C++ StructureSet::isEmpty方法代码示例

GetByIdStatus GetByIdStatus::computeFor(const StructureSet& set, StringImpl* uid)
{
    // For now we only handle the super simple self access case. We could handle the
    // prototype case in the future.
    
    if (set.isEmpty())
        return GetByIdStatus();

    if (toUInt32FromStringImpl(uid) != PropertyName::NotAnIndex)
        return GetByIdStatus(TakesSlowPath);
    
    GetByIdStatus result;
    result.m_state = Simple;
    result.m_wasSeenInJIT = false;
    for (unsigned i = 0; i < set.size(); ++i) {
        Structure* structure = set[i];
        if (structure->typeInfo().overridesGetOwnPropertySlot() && structure->typeInfo().type() != GlobalObjectType)
            return GetByIdStatus(TakesSlowPath);
        
        if (!structure->propertyAccessesAreCacheable())
            return GetByIdStatus(TakesSlowPath);
        
        unsigned attributes;
        PropertyOffset offset = structure->getConcurrently(uid, attributes);
        if (!isValidOffset(offset))
            return GetByIdStatus(TakesSlowPath); // It's probably a prototype lookup. Give up on life for now, even though we could totally be way smarter about it.
        if (attributes & Accessor)
            return GetByIdStatus(MakesCalls); // We could be smarter here, like strenght-reducing this to a Call.
        
        if (!result.appendVariant(GetByIdVariant(structure, offset)))
            return GetByIdStatus(TakesSlowPath);
    }
    
    return result;
}

PutByIdStatus PutByIdStatus::computeFor(JSGlobalObject* globalObject, const StructureSet& set, StringImpl* uid, bool isDirect)
{
    if (toUInt32FromStringImpl(uid) != PropertyName::NotAnIndex)
        return PutByIdStatus(TakesSlowPath);

    if (set.isEmpty())
        return PutByIdStatus();
    
    PutByIdStatus result;
    result.m_state = Simple;
    for (unsigned i = 0; i < set.size(); ++i) {
        Structure* structure = set[i];
        
        if (structure->typeInfo().overridesGetOwnPropertySlot() && structure->typeInfo().type() != GlobalObjectType)
            return PutByIdStatus(TakesSlowPath);

        if (!structure->propertyAccessesAreCacheable())
            return PutByIdStatus(TakesSlowPath);
    
        unsigned attributes;
        PropertyOffset offset = structure->getConcurrently(uid, attributes);
        if (isValidOffset(offset)) {
            if (attributes & CustomAccessor)
                return PutByIdStatus(MakesCalls);

            if (attributes & (Accessor | ReadOnly))
                return PutByIdStatus(TakesSlowPath);
            
            WatchpointSet* replaceSet = structure->propertyReplacementWatchpointSet(offset);
            if (!replaceSet || replaceSet->isStillValid()) {
                // When this executes, it'll create, and fire, this replacement watchpoint set.
                // That means that  this has probably never executed or that something fishy is
                // going on. Also, we cannot create or fire the watchpoint set from the concurrent
                // JIT thread, so even if we wanted to do this, we'd need to have a lazy thingy.
                // So, better leave this alone and take slow path.
                return PutByIdStatus(TakesSlowPath);
            }
            
            if (!result.appendVariant(PutByIdVariant::replace(structure, offset)))
                return PutByIdStatus(TakesSlowPath);
            continue;
        }
    
        // Our hypothesis is that we're doing a transition. Before we prove that this is really
        // true, we want to do some sanity checks.
    
        // Don't cache put transitions on dictionaries.
        if (structure->isDictionary())
            return PutByIdStatus(TakesSlowPath);

        // If the structure corresponds to something that isn't an object, then give up, since
        // we don't want to be adding properties to strings.
        if (structure->typeInfo().type() == StringType)
            return PutByIdStatus(TakesSlowPath);
    
        RefPtr<IntendedStructureChain> chain;
        if (!isDirect) {
            chain = adoptRef(new IntendedStructureChain(globalObject, structure));
        
            // If the prototype chain has setters or read-only properties, then give up.
            if (chain->mayInterceptStoreTo(uid))
                return PutByIdStatus(TakesSlowPath);
        
            // If the prototype chain hasn't been normalized (i.e. there are proxies or dictionaries)
            // then give up. The dictionary case would only happen if this structure has not been
            // used in an optimized put_by_id transition. And really the only reason why we would
            // bail here is that I don't really feel like having the optimizing JIT go and flatten
            // dictionaries if we have evidence to suggest that those objects were never used as
            // prototypes in a cacheable prototype access - i.e. there's a good chance that some of
            // the other checks below will fail.
            if (structure->isProxy() || !chain->isNormalized())
                return PutByIdStatus(TakesSlowPath);
        }
    
        // We only optimize if there is already a structure that the transition is cached to.
        Structure* transition = Structure::addPropertyTransitionToExistingStructureConcurrently(structure, uid, 0, offset);
        if (!transition)
            return PutByIdStatus(TakesSlowPath);
        ASSERT(isValidOffset(offset));
    
        bool didAppend = result.appendVariant(
            PutByIdVariant::transition(structure, transition, chain.get(), offset));
        if (!didAppend)
            return PutByIdStatus(TakesSlowPath);
    }
    
    return result;
}

PutByIdStatus PutByIdStatus::computeFor(JSGlobalObject* globalObject, const StructureSet& set, UniquedStringImpl* uid, bool isDirect)
{
    if (parseIndex(*uid))
        return PutByIdStatus(TakesSlowPath);

    if (set.isEmpty())
        return PutByIdStatus();
    
    PutByIdStatus result;
    result.m_state = Simple;
    for (unsigned i = 0; i < set.size(); ++i) {
        Structure* structure = set[i];
        
        if (structure->typeInfo().overridesGetOwnPropertySlot() && structure->typeInfo().type() != GlobalObjectType)
            return PutByIdStatus(TakesSlowPath);

        if (!structure->propertyAccessesAreCacheable())
            return PutByIdStatus(TakesSlowPath);
    
        unsigned attributes;
        PropertyOffset offset = structure->getConcurrently(uid, attributes);
        if (isValidOffset(offset)) {
            if (attributes & CustomAccessor)
                return PutByIdStatus(MakesCalls);

            if (attributes & (Accessor | ReadOnly))
                return PutByIdStatus(TakesSlowPath);
            
            WatchpointSet* replaceSet = structure->propertyReplacementWatchpointSet(offset);
            if (!replaceSet || replaceSet->isStillValid()) {
                // When this executes, it'll create, and fire, this replacement watchpoint set.
                // That means that  this has probably never executed or that something fishy is
                // going on. Also, we cannot create or fire the watchpoint set from the concurrent
                // JIT thread, so even if we wanted to do this, we'd need to have a lazy thingy.
                // So, better leave this alone and take slow path.
                return PutByIdStatus(TakesSlowPath);
            }

            PutByIdVariant variant =
                PutByIdVariant::replace(structure, offset, structure->inferredTypeDescriptorFor(uid));
            if (!result.appendVariant(variant))
                return PutByIdStatus(TakesSlowPath);
            continue;
        }
    
        // Our hypothesis is that we're doing a transition. Before we prove that this is really
        // true, we want to do some sanity checks.
    
        // Don't cache put transitions on dictionaries.
        if (structure->isDictionary())
            return PutByIdStatus(TakesSlowPath);

        // If the structure corresponds to something that isn't an object, then give up, since
        // we don't want to be adding properties to strings.
        if (!structure->typeInfo().isObject())
            return PutByIdStatus(TakesSlowPath);
    
        ObjectPropertyConditionSet conditionSet;
        if (!isDirect) {
            conditionSet = generateConditionsForPropertySetterMissConcurrently(
                globalObject->vm(), globalObject, structure, uid);
            if (!conditionSet.isValid())
                return PutByIdStatus(TakesSlowPath);
        }
    
        // We only optimize if there is already a structure that the transition is cached to.
        Structure* transition =
            Structure::addPropertyTransitionToExistingStructureConcurrently(structure, uid, 0, offset);
        if (!transition)
            return PutByIdStatus(TakesSlowPath);
        ASSERT(isValidOffset(offset));
    
        bool didAppend = result.appendVariant(
            PutByIdVariant::transition(
                structure, transition, conditionSet, offset,
                transition->inferredTypeDescriptorFor(uid)));
        if (!didAppend)
            return PutByIdStatus(TakesSlowPath);
    }
    
    return result;
}