Example #1
0
 VirtualRegister assign(const Vector<unsigned>& allocation, VirtualRegister src)
 {
     VirtualRegister result = src;
     if (result.isLocal()) {
         unsigned myAllocation = allocation[result.toLocal()];
         if (myAllocation == UINT_MAX)
             result = VirtualRegister();
         else
             result = virtualRegisterForLocal(myAllocation);
     }
     return result;
 }
Example #2
0
void OSREntryData::dumpInContext(PrintStream& out, DumpContext* context) const
{
    out.print("bc#", m_bytecodeIndex, ", machine code offset = ", m_machineCodeOffset);
    out.print(", stack rules = [");
    
    auto printOperand = [&] (VirtualRegister reg) {
        out.print(inContext(m_expectedValues.operand(reg), context), " (");
        VirtualRegister toReg;
        bool overwritten = false;
        for (OSREntryReshuffling reshuffling : m_reshufflings) {
            if (reg == VirtualRegister(reshuffling.fromOffset)) {
                toReg = VirtualRegister(reshuffling.toOffset);
                break;
            }
            if (reg == VirtualRegister(reshuffling.toOffset))
                overwritten = true;
        }
        if (!overwritten && !toReg.isValid())
            toReg = reg;
        if (toReg.isValid()) {
            if (toReg.isLocal() && !m_machineStackUsed.get(toReg.toLocal()))
                out.print("ignored");
            else
                out.print("maps to ", toReg);
        } else
            out.print("overwritten");
        if (reg.isLocal() && m_localsForcedDouble.get(reg.toLocal()))
            out.print(", forced double");
        if (reg.isLocal() && m_localsForcedAnyInt.get(reg.toLocal()))
            out.print(", forced machine int");
        out.print(")");
    };
    
    CommaPrinter comma;
    for (size_t argumentIndex = m_expectedValues.numberOfArguments(); argumentIndex--;) {
        out.print(comma, "arg", argumentIndex, ":");
        printOperand(virtualRegisterForArgument(argumentIndex));
    }
    for (size_t localIndex = 0; localIndex < m_expectedValues.numberOfLocals(); ++localIndex) {
        out.print(comma, "loc", localIndex, ":");
        printOperand(virtualRegisterForLocal(localIndex));
    }
    
    out.print("], machine stack used = ", m_machineStackUsed);
}
static void compileStub(
    unsigned exitID, JITCode* jitCode, OSRExit& exit, VM* vm, CodeBlock* codeBlock)
{
    StackMaps::Record* record = nullptr;
    
    for (unsigned i = jitCode->stackmaps.records.size(); i--;) {
        record = &jitCode->stackmaps.records[i];
        if (record->patchpointID == exit.m_stackmapID)
            break;
    }
    
    RELEASE_ASSERT(record->patchpointID == exit.m_stackmapID);
    
    // This code requires framePointerRegister is the same as callFrameRegister
    static_assert(MacroAssembler::framePointerRegister == GPRInfo::callFrameRegister, "MacroAssembler::framePointerRegister and GPRInfo::callFrameRegister must be the same");

    CCallHelpers jit(vm, codeBlock);
    
    // We need scratch space to save all registers, to build up the JS stack, to deal with unwind
    // fixup, pointers to all of the objects we materialize, and the elements inside those objects
    // that we materialize.
    
    // Figure out how much space we need for those object allocations.
    unsigned numMaterializations = 0;
    size_t maxMaterializationNumArguments = 0;
    for (ExitTimeObjectMaterialization* materialization : exit.m_materializations) {
        numMaterializations++;
        
        maxMaterializationNumArguments = std::max(
            maxMaterializationNumArguments,
            materialization->properties().size());
    }
    
    ScratchBuffer* scratchBuffer = vm->scratchBufferForSize(
        sizeof(EncodedJSValue) * (
            exit.m_values.size() + numMaterializations + maxMaterializationNumArguments) +
        requiredScratchMemorySizeInBytes() +
        codeBlock->calleeSaveRegisters()->size() * sizeof(uint64_t));
    EncodedJSValue* scratch = scratchBuffer ? static_cast<EncodedJSValue*>(scratchBuffer->dataBuffer()) : 0;
    EncodedJSValue* materializationPointers = scratch + exit.m_values.size();
    EncodedJSValue* materializationArguments = materializationPointers + numMaterializations;
    char* registerScratch = bitwise_cast<char*>(materializationArguments + maxMaterializationNumArguments);
    uint64_t* unwindScratch = bitwise_cast<uint64_t*>(registerScratch + requiredScratchMemorySizeInBytes());
    
    HashMap<ExitTimeObjectMaterialization*, EncodedJSValue*> materializationToPointer;
    unsigned materializationCount = 0;
    for (ExitTimeObjectMaterialization* materialization : exit.m_materializations) {
        materializationToPointer.add(
            materialization, materializationPointers + materializationCount++);
    }
    
    // Note that we come in here, the stack used to be as LLVM left it except that someone called pushToSave().
    // We don't care about the value they saved. But, we do appreciate the fact that they did it, because we use
    // that slot for saveAllRegisters().

    saveAllRegisters(jit, registerScratch);
    
    // Bring the stack back into a sane form and assert that it's sane.
    jit.popToRestore(GPRInfo::regT0);
    jit.checkStackPointerAlignment();
    
    if (vm->m_perBytecodeProfiler && codeBlock->jitCode()->dfgCommon()->compilation) {
        Profiler::Database& database = *vm->m_perBytecodeProfiler;
        Profiler::Compilation* compilation = codeBlock->jitCode()->dfgCommon()->compilation.get();
        
        Profiler::OSRExit* profilerExit = compilation->addOSRExit(
            exitID, Profiler::OriginStack(database, codeBlock, exit.m_codeOrigin),
            exit.m_kind, exit.m_kind == UncountableInvalidation);
        jit.add64(CCallHelpers::TrustedImm32(1), CCallHelpers::AbsoluteAddress(profilerExit->counterAddress()));
    }

    // The remaining code assumes that SP/FP are in the same state that they were in the FTL's
    // call frame.
    
    // Get the call frame and tag thingies.
    // Restore the exiting function's callFrame value into a regT4
    jit.move(MacroAssembler::TrustedImm64(TagTypeNumber), GPRInfo::tagTypeNumberRegister);
    jit.move(MacroAssembler::TrustedImm64(TagMask), GPRInfo::tagMaskRegister);
    
    // Do some value profiling.
    if (exit.m_profileDataFormat != DataFormatNone) {
        record->locations[0].restoreInto(jit, jitCode->stackmaps, registerScratch, GPRInfo::regT0);
        reboxAccordingToFormat(
            exit.m_profileDataFormat, jit, GPRInfo::regT0, GPRInfo::regT1, GPRInfo::regT2);
        
        if (exit.m_kind == BadCache || exit.m_kind == BadIndexingType) {
            CodeOrigin codeOrigin = exit.m_codeOriginForExitProfile;
            if (ArrayProfile* arrayProfile = jit.baselineCodeBlockFor(codeOrigin)->getArrayProfile(codeOrigin.bytecodeIndex)) {
                jit.load32(MacroAssembler::Address(GPRInfo::regT0, JSCell::structureIDOffset()), GPRInfo::regT1);
                jit.store32(GPRInfo::regT1, arrayProfile->addressOfLastSeenStructureID());
                jit.load8(MacroAssembler::Address(GPRInfo::regT0, JSCell::indexingTypeOffset()), GPRInfo::regT1);
                jit.move(MacroAssembler::TrustedImm32(1), GPRInfo::regT2);
                jit.lshift32(GPRInfo::regT1, GPRInfo::regT2);
                jit.or32(GPRInfo::regT2, MacroAssembler::AbsoluteAddress(arrayProfile->addressOfArrayModes()));
            }
        }

        if (!!exit.m_valueProfile)
            jit.store64(GPRInfo::regT0, exit.m_valueProfile.getSpecFailBucket(0));
    }

    // Materialize all objects. Don't materialize an object until all
    // of the objects it needs have been materialized. We break cycles
    // by populating objects late - we only consider an object as
    // needing another object if the later is needed for the
    // allocation of the former.

    HashSet<ExitTimeObjectMaterialization*> toMaterialize;
    for (ExitTimeObjectMaterialization* materialization : exit.m_materializations)
        toMaterialize.add(materialization);

    while (!toMaterialize.isEmpty()) {
        unsigned previousToMaterializeSize = toMaterialize.size();

        Vector<ExitTimeObjectMaterialization*> worklist;
        worklist.appendRange(toMaterialize.begin(), toMaterialize.end());
        for (ExitTimeObjectMaterialization* materialization : worklist) {
            // Check if we can do anything about this right now.
            bool allGood = true;
            for (ExitPropertyValue value : materialization->properties()) {
                if (!value.value().isObjectMaterialization())
                    continue;
                if (!value.location().neededForMaterialization())
                    continue;
                if (toMaterialize.contains(value.value().objectMaterialization())) {
                    // Gotta skip this one, since it needs a
                    // materialization that hasn't been materialized.
                    allGood = false;
                    break;
                }
            }
            if (!allGood)
                continue;

            // All systems go for materializing the object. First we
            // recover the values of all of its fields and then we
            // call a function to actually allocate the beast.
            // We only recover the fields that are needed for the allocation.
            for (unsigned propertyIndex = materialization->properties().size(); propertyIndex--;) {
                const ExitPropertyValue& property = materialization->properties()[propertyIndex];
                const ExitValue& value = property.value();
                if (!property.location().neededForMaterialization())
                    continue;

                compileRecovery(
                    jit, value, record, jitCode->stackmaps, registerScratch,
                    materializationToPointer);
                jit.storePtr(GPRInfo::regT0, materializationArguments + propertyIndex);
            }
            
            // This call assumes that we don't pass arguments on the stack.
            jit.setupArgumentsWithExecState(
                CCallHelpers::TrustedImmPtr(materialization),
                CCallHelpers::TrustedImmPtr(materializationArguments));
            jit.move(CCallHelpers::TrustedImmPtr(bitwise_cast<void*>(operationMaterializeObjectInOSR)), GPRInfo::nonArgGPR0);
            jit.call(GPRInfo::nonArgGPR0);
            jit.storePtr(GPRInfo::returnValueGPR, materializationToPointer.get(materialization));

            // Let everyone know that we're done.
            toMaterialize.remove(materialization);
        }
        
        // We expect progress! This ensures that we crash rather than looping infinitely if there
        // is something broken about this fixpoint. Or, this could happen if we ever violate the
        // "materializations form a DAG" rule.
        RELEASE_ASSERT(toMaterialize.size() < previousToMaterializeSize);
    }

    // Now that all the objects have been allocated, we populate them
    // with the correct values. This time we can recover all the
    // fields, including those that are only needed for the allocation.
    for (ExitTimeObjectMaterialization* materialization : exit.m_materializations) {
        for (unsigned propertyIndex = materialization->properties().size(); propertyIndex--;) {
            const ExitValue& value = materialization->properties()[propertyIndex].value();
            compileRecovery(
                jit, value, record, jitCode->stackmaps, registerScratch,
                materializationToPointer);
            jit.storePtr(GPRInfo::regT0, materializationArguments + propertyIndex);
        }

        // This call assumes that we don't pass arguments on the stack
        jit.setupArgumentsWithExecState(
            CCallHelpers::TrustedImmPtr(materialization),
            CCallHelpers::TrustedImmPtr(materializationToPointer.get(materialization)),
            CCallHelpers::TrustedImmPtr(materializationArguments));
        jit.move(CCallHelpers::TrustedImmPtr(bitwise_cast<void*>(operationPopulateObjectInOSR)), GPRInfo::nonArgGPR0);
        jit.call(GPRInfo::nonArgGPR0);
    }

    // Save all state from wherever the exit data tells us it was, into the appropriate place in
    // the scratch buffer. This also does the reboxing.
    
    for (unsigned index = exit.m_values.size(); index--;) {
        compileRecovery(
            jit, exit.m_values[index], record, jitCode->stackmaps, registerScratch,
            materializationToPointer);
        jit.store64(GPRInfo::regT0, scratch + index);
    }
    
    // Henceforth we make it look like the exiting function was called through a register
    // preservation wrapper. This implies that FP must be nudged down by a certain amount. Then
    // we restore the various things according to either exit.m_values or by copying from the
    // old frame, and finally we save the various callee-save registers into where the
    // restoration thunk would restore them from.
    
    // Before we start messing with the frame, we need to set aside any registers that the
    // FTL code was preserving.
    for (unsigned i = codeBlock->calleeSaveRegisters()->size(); i--;) {
        RegisterAtOffset entry = codeBlock->calleeSaveRegisters()->at(i);
        jit.load64(
            MacroAssembler::Address(MacroAssembler::framePointerRegister, entry.offset()),
            GPRInfo::regT0);
        jit.store64(GPRInfo::regT0, unwindScratch + i);
    }
    
    jit.load32(CCallHelpers::payloadFor(JSStack::ArgumentCount), GPRInfo::regT2);
    
    // Let's say that the FTL function had failed its arity check. In that case, the stack will
    // contain some extra stuff.
    //
    // We compute the padded stack space:
    //
    //     paddedStackSpace = roundUp(codeBlock->numParameters - regT2 + 1)
    //
    // The stack will have regT2 + CallFrameHeaderSize stuff.
    // We want to make the stack look like this, from higher addresses down:
    //
    //     - argument padding
    //     - actual arguments
    //     - call frame header

    // This code assumes that we're dealing with FunctionCode.
    RELEASE_ASSERT(codeBlock->codeType() == FunctionCode);
    
    jit.add32(
        MacroAssembler::TrustedImm32(-codeBlock->numParameters()), GPRInfo::regT2,
        GPRInfo::regT3);
    MacroAssembler::Jump arityIntact = jit.branch32(
        MacroAssembler::GreaterThanOrEqual, GPRInfo::regT3, MacroAssembler::TrustedImm32(0));
    jit.neg32(GPRInfo::regT3);
    jit.add32(MacroAssembler::TrustedImm32(1 + stackAlignmentRegisters() - 1), GPRInfo::regT3);
    jit.and32(MacroAssembler::TrustedImm32(-stackAlignmentRegisters()), GPRInfo::regT3);
    jit.add32(GPRInfo::regT3, GPRInfo::regT2);
    arityIntact.link(&jit);

    CodeBlock* baselineCodeBlock = jit.baselineCodeBlockFor(exit.m_codeOrigin);

    // First set up SP so that our data doesn't get clobbered by signals.
    unsigned conservativeStackDelta =
        (exit.m_values.numberOfLocals() + baselineCodeBlock->calleeSaveSpaceAsVirtualRegisters()) * sizeof(Register) +
        maxFrameExtentForSlowPathCall;
    conservativeStackDelta = WTF::roundUpToMultipleOf(
        stackAlignmentBytes(), conservativeStackDelta);
    jit.addPtr(
        MacroAssembler::TrustedImm32(-conservativeStackDelta),
        MacroAssembler::framePointerRegister, MacroAssembler::stackPointerRegister);
    jit.checkStackPointerAlignment();

    RegisterSet allFTLCalleeSaves = RegisterSet::ftlCalleeSaveRegisters();
    RegisterAtOffsetList* baselineCalleeSaves = baselineCodeBlock->calleeSaveRegisters();

    for (Reg reg = Reg::first(); reg <= Reg::last(); reg = reg.next()) {
        if (!allFTLCalleeSaves.get(reg))
            continue;
        unsigned unwindIndex = codeBlock->calleeSaveRegisters()->indexOf(reg);
        RegisterAtOffset* baselineRegisterOffset = baselineCalleeSaves->find(reg);

        if (reg.isGPR()) {
            GPRReg regToLoad = baselineRegisterOffset ? GPRInfo::regT0 : reg.gpr();

            if (unwindIndex == UINT_MAX) {
                // The FTL compilation didn't preserve this register. This means that it also
                // didn't use the register. So its value at the beginning of OSR exit should be
                // preserved by the thunk. Luckily, we saved all registers into the register
                // scratch buffer, so we can restore them from there.
                jit.load64(registerScratch + offsetOfReg(reg), regToLoad);
            } else {
                // The FTL compilation preserved the register. Its new value is therefore
                // irrelevant, but we can get the value that was preserved by using the unwind
                // data. We've already copied all unwind-able preserved registers into the unwind
                // scratch buffer, so we can get it from there.
                jit.load64(unwindScratch + unwindIndex, regToLoad);
            }

            if (baselineRegisterOffset)
                jit.store64(regToLoad, MacroAssembler::Address(MacroAssembler::framePointerRegister, baselineRegisterOffset->offset()));
        } else {
            FPRReg fpRegToLoad = baselineRegisterOffset ? FPRInfo::fpRegT0 : reg.fpr();

            if (unwindIndex == UINT_MAX)
                jit.loadDouble(MacroAssembler::TrustedImmPtr(registerScratch + offsetOfReg(reg)), fpRegToLoad);
            else
                jit.loadDouble(MacroAssembler::TrustedImmPtr(unwindScratch + unwindIndex), fpRegToLoad);

            if (baselineRegisterOffset)
                jit.storeDouble(fpRegToLoad, MacroAssembler::Address(MacroAssembler::framePointerRegister, baselineRegisterOffset->offset()));
        }
    }

    size_t baselineVirtualRegistersForCalleeSaves = baselineCodeBlock->calleeSaveSpaceAsVirtualRegisters();

    // Now get state out of the scratch buffer and place it back into the stack. The values are
    // already reboxed so we just move them.
    for (unsigned index = exit.m_values.size(); index--;) {
        VirtualRegister reg = exit.m_values.virtualRegisterForIndex(index);

        if (reg.isLocal() && reg.toLocal() < static_cast<int>(baselineVirtualRegistersForCalleeSaves))
            continue;

        jit.load64(scratch + index, GPRInfo::regT0);
        jit.store64(GPRInfo::regT0, AssemblyHelpers::addressFor(reg));
    }
    
    handleExitCounts(jit, exit);
    reifyInlinedCallFrames(jit, exit);
    adjustAndJumpToTarget(jit, exit, false);
    
    LinkBuffer patchBuffer(*vm, jit, codeBlock);
    exit.m_code = FINALIZE_CODE_IF(
        shouldDumpDisassembly() || Options::verboseOSR() || Options::verboseFTLOSRExit(),
        patchBuffer,
        ("FTL OSR exit #%u (%s, %s) from %s, with operands = %s, and record = %s",
            exitID, toCString(exit.m_codeOrigin).data(),
            exitKindToString(exit.m_kind), toCString(*codeBlock).data(),
            toCString(ignoringContext<DumpContext>(exit.m_values)).data(),
            toCString(*record).data()));
}
    void handleBlockForTryCatch(BasicBlock* block, InsertionSet& insertionSet)
    {
        HandlerInfo* currentExceptionHandler = nullptr;
        FastBitVector liveAtCatchHead;
        liveAtCatchHead.resize(m_graph.block(0)->variablesAtTail.numberOfLocals());

        HandlerInfo* cachedHandlerResult;
        CodeOrigin cachedCodeOrigin;
        auto catchHandler = [&] (CodeOrigin origin) -> HandlerInfo* {
            ASSERT(origin);
            if (origin == cachedCodeOrigin)
                return cachedHandlerResult;

            unsigned bytecodeIndexToCheck = origin.bytecodeIndex;

            cachedCodeOrigin = origin;

            while (1) {
                InlineCallFrame* inlineCallFrame = origin.inlineCallFrame;
                CodeBlock* codeBlock = m_graph.baselineCodeBlockFor(inlineCallFrame);
                if (HandlerInfo* handler = codeBlock->handlerForBytecodeOffset(bytecodeIndexToCheck)) {
                    liveAtCatchHead.clearAll();

                    unsigned catchBytecodeIndex = handler->target;
                    m_graph.forAllLocalsLiveInBytecode(CodeOrigin(catchBytecodeIndex, inlineCallFrame), [&] (VirtualRegister operand) {
                        liveAtCatchHead[operand.toLocal()] = true;
                    });

                    cachedHandlerResult = handler;
                    break;
                }

                if (!inlineCallFrame) {
                    cachedHandlerResult = nullptr;
                    break;
                }

                bytecodeIndexToCheck = inlineCallFrame->directCaller.bytecodeIndex;
                origin = inlineCallFrame->directCaller;
            }

            return cachedHandlerResult;
        };

        Operands<VariableAccessData*> currentBlockAccessData(block->variablesAtTail.numberOfArguments(), block->variablesAtTail.numberOfLocals(), nullptr);
        HashSet<InlineCallFrame*> seenInlineCallFrames;

        auto flushEverything = [&] (NodeOrigin origin, unsigned index) {
            RELEASE_ASSERT(currentExceptionHandler);
            auto flush = [&] (VirtualRegister operand, bool alwaysInsert) {
                if ((operand.isLocal() && liveAtCatchHead[operand.toLocal()]) 
                    || operand.isArgument()
                    || alwaysInsert) {

                    ASSERT(isValidFlushLocation(block, index, operand));

                    VariableAccessData* accessData = currentBlockAccessData.operand(operand);
                    if (!accessData)
                        accessData = newVariableAccessData(operand);

                    currentBlockAccessData.operand(operand) = accessData;

                    insertionSet.insertNode(index, SpecNone, 
                        Flush, origin, OpInfo(accessData));
                }
            };

            for (unsigned local = 0; local < block->variablesAtTail.numberOfLocals(); local++)
                flush(virtualRegisterForLocal(local), false);
            for (InlineCallFrame* inlineCallFrame : seenInlineCallFrames)
                flush(VirtualRegister(inlineCallFrame->stackOffset + CallFrame::thisArgumentOffset()), true);
            flush(VirtualRegister(CallFrame::thisArgumentOffset()), true);

            seenInlineCallFrames.clear();
        };

        for (unsigned nodeIndex = 0; nodeIndex < block->size(); nodeIndex++) {
            Node* node = block->at(nodeIndex);

            {
                HandlerInfo* newHandler = catchHandler(node->origin.semantic);
                if (newHandler != currentExceptionHandler && currentExceptionHandler)
                    flushEverything(node->origin, nodeIndex);
                currentExceptionHandler = newHandler;
            }

            if (currentExceptionHandler && (node->op() == SetLocal || node->op() == SetArgument)) {
                InlineCallFrame* inlineCallFrame = node->origin.semantic.inlineCallFrame;
                if (inlineCallFrame)
                    seenInlineCallFrames.add(inlineCallFrame);
                VirtualRegister operand = node->local();

                int stackOffset = inlineCallFrame ? inlineCallFrame->stackOffset : 0;
                if ((operand.isLocal() && liveAtCatchHead[operand.toLocal()])
                    || operand.isArgument()
                    || (operand.offset() == stackOffset + CallFrame::thisArgumentOffset())) {

                    ASSERT(isValidFlushLocation(block, nodeIndex, operand));

                    VariableAccessData* variableAccessData = currentBlockAccessData.operand(operand);
                    if (!variableAccessData)
                        variableAccessData = newVariableAccessData(operand);

                    insertionSet.insertNode(nodeIndex, SpecNone, 
                        Flush, node->origin, OpInfo(variableAccessData));
                }
            }

            if (node->accessesStack(m_graph))
                currentBlockAccessData.operand(node->local()) = node->variableAccessData();
        }

        if (currentExceptionHandler) {
            NodeOrigin origin = block->at(block->size() - 1)->origin;
            flushEverything(origin, block->size());
        }
    }
    bool run()
    {
        SharedSymbolTable* symbolTable = codeBlock()->symbolTable();

        // This enumerates the locals that we actually care about and packs them. So for example
        // if we use local 1, 3, 4, 5, 7, then we remap them: 1->0, 3->1, 4->2, 5->3, 7->4. We
        // treat a variable as being "used" if there exists an access to it (SetLocal, GetLocal,
        // Flush, PhantomLocal).
        
        BitVector usedLocals;
        
        // Collect those variables that are used from IR.
        bool hasGetLocalUnlinked = false;
        for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
            BasicBlock* block = m_graph.block(blockIndex);
            if (!block)
                continue;
            for (unsigned nodeIndex = block->size(); nodeIndex--;) {
                Node* node = block->at(nodeIndex);
                switch (node->op()) {
                case GetLocal:
                case SetLocal:
                case Flush:
                case PhantomLocal: {
                    VariableAccessData* variable = node->variableAccessData();
                    if (variable->local().isArgument())
                        break;
                    usedLocals.set(variable->local().toLocal());
                    break;
                }
                    
                case GetLocalUnlinked: {
                    VirtualRegister operand = node->unlinkedLocal();
                    if (operand.isArgument())
                        break;
                    usedLocals.set(operand.toLocal());
                    hasGetLocalUnlinked = true;
                    break;
                }
                    
                default:
                    break;
                }
            }
        }
        
        // Ensure that captured variables and captured inline arguments are pinned down.
        // They should have been because of flushes, except that the flushes can be optimized
        // away.
        if (symbolTable) {
            for (int i = symbolTable->captureStart(); i > symbolTable->captureEnd(); i--)
                usedLocals.set(VirtualRegister(i).toLocal());
        }
        if (codeBlock()->usesArguments()) {
            usedLocals.set(codeBlock()->argumentsRegister().toLocal());
            usedLocals.set(unmodifiedArgumentsRegister(codeBlock()->argumentsRegister()).toLocal());
        }
        if (codeBlock()->uncheckedActivationRegister().isValid())
            usedLocals.set(codeBlock()->activationRegister().toLocal());
        for (InlineCallFrameSet::iterator iter = m_graph.m_inlineCallFrames->begin(); !!iter; ++iter) {
            InlineCallFrame* inlineCallFrame = *iter;
            if (!inlineCallFrame->executable->usesArguments())
                continue;
            
            VirtualRegister argumentsRegister = m_graph.argumentsRegisterFor(inlineCallFrame);
            usedLocals.set(argumentsRegister.toLocal());
            usedLocals.set(unmodifiedArgumentsRegister(argumentsRegister).toLocal());
            
            for (unsigned argument = inlineCallFrame->arguments.size(); argument-- > 1;) {
                usedLocals.set(VirtualRegister(
                    virtualRegisterForArgument(argument).offset() +
                    inlineCallFrame->stackOffset).toLocal());
            }
        }
        
        Vector<unsigned> allocation(usedLocals.size());
        m_graph.m_nextMachineLocal = 0;
        for (unsigned i = 0; i < usedLocals.size(); ++i) {
            if (!usedLocals.get(i)) {
                allocation[i] = UINT_MAX;
                continue;
            }
            
            allocation[i] = m_graph.m_nextMachineLocal++;
        }
        
        for (unsigned i = m_graph.m_variableAccessData.size(); i--;) {
            VariableAccessData* variable = &m_graph.m_variableAccessData[i];
            if (!variable->isRoot())
                continue;
            
            if (variable->local().isArgument()) {
                variable->machineLocal() = variable->local();
                continue;
            }
            
            size_t local = variable->local().toLocal();
            if (local >= allocation.size())
                continue;
            
            if (allocation[local] == UINT_MAX)
                continue;
            
            variable->machineLocal() = virtualRegisterForLocal(
                allocation[variable->local().toLocal()]);
        }
        
        if (codeBlock()->usesArguments()) {
            VirtualRegister argumentsRegister = virtualRegisterForLocal(
                allocation[codeBlock()->argumentsRegister().toLocal()]);
            RELEASE_ASSERT(
                virtualRegisterForLocal(allocation[
                    unmodifiedArgumentsRegister(
                        codeBlock()->argumentsRegister()).toLocal()])
                == unmodifiedArgumentsRegister(argumentsRegister));
            codeBlock()->setArgumentsRegister(argumentsRegister);
        }
        
        if (codeBlock()->uncheckedActivationRegister().isValid()) {
            codeBlock()->setActivationRegister(
                virtualRegisterForLocal(allocation[codeBlock()->activationRegister().toLocal()]));
        }
        
        for (unsigned i = m_graph.m_inlineVariableData.size(); i--;) {
            InlineVariableData data = m_graph.m_inlineVariableData[i];
            InlineCallFrame* inlineCallFrame = data.inlineCallFrame;
            
            if (inlineCallFrame->executable->usesArguments()) {
                inlineCallFrame->argumentsRegister = virtualRegisterForLocal(
                    allocation[m_graph.argumentsRegisterFor(inlineCallFrame).toLocal()]);

                RELEASE_ASSERT(
                    virtualRegisterForLocal(allocation[unmodifiedArgumentsRegister(
                        m_graph.argumentsRegisterFor(inlineCallFrame)).toLocal()])
                    == unmodifiedArgumentsRegister(inlineCallFrame->argumentsRegister));
            }
            
            for (unsigned argument = inlineCallFrame->arguments.size(); argument-- > 1;) {
                ArgumentPosition& position = m_graph.m_argumentPositions[
                    data.argumentPositionStart + argument];
                VariableAccessData* variable = position.someVariable();
                ValueSource source;
                if (!variable)
                    source = ValueSource(SourceIsDead);
                else {
                    source = ValueSource::forFlushFormat(
                        variable->machineLocal(), variable->flushFormat());
                }
                inlineCallFrame->arguments[argument] = source.valueRecovery();
            }
            
            RELEASE_ASSERT(inlineCallFrame->isClosureCall == !!data.calleeVariable);
            if (inlineCallFrame->isClosureCall) {
                ValueSource source = ValueSource::forFlushFormat(
                    data.calleeVariable->machineLocal(),
                    data.calleeVariable->flushFormat());
                inlineCallFrame->calleeRecovery = source.valueRecovery();
            } else
                RELEASE_ASSERT(inlineCallFrame->calleeRecovery.isConstant());
        }
        
        if (symbolTable) {
            if (symbolTable->captureCount()) {
                unsigned captureStartLocal = allocation[
                    VirtualRegister(codeBlock()->symbolTable()->captureStart()).toLocal()];
                ASSERT(captureStartLocal != UINT_MAX);
                m_graph.m_machineCaptureStart = virtualRegisterForLocal(captureStartLocal).offset();
            } else
                m_graph.m_machineCaptureStart = virtualRegisterForLocal(0).offset();
        
            // This is an abomination. If we had captured an argument then the argument ends
            // up being "slow", meaning that loads of the argument go through an extra lookup
            // table.
            if (const SlowArgument* slowArguments = symbolTable->slowArguments()) {
                auto newSlowArguments = std::make_unique<SlowArgument[]>(
                    symbolTable->parameterCount());
                for (size_t i = symbolTable->parameterCount(); i--;) {
                    newSlowArguments[i] = slowArguments[i];
                    VirtualRegister reg = VirtualRegister(slowArguments[i].index);
                    if (reg.isLocal())
                        newSlowArguments[i].index = virtualRegisterForLocal(allocation[reg.toLocal()]).offset();
                }
            
                m_graph.m_slowArguments = std::move(newSlowArguments);
            }
        }
        
        // Fix GetLocalUnlinked's variable references.
        if (hasGetLocalUnlinked) {
            for (BlockIndex blockIndex = m_graph.numBlocks(); blockIndex--;) {
                BasicBlock* block = m_graph.block(blockIndex);
                if (!block)
                    continue;
                for (unsigned nodeIndex = block->size(); nodeIndex--;) {
                    Node* node = block->at(nodeIndex);
                    switch (node->op()) {
                    case GetLocalUnlinked: {
                        VirtualRegister operand = node->unlinkedLocal();
                        if (operand.isLocal())
                            operand = virtualRegisterForLocal(allocation[operand.toLocal()]);
                        node->setUnlinkedMachineLocal(operand);
                        break;
                    }
                        
                    default:
                        break;
                    }
                }
            }
        }
        
        return true;
    }