Source/JavaScriptCore/ftl/FTLOSRExit.h

/*
 * Copyright (C) 2013-2018 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. 
 */

#pragma once

#if ENABLE(FTL_JIT)

#include "B3ValueRep.h"
#include "CodeOrigin.h"
#include "DFGExitProfile.h"
#include "DFGNodeOrigin.h"
#include "DFGOSRExitBase.h"
#include "FTLAbbreviatedTypes.h"
#include "FTLExitTimeObjectMaterialization.h"
#include "FTLExitValue.h"
#include "FTLFormattedValue.h"
#include "FTLOSRExitHandle.h"
#include "FTLStackmapArgumentList.h"
#include "HandlerInfo.h"
#include "MethodOfGettingAValueProfile.h"
#include "Operands.h"
#include "Reg.h"
#include "ValueProfile.h"
#include "VirtualRegister.h"
#include <wtf/Bag.h>
#include <wtf/FixedVector.h>

namespace JSC {

class TrackedReferences;

namespace B3 {
class StackmapGenerationParams;
namespace Air {
struct GenerationContext;
} // namespace Air
} // namespace B3

namespace DFG {
struct NodeOrigin;
} // namespace DFG;

namespace FTL {

class State;
struct OSRExitDescriptorImpl;
struct OSRExitHandle;

class JITCode;

// Stores one ExitValue per operand of the exit (arguments, then locals, then tmps) as
// a byte stream: a tag byte followed by an optional payload.
//
//   0x00-0x3F  (tag + 1) consecutive dead values
//   0x40-0x43  InJSStack / AsInt32 / AsInt52 / AsDouble, flushed to the operand's own virtual register
//   0x44-0x47  the same, flushed to another virtual register: SLEB128 register offset follows
//   0x48       Constant: LEB128 index into JITCode::osrExitConstants follows
//   0x49       MaterializeNewObject: LEB128 index into OSRExitDescriptor::m_materializations follows
//   0x4A       Argument: DataFormat byte and LEB128 stackmap index follow
//
// Virtual registers are stored before the localsOffset adjustment; decode() applies it.
class OSRExitValues {
    WTF_MAKE_NONCOPYABLE(OSRExitValues);
public:
    OSRExitValues() = default;

    void encode(const Operands<ExitValue>&, const Bag<ExitTimeObjectMaterialization>&, JITCode&);
    FixedOperands<ExitValue> decode(const JITCode&, const Bag<ExitTimeObjectMaterialization>&) const;

private:
    FixedVector<uint8_t> m_bytes;
    unsigned m_numberOfArguments { 0 };
    unsigned m_numberOfLocals { 0 };
    unsigned m_numberOfTmps { 0 };
};

// Stores where B3 placed the exit arguments of every exit of a JITCode as one byte stream. An
// exit's entry is a LEB128 argument count followed by one B3::ValueRep per argument, which is a
// B3::ValueRep::Kind byte and then:
//
//   Register   the Reg index byte
//   Stack      the SLEB128 offset from the frame pointer
//   Constant   the SLEB128 value
class OSRExitValueReps {
    WTF_MAKE_NONCOPYABLE(OSRExitValueReps);
public:
    OSRExitValueReps() = default;

    unsigned append(std::span<const B3::ValueRep>);
    FixedVector<B3::ValueRep> decode(unsigned offset) const;
    void shrinkToFit() { m_bytes.shrinkToFit(); }

private:
    Vector<uint8_t> m_bytes;
};

struct OSRExitDescriptor {
private:
    WTF_MAKE_NONCOPYABLE(OSRExitDescriptor);
public:
    OSRExitDescriptor(DataFormat profileDataFormat, MethodOfGettingAValueProfile);

    // The first argument to the exit call may be a value we wish to profile.
    // If that's the case, the format will be not Invalid and we'll have a
    // method of getting a value profile. Note that all of the ExitArgument's
    // are already aware of this possible off-by-one, so there is no need to
    // correct them.
    DataFormat m_profileDataFormat;
    MethodOfGettingAValueProfile m_valueProfile;

    OSRExitValues m_values;
    Bag<ExitTimeObjectMaterialization> m_materializations;

    FixedOperands<ExitValue> values(const JITCode& jitCode) const { return m_values.decode(jitCode, m_materializations); }

    void validateReferences(const TrackedReferences&);

    // Call this once we have a place to emit the OSR exit jump and we have data about how the state
    // should be recovered. This effectively emits code that does the exit, though the code is really a
    // patchable jump and we emit the real code lazily. The description of how to emit the real code is
    // up to the OSRExit object, which this creates. Note that it's OK to drop the OSRExitHandle object
    // on the ground. It contains information that is mostly not useful if you use this API, since after
    // this call, the OSRExit is simply ready to go.
    Ref<OSRExitHandle> emitOSRExit(
        State&, ExitKind, const DFG::NodeOrigin&, CCallHelpers&, const B3::StackmapGenerationParams&,
        uint32_t dfgNodeIndex, unsigned offset);

    // In some cases you want an OSRExit to come into existence, but you don't want to emit it right now.
    // This will emit the OSR exit in a late path. You can't be sure exactly when that will happen, but
    // you know that it will be done by the time late path emission is done. So, a linker task will
    // surely happen after that. You can use the OSRExitHandle to retrieve the exit's label.
    //
    // This API is meant to be used for things like exception handling, where some patchpoint wants to
    // have a place to jump to for OSR exit. It doesn't care where that OSR exit is emitted so long as it
    // eventually gets access to its label.
    Ref<OSRExitHandle> emitOSRExitLater(
        State&, ExitKind, const DFG::NodeOrigin&, const B3::StackmapGenerationParams&,
        uint32_t dfgNodeIndex, unsigned offset);

private:
    // This is the low-level interface. It will create a handle representing the desire to emit code for
    // an OSR exit. You can call OSRExitHandle::emitExitThunk() once you have a place to emit it. Note
    // that the above two APIs are written in terms of this and OSRExitHandle::emitExitThunk().
    Ref<OSRExitHandle> prepareOSRExitHandle(
        State&, ExitKind, const DFG::NodeOrigin&, const B3::StackmapGenerationParams&,
        uint32_t dfgNodeIndex, unsigned offset);
};

struct OSRExit : public DFG::OSRExitBase {
    OSRExit(OSRExitDescriptor*, ExitKind, CodeOrigin, CodeOrigin codeOriginForExitProfile, bool wasHoisted, uint32_t dfgNodeIndex, unsigned valueRepsOffset);

    FixedVector<B3::ValueRep> valueReps(const JITCode&) const;

    unsigned m_valueRepsOffset;
    OSRExitDescriptor* m_descriptor;
    // This tells us where to place a jump.
    CodeLocationJump<JSInternalPtrTag> m_patchableJump;

    CodeLocationJump<JSInternalPtrTag> NODELETE codeLocationForRepatch(CodeBlock* ftlCodeBlock) const;
    void considerAddingAsFrequentExitSite(CodeBlock* profiledCodeBlock)
    {
        OSRExitBase::considerAddingAsFrequentExitSite(profiledCodeBlock, ExitFromFTL);
    }
};

} } // namespace JSC::FTL

#endif // ENABLE(FTL_JIT)