	{
	return state() == IsInvalidated;
	}

	// Like hasBeenInvalidated(), may be called from another thread.
	bool isStillValid() const
	{
	return !hasBeenInvalidated();
	}

	void add(Watchpoint*);

	void invalidate(VM& vm, const FireDetail& detail)
	{
	if (isFat())
	fat()->invalidate(vm, detail);
	else
	m_data = encodeState(IsInvalidated);
	}

	bool isBeingWatched() const
	{
	if (isFat())
	return fat()->isBeingWatched();
	return false;
	}

	void notifyWrite(VM& vm, JSCell* owner, JSCellType* value, const FireDetail& detail)
	{
	if (LIKELY(stateOnJSThread() == IsInvalidated))
	return;
	notifyWriteSlow(vm, owner, value, detail);
	}

	void notifyWrite(VM& vm, JSCell* owner, JSCellType* value, const char* reason)
	{
	if (LIKELY(stateOnJSThread() == IsInvalidated))
	return;
	notifyWriteSlow(vm, owner, value, reason);
	}

	void finalizeUnconditionally(VM&);

	private:
	class InferredValueWatchpointSet final : public WatchpointSet {
	public:
	InferredValueWatchpointSet(WatchpointState state, JSCellType* value)
	: WatchpointSet(state)
	, m_value(value)
	{
	}

	JSCellType* inferredValue() const { return m_value; }

	void invalidate(VM& vm, const FireDetail& detail)
	{
	m_value = nullptr;
	WatchpointSet::invalidate(vm, detail);
	}

	void notifyWriteSlow(VM&, JSCell* owner, JSCellType*, const FireDetail&);

	private:
	JSCellType* m_value;
	};

	static constexpr uintptr_t IsThinFlag = 1;
	static constexpr uintptr_t StateMask = 6;
	static constexpr uintptr_t StateShift = 1;
	static constexpr uintptr_t ValueMask = ~static_cast<uintptr_t>(IsThinFlag \| StateMask);

	static bool isThin(uintptr_t data) { return data & IsThinFlag; }
	static bool isFat(uintptr_t data) { return !isThin(data); }

	static WatchpointState decodeState(uintptr_t data)
	{
	ASSERT(isThin(data));
	return static_cast<WatchpointState>((data & StateMask) >> StateShift);
	}

	static uintptr_t encodeState(WatchpointState state)
	{
	return (static_cast<uintptr_t>(state) << StateShift) \| IsThinFlag;
	}

	bool isThin() const { return isThin(m_data); }
	bool isFat() const { return isFat(m_data); };

	static InferredValueWatchpointSet* fat(uintptr_t data)
	{
	return bitwise_cast<InferredValueWatchpointSet*>(data);
	}

	InferredValueWatchpointSet* fat()
	{
	ASSERT(isFat());
	return fat(m_data);
	}

	const InferredValueWatchpointSet* fat() const
	{
	ASSERT(isFat());
	return fat(m_data);
	}

	InferredValueWatchpointSet* inflate()
	{
	if (LIKELY(isFat()))
	return fat();
	return inflateSlow();
	}

	InferredValueWatchpointSet* inflateSlow();
	void freeFat();

	void notifyWriteSlow(VM&, JSCell* owner, JSCellType*, const FireDetail&);
	void notifyWriteSlow(VM&, JSCell* owner, JSCellType, const char reason);

	uintptr_t m_data;
	};

	template<typename JSCellType>
	void InferredValue<JSCellType>::InferredValueWatchpointSet::notifyWriteSlow(VM& vm, JSCell* owner, JSCellType* value, const FireDetail& detail)
	{
	switch (state()) {
	case ClearWatchpoint:
	m_value = value;
	vm.heap.writeBarrier(owner, value);
	startWatching();
	return;

	case IsWatched:
	ASSERT(!!m_value);
	if (m_value == value)
	return;
	invalidate(vm, detail);
	return;

	case IsInvalidated:
	ASSERT_NOT_REACHED();
	return;
	}

	ASSERT_NOT_REACHED();
	}

	template<typename JSCellType>
	void InferredValue<JSCellType>::notifyWriteSlow(VM& vm, JSCell* owner, JSCellType* value, const FireDetail& detail)
	{
	uintptr_t data = m_data;
	if (isFat(data)) {
	fat(data)->notifyWriteSlow(vm, owner, value, detail);
	return;
	}

	switch (state()) {
	case ClearWatchpoint:
	ASSERT(decodeState(m_data) != IsInvalidated);
	m_data = (bitwise_cast<uintptr_t>(value) & ValueMask) \| encodeState(IsWatched);
	vm.heap.writeBarrier(owner, value);
	return;

	case IsWatched:
	ASSERT(!!inferredValue());
	if (inferredValue() == value)
	return;
	invalidate(vm, detail);
	return;

	case IsInvalidated:
	ASSERT_NOT_REACHED();
	return;
	}

	ASSERT_NOT_REACHED();
	}

	template<typename JSCellType>
	void InferredValue<JSCellType>::notifyWriteSlow(VM& vm, JSCell* owner, JSCellType* value, const char* reason)
	{
	notifyWriteSlow(vm, owner, value, StringFireDetail(reason));
	}

	template<typename JSCellType>
	void InferredValue<JSCellType>::add(Watchpoint* watchpoint)
	{
	inflate()->add(watchpoint);
	}

	template<typename JSCellType>
	auto InferredValue<JSCellType>::inflateSlow() -> InferredValueWatchpointSet*
	{
	ASSERT(isThin());
	ASSERT(!isCompilationThread());
	uintptr_t data = m_data;
	InferredValueWatchpointSet* fat = adoptRef(new InferredValueWatchpointSet(decodeState(m_data), bitwise_cast<JSCellType*>(data & ValueMask))).leakRef();
	WTF::storeStoreFence();
	m_data = bitwise_cast<uintptr_t>(fat);
	return fat;
	}

	template<typename JSCellType>
	void InferredValue<JSCellType>::freeFat()
	{
	ASSERT(isFat());
	fat()->deref();
	}

	} // namespace JSC