Source/JavaScriptCore/bytecode/PolyProtoAccessChain.cpp

/*
 * Copyright (C) 2017 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *    notice, this list of conditions and the following disclaimer in the
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 *
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#include "config.h"
#include "PolyProtoAccessChain.h"

#include "JSCInlines.h"
#include "JSObject.h"

namespace JSC {

std::unique_ptr<PolyProtoAccessChain> PolyProtoAccessChain::create(JSGlobalObject* globalObject, JSCell* base, const PropertySlot& slot, bool& usesPolyProto)
{
    JSObject* target = slot.isUnset() ? nullptr : slot.slotBase();
    return create(globalObject, base, target, usesPolyProto);
}

std::unique_ptr<PolyProtoAccessChain> PolyProtoAccessChain::create(JSGlobalObject* globalObject, JSCell* base, JSObject* target, bool& usesPolyProto)
{
    JSCell* current = base;
    VM& vm = *base->vm();

    bool found = false;

    usesPolyProto = false;

    std::unique_ptr<PolyProtoAccessChain> result(new PolyProtoAccessChain());

    for (unsigned iterationNumber = 0; true; ++iterationNumber) {
        Structure* structure = current->structure(vm);

        if (!structure->propertyAccessesAreCacheable())
            return nullptr;

        if (structure->isProxy())
            return nullptr;

        if (structure->isDictionary()) {
            ASSERT(structure->isObject());
            if (structure->hasBeenFlattenedBefore())
                return nullptr;

            structure->flattenDictionaryStructure(vm, asObject(current));
        }

        // To save memory, we don't include the base in the chain. We let
        // AccessCase provide the base to us as needed.
        if (iterationNumber)
            result->m_chain.append(structure);
        else
            RELEASE_ASSERT(current == base);

        if (current == target) {
            found = true;
            break;
        }

        // We only have poly proto if we need to access our prototype via
        // the poly proto protocol. If the slot base is the only poly proto
        // thing in the chain, and we have a cache hit on it, then we're not
        // poly proto.
        usesPolyProto |= structure->hasPolyProto();

        JSValue prototype = structure->prototypeForLookup(globalObject, current);
        if (prototype.isNull())
            break;
        current = asObject(prototype);
    }

    if (!found && !!target)
        return nullptr;

    return result;
}

bool PolyProtoAccessChain::needImpurePropertyWatchpoint() const
{
    for (Structure* structure : m_chain) {
        if (structure->needImpurePropertyWatchpoint())
            return true;
    }
    return false;
}

bool PolyProtoAccessChain::operator==(const PolyProtoAccessChain& other) const
{
    return m_chain == other.m_chain;
}

void PolyProtoAccessChain::dump(Structure* baseStructure, PrintStream& out) const
{
    out.print("PolyPolyProtoAccessChain: [\n");
    forEach(baseStructure, [&] (Structure* structure, bool) {
        out.print("\t");
        structure->dump(out);
        out.print("\n");
    });
}

}