path: root/Source/JavaScriptCore/dfg/DFGJITCompiler.cpp

/*
 * Copyright (C) 2011, 2013-2015 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.
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 *    notice, this list of conditions and the following disclaimer in the
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#include "config.h"
#include "DFGJITCompiler.h"

#if ENABLE(DFG_JIT)

#include "CodeBlock.h"
#include "DFGFailedFinalizer.h"
#include "DFGInlineCacheWrapperInlines.h"
#include "DFGJITCode.h"
#include "DFGJITFinalizer.h"
#include "DFGOSRExitCompiler.h"
#include "DFGOperations.h"
#include "DFGRegisterBank.h"
#include "DFGSlowPathGenerator.h"
#include "DFGSpeculativeJIT.h"
#include "DFGThunks.h"
#include "JSCJSValueInlines.h"
#include "LinkBuffer.h"
#include "MaxFrameExtentForSlowPathCall.h"
#include "JSCInlines.h"
#include "VM.h"

namespace JSC { namespace DFG {

JITCompiler::JITCompiler(Graph& dfg)
    : CCallHelpers(&dfg.m_vm, dfg.m_codeBlock)
    , m_graph(dfg)
    , m_jitCode(adoptRef(new JITCode()))
    , m_blockHeads(dfg.numBlocks())
    , m_pcToCodeOriginMapBuilder(dfg.m_vm)
{
    if (shouldDumpDisassembly() || m_graph.m_vm.m_perBytecodeProfiler)
        m_disassembler = std::make_unique<Disassembler>(dfg);
}

JITCompiler::~JITCompiler()
{
}

void JITCompiler::linkOSRExits()
{
    ASSERT(m_jitCode->osrExit.size() == m_exitCompilationInfo.size());
    if (m_graph.compilation()) {
        for (unsigned i = 0; i < m_jitCode->osrExit.size(); ++i) {
            OSRExitCompilationInfo& info = m_exitCompilationInfo[i];
            Vector<Label> labels;
            if (!info.m_failureJumps.empty()) {
                for (unsigned j = 0; j < info.m_failureJumps.jumps().size(); ++j)
                    labels.append(info.m_failureJumps.jumps()[j].label());
            } else
                labels.append(info.m_replacementSource);
            m_exitSiteLabels.append(labels);
        }
    }
    
    for (unsigned i = 0; i < m_jitCode->osrExit.size(); ++i) {
        OSRExit& exit = m_jitCode->osrExit[i];
        OSRExitCompilationInfo& info = m_exitCompilationInfo[i];
        JumpList& failureJumps = info.m_failureJumps;
        if (!failureJumps.empty())
            failureJumps.link(this);
        else
            info.m_replacementDestination = label();

        jitAssertHasValidCallFrame();
        store32(TrustedImm32(i), &vm()->osrExitIndex);
        exit.setPatchableCodeOffset(patchableJump());
    }
}

void JITCompiler::compileEntry()
{
    // This code currently matches the old JIT. In the function header we need to
    // save return address and call frame via the prologue and perform a fast stack check.
    // FIXME: https://bugs.webkit.org/show_bug.cgi?id=56292
    // We'll need to convert the remaining cti_ style calls (specifically the stack
    // check) which will be dependent on stack layout. (We'd need to account for this in
    // both normal return code and when jumping to an exception handler).
    emitFunctionPrologue();
    emitPutToCallFrameHeader(m_codeBlock, JSStack::CodeBlock);
}

void JITCompiler::compileSetupRegistersForEntry()
{
    emitSaveCalleeSaves();
    emitMaterializeTagCheckRegisters();    
}

void JITCompiler::compileEntryExecutionFlag()
{
#if ENABLE(FTL_JIT)
    if (m_graph.m_plan.canTierUpAndOSREnter)
        store8(TrustedImm32(0), &m_jitCode->neverExecutedEntry);
#endif // ENABLE(FTL_JIT)
}

void JITCompiler::compileBody()
{
    // We generate the speculative code path, followed by OSR exit code to return
    // to the old JIT code if speculations fail.

    bool compiledSpeculative = m_speculative->compile();
    ASSERT_UNUSED(compiledSpeculative, compiledSpeculative);
}

void JITCompiler::compileExceptionHandlers()
{
    if (!m_exceptionChecksWithCallFrameRollback.empty()) {
        m_exceptionChecksWithCallFrameRollback.link(this);

        copyCalleeSavesToVMCalleeSavesBuffer();

        // lookupExceptionHandlerFromCallerFrame is passed two arguments, the VM and the exec (the CallFrame*).
        move(TrustedImmPtr(vm()), GPRInfo::argumentGPR0);
        move(GPRInfo::callFrameRegister, GPRInfo::argumentGPR1);
        addPtr(TrustedImm32(m_graph.stackPointerOffset() * sizeof(Register)), GPRInfo::callFrameRegister, stackPointerRegister);

#if CPU(X86)
        // FIXME: should use the call abstraction, but this is currently in the SpeculativeJIT layer!
        poke(GPRInfo::argumentGPR0);
        poke(GPRInfo::argumentGPR1, 1);
#endif
        m_calls.append(CallLinkRecord(call(), lookupExceptionHandlerFromCallerFrame));

        jumpToExceptionHandler();
    }

    if (!m_exceptionChecks.empty()) {
        m_exceptionChecks.link(this);

        copyCalleeSavesToVMCalleeSavesBuffer();

        // lookupExceptionHandler is passed two arguments, the VM and the exec (the CallFrame*).
        move(TrustedImmPtr(vm()), GPRInfo::argumentGPR0);
        move(GPRInfo::callFrameRegister, GPRInfo::argumentGPR1);

#if CPU(X86)
        // FIXME: should use the call abstraction, but this is currently in the SpeculativeJIT layer!
        poke(GPRInfo::argumentGPR0);
        poke(GPRInfo::argumentGPR1, 1);
#endif
        m_calls.append(CallLinkRecord(call(), lookupExceptionHandler));

        jumpToExceptionHandler();
    }
}

void JITCompiler::link(LinkBuffer& linkBuffer)
{
    // Link the code, populate data in CodeBlock data structures.
    m_jitCode->common.frameRegisterCount = m_graph.frameRegisterCount();
    m_jitCode->common.requiredRegisterCountForExit = m_graph.requiredRegisterCountForExit();

    if (!m_graph.m_plan.inlineCallFrames->isEmpty())
        m_jitCode->common.inlineCallFrames = m_graph.m_plan.inlineCallFrames;
    
#if USE(JSVALUE32_64)
    m_jitCode->common.doubleConstants = WTFMove(m_graph.m_doubleConstants);
#endif
    
    m_graph.registerFrozenValues();

    BitVector usedJumpTables;
    for (Bag<SwitchData>::iterator iter = m_graph.m_switchData.begin(); !!iter; ++iter) {
        SwitchData& data = **iter;
        if (!data.didUseJumpTable)
            continue;
        
        if (data.kind == SwitchString)
            continue;
        
        RELEASE_ASSERT(data.kind == SwitchImm || data.kind == SwitchChar);
        
        usedJumpTables.set(data.switchTableIndex);
        SimpleJumpTable& table = m_codeBlock->switchJumpTable(data.switchTableIndex);
        table.ctiDefault = linkBuffer.locationOf(m_blockHeads[data.fallThrough.block->index]);
        table.ctiOffsets.grow(table.branchOffsets.size());
        for (unsigned j = table.ctiOffsets.size(); j--;)
            table.ctiOffsets[j] = table.ctiDefault;
        for (unsigned j = data.cases.size(); j--;) {
            SwitchCase& myCase = data.cases[j];
            table.ctiOffsets[myCase.value.switchLookupValue(data.kind) - table.min] =
                linkBuffer.locationOf(m_blockHeads[myCase.target.block->index]);
        }
    }
    
    for (unsigned i = m_codeBlock->numberOfSwitchJumpTables(); i--;) {
        if (usedJumpTables.get(i))
            continue;
        
        m_codeBlock->switchJumpTable(i).clear();
    }

    // NOTE: we cannot clear string switch tables because (1) we're running concurrently
    // and we cannot deref StringImpl's and (2) it would be weird to deref those
    // StringImpl's since we refer to them.
    for (Bag<SwitchData>::iterator switchDataIter = m_graph.m_switchData.begin(); !!switchDataIter; ++switchDataIter) {
        SwitchData& data = **switchDataIter;
        if (!data.didUseJumpTable)
            continue;
        
        if (data.kind != SwitchString)
            continue;
        
        StringJumpTable& table = m_codeBlock->stringSwitchJumpTable(data.switchTableIndex);
        table.ctiDefault = linkBuffer.locationOf(m_blockHeads[data.fallThrough.block->index]);
        StringJumpTable::StringOffsetTable::iterator iter;
        StringJumpTable::StringOffsetTable::iterator end = table.offsetTable.end();
        for (iter = table.offsetTable.begin(); iter != end; ++iter)
            iter->value.ctiOffset = table.ctiDefault;
        for (unsigned j = data.cases.size(); j--;) {
            SwitchCase& myCase = data.cases[j];
            iter = table.offsetTable.find(myCase.value.stringImpl());
            RELEASE_ASSERT(iter != end);
            iter->value.ctiOffset = linkBuffer.locationOf(m_blockHeads[myCase.target.block->index]);
        }
    }

    // Link all calls out from the JIT code to their respective functions.
    for (unsigned i = 0; i < m_calls.size(); ++i)
        linkBuffer.link(m_calls[i].m_call, m_calls[i].m_function);

    for (unsigned i = m_getByIds.size(); i--;)
        m_getByIds[i].finalize(linkBuffer);
    for (unsigned i = m_putByIds.size(); i--;)
        m_putByIds[i].finalize(linkBuffer);

    for (unsigned i = 0; i < m_ins.size(); ++i) {
        StructureStubInfo& info = *m_ins[i].m_stubInfo;
        CodeLocationCall callReturnLocation = linkBuffer.locationOf(m_ins[i].m_slowPathGenerator->call());
        info.patch.deltaCallToDone = differenceBetweenCodePtr(callReturnLocation, linkBuffer.locationOf(m_ins[i].m_done));
        info.patch.deltaCallToJump = differenceBetweenCodePtr(callReturnLocation, linkBuffer.locationOf(m_ins[i].m_jump));
        info.callReturnLocation = callReturnLocation;
        info.patch.deltaCallToSlowCase = differenceBetweenCodePtr(callReturnLocation, linkBuffer.locationOf(m_ins[i].m_slowPathGenerator->label()));
    }
    
    for (unsigned i = 0; i < m_jsCalls.size(); ++i) {
        JSCallRecord& record = m_jsCalls[i];
        CallLinkInfo& info = *record.m_info;
        linkBuffer.link(record.m_slowCall, FunctionPtr(m_vm->getCTIStub(linkCallThunkGenerator).code().executableAddress()));
        info.setCallLocations(linkBuffer.locationOfNearCall(record.m_slowCall),
            linkBuffer.locationOf(record.m_targetToCheck),
            linkBuffer.locationOfNearCall(record.m_fastCall));
    }
    
    MacroAssemblerCodeRef osrExitThunk = vm()->getCTIStub(osrExitGenerationThunkGenerator);
    CodeLocationLabel target = CodeLocationLabel(osrExitThunk.code());
    for (unsigned i = 0; i < m_jitCode->osrExit.size(); ++i) {
        OSRExit& exit = m_jitCode->osrExit[i];
        OSRExitCompilationInfo& info = m_exitCompilationInfo[i];
        linkBuffer.link(exit.getPatchableCodeOffsetAsJump(), target);
        exit.correctJump(linkBuffer);
        if (info.m_replacementSource.isSet()) {
            m_jitCode->common.jumpReplacements.append(JumpReplacement(
                linkBuffer.locationOf(info.m_replacementSource),
                linkBuffer.locationOf(info.m_replacementDestination)));
        }
    }
    
    if (m_graph.compilation()) {
        ASSERT(m_exitSiteLabels.size() == m_jitCode->osrExit.size());
        for (unsigned i = 0; i < m_exitSiteLabels.size(); ++i) {
            Vector<Label>& labels = m_exitSiteLabels[i];
            Vector<const void*> addresses;
            for (unsigned j = 0; j < labels.size(); ++j)
                addresses.append(linkBuffer.locationOf(labels[j]).executableAddress());
            m_graph.compilation()->addOSRExitSite(addresses);
        }
    } else
        ASSERT(!m_exitSiteLabels.size());

    m_jitCode->common.compilation = m_graph.compilation();
    
    // Link new DFG exception handlers and remove baseline JIT handlers.
    m_codeBlock->clearExceptionHandlers();
    for (unsigned  i = 0; i < m_exceptionHandlerOSRExitCallSites.size(); i++) {
        OSRExitCompilationInfo& info = m_exceptionHandlerOSRExitCallSites[i].exitInfo;
        if (info.m_replacementDestination.isSet()) {
            // If this is is *not* set, it means that we already jumped to the OSR exit in pure generated control flow.
            // i.e, we explicitly emitted an exceptionCheck that we know will be caught in this machine frame.
            // If this *is set*, it means we will be landing at this code location from genericUnwind from an
            // exception thrown in a child call frame.
            CodeLocationLabel catchLabel = linkBuffer.locationOf(info.m_replacementDestination);
            HandlerInfo newExceptionHandler = m_exceptionHandlerOSRExitCallSites[i].baselineExceptionHandler;
            CallSiteIndex callSite = m_exceptionHandlerOSRExitCallSites[i].callSiteIndex;
            newExceptionHandler.start = callSite.bits();
            newExceptionHandler.end = callSite.bits() + 1;
            newExceptionHandler.nativeCode = catchLabel;
            m_codeBlock->appendExceptionHandler(newExceptionHandler);
        }
    }

    if (m_pcToCodeOriginMapBuilder.didBuildMapping())
        m_codeBlock->setPCToCodeOriginMap(std::make_unique<PCToCodeOriginMap>(WTFMove(m_pcToCodeOriginMapBuilder), linkBuffer));
}

void JITCompiler::compile()
{
    SamplingRegion samplingRegion("DFG Backend");

    setStartOfCode();
    compileEntry();
    m_speculative = std::make_unique<SpeculativeJIT>(*this);

    // Plant a check that sufficient space is available in the JSStack.
    addPtr(TrustedImm32(virtualRegisterForLocal(m_graph.requiredRegisterCountForExecutionAndExit() - 1).offset() * sizeof(Register)), GPRInfo::callFrameRegister, GPRInfo::regT1);
    Jump stackOverflow = branchPtr(Above, AbsoluteAddress(m_vm->addressOfStackLimit()), GPRInfo::regT1);

    addPtr(TrustedImm32(m_graph.stackPointerOffset() * sizeof(Register)), GPRInfo::callFrameRegister, stackPointerRegister);
    checkStackPointerAlignment();
    compileSetupRegistersForEntry();
    compileEntryExecutionFlag();
    compileBody();
    setEndOfMainPath();

    // === Footer code generation ===
    //
    // Generate the stack overflow handling; if the stack check in the entry head fails,
    // we need to call out to a helper function to throw the StackOverflowError.
    stackOverflow.link(this);

    emitStoreCodeOrigin(CodeOrigin(0));

    if (maxFrameExtentForSlowPathCall)
        addPtr(TrustedImm32(-maxFrameExtentForSlowPathCall), stackPointerRegister);

    m_speculative->callOperationWithCallFrameRollbackOnException(operationThrowStackOverflowError, m_codeBlock);

    // Generate slow path code.
    m_speculative->runSlowPathGenerators(m_pcToCodeOriginMapBuilder);
    m_pcToCodeOriginMapBuilder.appendItem(label(), PCToCodeOriginMapBuilder::defaultCodeOrigin());
    
    compileExceptionHandlers();
    linkOSRExits();
    
    // Create OSR entry trampolines if necessary.
    m_speculative->createOSREntries();
    setEndOfCode();

    auto linkBuffer = std::make_unique<LinkBuffer>(*m_vm, *this, m_codeBlock, JITCompilationCanFail);
    if (linkBuffer->didFailToAllocate()) {
        m_graph.m_plan.finalizer = std::make_unique<FailedFinalizer>(m_graph.m_plan);
        return;
    }
    
    link(*linkBuffer);
    m_speculative->linkOSREntries(*linkBuffer);

    m_jitCode->shrinkToFit();
    codeBlock()->shrinkToFit(CodeBlock::LateShrink);

    disassemble(*linkBuffer);
    
    m_graph.m_plan.finalizer = std::make_unique<JITFinalizer>(
        m_graph.m_plan, m_jitCode.release(), WTFMove(linkBuffer));
}

void JITCompiler::compileFunction()
{
    SamplingRegion samplingRegion("DFG Backend");
    
    setStartOfCode();
    compileEntry();

    // === Function header code generation ===
    // This is the main entry point, without performing an arity check.
    // If we needed to perform an arity check we will already have moved the return address,
    // so enter after this.
    Label fromArityCheck(this);
    // Plant a check that sufficient space is available in the JSStack.
    addPtr(TrustedImm32(virtualRegisterForLocal(m_graph.requiredRegisterCountForExecutionAndExit() - 1).offset() * sizeof(Register)), GPRInfo::callFrameRegister, GPRInfo::regT1);
    Jump stackOverflow = branchPtr(Above, AbsoluteAddress(m_vm->addressOfStackLimit()), GPRInfo::regT1);

    // Move the stack pointer down to accommodate locals
    addPtr(TrustedImm32(m_graph.stackPointerOffset() * sizeof(Register)), GPRInfo::callFrameRegister, stackPointerRegister);
    checkStackPointerAlignment();

    compileSetupRegistersForEntry();
    compileEntryExecutionFlag();

    // === Function body code generation ===
    m_speculative = std::make_unique<SpeculativeJIT>(*this);
    compileBody();
    setEndOfMainPath();

    // === Function footer code generation ===
    //
    // Generate code to perform the stack overflow handling (if the stack check in
    // the function header fails), and generate the entry point with arity check.
    //
    // Generate the stack overflow handling; if the stack check in the function head fails,
    // we need to call out to a helper function to throw the StackOverflowError.
    stackOverflow.link(this);

    emitStoreCodeOrigin(CodeOrigin(0));

    if (maxFrameExtentForSlowPathCall)
        addPtr(TrustedImm32(-maxFrameExtentForSlowPathCall), stackPointerRegister);

    m_speculative->callOperationWithCallFrameRollbackOnException(operationThrowStackOverflowError, m_codeBlock);
    
    // The fast entry point into a function does not check the correct number of arguments
    // have been passed to the call (we only use the fast entry point where we can statically
    // determine the correct number of arguments have been passed, or have already checked).
    // In cases where an arity check is necessary, we enter here.
    // FIXME: change this from a cti call to a DFG style operation (normal C calling conventions).
    m_arityCheck = label();
    compileEntry();

    load32(AssemblyHelpers::payloadFor((VirtualRegister)JSStack::ArgumentCount), GPRInfo::regT1);
    branch32(AboveOrEqual, GPRInfo::regT1, TrustedImm32(m_codeBlock->numParameters())).linkTo(fromArityCheck, this);
    emitStoreCodeOrigin(CodeOrigin(0));
    if (maxFrameExtentForSlowPathCall)
        addPtr(TrustedImm32(-maxFrameExtentForSlowPathCall), stackPointerRegister);
    m_speculative->callOperationWithCallFrameRollbackOnException(m_codeBlock->m_isConstructor ? operationConstructArityCheck : operationCallArityCheck, GPRInfo::regT0);
    if (maxFrameExtentForSlowPathCall)
        addPtr(TrustedImm32(maxFrameExtentForSlowPathCall), stackPointerRegister);
    branchTest32(Zero, GPRInfo::returnValueGPR).linkTo(fromArityCheck, this);
    emitStoreCodeOrigin(CodeOrigin(0));
    move(GPRInfo::returnValueGPR, GPRInfo::argumentGPR0);
    m_callArityFixup = call();
    jump(fromArityCheck);
    
    // Generate slow path code.
    m_speculative->runSlowPathGenerators(m_pcToCodeOriginMapBuilder);
    m_pcToCodeOriginMapBuilder.appendItem(label(), PCToCodeOriginMapBuilder::defaultCodeOrigin());
    
    compileExceptionHandlers();
    linkOSRExits();
    
    // Create OSR entry trampolines if necessary.
    m_speculative->createOSREntries();
    setEndOfCode();

    // === Link ===
    auto linkBuffer = std::make_unique<LinkBuffer>(*m_vm, *this, m_codeBlock, JITCompilationCanFail);
    if (linkBuffer->didFailToAllocate()) {
        m_graph.m_plan.finalizer = std::make_unique<FailedFinalizer>(m_graph.m_plan);
        return;
    }
    link(*linkBuffer);
    m_speculative->linkOSREntries(*linkBuffer);
    
    m_jitCode->shrinkToFit();
    codeBlock()->shrinkToFit(CodeBlock::LateShrink);
    
    linkBuffer->link(m_callArityFixup, FunctionPtr((m_vm->getCTIStub(arityFixupGenerator)).code().executableAddress()));
    
    disassemble(*linkBuffer);

    MacroAssemblerCodePtr withArityCheck = linkBuffer->locationOf(m_arityCheck);

    m_graph.m_plan.finalizer = std::make_unique<JITFinalizer>(
        m_graph.m_plan, m_jitCode.release(), WTFMove(linkBuffer), withArityCheck);
}

void JITCompiler::disassemble(LinkBuffer& linkBuffer)
{
    if (shouldDumpDisassembly()) {
        m_disassembler->dump(linkBuffer);
        linkBuffer.didAlreadyDisassemble();
    }
    
    if (m_graph.m_plan.compilation)
        m_disassembler->reportToProfiler(m_graph.m_plan.compilation.get(), linkBuffer);
}

#if USE(JSVALUE32_64)
void* JITCompiler::addressOfDoubleConstant(Node* node)
{
    double value = node->asNumber();
    int64_t valueBits = bitwise_cast<int64_t>(value);
    auto it = m_graph.m_doubleConstantsMap.find(valueBits);
    if (it != m_graph.m_doubleConstantsMap.end())
        return it->second;

    if (!m_graph.m_doubleConstants)
        m_graph.m_doubleConstants = std::make_unique<Bag<double>>();

    double* addressInConstantPool = m_graph.m_doubleConstants->add();
    *addressInConstantPool = value;
    m_graph.m_doubleConstantsMap[valueBits] = addressInConstantPool;
    return addressInConstantPool;
}
#endif

void JITCompiler::noticeOSREntry(BasicBlock& basicBlock, JITCompiler::Label blockHead, LinkBuffer& linkBuffer)
{
    // OSR entry is not allowed into blocks deemed unreachable by control flow analysis.
    if (!basicBlock.intersectionOfCFAHasVisited)
        return;
        
    OSREntryData* entry = m_jitCode->appendOSREntryData(basicBlock.bytecodeBegin, linkBuffer.offsetOf(blockHead));
    
    entry->m_expectedValues = basicBlock.intersectionOfPastValuesAtHead;
        
    // Fix the expected values: in our protocol, a dead variable will have an expected
    // value of (None, []). But the old JIT may stash some values there. So we really
    // need (Top, TOP).
    for (size_t argument = 0; argument < basicBlock.variablesAtHead.numberOfArguments(); ++argument) {
        Node* node = basicBlock.variablesAtHead.argument(argument);
        if (!node || !node->shouldGenerate())
            entry->m_expectedValues.argument(argument).makeHeapTop();
    }
    for (size_t local = 0; local < basicBlock.variablesAtHead.numberOfLocals(); ++local) {
        Node* node = basicBlock.variablesAtHead.local(local);
        if (!node || !node->shouldGenerate())
            entry->m_expectedValues.local(local).makeHeapTop();
        else {
            VariableAccessData* variable = node->variableAccessData();
            entry->m_machineStackUsed.set(variable->machineLocal().toLocal());
                
            switch (variable->flushFormat()) {
            case FlushedDouble:
                entry->m_localsForcedDouble.set(local);
                break;
            case FlushedInt52:
                entry->m_localsForcedMachineInt.set(local);
                break;
            default:
                break;
            }
            
            if (variable->local() != variable->machineLocal()) {
                entry->m_reshufflings.append(
                    OSREntryReshuffling(
                        variable->local().offset(), variable->machineLocal().offset()));
            }
        }
    }
        
    entry->m_reshufflings.shrinkToFit();
}

void JITCompiler::appendExceptionHandlingOSRExit(ExitKind kind, unsigned eventStreamIndex, CodeOrigin opCatchOrigin, HandlerInfo* exceptionHandler, CallSiteIndex callSite, MacroAssembler::JumpList jumpsToFail)
{
    OSRExit exit(kind, JSValueRegs(), graph().methodOfGettingAValueProfileFor(nullptr), m_speculative.get(), eventStreamIndex);
    exit.m_codeOrigin = opCatchOrigin;
    exit.m_exceptionHandlerCallSiteIndex = callSite;
    OSRExitCompilationInfo& exitInfo = appendExitInfo(jumpsToFail);
    jitCode()->appendOSRExit(exit);
    m_exceptionHandlerOSRExitCallSites.append(ExceptionHandlingOSRExitInfo { exitInfo, *exceptionHandler, callSite });
}

void JITCompiler::exceptionCheck()
{
    // It's important that we use origin.forExit here. Consider if we hoist string
    // addition outside a loop, and that we exit at the point of that concatenation
    // from an out of memory exception.
    // If the original loop had a try/catch around string concatenation, if we "catch"
    // that exception inside the loop, then the loops induction variable will be undefined 
    // in the OSR exit value recovery. It's more defensible for the string concatenation, 
    // then, to not be caught by the for loops' try/catch.
    // Here is the program I'm speaking about:
    //
    // >>>> lets presume "c = a + b" gets hoisted here.
    // for (var i = 0; i < length; i++) {
    //     try {
    //         c = a + b
    //     } catch(e) { 
    //         If we threw an out of memory error, and we cought the exception
    //         right here, then "i" would almost certainly be undefined, which
    //         would make no sense.
    //         ... 
    //     }
    // }
    CodeOrigin opCatchOrigin;
    HandlerInfo* exceptionHandler;
    bool willCatchException = m_graph.willCatchExceptionInMachineFrame(m_speculative->m_currentNode->origin.forExit, opCatchOrigin, exceptionHandler); 
    if (willCatchException) {
        unsigned streamIndex = m_speculative->m_outOfLineStreamIndex != UINT_MAX ? m_speculative->m_outOfLineStreamIndex : m_speculative->m_stream->size();
        MacroAssembler::Jump hadException = emitNonPatchableExceptionCheck();
        // We assume here that this is called after callOpeartion()/appendCall() is called.
        appendExceptionHandlingOSRExit(ExceptionCheck, streamIndex, opCatchOrigin, exceptionHandler, m_jitCode->common.lastCallSite(), hadException);
    } else
        m_exceptionChecks.append(emitExceptionCheck());
}

CallSiteIndex JITCompiler::recordCallSiteAndGenerateExceptionHandlingOSRExitIfNeeded(const CodeOrigin& callSiteCodeOrigin, unsigned eventStreamIndex)
{
    CodeOrigin opCatchOrigin;
    HandlerInfo* exceptionHandler;
    bool willCatchException = m_graph.willCatchExceptionInMachineFrame(callSiteCodeOrigin, opCatchOrigin, exceptionHandler);
    CallSiteIndex callSite = addCallSite(callSiteCodeOrigin);
    if (willCatchException)
        appendExceptionHandlingOSRExit(GenericUnwind, eventStreamIndex, opCatchOrigin, exceptionHandler, callSite);
    return callSite;
}

void JITCompiler::setEndOfMainPath()
{
    m_pcToCodeOriginMapBuilder.appendItem(labelIgnoringWatchpoints(), m_speculative->m_origin.semantic);
    if (LIKELY(!m_disassembler))
        return;
    m_disassembler->setEndOfMainPath(labelIgnoringWatchpoints());
}

void JITCompiler::setEndOfCode()
{
    m_pcToCodeOriginMapBuilder.appendItem(labelIgnoringWatchpoints(), PCToCodeOriginMapBuilder::defaultCodeOrigin());
    if (LIKELY(!m_disassembler))
        return;
    m_disassembler->setEndOfCode(labelIgnoringWatchpoints());
}

} } // namespace JSC::DFG

#endif // ENABLE(DFG_JIT)