PutByIdStatus.cpp   [plain text]

/*
 * Copyright (C) 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.
 *
 * 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. 
 */

#include "config.h"
#include "PutByIdStatus.h"

#include "CodeBlock.h"
#include "LLIntData.h"
#include "LowLevelInterpreter.h"
#include "Operations.h"
#include "Structure.h"
#include "StructureChain.h"

namespace JSC {

PutByIdStatus PutByIdStatus::computeFromLLInt(CodeBlock* profiledBlock, unsigned bytecodeIndex, Identifier& ident)
{
    UNUSED_PARAM(profiledBlock);
    UNUSED_PARAM(bytecodeIndex);
    UNUSED_PARAM(ident);
#if ENABLE(LLINT)
    Instruction* instruction = profiledBlock->instructions().begin() + bytecodeIndex;

    Structure* structure = instruction[4].u.structure.get();
    if (!structure)
        return PutByIdStatus(NoInformation, 0, 0, 0, invalidOffset);
    
    if (instruction[0].u.opcode == LLInt::getOpcode(llint_op_put_by_id)
        || instruction[0].u.opcode == LLInt::getOpcode(llint_op_put_by_id_out_of_line)) {
        PropertyOffset offset = structure->get(*profiledBlock->vm(), ident);
        if (!isValidOffset(offset))
            return PutByIdStatus(NoInformation, 0, 0, 0, invalidOffset);
        
        return PutByIdStatus(SimpleReplace, structure, 0, 0, offset);
    }
    
    ASSERT(structure->transitionWatchpointSetHasBeenInvalidated());
    
    ASSERT(instruction[0].u.opcode == LLInt::getOpcode(llint_op_put_by_id_transition_direct)
           || instruction[0].u.opcode == LLInt::getOpcode(llint_op_put_by_id_transition_normal)
           || instruction[0].u.opcode == LLInt::getOpcode(llint_op_put_by_id_transition_direct_out_of_line)
           || instruction[0].u.opcode == LLInt::getOpcode(llint_op_put_by_id_transition_normal_out_of_line));
    
    Structure* newStructure = instruction[6].u.structure.get();
    StructureChain* chain = instruction[7].u.structureChain.get();
    ASSERT(newStructure);
    ASSERT(chain);
    
    PropertyOffset offset = newStructure->get(*profiledBlock->vm(), ident);
    if (!isValidOffset(offset))
        return PutByIdStatus(NoInformation, 0, 0, 0, invalidOffset);
    
    return PutByIdStatus(SimpleTransition, structure, newStructure, chain, offset);
#else
    return PutByIdStatus(NoInformation, 0, 0, 0, invalidOffset);
#endif
}

PutByIdStatus PutByIdStatus::computeFor(CodeBlock* profiledBlock, unsigned bytecodeIndex, Identifier& ident)
{
    UNUSED_PARAM(profiledBlock);
    UNUSED_PARAM(bytecodeIndex);
    UNUSED_PARAM(ident);
#if ENABLE(JIT) && ENABLE(VALUE_PROFILER)
    if (!profiledBlock->numberOfStructureStubInfos())
        return computeFromLLInt(profiledBlock, bytecodeIndex, ident);
    
    if (profiledBlock->likelyToTakeSlowCase(bytecodeIndex))
        return PutByIdStatus(TakesSlowPath, 0, 0, 0, invalidOffset);
    
    StructureStubInfo& stubInfo = profiledBlock->getStubInfo(bytecodeIndex);
    if (!stubInfo.seen)
        return computeFromLLInt(profiledBlock, bytecodeIndex, ident);
    
    if (stubInfo.resetByGC)
        return PutByIdStatus(TakesSlowPath, 0, 0, 0, invalidOffset);

    switch (stubInfo.accessType) {
    case access_unset:
        // If the JIT saw it but didn't optimize it, then assume that this takes slow path.
        return PutByIdStatus(TakesSlowPath, 0, 0, 0, invalidOffset);
        
    case access_put_by_id_replace: {
        PropertyOffset offset = stubInfo.u.putByIdReplace.baseObjectStructure->get(
            *profiledBlock->vm(), ident);
        if (isValidOffset(offset)) {
            return PutByIdStatus(
                SimpleReplace,
                stubInfo.u.putByIdReplace.baseObjectStructure.get(),
                0, 0,
                offset);
        }
        return PutByIdStatus(TakesSlowPath, 0, 0, 0, invalidOffset);
    }
        
    case access_put_by_id_transition_normal:
    case access_put_by_id_transition_direct: {
        ASSERT(stubInfo.u.putByIdTransition.previousStructure->transitionWatchpointSetHasBeenInvalidated());
        PropertyOffset offset = stubInfo.u.putByIdTransition.structure->get(
            *profiledBlock->vm(), ident);
        if (isValidOffset(offset)) {
            return PutByIdStatus(
                SimpleTransition,
                stubInfo.u.putByIdTransition.previousStructure.get(),
                stubInfo.u.putByIdTransition.structure.get(),
                stubInfo.u.putByIdTransition.chain.get(),
                offset);
        }
        return PutByIdStatus(TakesSlowPath, 0, 0, 0, invalidOffset);
    }
        
    default:
        return PutByIdStatus(TakesSlowPath, 0, 0, 0, invalidOffset);
    }
#else // ENABLE(JIT)
    return PutByIdStatus(NoInformation, 0, 0, 0, invalidOffset);
#endif // ENABLE(JIT)
}

PutByIdStatus PutByIdStatus::computeFor(VM& vm, JSGlobalObject* globalObject, Structure* structure, Identifier& ident, bool isDirect)
{
    if (PropertyName(ident).asIndex() != PropertyName::NotAnIndex)
        return PutByIdStatus(TakesSlowPath);
    
    if (structure->typeInfo().overridesGetOwnPropertySlot())
        return PutByIdStatus(TakesSlowPath);

    if (!structure->propertyAccessesAreCacheable())
        return PutByIdStatus(TakesSlowPath);
    
    unsigned attributes;
    JSCell* specificValue;
    PropertyOffset offset = structure->get(vm, ident, attributes, specificValue);
    if (isValidOffset(offset)) {
        if (attributes & (Accessor | ReadOnly))
            return PutByIdStatus(TakesSlowPath);
        if (specificValue) {
            // We need the PutById slow path to verify that we're storing the right value into
            // the specialized slot.
            return PutByIdStatus(TakesSlowPath);
        }
        return PutByIdStatus(SimpleReplace, structure, 0, 0, offset);
    }
    
    // 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);
    
    if (!isDirect) {
        // If the prototype chain has setters or read-only properties, then give up.
        if (structure->prototypeChainMayInterceptStoreTo(vm, ident))
            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 (!isPrototypeChainNormalized(globalObject, structure))
            return PutByIdStatus(TakesSlowPath);
    }
    
    // We only optimize if there is already a structure that the transition is cached to.
    // Among other things, this allows us to guard against a transition with a specific
    // value.
    //
    // - If we're storing a value that could be specific: this would only be a problem if
    //   the existing transition did have a specific value already, since if it didn't,
    //   then we would behave "as if" we were not storing a specific value. If it did
    //   have a specific value, then we'll know - the fact that we pass 0 for
    //   specificValue will tell us.
    //
    // - If we're not storing a value that could be specific: again, this would only be a
    //   problem if the existing transition did have a specific value, which we check for
    //   by passing 0 for the specificValue.
    Structure* transition = Structure::addPropertyTransitionToExistingStructure(structure, ident, 0, 0, offset);
    if (!transition)
        return PutByIdStatus(TakesSlowPath); // This occurs in bizarre cases only. See above.
    ASSERT(!transition->transitionDidInvolveSpecificValue());
    ASSERT(isValidOffset(offset));
    
    return PutByIdStatus(
        SimpleTransition, structure, transition,
        structure->prototypeChain(vm, globalObject), offset);
}

} // namespace JSC