/*
 * Copyright (C) 2007, 2008, 2012 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.
 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "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
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 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef SymbolTable_h
#define SymbolTable_h

#include "ConstantMode.h"
#include "InferredValue.h"
#include "JSObject.h"
#include "ScopedArgumentsTable.h"
#include "VarOffset.h"
#include "Watchpoint.h"
#include "VirtualRegister.h"
#include <wtf/AlwaysInline.h>
#include <wtf/HashTraits.h>
#include <wtf/PassOwnPtr.h>
#include <wtf/Vector.h>
#include <wtf/text/UniquedStringImpl.h>

namespace JSC {

class SymbolTable;

static ALWAYS_INLINE int missingSymbolMarker() { return std::numeric_limits<int>::max(); }

// The bit twiddling in this class assumes that every register index is a
// reasonably small positive or negative number, and therefore has its high
// four bits all set or all unset.

// In addition to implementing semantics-mandated variable attributes and
// implementation-mandated variable indexing, this class also implements
// watchpoints to be used for JIT optimizations. Because watchpoints are
// meant to be relatively rare, this class optimizes heavily for the case
// that they are not being used. To that end, this class uses the thin-fat
// idiom: either it is thin, in which case it contains an in-place encoded
// word that consists of attributes, the index, and a bit saying that it is
// thin; or it is fat, in which case it contains a pointer to a malloc'd
// data structure and a bit saying that it is fat. The malloc'd data
// structure will be malloced a second time upon copy, to preserve the
// property that in-place edits to SymbolTableEntry do not manifest in any
// copies. However, the malloc'd FatEntry data structure contains a ref-
// counted pointer to a shared WatchpointSet. Thus, in-place edits of the
// WatchpointSet will manifest in all copies. Here's a picture:
//
// SymbolTableEntry --> FatEntry --> WatchpointSet
//
// If you make a copy of a SymbolTableEntry, you will have:
//
// original: SymbolTableEntry --> FatEntry --> WatchpointSet
// copy:     SymbolTableEntry --> FatEntry -----^

struct SymbolTableEntry {
private:
    static VarOffset varOffsetFromBits(intptr_t bits)
    {
        VarKind kind;
        intptr_t kindBits = bits & KindBitsMask;
        if (kindBits <= UnwatchableScopeKindBits)
            kind = VarKind::Scope;
        else if (kindBits == StackKindBits)
            kind = VarKind::Stack;
        else
            kind = VarKind::DirectArgument;
        return VarOffset::assemble(kind, static_cast<int>(bits >> FlagBits));
    }

    static ScopeOffset scopeOffsetFromBits(intptr_t bits)
    {
        ASSERT((bits & KindBitsMask) <= UnwatchableScopeKindBits);
        return ScopeOffset(static_cast<int>(bits >> FlagBits));
    }

public:
	// Use the SymbolTableEntry::Fast class, either via implicit cast or by calling
	// getFast(), when you (1) only care about isNull(), getIndex(), and isReadOnly(),
	// and (2) you are in a hot path where you need to minimize the number of times
	// that you branch on isFat() when getting the bits().
	class Fast {
	public:
		Fast()
			: m_bits(SlimFlag)
		{
		}

		ALWAYS_INLINE Fast(const SymbolTableEntry& entry)
			: m_bits(entry.bits())
		{
		}

		bool isNull() const
		{
			return !(m_bits & ~SlimFlag);
		}

        VarOffset varOffset() const
        {
            return varOffsetFromBits(m_bits);
        }

        // Asserts if the offset is anything but a scope offset. This structures the assertions
        // in a way that may result in better code, even in release, than doing
        // varOffset().scopeOffset().
        ScopeOffset scopeOffset() const
        {
            return scopeOffsetFromBits(m_bits);
        }

		bool isReadOnly() const
		{
			return m_bits & ReadOnlyFlag;
		}

        bool isDontEnum() const
        {
            return m_bits & DontEnumFlag;
        }

		unsigned getAttributes() const
		{
			unsigned attributes = 0;
            if (isReadOnly())
				attributes |= ReadOnly;
            if (isDontEnum())
				attributes |= DontEnum;
			return attributes;
		}

		bool isFat() const
		{
			return !(m_bits & SlimFlag);
		}

	private:
		friend struct SymbolTableEntry;
		intptr_t m_bits;
	};

	SymbolTableEntry()
		: m_bits(SlimFlag)
	{
	}

    SymbolTableEntry(VarOffset offset)
        : m_bits(SlimFlag)
    {
        ASSERT(isValidVarOffset(offset));
        pack(offset, true, false, false);
    }

    SymbolTableEntry(VarOffset offset, unsigned attributes)
        : m_bits(SlimFlag)
    {
        ASSERT(isValidVarOffset(offset));
        pack(offset, true, attributes & ReadOnly, attributes & DontEnum);
    }

	~SymbolTableEntry()
	{
		freeFatEntry();
	}

	SymbolTableEntry(const SymbolTableEntry& other)
		: m_bits(SlimFlag)
	{
		*this = other;
	}

	SymbolTableEntry& operator=(const SymbolTableEntry& other)
	{
		if (UNLIKELY(other.isFat()))
			return copySlow(other);
		freeFatEntry();
		m_bits = other.m_bits;
		return *this;
	}

	bool isNull() const
	{
		return !(bits() & ~SlimFlag);
	}


    VarOffset varOffset() const
    {
        return varOffsetFromBits(bits());
    }

    bool isWatchable() const
    {
        return (m_bits & KindBitsMask) == ScopeKindBits;
    }

    // Asserts if the offset is anything but a scope offset. This structures the assertions
    // in a way that may result in better code, even in release, than doing
    // varOffset().scopeOffset().
    ScopeOffset scopeOffset() const
    {
        return scopeOffsetFromBits(bits());
    }

	ALWAYS_INLINE Fast getFast() const
	{
		return Fast(*this);
	}

	ALWAYS_INLINE Fast getFast(bool& wasFat) const
	{
		Fast result;
		wasFat = isFat();
		if (wasFat)
			result.m_bits = fatEntry()->m_bits | SlimFlag;
		else
			result.m_bits = m_bits;
		return result;
	}

	unsigned getAttributes() const
	{
		return getFast().getAttributes();
	}

    void setAttributes(unsigned attributes)
    {
        pack(varOffset(), isWatchable(), attributes & ReadOnly, attributes & DontEnum);
    }

	bool isReadOnly() const
	{
		return bits() & ReadOnlyFlag;
	}

    ConstantMode constantMode() const
    {
        return modeForIsConstant(isReadOnly());
    }

    bool isDontEnum() const
    {
        return bits() & DontEnumFlag;
    }

    void disableWatching(JSGlobalData& vm)
    {
        if (WatchpointSet* set = watchpointSet())
            set->invalidate(vm/*, "Disabling watching in symbol table"*/);
        if (varOffset().isScope())
            pack(varOffset(), false, isReadOnly(), isDontEnum());
    }

    void prepareToWatch();

	void addWatchpoint(Watchpoint*);

    // This watchpoint set is initialized clear, and goes through the following state transitions:
    //
    // First write to this var, in any scope that has this symbol table: Clear->IsWatched.
    //
    // Second write to this var, in any scope that has this symbol table: IsWatched->IsInvalidated.
    //
    // We ensure that we touch the set (i.e. trigger its state transition) after we do the write. This
    // means that if you're in the compiler thread, and you:
    //
    // 1) Observe that the set IsWatched and commit to adding your watchpoint.
    // 2) Load a value from any scope that has this watchpoint set.
    //
    // Then you can be sure that that value is either going to be the correct value for that var forever,
    // or the watchpoint set will invalidate and you'll get fired.
    //
    // It's possible to write a program that first creates multiple scopes with the same var, and then
    // initializes that var in just one of them. This means that a compilation could constant-fold to one
    // of the scopes that still has an undefined value for this variable. That's fine, because at that
    // point any write to any of the instances of that variable would fire the watchpoint.
    WatchpointSet* watchpointSet()
	{
		if (!isFat())
			return 0;
		return fatEntry()->m_watchpoints.get();
	}

private:
	static const intptr_t SlimFlag = 0x1;
	static const intptr_t ReadOnlyFlag = 0x2;
	static const intptr_t DontEnumFlag = 0x4;
	static const intptr_t NotNullFlag = 0x8;
    static const intptr_t KindBitsMask = 0x30;
    static const intptr_t ScopeKindBits = 0x00;
    static const intptr_t UnwatchableScopeKindBits = 0x10;
    static const intptr_t StackKindBits = 0x20;
    static const intptr_t DirectArgumentKindBits = 0x30;
    static const intptr_t FlagBits = 6;

	class FatEntry {
		WTF_MAKE_FAST_ALLOCATED;
	public:
		FatEntry(intptr_t bits)
		: m_bits(bits & ~SlimFlag)
		{
		}

		intptr_t m_bits; // always has FatFlag set and exactly matches what the bits would have been if this wasn't fat.

		RefPtr<WatchpointSet> m_watchpoints;
	};

	SymbolTableEntry& copySlow(const SymbolTableEntry&);
	JS_EXPORT_PRIVATE void notifyWriteSlow(JSGlobalData& vm, JSValue);

	bool isFat() const
	{
		return !(m_bits & SlimFlag);
	}

	const FatEntry* fatEntry() const
	{
		ASSERT(isFat());
		return bitwise_cast<const FatEntry*>(m_bits);
	}

	FatEntry* fatEntry()
	{
		ASSERT(isFat());
		return bitwise_cast<FatEntry*>(m_bits);
	}

	FatEntry* inflate()
	{
		if (LIKELY(isFat()))
			return fatEntry();
		return inflateSlow();
	}

	FatEntry* inflateSlow();

	ALWAYS_INLINE intptr_t bits() const
	{
		if (isFat())
			return fatEntry()->m_bits;
		return m_bits;
	}

	ALWAYS_INLINE intptr_t& bits()
	{
		if (isFat())
			return fatEntry()->m_bits;
		return m_bits;
	}

	void freeFatEntry()
	{
		if (LIKELY(!isFat()))
			return;
		freeFatEntrySlow();
	}

	void freeFatEntrySlow();

    void pack(VarOffset offset, bool isWatchable, bool readOnly, bool dontEnum)
    {
        ASSERT(!isFat());
        intptr_t& bitsRef = bits();
        bitsRef =
            (static_cast<intptr_t>(offset.rawOffset()) << FlagBits) | NotNullFlag | SlimFlag;
        if (readOnly)
            bitsRef |= ReadOnlyFlag;
        if (dontEnum)
            bitsRef |= DontEnumFlag;
        switch (offset.kind()) {
        case VarKind::Scope:
            if (isWatchable)
                bitsRef |= ScopeKindBits;
            else
                bitsRef |= UnwatchableScopeKindBits;
            break;
        case VarKind::Stack:
            bitsRef |= StackKindBits;
            break;
        case VarKind::DirectArgument:
            bitsRef |= DirectArgumentKindBits;
            break;
        default:
            RELEASE_ASSERT_NOT_REACHED();
            break;
        }
    }

    static bool isValidVarOffset(VarOffset offset)
    {
        return ((static_cast<intptr_t>(offset.rawOffset()) << FlagBits) >> FlagBits) == static_cast<intptr_t>(offset.rawOffset());
    }

	intptr_t m_bits;
};

struct SymbolTableIndexHashTraits : HashTraits<SymbolTableEntry> {
	static const bool needsDestruction = true;
};

class SymbolTable : public JSCell {
public:
	typedef JSCell Base;

	typedef HashMap<RefPtr<UniquedStringImpl>, SymbolTableEntry, IdentifierRepHash, HashTraits<RefPtr<UniquedStringImpl> >, SymbolTableIndexHashTraits> Map;
    typedef HashMap<VarOffset, RefPtr<UniquedStringImpl>> OffsetToVariableMap;
	typedef Vector<SymbolTableEntry*> LocalToEntryVec;

	static SymbolTable* create(JSGlobalData& globalData)
	{
		SymbolTable* sharedSymbolTable = new (NotNull, allocateCell<SymbolTable>(globalData.heap)) SymbolTable(globalData);
		sharedSymbolTable->finishCreation(globalData);
		return sharedSymbolTable;
	}

    static SymbolTable* createNameScopeTable(VM& vm, const Identifier& ident, unsigned attributes)
    {
    	SymbolTable* result = create(vm);
        result->add(ident.impl(), SymbolTableEntry(VarOffset(ScopeOffset(0)), attributes));
        return result;
    }

	static const bool needsDestruction = true;
	static const bool hasImmortalStructure = true;
	static void destroy(JSCell*);

	static Structure* createStructure(JSGlobalData& globalData, JSGlobalObject* globalObject, JSValue prototype)
	{
		return Structure::create(globalData, globalObject, prototype, TypeInfo(CellType, StructureFlags), info());
	}

    // You must hold the lock until after you're done with the iterator.
    Map::iterator find(UniquedStringImpl* key)
    {
        return m_map.find(key);
    }

    SymbolTableEntry get(UniquedStringImpl* key) const
    {
        return m_map.get(key);
    }

    SymbolTableEntry inlineGet(UniquedStringImpl* key) const
    {
        return m_map.inlineGet(key);
    }

    Map::iterator begin()
    {
        return m_map.begin();
    }

    Map::iterator end()
    {
        return m_map.end();
    }

    size_t size() const
    {
        return m_map.size();
    }

    ScopeOffset maxScopeOffset() const
    {
        return m_maxScopeOffset;
    }

    void didUseScopeOffset(ScopeOffset offset)
    {
        if (!m_maxScopeOffset || m_maxScopeOffset < offset)
            m_maxScopeOffset = offset;
    }

    void didUseVarOffset(VarOffset offset)
    {
        if (offset.isScope())
            didUseScopeOffset(offset.scopeOffset());
    }

    unsigned scopeSize() const
    {
        ScopeOffset maxScopeOffset = this->maxScopeOffset();

        // Do some calculation that relies on invalid scope offset plus one being zero.
        unsigned fastResult = maxScopeOffset.offsetUnchecked() + 1;

        // Assert that this works.
        ASSERT(fastResult == (!maxScopeOffset ? 0 : maxScopeOffset.offset() + 1));

        return fastResult;
    }

    ScopeOffset nextScopeOffset() const
    {
        return ScopeOffset(scopeSize());
    }

    ScopeOffset takeNextScopeOffset()
    {
        ScopeOffset result = nextScopeOffset();
        m_maxScopeOffset = result;
        return result;
    }

    void add(UniquedStringImpl* key, const SymbolTableEntry& entry)
    {
        RELEASE_ASSERT(!m_localToEntry);
        didUseVarOffset(entry.varOffset());
        Map::AddResult result = m_map.add(key, entry);
        ASSERT_UNUSED(result, result.isNewEntry);
    }

    void set(UniquedStringImpl* key, const SymbolTableEntry& entry)
    {
        RELEASE_ASSERT(!m_localToEntry);
        didUseVarOffset(entry.varOffset());
        m_map.set(key, entry);
    }

    bool contains(UniquedStringImpl* key)
    {
        return m_map.contains(key);
    }

    // The principle behind ScopedArgumentsTable modifications is that we will create one and
    // leave it unlocked - thereby allowing in-place changes - until someone asks for a pointer to
    // the table. Then, we will lock it. Then both our future changes and their future changes
    // will first have to make a copy. This discipline means that usually when we create a
    // ScopedArguments object, we don't have to make a copy of the ScopedArgumentsTable - instead
    // we just take a reference to one that we already have.

    uint32_t argumentsLength() const
    {
        if (!m_arguments)
            return 0;
        return m_arguments->length();
    }

    void setArgumentsLength(VM& vm, uint32_t length)
    {
        if (UNLIKELY(!m_arguments))
            m_arguments.set(vm, this, ScopedArgumentsTable::create(vm));
        m_arguments.set(vm, this, m_arguments->setLength(vm, length));
    }

    ScopeOffset argumentOffset(uint32_t i) const
    {
        ASSERT_WITH_SECURITY_IMPLICATION(m_arguments);
        return m_arguments->get(i);
    }

    void setArgumentOffset(VM& vm, uint32_t i, ScopeOffset offset)
    {
        ASSERT_WITH_SECURITY_IMPLICATION(m_arguments);
        m_arguments.set(vm, this, m_arguments->set(vm, i, offset));
    }

    ScopedArgumentsTable* arguments() const
    {
        if (!m_arguments)
            return 0;
        m_arguments->lock();
        return m_arguments.get();
    }

    const LocalToEntryVec& localToEntry();
    SymbolTableEntry* entryFor(ScopeOffset);

	bool usesNonStrictEval() { return m_usesNonStrictEval; }
	void setUsesNonStrictEval(bool usesNonStrictEval) { m_usesNonStrictEval = usesNonStrictEval; }

    enum ScopeType {
        VarScope,
        GlobalLexicalScope,
        LexicalScope,
        CatchScope,
        FunctionNameScope
    };
    void setScopeType(ScopeType type) { m_scopeType = type; }
    ScopeType scopeType() const { return static_cast<ScopeType>(m_scopeType); }

	SymbolTable* cloneScopePart(VM&);

    InferredValue* singletonScope() { return m_singletonScope.get(); }

    static void visitChildren(JSCell*, SlotVisitor&);

	DECLARE_EXPORT_INFO;

private:
	SymbolTable(JSGlobalData&);
	~SymbolTable();

    JS_EXPORT_PRIVATE void finishCreation(VM&);

    Map m_map;
    ScopeOffset m_maxScopeOffset;

    bool m_usesNonStrictEval : 1;
    unsigned m_scopeType : 3; // ScopeType

    WriteBarrier<ScopedArgumentsTable> m_arguments;
    WriteBarrier<InferredValue> m_singletonScope;

    OwnPtr<LocalToEntryVec> m_localToEntry;
};

} // namespace JSC

#endif // SymbolTable_h
