Source/JavaScriptCore/dfg/DFGAbstractValue.h - third_party/webkit - Git at Google

 /*
  * Copyright (C) 2011-2016 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.
  */

 #ifndef DFGAbstractValue_h
 #define DFGAbstractValue_h

 #if ENABLE(DFG_JIT)

 #include "ArrayProfile.h"
 #include "DFGFiltrationResult.h"
 #include "DFGFrozenValue.h"
 #include "DFGNodeFlags.h"
 #include "DFGStructureAbstractValue.h"
 #include "DFGStructureClobberState.h"
 #include "InferredType.h"
 #include "JSCell.h"
 #include "ResultType.h"
 #include "SpeculatedType.h"
 #include "DumpContext.h"
 #include "StructureSet.h"

 namespace JSC {

 class TrackedReferences;

 namespace DFG {

 class Graph;
 struct Node;

 struct AbstractValue {
     AbstractValue()
         : m_type(SpecNone)
         , m_arrayModes(0)
     {
 #if USE(JSVALUE64) && !defined(NDEBUG)
         // The WTF Traits for AbstractValue allow the initialization of values with bzero().
         // We verify the correctness of this assumption here.
         static bool needsDefaultConstructorCheck = true;
         if (needsDefaultConstructorCheck) {
             needsDefaultConstructorCheck = false;
             ensureCanInitializeWithZeros();
         }
 #endif
     }

     void clear()
     {
         m_type = SpecNone;
         m_arrayModes = 0;
         m_structure.clear();
         m_value = JSValue();
         checkConsistency();
     }

     bool isClear() const { return m_type == SpecNone; }
     bool operator!() const { return isClear(); }

     void makeHeapTop()
     {
         makeTop(SpecHeapTop);
     }

     void makeBytecodeTop()
     {
         makeTop(SpecBytecodeTop);
     }

     void makeFullTop()
     {
         makeTop(SpecFullTop);
     }

     void clobberStructures()
     {
         if (m_type & SpecCell) {
             m_structure.clobber();
             clobberArrayModes();
         } else {
             ASSERT(m_structure.isClear());
             ASSERT(!m_arrayModes);
         }
         checkConsistency();
     }

     static void clobberStructuresFor(AbstractValue& value)
     {
         value.clobberStructures();
     }

     void observeInvalidationPoint()
     {
         m_structure.observeInvalidationPoint();
         checkConsistency();
     }

     static void observeInvalidationPointFor(AbstractValue& value)
     {
         value.observeInvalidationPoint();
     }

     void observeTransition(Structure* from, Structure* to)
     {
         if (m_type & SpecCell) {
             m_structure.observeTransition(from, to);
             observeIndexingTypeTransition(from->indexingType(), to->indexingType());
         }
         checkConsistency();
     }

     void observeTransitions(const TransitionVector& vector);

     class TransitionObserver {
     public:
         TransitionObserver(Structure* from, Structure* to)
             : m_from(from)
             , m_to(to)
         {
         }

         void operator()(AbstractValue& value)
         {
             value.observeTransition(m_from, m_to);
         }
     private:
         Structure* m_from;
         Structure* m_to;
     };

     class TransitionsObserver {
     public:
         TransitionsObserver(const TransitionVector& vector)
             : m_vector(vector)
         {
         }

         void operator()(AbstractValue& value)
         {
             value.observeTransitions(m_vector);
         }
     private:
         const TransitionVector& m_vector;
     };

     void clobberValue()
     {
         m_value = JSValue();
     }

     bool isHeapTop() const
     {
         return (m_type | SpecHeapTop) == m_type
             && m_structure.isTop()
             && m_arrayModes == ALL_ARRAY_MODES
             && !m_value;
     }

     bool valueIsTop() const
     {
         return !m_value && m_type;
     }

     JSValue value() const
     {
         return m_value;
     }

     static AbstractValue heapTop()
     {
         AbstractValue result;
         result.makeHeapTop();
         return result;
     }

     static AbstractValue bytecodeTop()
     {
         AbstractValue result;
         result.makeBytecodeTop();
         return result;
     }

     static AbstractValue fullTop()
     {
         AbstractValue result;
         result.makeFullTop();
         return result;
     }

     void set(Graph&, const FrozenValue&, StructureClobberState);
     void set(Graph&, Structure*);
     void set(Graph&, const StructureSet&);

     // Set this value to represent the given set of types as precisely as possible.
     void setType(Graph&, SpeculatedType);

     // As above, but only valid for non-cell types.
     void setType(SpeculatedType type)
     {
         RELEASE_ASSERT(!(type & SpecCell));
         m_structure.clear();
         m_arrayModes = 0;
         m_type = type;
         m_value = JSValue();
         checkConsistency();
     }

     void set(Graph&, const InferredType::Descriptor&);
     void set(Graph&, const InferredType::Descriptor&, StructureClobberState);

     void fixTypeForRepresentation(Graph&, NodeFlags representation, Node* = nullptr);
     void fixTypeForRepresentation(Graph&, Node*);

     bool operator==(const AbstractValue& other) const
     {
         return m_type == other.m_type
             && m_arrayModes == other.m_arrayModes
             && m_structure == other.m_structure
             && m_value == other.m_value;
     }
     bool operator!=(const AbstractValue& other) const
     {
         return !(*this == other);
     }

     bool merge(const AbstractValue& other)
     {
         if (other.isClear())
             return false;

 #if !ASSERT_DISABLED
         AbstractValue oldMe = *this;
 #endif
         bool result = false;
         if (isClear()) {
             *this = other;
             result = !other.isClear();
         } else {
             result |= mergeSpeculation(m_type, other.m_type);
             result |= mergeArrayModes(m_arrayModes, other.m_arrayModes);
             result |= m_structure.merge(other.m_structure);
             if (m_value != other.m_value) {
                 result |= !!m_value;
                 m_value = JSValue();
             }
         }
         checkConsistency();
         ASSERT(result == (*this != oldMe));
         return result;
     }

     bool mergeOSREntryValue(Graph&, JSValue);

     void merge(SpeculatedType type)
     {
         mergeSpeculation(m_type, type);

         if (type & SpecCell) {
             m_structure.makeTop();
             m_arrayModes = ALL_ARRAY_MODES;
         }
         m_value = JSValue();

         checkConsistency();
     }

     bool couldBeType(SpeculatedType desiredType) const
     {
         return !!(m_type & desiredType);
     }

     bool isType(SpeculatedType desiredType) const
     {
         return !(m_type & ~desiredType);
     }

     bool isType(Graph&, const InferredType::Descriptor&) const;

     // Filters the value using the given structure set. If the admittedTypes argument is not passed, this
     // implicitly filters by the types implied by the structure set, which are usually a subset of
     // SpecCell. Hence, after this call, the value will no longer have any non-cell members. But, you can
     // use admittedTypes to preserve some non-cell types. Note that it's wrong for admittedTypes to overlap
     // with SpecCell.
     FiltrationResult filter(Graph&, const StructureSet&, SpeculatedType admittedTypes = SpecNone);

     FiltrationResult filterArrayModes(ArrayModes);
     FiltrationResult filter(SpeculatedType);
     FiltrationResult filterByValue(const FrozenValue& value);
     FiltrationResult filter(const AbstractValue&);

     FiltrationResult filter(Graph&, const InferredType::Descriptor&);

     FiltrationResult changeStructure(Graph&, const StructureSet&);

     bool contains(Structure*) const;

     bool validate(JSValue value) const
     {
         if (isHeapTop())
             return true;

         if (!!m_value && m_value != value)
             return false;

         if (mergeSpeculations(m_type, speculationFromValue(value)) != m_type)
             return false;

         if (value.isEmpty()) {
             ASSERT(m_type & SpecEmpty);
             return true;
         }

         if (!!value && value.isCell()) {
             ASSERT(m_type & SpecCell);
             Structure* structure = value.asCell()->structure();
             return m_structure.contains(structure)
                 && (m_arrayModes & asArrayModes(structure->indexingType()));
         }

         return true;
     }

     bool hasClobberableState() const
     {
         return m_structure.isNeitherClearNorTop()
             || !arrayModesAreClearOrTop(m_arrayModes);
     }

 #if ASSERT_DISABLED
     void checkConsistency() const { }
     void assertIsRegistered(Graph&) const { }
 #else
     void checkConsistency() const;
     void assertIsRegistered(Graph&) const;
 #endif

     ResultType resultType() const;

     void dumpInContext(PrintStream&, DumpContext*) const;
     void dump(PrintStream&) const;

     void validateReferences(const TrackedReferences&);

     // This is a proven constraint on the structures that this value can have right
     // now. The structure of the current value must belong to this set. The set may
     // be TOP, indicating that it is the set of all possible structures, in which
     // case the current value can have any structure. The set may be BOTTOM (empty)
     // in which case this value cannot be a cell. This is all subject to change
     // anytime a new value is assigned to this one, anytime there is a control flow
     // merge, or most crucially, anytime a side-effect or structure check happens.
     // In case of a side-effect, we must assume that any value with a structure that
     // isn't being watched may have had its structure changed, hence contravening
     // our proof. In such a case we make the proof valid again by switching this to
     // TOP (i.e. claiming that we have proved that this value may have any
     // structure).
     StructureAbstractValue m_structure;

     // This is a proven constraint on the possible types that this value can have
     // now or any time in the future, unless it is reassigned. This field is
     // impervious to side-effects. The relationship between this field, and the
     // structure fields above, is as follows. The fields above constraint the
     // structures that a cell may have, but they say nothing about whether or not
     // the value is known to be a cell. More formally, the m_structure is itself an
     // abstract value that consists of the union of the set of all non-cell values
     // and the set of cell values that have the given structure. This abstract
     // value is then the intersection of the m_structure and the set of values
     // whose type is m_type. So, for example if m_type is SpecFinal|SpecInt32Only and
     // m_structure is [0x12345] then this abstract value corresponds to the set of
     // all integers unified with the set of all objects with structure 0x12345.
     SpeculatedType m_type;

     // This is a proven constraint on the possible indexing types that this value
     // can have right now. It also implicitly constraints the set of structures
     // that the value may have right now, since a structure has an immutable
     // indexing type. This is subject to change upon reassignment, or any side
     // effect that makes non-obvious changes to the heap.
     ArrayModes m_arrayModes;

     // This is a proven constraint on the possible values that this value can
     // have now or any time in the future, unless it is reassigned. Note that this
     // implies nothing about the structure. Oddly, JSValue() (i.e. the empty value)
     // means either BOTTOM or TOP depending on the state of m_type: if m_type is
     // BOTTOM then JSValue() means BOTTOM; if m_type is not BOTTOM then JSValue()
     // means TOP. Also note that this value isn't necessarily known to the GC
     // (strongly or even weakly - it may be an "fragile" value, see
     // DFGValueStrength.h). If you perform any optimization based on a cell m_value
     // that requires that the value be kept alive, you must call freeze() on that
     // value, which will turn it into a weak value.
     JSValue m_value;

 private:
     void clobberArrayModes()
     {
         // FIXME: We could make this try to predict the set of array modes that this object
         // could have in the future. For now, just do the simple thing.
         m_arrayModes = ALL_ARRAY_MODES;
     }

     void observeIndexingTypeTransition(IndexingType from, IndexingType to)
     {
         if (m_arrayModes & asArrayModes(from))
             m_arrayModes |= asArrayModes(to);
     }

     bool validateType(JSValue value) const
     {
         if (isHeapTop())
             return true;

         // Constant folding always represents Int52's in a double (i.e. AnyIntAsDouble).
         // So speculationFromValue(value) for an Int52 value will return AnyIntAsDouble,
         // and that's fine - the type validates just fine.
         SpeculatedType type = m_type;
         if (type & SpecInt52Only)
             type |= SpecAnyIntAsDouble;

         if (mergeSpeculations(type, speculationFromValue(value)) != type)
             return false;

         if (value.isEmpty()) {
             ASSERT(m_type & SpecEmpty);
             return true;
         }

         return true;
     }

     void makeTop(SpeculatedType top)
     {
         m_type |= top;
         m_arrayModes = ALL_ARRAY_MODES;
         m_structure.makeTop();
         m_value = JSValue();
         checkConsistency();
     }

     void filterValueByType();
     void filterArrayModesByType();

 #if USE(JSVALUE64) && !defined(NDEBUG)
     void ensureCanInitializeWithZeros();
 #endif

     bool shouldBeClear() const;
     FiltrationResult normalizeClarity();
     FiltrationResult normalizeClarity(Graph&);
 };

 } } // namespace JSC::DFG

 #if USE(JSVALUE64)
 namespace WTF {
 template <>
 struct VectorTraits<JSC::DFG::AbstractValue> : VectorTraitsBase<false, JSC::DFG::AbstractValue> {
     static const bool canInitializeWithMemset = true;
 };

 template <>
 struct HashTraits<JSC::DFG::AbstractValue> : GenericHashTraits<JSC::DFG::AbstractValue> {
     static const bool emptyValueIsZero = true;
 };
 };
 #endif // USE(JSVALUE64)

 #endif // ENABLE(DFG_JIT)

 #endif // DFGAbstractValue_h
	/*
	* Copyright (C) 2011-2016 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.
	*/

	#ifndef DFGAbstractValue_h
	#define DFGAbstractValue_h

	#if ENABLE(DFG_JIT)

	#include "ArrayProfile.h"
	#include "DFGFiltrationResult.h"
	#include "DFGFrozenValue.h"
	#include "DFGNodeFlags.h"
	#include "DFGStructureAbstractValue.h"
	#include "DFGStructureClobberState.h"
	#include "InferredType.h"
	#include "JSCell.h"
	#include "ResultType.h"
	#include "SpeculatedType.h"
	#include "DumpContext.h"
	#include "StructureSet.h"

	namespace JSC {

	class TrackedReferences;

	namespace DFG {

	class Graph;
	struct Node;

	struct AbstractValue {
	AbstractValue()
	: m_type(SpecNone)
	, m_arrayModes(0)
	{
	#if USE(JSVALUE64) && !defined(NDEBUG)
	// The WTF Traits for AbstractValue allow the initialization of values with bzero().
	// We verify the correctness of this assumption here.
	static bool needsDefaultConstructorCheck = true;
	if (needsDefaultConstructorCheck) {
	needsDefaultConstructorCheck = false;
	ensureCanInitializeWithZeros();
	}
	#endif
	}

	void clear()
	{
	m_type = SpecNone;
	m_arrayModes = 0;
	m_structure.clear();
	m_value = JSValue();
	checkConsistency();
	}

	bool isClear() const { return m_type == SpecNone; }
	bool operator!() const { return isClear(); }

	void makeHeapTop()
	{
	makeTop(SpecHeapTop);
	}

	void makeBytecodeTop()
	{
	makeTop(SpecBytecodeTop);
	}

	void makeFullTop()
	{
	makeTop(SpecFullTop);
	}

	void clobberStructures()
	{
	if (m_type & SpecCell) {
	m_structure.clobber();
	clobberArrayModes();
	} else {
	ASSERT(m_structure.isClear());
	ASSERT(!m_arrayModes);
	}
	checkConsistency();
	}

	static void clobberStructuresFor(AbstractValue& value)
	{
	value.clobberStructures();
	}

	void observeInvalidationPoint()
	{
	m_structure.observeInvalidationPoint();
	checkConsistency();
	}

	static void observeInvalidationPointFor(AbstractValue& value)
	{
	value.observeInvalidationPoint();
	}

	void observeTransition(Structure* from, Structure* to)
	{
	if (m_type & SpecCell) {
	m_structure.observeTransition(from, to);
	observeIndexingTypeTransition(from->indexingType(), to->indexingType());
	}
	checkConsistency();
	}

	void observeTransitions(const TransitionVector& vector);

	class TransitionObserver {
	public:
	TransitionObserver(Structure* from, Structure* to)
	: m_from(from)
	, m_to(to)
	{
	}

	void operator()(AbstractValue& value)
	{
	value.observeTransition(m_from, m_to);
	}
	private:
	Structure* m_from;
	Structure* m_to;
	};

	class TransitionsObserver {
	public:
	TransitionsObserver(const TransitionVector& vector)
	: m_vector(vector)
	{
	}

	void operator()(AbstractValue& value)
	{
	value.observeTransitions(m_vector);
	}
	private:
	const TransitionVector& m_vector;
	};

	void clobberValue()
	{
	m_value = JSValue();
	}

	bool isHeapTop() const
	{
	return (m_type \| SpecHeapTop) == m_type
	&& m_structure.isTop()
	&& m_arrayModes == ALL_ARRAY_MODES
	&& !m_value;
	}

	bool valueIsTop() const
	{
	return !m_value && m_type;
	}

	JSValue value() const
	{
	return m_value;
	}

	static AbstractValue heapTop()
	{
	AbstractValue result;
	result.makeHeapTop();
	return result;
	}

	static AbstractValue bytecodeTop()
	{
	AbstractValue result;
	result.makeBytecodeTop();
	return result;
	}

	static AbstractValue fullTop()
	{
	AbstractValue result;
	result.makeFullTop();
	return result;
	}

	void set(Graph&, const FrozenValue&, StructureClobberState);
	void set(Graph&, Structure*);
	void set(Graph&, const StructureSet&);

	// Set this value to represent the given set of types as precisely as possible.
	void setType(Graph&, SpeculatedType);

	// As above, but only valid for non-cell types.
	void setType(SpeculatedType type)
	{
	RELEASE_ASSERT(!(type & SpecCell));
	m_structure.clear();
	m_arrayModes = 0;
	m_type = type;
	m_value = JSValue();
	checkConsistency();
	}

	void set(Graph&, const InferredType::Descriptor&);
	void set(Graph&, const InferredType::Descriptor&, StructureClobberState);

	void fixTypeForRepresentation(Graph&, NodeFlags representation, Node* = nullptr);
	void fixTypeForRepresentation(Graph&, Node*);

	bool operator==(const AbstractValue& other) const
	{
	return m_type == other.m_type
	&& m_arrayModes == other.m_arrayModes
	&& m_structure == other.m_structure
	&& m_value == other.m_value;
	}
	bool operator!=(const AbstractValue& other) const
	{
	return !(*this == other);
	}

	bool merge(const AbstractValue& other)
	{
	if (other.isClear())
	return false;

	#if !ASSERT_DISABLED
	AbstractValue oldMe = *this;
	#endif
	bool result = false;
	if (isClear()) {
	*this = other;
	result = !other.isClear();
	} else {
	result \|= mergeSpeculation(m_type, other.m_type);
	result \|= mergeArrayModes(m_arrayModes, other.m_arrayModes);
	result \|= m_structure.merge(other.m_structure);
	if (m_value != other.m_value) {
	result \|= !!m_value;
	m_value = JSValue();
	}
	}
	checkConsistency();
	ASSERT(result == (*this != oldMe));
	return result;
	}

	bool mergeOSREntryValue(Graph&, JSValue);

	void merge(SpeculatedType type)
	{
	mergeSpeculation(m_type, type);

	if (type & SpecCell) {
	m_structure.makeTop();
	m_arrayModes = ALL_ARRAY_MODES;
	}
	m_value = JSValue();

	checkConsistency();
	}

	bool couldBeType(SpeculatedType desiredType) const
	{
	return !!(m_type & desiredType);
	}

	bool isType(SpeculatedType desiredType) const
	{
	return !(m_type & ~desiredType);
	}

	bool isType(Graph&, const InferredType::Descriptor&) const;

	// Filters the value using the given structure set. If the admittedTypes argument is not passed, this
	// implicitly filters by the types implied by the structure set, which are usually a subset of
	// SpecCell. Hence, after this call, the value will no longer have any non-cell members. But, you can
	// use admittedTypes to preserve some non-cell types. Note that it's wrong for admittedTypes to overlap
	// with SpecCell.
	FiltrationResult filter(Graph&, const StructureSet&, SpeculatedType admittedTypes = SpecNone);

	FiltrationResult filterArrayModes(ArrayModes);
	FiltrationResult filter(SpeculatedType);
	FiltrationResult filterByValue(const FrozenValue& value);
	FiltrationResult filter(const AbstractValue&);

	FiltrationResult filter(Graph&, const InferredType::Descriptor&);

	FiltrationResult changeStructure(Graph&, const StructureSet&);

	bool contains(Structure*) const;

	bool validate(JSValue value) const
	{
	if (isHeapTop())
	return true;

	if (!!m_value && m_value != value)
	return false;

	if (mergeSpeculations(m_type, speculationFromValue(value)) != m_type)
	return false;

	if (value.isEmpty()) {
	ASSERT(m_type & SpecEmpty);
	return true;
	}

	if (!!value && value.isCell()) {
	ASSERT(m_type & SpecCell);
	Structure* structure = value.asCell()->structure();
	return m_structure.contains(structure)
	&& (m_arrayModes & asArrayModes(structure->indexingType()));
	}

	return true;
	}

	bool hasClobberableState() const
	{
	return m_structure.isNeitherClearNorTop()
	\|\| !arrayModesAreClearOrTop(m_arrayModes);
	}

	#if ASSERT_DISABLED
	void checkConsistency() const { }
	void assertIsRegistered(Graph&) const { }
	#else
	void checkConsistency() const;
	void assertIsRegistered(Graph&) const;
	#endif

	ResultType resultType() const;

	void dumpInContext(PrintStream&, DumpContext*) const;
	void dump(PrintStream&) const;

	void validateReferences(const TrackedReferences&);

	// This is a proven constraint on the structures that this value can have right
	// now. The structure of the current value must belong to this set. The set may
	// be TOP, indicating that it is the set of all possible structures, in which
	// case the current value can have any structure. The set may be BOTTOM (empty)
	// in which case this value cannot be a cell. This is all subject to change
	// anytime a new value is assigned to this one, anytime there is a control flow
	// merge, or most crucially, anytime a side-effect or structure check happens.
	// In case of a side-effect, we must assume that any value with a structure that
	// isn't being watched may have had its structure changed, hence contravening
	// our proof. In such a case we make the proof valid again by switching this to
	// TOP (i.e. claiming that we have proved that this value may have any
	// structure).
	StructureAbstractValue m_structure;

	// This is a proven constraint on the possible types that this value can have
	// now or any time in the future, unless it is reassigned. This field is
	// impervious to side-effects. The relationship between this field, and the
	// structure fields above, is as follows. The fields above constraint the
	// structures that a cell may have, but they say nothing about whether or not
	// the value is known to be a cell. More formally, the m_structure is itself an
	// abstract value that consists of the union of the set of all non-cell values
	// and the set of cell values that have the given structure. This abstract
	// value is then the intersection of the m_structure and the set of values
	// whose type is m_type. So, for example if m_type is SpecFinal\|SpecInt32Only and
	// m_structure is [0x12345] then this abstract value corresponds to the set of
	// all integers unified with the set of all objects with structure 0x12345.
	SpeculatedType m_type;

	// This is a proven constraint on the possible indexing types that this value
	// can have right now. It also implicitly constraints the set of structures
	// that the value may have right now, since a structure has an immutable
	// indexing type. This is subject to change upon reassignment, or any side
	// effect that makes non-obvious changes to the heap.
	ArrayModes m_arrayModes;

	// This is a proven constraint on the possible values that this value can
	// have now or any time in the future, unless it is reassigned. Note that this
	// implies nothing about the structure. Oddly, JSValue() (i.e. the empty value)
	// means either BOTTOM or TOP depending on the state of m_type: if m_type is
	// BOTTOM then JSValue() means BOTTOM; if m_type is not BOTTOM then JSValue()
	// means TOP. Also note that this value isn't necessarily known to the GC
	// (strongly or even weakly - it may be an "fragile" value, see
	// DFGValueStrength.h). If you perform any optimization based on a cell m_value
	// that requires that the value be kept alive, you must call freeze() on that
	// value, which will turn it into a weak value.
	JSValue m_value;

	private:
	void clobberArrayModes()
	{
	// FIXME: We could make this try to predict the set of array modes that this object
	// could have in the future. For now, just do the simple thing.
	m_arrayModes = ALL_ARRAY_MODES;
	}

	void observeIndexingTypeTransition(IndexingType from, IndexingType to)
	{
	if (m_arrayModes & asArrayModes(from))
	m_arrayModes \|= asArrayModes(to);
	}

	bool validateType(JSValue value) const
	{
	if (isHeapTop())
	return true;

	// Constant folding always represents Int52's in a double (i.e. AnyIntAsDouble).
	// So speculationFromValue(value) for an Int52 value will return AnyIntAsDouble,
	// and that's fine - the type validates just fine.
	SpeculatedType type = m_type;
	if (type & SpecInt52Only)
	type \|= SpecAnyIntAsDouble;

	if (mergeSpeculations(type, speculationFromValue(value)) != type)
	return false;

	if (value.isEmpty()) {
	ASSERT(m_type & SpecEmpty);
	return true;
	}

	return true;
	}

	void makeTop(SpeculatedType top)
	{
	m_type \|= top;
	m_arrayModes = ALL_ARRAY_MODES;
	m_structure.makeTop();
	m_value = JSValue();
	checkConsistency();
	}

	void filterValueByType();
	void filterArrayModesByType();

	#if USE(JSVALUE64) && !defined(NDEBUG)
	void ensureCanInitializeWithZeros();
	#endif

	bool shouldBeClear() const;
	FiltrationResult normalizeClarity();
	FiltrationResult normalizeClarity(Graph&);
	};

	} } // namespace JSC::DFG

	#if USE(JSVALUE64)
	namespace WTF {
	template <>
	struct VectorTraits<JSC::DFG::AbstractValue> : VectorTraitsBase<false, JSC::DFG::AbstractValue> {
	static const bool canInitializeWithMemset = true;
	};

	template <>
	struct HashTraits<JSC::DFG::AbstractValue> : GenericHashTraits<JSC::DFG::AbstractValue> {
	static const bool emptyValueIsZero = true;
	};
	};
	#endif // USE(JSVALUE64)

	#endif // ENABLE(DFG_JIT)

	#endif // DFGAbstractValue_h