path: root/js/src/jit/CacheIRCompiler.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef jit_CacheIRCompiler_h
#define jit_CacheIRCompiler_h

#include "mozilla/Maybe.h"

#include "jit/CacheIR.h"
#include "jit/JitOptions.h"
#include "jit/MacroAssembler.h"
#include "jit/SharedICRegisters.h"
#include "js/ScalarType.h"  // js::Scalar::Type

namespace js {

class TypedArrayObject;

namespace jit {

class BaselineCacheIRCompiler;
class IonCacheIRCompiler;

enum class ICStubEngine : uint8_t;

// [SMDOC] CacheIR Value Representation and Tracking
//
// While compiling an IC stub the CacheIR compiler needs to keep track of the
// physical location for each logical piece of data we care about, as well as
// ensure that in the case of a stub failing, we are able to restore the input
// state so that a subsequent stub can attempt to provide a value.
//
// OperandIds are created in the CacheIR front-end to keep track of values that
// are passed between CacheIR ops during the execution of a given CacheIR stub.
// In the CacheRegisterAllocator these OperandIds are given OperandLocations,
// that represent the physical location of the OperandId at a given point in
// time during CacheRegister allocation.
//
// In the CacheRegisterAllocator physical locations include the stack, and
// registers, as well as whether or not the value has been unboxed or not.
// Constants are also represented separately to provide for on-demand
// materialization.
//
// Intra-op Register allocation:
//
// During the emission of a CacheIR op, code can ask the CacheRegisterAllocator
// for access to a particular OperandId, and the register allocator will
// generate the required code to fill that request.
//
// Input OperandIds should be considered as immutable, and should not be mutated
// during the execution of a stub.
//
// There are also a number of RAII classes that interact with the register
// allocator, in order to provide access to more registers than just those
// provided for by the OperandIds.
//
// - AutoOutputReg: The register which will hold the output value of the stub.
// - AutoScratchReg: By default, an arbitrary scratch register, however a
//   specific register can be requested.
// - AutoScratchRegMaybeOutput: Any arbitrary scratch register, but the output
//   register may be used as well.
//
// These RAII classes take ownership of a register for the duration of their
// lifetime so they can be used for computation or output. The register
// allocator can spill values with OperandLocations in order to try to ensure
// that a register is made available for use.
//
// If a specific register is required (via AutoScratchRegister), it should be
// the first register acquired, as the register rallocator will be unable to
// allocate the fixed register if the current op is using it for something else.
//
// If no register can be provided after attempting to spill, a
// MOZ_RELEASE_ASSERT ensures the browser will crash. The register allocator is
// not provided enough information in its current design to insert spills and
// fills at arbitrary locations, and so it can fail to find an allocation
// solution. However, this will only happen within the implementation of an
// operand emitter, and because the cache register allocator is mostly
// determinstic, so long as the operand id emitter is tested, this won't
// suddenly crop up in an arbitrary webpage. It's worth noting the most
// difficult platform to support is x86-32, because it has the least number of
// registers available.
//
// FailurePaths checkpoint the state of the register allocator so that the input
// state can be recomputed from the current state before jumping to the next
// stub in the IC chain. An important invariant is that the FailurePath must be
// allocated for each op after all the manipulation of OperandLocations has
// happened, so that its recording is correct.
//
// Inter-op Register Allocation:
//
// The RAII register management classes are RAII because all register state
// outside the OperandLocations is reset before the compilation of each
// individual CacheIR op. This means that you cannot rely on a value surviving
// between ops, even if you use the ability of AutoScratchRegister to name a
// specific register. Values that need to be preserved between ops must be given
// an OperandId.

// Represents a Value on the Baseline frame's expression stack. Slot 0 is the
// value on top of the stack (the most recently pushed value), slot 1 is the
// value pushed before that, etc.
class BaselineFrameSlot {
  uint32_t slot_;

 public:
  explicit BaselineFrameSlot(uint32_t slot) : slot_(slot) {}
  uint32_t slot() const { return slot_; }

  bool operator==(const BaselineFrameSlot& other) const {
    return slot_ == other.slot_;
  }
  bool operator!=(const BaselineFrameSlot& other) const {
    return slot_ != other.slot_;
  }
};

// OperandLocation represents the location of an OperandId. The operand is
// either in a register or on the stack, and is either boxed or unboxed.
class OperandLocation {
 public:
  enum Kind {
    Uninitialized = 0,
    PayloadReg,
    DoubleReg,
    ValueReg,
    PayloadStack,
    ValueStack,
    BaselineFrame,
    Constant,
  };

 private:
  Kind kind_;

  union Data {
    struct {
      Register reg;
      JSValueType type;
    } payloadReg;
    FloatRegister doubleReg;
    ValueOperand valueReg;
    struct {
      uint32_t stackPushed;
      JSValueType type;
    } payloadStack;
    uint32_t valueStackPushed;
    BaselineFrameSlot baselineFrameSlot;
    Value constant;

    Data() : valueStackPushed(0) {}
  };
  Data data_;

 public:
  OperandLocation() : kind_(Uninitialized) {}

  Kind kind() const { return kind_; }

  void setUninitialized() { kind_ = Uninitialized; }

  ValueOperand valueReg() const {
    MOZ_ASSERT(kind_ == ValueReg);
    return data_.valueReg;
  }
  Register payloadReg() const {
    MOZ_ASSERT(kind_ == PayloadReg);
    return data_.payloadReg.reg;
  }
  FloatRegister doubleReg() const {
    MOZ_ASSERT(kind_ == DoubleReg);
    return data_.doubleReg;
  }
  uint32_t payloadStack() const {
    MOZ_ASSERT(kind_ == PayloadStack);
    return data_.payloadStack.stackPushed;
  }
  uint32_t valueStack() const {
    MOZ_ASSERT(kind_ == ValueStack);
    return data_.valueStackPushed;
  }
  JSValueType payloadType() const {
    if (kind_ == PayloadReg) {
      return data_.payloadReg.type;
    }
    MOZ_ASSERT(kind_ == PayloadStack);
    return data_.payloadStack.type;
  }
  Value constant() const {
    MOZ_ASSERT(kind_ == Constant);
    return data_.constant;
  }
  BaselineFrameSlot baselineFrameSlot() const {
    MOZ_ASSERT(kind_ == BaselineFrame);
    return data_.baselineFrameSlot;
  }

  void setPayloadReg(Register reg, JSValueType type) {
    kind_ = PayloadReg;
    data_.payloadReg.reg = reg;
    data_.payloadReg.type = type;
  }
  void setDoubleReg(FloatRegister reg) {
    kind_ = DoubleReg;
    data_.doubleReg = reg;
  }
  void setValueReg(ValueOperand reg) {
    kind_ = ValueReg;
    data_.valueReg = reg;
  }
  void setPayloadStack(uint32_t stackPushed, JSValueType type) {
    kind_ = PayloadStack;
    data_.payloadStack.stackPushed = stackPushed;
    data_.payloadStack.type = type;
  }
  void setValueStack(uint32_t stackPushed) {
    kind_ = ValueStack;
    data_.valueStackPushed = stackPushed;
  }
  void setConstant(const Value& v) {
    kind_ = Constant;
    data_.constant = v;
  }
  void setBaselineFrame(BaselineFrameSlot slot) {
    kind_ = BaselineFrame;
    data_.baselineFrameSlot = slot;
  }

  bool isUninitialized() const { return kind_ == Uninitialized; }
  bool isInRegister() const { return kind_ == PayloadReg || kind_ == ValueReg; }
  bool isOnStack() const {
    return kind_ == PayloadStack || kind_ == ValueStack;
  }

  size_t stackPushed() const {
    if (kind_ == PayloadStack) {
      return data_.payloadStack.stackPushed;
    }
    MOZ_ASSERT(kind_ == ValueStack);
    return data_.valueStackPushed;
  }
  size_t stackSizeInBytes() const {
    if (kind_ == PayloadStack) {
      return sizeof(uintptr_t);
    }
    MOZ_ASSERT(kind_ == ValueStack);
    return sizeof(js::Value);
  }
  void adjustStackPushed(int32_t diff) {
    if (kind_ == PayloadStack) {
      data_.payloadStack.stackPushed += diff;
      return;
    }
    MOZ_ASSERT(kind_ == ValueStack);
    data_.valueStackPushed += diff;
  }

  bool aliasesReg(Register reg) const {
    if (kind_ == PayloadReg) {
      return payloadReg() == reg;
    }
    if (kind_ == ValueReg) {
      return valueReg().aliases(reg);
    }
    return false;
  }
  bool aliasesReg(ValueOperand reg) const {
#if defined(JS_NUNBOX32)
    return aliasesReg(reg.typeReg()) || aliasesReg(reg.payloadReg());
#else
    return aliasesReg(reg.valueReg());
#endif
  }

  bool aliasesReg(const OperandLocation& other) const;

  bool operator==(const OperandLocation& other) const;
  bool operator!=(const OperandLocation& other) const {
    return !operator==(other);
  }
};

struct SpilledRegister {
  Register reg;
  uint32_t stackPushed;

  SpilledRegister(Register reg, uint32_t stackPushed)
      : reg(reg), stackPushed(stackPushed) {}
  bool operator==(const SpilledRegister& other) const {
    return reg == other.reg && stackPushed == other.stackPushed;
  }
  bool operator!=(const SpilledRegister& other) const {
    return !(*this == other);
  }
};

using SpilledRegisterVector = Vector<SpilledRegister, 2, SystemAllocPolicy>;

// Class to track and allocate registers while emitting IC code.
class MOZ_RAII CacheRegisterAllocator {
  // The original location of the inputs to the cache.
  Vector<OperandLocation, 4, SystemAllocPolicy> origInputLocations_;

  // The current location of each operand.
  Vector<OperandLocation, 8, SystemAllocPolicy> operandLocations_;

  // Free lists for value- and payload-slots on stack
  Vector<uint32_t, 2, SystemAllocPolicy> freeValueSlots_;
  Vector<uint32_t, 2, SystemAllocPolicy> freePayloadSlots_;

  // The registers allocated while emitting the current CacheIR op.
  // This prevents us from allocating a register and then immediately
  // clobbering it for something else, while we're still holding on to it.
  LiveGeneralRegisterSet currentOpRegs_;

  const AllocatableGeneralRegisterSet allocatableRegs_;

  // Registers that are currently unused and available.
  AllocatableGeneralRegisterSet availableRegs_;

  // Registers that are available, but before use they must be saved and
  // then restored when returning from the stub.
  AllocatableGeneralRegisterSet availableRegsAfterSpill_;

  // Registers we took from availableRegsAfterSpill_ and spilled to the stack.
  SpilledRegisterVector spilledRegs_;

  // The number of bytes pushed on the native stack.
  uint32_t stackPushed_;

#ifdef DEBUG
  // Flag used to assert individual CacheIR instructions don't allocate
  // registers after calling addFailurePath.
  bool addedFailurePath_;
#endif

  // The index of the CacheIR instruction we're currently emitting.
  uint32_t currentInstruction_;

  // Whether the stack contains a double spilled by AutoScratchFloatRegister.
  bool hasAutoScratchFloatRegisterSpill_ = false;

  const CacheIRWriter& writer_;

  CacheRegisterAllocator(const CacheRegisterAllocator&) = delete;
  CacheRegisterAllocator& operator=(const CacheRegisterAllocator&) = delete;

  void freeDeadOperandLocations(MacroAssembler& masm);

  void spillOperandToStack(MacroAssembler& masm, OperandLocation* loc);
  void spillOperandToStackOrRegister(MacroAssembler& masm,
                                     OperandLocation* loc);

  void popPayload(MacroAssembler& masm, OperandLocation* loc, Register dest);
  void popValue(MacroAssembler& masm, OperandLocation* loc, ValueOperand dest);
  Address valueAddress(MacroAssembler& masm, const OperandLocation* loc) const;

#ifdef DEBUG
  void assertValidState() const;
#endif

 public:
  friend class AutoScratchRegister;
  friend class AutoScratchRegisterExcluding;

  explicit CacheRegisterAllocator(const CacheIRWriter& writer)
      : allocatableRegs_(GeneralRegisterSet::All()),
        stackPushed_(0),
#ifdef DEBUG
        addedFailurePath_(false),
#endif
        currentInstruction_(0),
        writer_(writer) {
  }

  [[nodiscard]] bool init();

  void initAvailableRegs(const AllocatableGeneralRegisterSet& available) {
    availableRegs_ = available;
  }
  void initAvailableRegsAfterSpill();

  void fixupAliasedInputs(MacroAssembler& masm);

  OperandLocation operandLocation(size_t i) const {
    return operandLocations_[i];
  }
  void setOperandLocation(size_t i, const OperandLocation& loc) {
    operandLocations_[i] = loc;
  }

  OperandLocation origInputLocation(size_t i) const {
    return origInputLocations_[i];
  }
  void initInputLocation(size_t i, ValueOperand reg) {
    origInputLocations_[i].setValueReg(reg);
    operandLocations_[i].setValueReg(reg);
  }
  void initInputLocation(size_t i, Register reg, JSValueType type) {
    origInputLocations_[i].setPayloadReg(reg, type);
    operandLocations_[i].setPayloadReg(reg, type);
  }
  void initInputLocation(size_t i, FloatRegister reg) {
    origInputLocations_[i].setDoubleReg(reg);
    operandLocations_[i].setDoubleReg(reg);
  }
  void initInputLocation(size_t i, const Value& v) {
    origInputLocations_[i].setConstant(v);
    operandLocations_[i].setConstant(v);
  }
  void initInputLocation(size_t i, BaselineFrameSlot slot) {
    origInputLocations_[i].setBaselineFrame(slot);
    operandLocations_[i].setBaselineFrame(slot);
  }

  void initInputLocation(size_t i, const TypedOrValueRegister& reg);
  void initInputLocation(size_t i, const ConstantOrRegister& value);

  const SpilledRegisterVector& spilledRegs() const { return spilledRegs_; }

  [[nodiscard]] bool setSpilledRegs(const SpilledRegisterVector& regs) {
    spilledRegs_.clear();
    return spilledRegs_.appendAll(regs);
  }

  bool hasAutoScratchFloatRegisterSpill() const {
    return hasAutoScratchFloatRegisterSpill_;
  }
  void setHasAutoScratchFloatRegisterSpill(bool b) {
    MOZ_ASSERT(hasAutoScratchFloatRegisterSpill_ != b);
    hasAutoScratchFloatRegisterSpill_ = b;
  }

  void nextOp() {
#ifdef DEBUG
    assertValidState();
    addedFailurePath_ = false;
#endif
    currentOpRegs_.clear();
    currentInstruction_++;
  }

#ifdef DEBUG
  void setAddedFailurePath() {
    MOZ_ASSERT(!addedFailurePath_, "multiple failure paths for instruction");
    addedFailurePath_ = true;
  }
#endif

  bool isDeadAfterInstruction(OperandId opId) const {
    return writer_.operandIsDead(opId.id(), currentInstruction_ + 1);
  }

  uint32_t stackPushed() const { return stackPushed_; }
  void setStackPushed(uint32_t pushed) { stackPushed_ = pushed; }

  bool isAllocatable(Register reg) const { return allocatableRegs_.has(reg); }

  // Allocates a new register.
  Register allocateRegister(MacroAssembler& masm);
  ValueOperand allocateValueRegister(MacroAssembler& masm);

  void allocateFixedRegister(MacroAssembler& masm, Register reg);
  void allocateFixedValueRegister(MacroAssembler& masm, ValueOperand reg);

  // Releases a register so it can be reused later.
  void releaseRegister(Register reg) {
    MOZ_ASSERT(currentOpRegs_.has(reg));
    availableRegs_.add(reg);
    currentOpRegs_.take(reg);
  }
  void releaseValueRegister(ValueOperand reg) {
#ifdef JS_NUNBOX32
    releaseRegister(reg.payloadReg());
    releaseRegister(reg.typeReg());
#else
    releaseRegister(reg.valueReg());
#endif
  }

  // Removes spilled values from the native stack. This should only be
  // called after all registers have been allocated.
  void discardStack(MacroAssembler& masm);

  Address addressOf(MacroAssembler& masm, BaselineFrameSlot slot) const;
  BaseValueIndex addressOf(MacroAssembler& masm, Register argcReg,
                           BaselineFrameSlot slot) const;

  // Returns the register for the given operand. If the operand is currently
  // not in a register, it will load it into one.
  ValueOperand useValueRegister(MacroAssembler& masm, ValOperandId val);
  ValueOperand useFixedValueRegister(MacroAssembler& masm, ValOperandId valId,
                                     ValueOperand reg);
  Register useRegister(MacroAssembler& masm, TypedOperandId typedId);

  ConstantOrRegister useConstantOrRegister(MacroAssembler& masm,
                                           ValOperandId val);

  // Allocates an output register for the given operand.
  Register defineRegister(MacroAssembler& masm, TypedOperandId typedId);
  ValueOperand defineValueRegister(MacroAssembler& masm, ValOperandId val);

  // Loads (potentially coercing) and unboxes a value into a float register
  // This is infallible, as there should have been a previous guard
  // to ensure the value is already a number.
  // Does not change the allocator's state.
  void ensureDoubleRegister(MacroAssembler& masm, NumberOperandId op,
                            FloatRegister dest) const;

  // Loads an unboxed value into a scratch register. This can be useful
  // especially on 32-bit x86 when there are not enough registers for
  // useRegister.
  // Does not change the allocator's state.
  void copyToScratchRegister(MacroAssembler& masm, TypedOperandId typedId,
                             Register dest) const;

  // Returns |val|'s JSValueType or JSVAL_TYPE_UNKNOWN.
  JSValueType knownType(ValOperandId val) const;

  // Emits code to restore registers and stack to the state at the start of
  // the stub.
  void restoreInputState(MacroAssembler& masm, bool discardStack = true);

  // Returns the set of registers storing the IC input operands.
  GeneralRegisterSet inputRegisterSet() const;

  void saveIonLiveRegisters(MacroAssembler& masm, LiveRegisterSet liveRegs,
                            Register scratch, IonScript* ionScript);
  void restoreIonLiveRegisters(MacroAssembler& masm, LiveRegisterSet liveRegs);
};

// RAII class to allocate a scratch register and release it when we're done
// with it.
class MOZ_RAII AutoScratchRegister {
  CacheRegisterAllocator& alloc_;
  Register reg_;

  AutoScratchRegister(const AutoScratchRegister&) = delete;
  void operator=(const AutoScratchRegister&) = delete;

 public:
  AutoScratchRegister(CacheRegisterAllocator& alloc, MacroAssembler& masm,
                      Register reg = InvalidReg)
      : alloc_(alloc) {
    if (reg != InvalidReg) {
      alloc.allocateFixedRegister(masm, reg);
      reg_ = reg;
    } else {
      reg_ = alloc.allocateRegister(masm);
    }
    MOZ_ASSERT(alloc_.currentOpRegs_.has(reg_));
  }
  ~AutoScratchRegister() { alloc_.releaseRegister(reg_); }

  Register get() const { return reg_; }
  operator Register() const { return reg_; }
};

// On x86, spectreBoundsCheck32 can emit better code if it has a scratch
// register and index masking is enabled.
class MOZ_RAII AutoSpectreBoundsScratchRegister {
  mozilla::Maybe<AutoScratchRegister> scratch_;
  Register reg_ = InvalidReg;

  AutoSpectreBoundsScratchRegister(const AutoSpectreBoundsScratchRegister&) =
      delete;
  void operator=(const AutoSpectreBoundsScratchRegister&) = delete;

 public:
  AutoSpectreBoundsScratchRegister(CacheRegisterAllocator& alloc,
                                   MacroAssembler& masm) {
#ifdef JS_CODEGEN_X86
    if (JitOptions.spectreIndexMasking) {
      scratch_.emplace(alloc, masm);
      reg_ = scratch_->get();
    }
#endif
  }

  Register get() const { return reg_; }
  operator Register() const { return reg_; }
};

// Scratch Register64. Implemented with a single AutoScratchRegister on 64-bit
// platforms and two AutoScratchRegisters on 32-bit platforms.
class MOZ_RAII AutoScratchRegister64 {
  AutoScratchRegister reg1_;
#if JS_BITS_PER_WORD == 32
  AutoScratchRegister reg2_;
#endif

 public:
  AutoScratchRegister64(const AutoScratchRegister64&) = delete;
  void operator=(const AutoScratchRegister64&) = delete;

#if JS_BITS_PER_WORD == 32
  AutoScratchRegister64(CacheRegisterAllocator& alloc, MacroAssembler& masm)
      : reg1_(alloc, masm), reg2_(alloc, masm) {}

  Register64 get() const { return Register64(reg1_, reg2_); }
#else
  AutoScratchRegister64(CacheRegisterAllocator& alloc, MacroAssembler& masm)
      : reg1_(alloc, masm) {}

  Register64 get() const { return Register64(reg1_); }
#endif

  operator Register64() const { return get(); }
};

// The FailurePath class stores everything we need to generate a failure path
// at the end of the IC code. The failure path restores the input registers, if
// needed, and jumps to the next stub.
class FailurePath {
  Vector<OperandLocation, 4, SystemAllocPolicy> inputs_;
  SpilledRegisterVector spilledRegs_;
  NonAssertingLabel label_;
  uint32_t stackPushed_;
#ifdef DEBUG
  // Flag to ensure FailurePath::label() isn't taken while there's a scratch
  // float register which still needs to be restored.
  bool hasAutoScratchFloatRegister_ = false;
#endif

 public:
  FailurePath() = default;

  FailurePath(FailurePath&& other)
      : inputs_(std::move(other.inputs_)),
        spilledRegs_(std::move(other.spilledRegs_)),
        label_(other.label_),
        stackPushed_(other.stackPushed_) {}

  Label* labelUnchecked() { return &label_; }
  Label* label() {
    MOZ_ASSERT(!hasAutoScratchFloatRegister_);
    return labelUnchecked();
  }

  void setStackPushed(uint32_t i) { stackPushed_ = i; }
  uint32_t stackPushed() const { return stackPushed_; }

  [[nodiscard]] bool appendInput(const OperandLocation& loc) {
    return inputs_.append(loc);
  }
  OperandLocation input(size_t i) const { return inputs_[i]; }

  const SpilledRegisterVector& spilledRegs() const { return spilledRegs_; }

  [[nodiscard]] bool setSpilledRegs(const SpilledRegisterVector& regs) {
    MOZ_ASSERT(spilledRegs_.empty());
    return spilledRegs_.appendAll(regs);
  }

  // If canShareFailurePath(other) returns true, the same machine code will
  // be emitted for two failure paths, so we can share them.
  bool canShareFailurePath(const FailurePath& other) const;

  void setHasAutoScratchFloatRegister() {
#ifdef DEBUG
    MOZ_ASSERT(!hasAutoScratchFloatRegister_);
    hasAutoScratchFloatRegister_ = true;
#endif
  }

  void clearHasAutoScratchFloatRegister() {
#ifdef DEBUG
    MOZ_ASSERT(hasAutoScratchFloatRegister_);
    hasAutoScratchFloatRegister_ = false;
#endif
  }
};

/**
 * Wrap an offset so that a call can decide to embed a constant
 * or load from the stub data.
 */
class StubFieldOffset {
 private:
  uint32_t offset_;
  StubField::Type type_;

 public:
  StubFieldOffset(uint32_t offset, StubField::Type type)
      : offset_(offset), type_(type) {}

  uint32_t getOffset() { return offset_; }
  StubField::Type getStubFieldType() { return type_; }
};

class AutoOutputRegister;

// Base class for BaselineCacheIRCompiler and IonCacheIRCompiler.
class MOZ_RAII CacheIRCompiler {
 protected:
  friend class AutoOutputRegister;
  friend class AutoStubFrame;
  friend class AutoSaveLiveRegisters;
  friend class AutoCallVM;
  friend class AutoScratchFloatRegister;
  friend class AutoAvailableFloatRegister;

  enum class Mode { Baseline, Ion };

  bool preparedForVMCall_;

  bool isBaseline();
  bool isIon();
  BaselineCacheIRCompiler* asBaseline();
  IonCacheIRCompiler* asIon();

  JSContext* cx_;
  const CacheIRWriter& writer_;
  StackMacroAssembler masm;

  CacheRegisterAllocator allocator;
  Vector<FailurePath, 4, SystemAllocPolicy> failurePaths;

  // Float registers that are live. Registers not in this set can be
  // clobbered and don't need to be saved before performing a VM call.
  // Doing this for non-float registers is a bit more complicated because
  // the IC register allocator allocates GPRs.
  LiveFloatRegisterSet liveFloatRegs_;

  mozilla::Maybe<TypedOrValueRegister> outputUnchecked_;
  Mode mode_;

  // Distance from the IC to the stub data; mostly will be
  // sizeof(stubType)
  uint32_t stubDataOffset_;

  enum class StubFieldPolicy { Address, Constant };

  StubFieldPolicy stubFieldPolicy_;

  CacheIRCompiler(JSContext* cx, const CacheIRWriter& writer,
                  uint32_t stubDataOffset, Mode mode, StubFieldPolicy policy)
      : preparedForVMCall_(false),
        cx_(cx),
        writer_(writer),
        allocator(writer_),
        liveFloatRegs_(FloatRegisterSet::All()),
        mode_(mode),
        stubDataOffset_(stubDataOffset),
        stubFieldPolicy_(policy) {
    MOZ_ASSERT(!writer.failed());
  }

  [[nodiscard]] bool addFailurePath(FailurePath** failure);
  [[nodiscard]] bool emitFailurePath(size_t i);

  // Returns the set of volatile float registers that are live. These
  // registers need to be saved when making non-GC calls with callWithABI.
  FloatRegisterSet liveVolatileFloatRegs() const {
    return FloatRegisterSet::Intersect(liveFloatRegs_.set(),
                                       FloatRegisterSet::Volatile());
  }

  bool objectGuardNeedsSpectreMitigations(ObjOperandId objId) const {
    // Instructions like GuardShape need Spectre mitigations if
    // (1) mitigations are enabled and (2) the object is used by other
    // instructions (if the object is *not* used by other instructions,
    // zeroing its register is pointless).
    return JitOptions.spectreObjectMitigationsMisc &&
           !allocator.isDeadAfterInstruction(objId);
  }

  void emitRegisterEnumerator(Register enumeratorsList, Register iter,
                              Register scratch);

 private:
  void emitPostBarrierShared(Register obj, const ConstantOrRegister& val,
                             Register scratch, Register maybeIndex);

  void emitPostBarrierShared(Register obj, ValueOperand val, Register scratch,
                             Register maybeIndex) {
    emitPostBarrierShared(obj, ConstantOrRegister(val), scratch, maybeIndex);
  }

 protected:
  template <typename T>
  void emitPostBarrierSlot(Register obj, const T& val, Register scratch) {
    emitPostBarrierShared(obj, val, scratch, InvalidReg);
  }

  template <typename T>
  void emitPostBarrierElement(Register obj, const T& val, Register scratch,
                              Register index) {
    MOZ_ASSERT(index != InvalidReg);
    emitPostBarrierShared(obj, val, scratch, index);
  }

  bool emitComparePointerResultShared(JSOp op, TypedOperandId lhsId,
                                      TypedOperandId rhsId);

  [[nodiscard]] bool emitMathFunctionNumberResultShared(
      UnaryMathFunction fun, FloatRegister inputScratch, ValueOperand output);

  template <typename Fn, Fn fn>
  [[nodiscard]] bool emitBigIntBinaryOperationShared(BigIntOperandId lhsId,
                                                     BigIntOperandId rhsId);

  template <typename Fn, Fn fn>
  [[nodiscard]] bool emitBigIntUnaryOperationShared(BigIntOperandId inputId);

  bool emitDoubleIncDecResult(bool isInc, NumberOperandId inputId);

  using AtomicsReadWriteModifyFn = int32_t (*)(TypedArrayObject*, int32_t,
                                               int32_t);

  [[nodiscard]] bool emitAtomicsReadModifyWriteResult(
      ObjOperandId objId, Int32OperandId indexId, Int32OperandId valueId,
      Scalar::Type elementType, AtomicsReadWriteModifyFn fn);

  CACHE_IR_COMPILER_SHARED_GENERATED

  void emitLoadStubField(StubFieldOffset val, Register dest);
  void emitLoadStubFieldConstant(StubFieldOffset val, Register dest);
  Address emitAddressFromStubField(StubFieldOffset val, Register base);

  uintptr_t readStubWord(uint32_t offset, StubField::Type type) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    MOZ_ASSERT((offset % sizeof(uintptr_t)) == 0);
    return writer_.readStubFieldForIon(offset, type).asWord();
  }
  uint64_t readStubInt64(uint32_t offset, StubField::Type type) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    MOZ_ASSERT((offset % sizeof(uintptr_t)) == 0);
    return writer_.readStubFieldForIon(offset, type).asInt64();
  }
  int32_t int32StubField(uint32_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return readStubWord(offset, StubField::Type::RawInt32);
  }
  uint32_t uint32StubField(uint32_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return readStubWord(offset, StubField::Type::RawInt32);
  }
  Shape* shapeStubField(uint32_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return (Shape*)readStubWord(offset, StubField::Type::Shape);
  }
  JSObject* objectStubField(uint32_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return (JSObject*)readStubWord(offset, StubField::Type::JSObject);
  }
  // This accessor is for cases where the stubField policy is
  // being respected through other means, so we don't check the
  // policy here. (see LoadNewObjectFromTemplateResult)
  JSObject* objectStubFieldUnchecked(uint32_t offset) {
    return (JSObject*)writer_
        .readStubFieldForIon(offset, StubField::Type::JSObject)
        .asWord();
  }
  JSString* stringStubField(uint32_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return (JSString*)readStubWord(offset, StubField::Type::String);
  }
  JS::Symbol* symbolStubField(uint32_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return (JS::Symbol*)readStubWord(offset, StubField::Type::Symbol);
  }
  ObjectGroup* groupStubField(uint32_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return (ObjectGroup*)readStubWord(offset, StubField::Type::ObjectGroup);
  }
  JS::Compartment* compartmentStubField(uint32_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return (JS::Compartment*)readStubWord(offset, StubField::Type::RawPointer);
  }
  const JSClass* classStubField(uintptr_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return (const JSClass*)readStubWord(offset, StubField::Type::RawPointer);
  }
  const void* proxyHandlerStubField(uintptr_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return (const void*)readStubWord(offset, StubField::Type::RawPointer);
  }
  const void* pointerStubField(uintptr_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return (const void*)readStubWord(offset, StubField::Type::RawPointer);
  }
  jsid idStubField(uint32_t offset) {
    MOZ_ASSERT(stubFieldPolicy_ == StubFieldPolicy::Constant);
    return jsid::fromRawBits(readStubWord(offset, StubField::Type::Id));
  }

#ifdef DEBUG
  void assertFloatRegisterAvailable(FloatRegister reg);
#endif

 public:
  void callVMInternal(MacroAssembler& masm, VMFunctionId id);
  template <typename Fn, Fn fn>
  void callVM(MacroAssembler& masm);
};

// Ensures the IC's output register is available for writing.
class MOZ_RAII AutoOutputRegister {
  TypedOrValueRegister output_;
  CacheRegisterAllocator& alloc_;

  AutoOutputRegister(const AutoOutputRegister&) = delete;
  void operator=(const AutoOutputRegister&) = delete;

 public:
  explicit AutoOutputRegister(CacheIRCompiler& compiler);
  ~AutoOutputRegister();

  Register maybeReg() const {
    if (output_.hasValue()) {
      return output_.valueReg().scratchReg();
    }
    if (!output_.typedReg().isFloat()) {
      return output_.typedReg().gpr();
    }
    return InvalidReg;
  }

  bool hasValue() const { return output_.hasValue(); }
  ValueOperand valueReg() const { return output_.valueReg(); }
  AnyRegister typedReg() const { return output_.typedReg(); }

  JSValueType type() const {
    MOZ_ASSERT(!hasValue());
    return ValueTypeFromMIRType(output_.type());
  }

  operator TypedOrValueRegister() const { return output_; }
};

enum class CallCanGC { CanGC, CanNotGC };

// Instructions that have to perform a callVM require a stub frame. Call its
// enter() and leave() methods to enter/leave the stub frame.
// Hoisted from jit/BaselineCacheIRCompiler.cpp. See there for method
// definitions.
class MOZ_RAII AutoStubFrame {
  BaselineCacheIRCompiler& compiler;
#ifdef DEBUG
  uint32_t framePushedAtEnterStubFrame_;
#endif

  AutoStubFrame(const AutoStubFrame&) = delete;
  void operator=(const AutoStubFrame&) = delete;

 public:
  explicit AutoStubFrame(BaselineCacheIRCompiler& compiler);

  void enter(MacroAssembler& masm, Register scratch,
             CallCanGC canGC = CallCanGC::CanGC);
  void leave(MacroAssembler& masm, bool calledIntoIon = false);

#ifdef DEBUG
  ~AutoStubFrame();
#endif
};
// AutoSaveLiveRegisters must be used when we make a call that can GC. The
// constructor ensures all live registers are stored on the stack (where the GC
// expects them) and the destructor restores these registers.
class MOZ_RAII AutoSaveLiveRegisters {
  IonCacheIRCompiler& compiler_;

  AutoSaveLiveRegisters(const AutoSaveLiveRegisters&) = delete;
  void operator=(const AutoSaveLiveRegisters&) = delete;

 public:
  explicit AutoSaveLiveRegisters(IonCacheIRCompiler& compiler);

  ~AutoSaveLiveRegisters();
};
// Like AutoScratchRegister, but reuse a register of |output| if possible.
class MOZ_RAII AutoScratchRegisterMaybeOutput {
  mozilla::Maybe<AutoScratchRegister> scratch_;
  Register scratchReg_;

  AutoScratchRegisterMaybeOutput(const AutoScratchRegisterMaybeOutput&) =
      delete;
  void operator=(const AutoScratchRegisterMaybeOutput&) = delete;

 public:
  AutoScratchRegisterMaybeOutput(CacheRegisterAllocator& alloc,
                                 MacroAssembler& masm,
                                 const AutoOutputRegister& output) {
    scratchReg_ = output.maybeReg();
    if (scratchReg_ == InvalidReg) {
      scratch_.emplace(alloc, masm);
      scratchReg_ = scratch_.ref();
    }
  }

  Register get() const { return scratchReg_; }
  operator Register() const { return scratchReg_; }
};

// Like AutoScratchRegisterMaybeOutput, but tries to use the ValueOperand's
// type register for the scratch register on 32-bit.
//
// Word of warning: Passing an instance of this class and AutoOutputRegister to
// functions may not work correctly, because no guarantee is given that the type
// register is used last when modifying the output's ValueOperand.
class MOZ_RAII AutoScratchRegisterMaybeOutputType {
  mozilla::Maybe<AutoScratchRegister> scratch_;
  Register scratchReg_;

 public:
  AutoScratchRegisterMaybeOutputType(CacheRegisterAllocator& alloc,
                                     MacroAssembler& masm,
                                     const AutoOutputRegister& output) {
#if defined(JS_NUNBOX32)
    scratchReg_ = output.hasValue() ? output.valueReg().typeReg() : InvalidReg;
#else
    scratchReg_ = InvalidReg;
#endif
    if (scratchReg_ == InvalidReg) {
      scratch_.emplace(alloc, masm);
      scratchReg_ = scratch_.ref();
    }
  }

  AutoScratchRegisterMaybeOutputType(
      const AutoScratchRegisterMaybeOutputType&) = delete;

  void operator=(const AutoScratchRegisterMaybeOutputType&) = delete;

  operator Register() const { return scratchReg_; }
};

// AutoCallVM is a wrapper class that unifies methods shared by
// IonCacheIRCompiler and BaselineCacheIRCompiler that perform a callVM, but
// require stub specific functionality before performing the VM call.
//
// Expected Usage:
//
//   OPs with implementations that may be unified by this class must:
//     - Be listed in the CACHEIR_OPS list but not in the CACHE_IR_SHARED_OPS
//     list
//     - Differ only in their use of `AutoSaveLiveRegisters`,
//       `AutoOutputRegister`, and `AutoScratchRegister`. The Ion
//       implementation will use `AutoSaveLiveRegisters` and
//       `AutoOutputRegister`, while the Baseline implementation will use
//       `AutoScratchRegister`.
//     - Both use the `callVM` method.
//
//   Using AutoCallVM:
//     - The constructor initializes `AutoOutputRegister` for both compiler
//       types. Additionally it initializes an `AutoSaveLiveRegisters` for
//       CacheIRCompilers with the mode Ion, and initializes
//       `AutoScratchRegisterMaybeOutput` and `AutoStubFrame` variables for
//       compilers with mode Baseline.
//     - The `prepare()` method calls the IonCacheIRCompiler method
//       `prepareVMCall` for IonCacheIRCompilers, calls the `enter()` method of
//       `AutoStubFrame` for BaselineCacheIRCompilers, and calls the
//       `discardStack` method of the `Register` class for both compiler types.
//     - The `call()` method invokes `callVM` on the CacheIRCompiler and stores
//       the call result according to its type. Finally it calls the `leave`
//       method of `AutoStubFrame` for BaselineCacheIRCompilers.
//
//   Expected Usage Example:
//     See: `CacheIRCompiler::emitCallGetSparseElementResult()`
//
// Restrictions:
//   - OPs that do not meet the criteria listed above can not be unified with
//     AutoCallVM
//

class MOZ_RAII AutoCallVM {
  MacroAssembler& masm_;
  CacheIRCompiler* compiler_;
  CacheRegisterAllocator& allocator_;
  mozilla::Maybe<AutoOutputRegister> output_;

  // Baseline specific stuff
  mozilla::Maybe<AutoStubFrame> stubFrame_;
  mozilla::Maybe<AutoScratchRegisterMaybeOutput> scratch_;

  // Ion specific stuff
  mozilla::Maybe<AutoSaveLiveRegisters> save_;

  void storeResult(JSValueType returnType);

  template <typename Fn>
  void storeResult();

  void leaveBaselineStubFrame();

 public:
  AutoCallVM(MacroAssembler& masm, CacheIRCompiler* compiler,
             CacheRegisterAllocator& allocator);

  void prepare();

  template <typename Fn, Fn fn>
  void call() {
    compiler_->callVM<Fn, fn>(masm_);
    storeResult<Fn>();
    leaveBaselineStubFrame();
  }

  template <typename Fn, Fn fn>
  void callNoResult() {
    compiler_->callVM<Fn, fn>(masm_);
    leaveBaselineStubFrame();
  }

  ValueOperand outputValueReg() const { return output_->valueReg(); }
};

// RAII class to allocate FloatReg0 as a scratch register and release it when
// we're done with it. The previous contents of FloatReg0 may be spilled on the
// stack and, if necessary, are restored when the destructor runs.
//
// When FailurePath is passed to the constructor, FailurePath::label() must not
// be used during the life time of the AutoScratchFloatRegister. Instead use
// AutoScratchFloatRegister::failure().
class MOZ_RAII AutoScratchFloatRegister {
  Label failurePopReg_{};
  CacheIRCompiler* compiler_;
  FailurePath* failure_;

  AutoScratchFloatRegister(const AutoScratchFloatRegister&) = delete;
  void operator=(const AutoScratchFloatRegister&) = delete;

 public:
  explicit AutoScratchFloatRegister(CacheIRCompiler* compiler)
      : AutoScratchFloatRegister(compiler, nullptr) {}

  AutoScratchFloatRegister(CacheIRCompiler* compiler, FailurePath* failure);

  ~AutoScratchFloatRegister();

  Label* failure();

  FloatRegister get() const { return FloatReg0; }
  operator FloatRegister() const { return FloatReg0; }
};

// This class can be used to assert a certain FloatRegister is available. In
// Baseline mode, all float registers are available. In Ion mode, only the
// registers added as fixed temps in LIRGenerator are available.
class MOZ_RAII AutoAvailableFloatRegister {
  FloatRegister reg_;

  AutoAvailableFloatRegister(const AutoAvailableFloatRegister&) = delete;
  void operator=(const AutoAvailableFloatRegister&) = delete;

 public:
  explicit AutoAvailableFloatRegister(CacheIRCompiler& compiler,
                                      FloatRegister reg)
      : reg_(reg) {
#ifdef DEBUG
    compiler.assertFloatRegisterAvailable(reg);
#endif
  }

  FloatRegister get() const { return reg_; }
  operator FloatRegister() const { return reg_; }
};

// See the 'Sharing Baseline stub code' comment in CacheIR.h for a description
// of this class.
class CacheIRStubInfo {
  // These fields don't require 8 bits, but GCC complains if these fields are
  // smaller than the size of the enums.
  CacheKind kind_ : 8;
  ICStubEngine engine_ : 8;
  bool makesGCCalls_ : 1;
  uint8_t stubDataOffset_;

  const uint8_t* code_;
  uint32_t length_;
  const uint8_t* fieldTypes_;

  CacheIRStubInfo(CacheKind kind, ICStubEngine engine, bool makesGCCalls,
                  uint32_t stubDataOffset, const uint8_t* code,
                  uint32_t codeLength, const uint8_t* fieldTypes)
      : kind_(kind),
        engine_(engine),
        makesGCCalls_(makesGCCalls),
        stubDataOffset_(stubDataOffset),
        code_(code),
        length_(codeLength),
        fieldTypes_(fieldTypes) {
    MOZ_ASSERT(kind_ == kind, "Kind must fit in bitfield");
    MOZ_ASSERT(engine_ == engine, "Engine must fit in bitfield");
    MOZ_ASSERT(stubDataOffset_ == stubDataOffset,
               "stubDataOffset must fit in uint8_t");
  }

  CacheIRStubInfo(const CacheIRStubInfo&) = delete;
  CacheIRStubInfo& operator=(const CacheIRStubInfo&) = delete;

 public:
  CacheKind kind() const { return kind_; }
  ICStubEngine engine() const { return engine_; }
  bool makesGCCalls() const { return makesGCCalls_; }

  const uint8_t* code() const { return code_; }
  uint32_t codeLength() const { return length_; }
  uint32_t stubDataOffset() const { return stubDataOffset_; }

  size_t stubDataSize() const;

  StubField::Type fieldType(uint32_t i) const {
    return (StubField::Type)fieldTypes_[i];
  }

  static CacheIRStubInfo* New(CacheKind kind, ICStubEngine engine,
                              bool canMakeCalls, uint32_t stubDataOffset,
                              const CacheIRWriter& writer);

  template <class Stub, class T>
  js::GCPtr<T>& getStubField(Stub* stub, uint32_t offset) const;

  template <class T>
  js::GCPtr<T>& getStubField(ICCacheIRStub* stub, uint32_t offset) const {
    return getStubField<ICCacheIRStub, T>(stub, offset);
  }

  uintptr_t getStubRawWord(const uint8_t* stubData, uint32_t offset) const;
  uintptr_t getStubRawWord(ICCacheIRStub* stub, uint32_t offset) const;

  int64_t getStubRawInt64(const uint8_t* stubData, uint32_t offset) const;
  int64_t getStubRawInt64(ICCacheIRStub* stub, uint32_t offset) const;

  void replaceStubRawWord(uint8_t* stubData, uint32_t offset, uintptr_t oldWord,
                          uintptr_t newWord) const;
};

template <typename T>
void TraceCacheIRStub(JSTracer* trc, T* stub, const CacheIRStubInfo* stubInfo);

}  // namespace jit
}  // namespace js

#endif /* jit_CacheIRCompiler_h */