Source/JavaScriptCore/bytecode/ObjectAllocationProfileInlines.h

/*
 * 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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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#pragma once

#include "ObjectAllocationProfile.h"

#include "JSFunctionInlines.h"

namespace JSC {

ALWAYS_INLINE void ObjectAllocationProfile::initializeProfile(VM& vm, JSGlobalObject* globalObject, JSCell* owner, JSObject* prototype, unsigned inferredInlineCapacity, JSFunction* constructor, FunctionRareData* functionRareData)
{
    ASSERT(!m_allocator);
    ASSERT(!m_structure);
    ASSERT(!m_inlineCapacity);

    // FIXME: When going poly proto, we should make an allocator and teach
    // create_this' fast path how to allocate a poly proto object.
    // https://bugs.webkit.org/show_bug.cgi?id=177517
    bool isPolyProto = false;
    FunctionExecutable* executable = nullptr;
    if (constructor) {
        // FIXME: A JSFunction should watch the poly proto watchpoint if it is not invalidated.
        // That way it can clear this object allocation profile to ensure it stops allocating
        // mono proto |this| values when it knows that it should be allocating poly proto
        // |this| values:
        // https://bugs.webkit.org/show_bug.cgi?id=177792

        executable = constructor->jsExecutable();

        if (Structure* structure = executable->cachedPolyProtoStructure()) {
            RELEASE_ASSERT(structure->typeInfo().type() == FinalObjectType);
            m_allocator = Allocator();
            m_structure.set(vm, owner, structure);
            m_inlineCapacity = structure->inlineCapacity();
            return;
        }

        isPolyProto = false;
        if (Options::forcePolyProto())
            isPolyProto = true;
        else
            isPolyProto = executable->ensurePolyProtoWatchpoint().hasBeenInvalidated() && executable->singletonFunction()->hasBeenInvalidated();
    }

    unsigned inlineCapacity = 0;
    if (inferredInlineCapacity < JSFinalObject::defaultInlineCapacity()) {
        // Try to shrink the object based on static analysis.
        inferredInlineCapacity += possibleDefaultPropertyCount(vm, prototype);

        if (!inferredInlineCapacity) {
            // Empty objects are rare, so most likely the static analyzer just didn't
            // see the real initializer function. This can happen with helper functions.
            inferredInlineCapacity = JSFinalObject::defaultInlineCapacity();
        } else if (inferredInlineCapacity > JSFinalObject::defaultInlineCapacity()) {
            // Default properties are weak guesses, so don't allow them to turn a small
            // object into a large object.
            inferredInlineCapacity = JSFinalObject::defaultInlineCapacity();
        }

        inlineCapacity = inferredInlineCapacity;
        ASSERT(inlineCapacity < JSFinalObject::maxInlineCapacity());
    } else {
        // Normal or large object.
        inlineCapacity = inferredInlineCapacity;
        if (inlineCapacity > JSFinalObject::maxInlineCapacity())
            inlineCapacity = JSFinalObject::maxInlineCapacity();
    }

    if (isPolyProto) {
        ++inlineCapacity;
        inlineCapacity = std::min(inlineCapacity, JSFinalObject::maxInlineCapacity());
    }

    ASSERT(inlineCapacity > 0);
    ASSERT(inlineCapacity <= JSFinalObject::maxInlineCapacity());

    size_t allocationSize = JSFinalObject::allocationSize(inlineCapacity);
    Allocator allocator = subspaceFor<JSFinalObject>(vm)->allocatorForNonVirtual(allocationSize, AllocatorForMode::EnsureAllocator);

    // Take advantage of extra inline capacity available in the size class.
    if (allocator) {
        size_t slop = (allocator.cellSize(vm.heap) - allocationSize) / sizeof(WriteBarrier<Unknown>);
        inlineCapacity += slop;
        if (inlineCapacity > JSFinalObject::maxInlineCapacity())
            inlineCapacity = JSFinalObject::maxInlineCapacity();
    }

    Structure* structure = vm.structureCache.emptyObjectStructureForPrototype(globalObject, prototype, inlineCapacity, isPolyProto, executable);

    if (isPolyProto) {
        ASSERT(structure->hasPolyProto());
        m_allocator = Allocator();
        executable->setCachedPolyProtoStructure(vm, structure);
    } else {
        if (executable) {
            ASSERT(constructor);
            ASSERT(functionRareData);
            InlineWatchpointSet& polyProtoWatchpointSet = executable->ensurePolyProtoWatchpoint();
            structure->ensureRareData(vm)->setSharedPolyProtoWatchpoint(executable->sharedPolyProtoWatchpoint());
            if (polyProtoWatchpointSet.isStillValid() && !functionRareData->hasAllocationProfileClearingWatchpoint()) {
                // If we happen to go poly proto in the future, we want to clear this particular
                // object allocation profile so we can transition to allocating poly proto objects.
                Watchpoint* watchpoint = functionRareData->createAllocationProfileClearingWatchpoint();
                polyProtoWatchpointSet.add(watchpoint);
            }
        }

        m_allocator = allocator;
    }

    // Ensure that if another thread sees the structure, it will see it properly created
    WTF::storeStoreFence();

    m_structure.set(vm, owner, structure);
    m_inlineCapacity = inlineCapacity;
}

ALWAYS_INLINE unsigned ObjectAllocationProfile::possibleDefaultPropertyCount(VM& vm, JSObject* prototype)
{
    if (prototype == prototype->globalObject()->objectPrototype())
        return 0;

    size_t count = 0;
    PropertyNameArray propertyNameArray(&vm, PropertyNameMode::StringsAndSymbols, PrivateSymbolMode::Include);
    prototype->structure()->getPropertyNamesFromStructure(vm, propertyNameArray, EnumerationMode());
    PropertyNameArrayData::PropertyNameVector& propertyNameVector = propertyNameArray.data()->propertyNameVector();
    for (size_t i = 0; i < propertyNameVector.size(); ++i) {
        JSValue value = prototype->getDirect(vm, propertyNameVector[i]);

        // Functions are common, and are usually class-level objects that are not overridden.
        if (jsDynamicCast<JSFunction*>(vm, value))
            continue;

        ++count;

    }
    return count;
}

} // namespace JSC