Quelle  Snapshots.cpp   Sprache: C

/* -*- 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/. */

#include "jit/Snapshots.h"

#include "jit/JitSpewer.h"
#ifdef TRACK_SNAPSHOTS
#  include "jit/LIR.h"
#endif
#include "jit/MIR-wasm.h"
#include "jit/MIR.h"
#include "jit/Recover.h"
#include "js/Printer.h"

using namespace js;
using namespace js::jit;

// [SMDOC] IonMonkey Snapshot encoding
//
// Encodings:
//   [ptr] A fixed-size pointer.
//   [vwu] A variable-width unsigned integer.
//   [vws] A variable-width signed integer.
//    [u8] An 8-bit unsigned integer.
//   [u8'] An 8-bit unsigned integer which is potentially extended with packed
//         data.
//   [u8"] Packed data which is stored and packed in the previous [u8'].
//  [vwu*] A list of variable-width unsigned integers.
//   [pld] Payload of Recover Value Allocation:
//         PAYLOAD_NONE:
//           There is no payload.
//
//         PAYLOAD_INDEX:
//           [vwu] Index, such as the constant pool index.
//
//         PAYLOAD_STACK_OFFSET:
//           [vws] Stack offset based on the base of the Ion frame.
//
//         PAYLOAD_GPR:
//            [u8] Code of the general register.
//
//         PAYLOAD_FPU:
//            [u8] Code of the FPU register.
//
//         PAYLOAD_PACKED_TAG:
//           [u8"] Bits 5-7: JSValueType is encoded on the low bits of the Mode
//                           of the RValueAllocation.
//
// Snapshot header:
//
//   [vwu] bits ((n+1)-31]: recover instruction offset
//         bits [0,n): bailout kind (n = SNAPSHOT_BAILOUTKIND_BITS)
//
// Snapshot body, repeated "frame count" times, from oldest frame to newest
// frame. Note that the first frame doesn't have the "parent PC" field.
//
//   [ptr] Debug only: JSScript*
//   [vwu] pc offset
//   [vwu] # of RVA's indexes, including nargs
//  [vwu*] List of indexes to R(ecover)ValueAllocation table. Contains
//         nargs + nfixed + stackDepth items.
//
// Recover value allocations are encoded at the end of the Snapshot buffer, and
// they are padded on ALLOCATION_TABLE_ALIGNMENT.  The encoding of each
// allocation is determined by the RValueAllocation::Layout, which can be
// obtained from the RValueAllocation::Mode with layoutFromMode function.  The
// layout structure list the type of payload which are used to serialized /
// deserialized / dumped the content of the allocations.
//
// R(ecover)ValueAllocation items:
//   [u8'] Mode, which defines the type of the payload as well as the
//         interpretation.
//   [pld] first payload (packed tag, index, stack offset, register, ...)
//   [pld] second payload (register, stack offset, none)
//
//       Modes:
//         CONSTANT [INDEX]
//           Index into the constant pool.
//
//         CST_UNDEFINED []
//           Constant value which correspond to the "undefined" JS value.
//
//         CST_NULL []
//           Constant value which correspond to the "null" JS value.
//
//         DOUBLE_REG [FPU_REG]
//           Double value stored in a FPU register.
//
//         ANY_FLOAT_REG [FPU_REG]
//           Any Float value (float32, simd) stored in a FPU register.
//
//         ANY_FLOAT_STACK [STACK_OFFSET]
//           Any Float value (float32, simd) stored on the stack.
//
//         UNTYPED_REG   [GPR_REG]
//         UNTYPED_STACK [STACK_OFFSET]
//         UNTYPED_REG_REG     [GPR_REG,      GPR_REG]
//         UNTYPED_REG_STACK   [GPR_REG,      STACK_OFFSET]
//         UNTYPED_STACK_REG   [STACK_OFFSET, GPR_REG]
//         UNTYPED_STACK_STACK [STACK_OFFSET, STACK_OFFSET]
//           Value with dynamically known type. On 32 bits architecture, the
//           first register/stack-offset correspond to the holder of the type,
//           and the second correspond to the payload of the JS Value.
//
//         RECOVER_INSTRUCTION [INDEX]
//           Index into the list of recovered instruction results.
//
//         RI_WITH_DEFAULT_CST [INDEX] [INDEX]
//           The first payload is the index into the list of recovered
//           instruction results.  The second payload is the index in the
//           constant pool.
//
//         INTPTR_CST [INDEX]:          (32-bit platform)
//         INTPTR_CST [INDEX] [INDEX]:  (64-bit platform)
//           Unpacked IntPtr value stored in intptr_t. Split into either one or
//           two int32_t values, whose indices into the constant pool is stored
//           in the payloads.
//
//         INTPTR_REG [GPR_REG]:
//           Unpacked IntPtr value stored in intptr_t. Payload is stored in a
//           register.
//
//         INTPTR_STACK [STACK_OFFSET]:
//           Unpacked IntPtr value stored in intptr_t. Payload is stored at an
//           offset on the stack.
//
//         TYPED_REG [PACKED_TAG, GPR_REG]:
//           Value with statically known type, which payload is stored in a
//           register.
//
//         TYPED_STACK [PACKED_TAG, STACK_OFFSET]:
//           Value with statically known type, which payload is stored at an
//           offset on the stack.
//
//         INT64_CST [INDEX] [INDEX]:
//           Unpacked Int64 value stored in int64_t. Split into two int32_t
//           values, whose indices into the constant pool is stored in the
//           payloads.
//
//         INT64_REG    [GPR_REG]:
//         INT64_STACK  [STACK_OFFSET]:
//         INT64_REG_REG      [GPR_REG,      GPR_REG]
//         INT64_REG_STACK    [GPR_REG,      STACK_OFFSET]
//         INT64_STACK_REG    [STACK_OFFSET, GPR_REG]
//         INT64_STACK_STACK  [STACK_OFFSET, STACK_OFFSET]
//           Unpacked Int64 value. On 32 bits architecture, the first
//           register/stack-offset correspond to the low 32-bits, and the
//           second correspond to the high 32-bits.
//

const RValueAllocation::Layout& RValueAllocation::layoutFromMode(Mode mode) {
  switch (mode) {
    case CONSTANT: {
      static const RValueAllocation::Layout layout = {PAYLOAD_INDEX,
                                                      PAYLOAD_NONE, "constant"};
      return layout;
    }

    case CST_UNDEFINED: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_NONE, PAYLOAD_NONE, "undefined"};
      return layout;
    }

    case CST_NULL: {
      static const RValueAllocation::Layout layout = {PAYLOAD_NONE,
                                                      PAYLOAD_NONE, "null"};
      return layout;
    }

    case DOUBLE_REG: {
      static const RValueAllocation::Layout layout = {PAYLOAD_FPU, PAYLOAD_NONE,
                                                      "double"};
      return layout;
    }
    case ANY_FLOAT_REG: {
      static const RValueAllocation::Layout layout = {PAYLOAD_FPU, PAYLOAD_NONE,
                                                      "float register content"};
      return layout;
    }
    case ANY_FLOAT_STACK: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_STACK_OFFSET, PAYLOAD_NONE, "float register content"};
      return layout;
    }
#if defined(JS_NUNBOX32)
    case UNTYPED_REG_REG: {
      static const RValueAllocation::Layout layout = {PAYLOAD_GPR, PAYLOAD_GPR,
                                                      "value"};
      return layout;
    }
    case UNTYPED_REG_STACK: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_GPR, PAYLOAD_STACK_OFFSET, "value"};
      return layout;
    }
    case UNTYPED_STACK_REG: {
      static const RValueAllocation::Layout layout = {PAYLOAD_STACK_OFFSET,
                                                      PAYLOAD_GPR, "value"};
      return layout;
    }
    case UNTYPED_STACK_STACK: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_STACK_OFFSET, PAYLOAD_STACK_OFFSET, "value"};
      return layout;
    }
#elif defined(JS_PUNBOX64)
    case UNTYPED_REG: {
      static const RValueAllocation::Layout layout = {PAYLOAD_GPR, PAYLOAD_NONE,
                                                      "value"};
      return layout;
    }
    case UNTYPED_STACK: {
      static const RValueAllocation::Layout layout = {PAYLOAD_STACK_OFFSET,
                                                      PAYLOAD_NONE, "value"};
      return layout;
    }
#endif
    case RECOVER_INSTRUCTION: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_INDEX, PAYLOAD_NONE, "instruction"};
      return layout;
    }
    case RI_WITH_DEFAULT_CST: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_INDEX, PAYLOAD_INDEX, "instruction with default"};
      return layout;
    }

    case INTPTR_CST: {
#if !defined(JS_64BIT)
      static const RValueAllocation::Layout layout = {
          PAYLOAD_INDEX, PAYLOAD_NONE, "unpacked intptr constant"};
      static_assert(sizeof(int32_t) == sizeof(intptr_t));
#else
      static const RValueAllocation::Layout layout = {
          PAYLOAD_INDEX, PAYLOAD_INDEX, "unpacked intptr constant"};
      static_assert(2 * sizeof(int32_t) == sizeof(intptr_t));
#endif
      return layout;
    }

    case INTPTR_REG: {
      static const RValueAllocation::Layout layout = {PAYLOAD_GPR, PAYLOAD_NONE,
                                                      "unpacked intptr"};
      return layout;
    }

    case INTPTR_STACK: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_STACK_OFFSET, PAYLOAD_NONE, "unpacked intptr"};
      return layout;
    }

    case INT64_CST: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_INDEX, PAYLOAD_INDEX, "unpacked int64 constant"};
      static_assert(2 * sizeof(int32_t) == sizeof(int64_t));
      return layout;
    }

#if defined(JS_NUNBOX32)
    case INT64_REG_REG: {
      static const RValueAllocation::Layout layout = {PAYLOAD_GPR, PAYLOAD_GPR,
                                                      "unpacked int64"};
      return layout;
    }

    case INT64_REG_STACK: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_GPR, PAYLOAD_STACK_OFFSET, "unpacked int64"};
      return layout;
    }

    case INT64_STACK_REG: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_STACK_OFFSET, PAYLOAD_GPR, "unpacked int64"};
      return layout;
    }

    case INT64_STACK_STACK: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_STACK_OFFSET, PAYLOAD_STACK_OFFSET, "unpacked int64"};
      return layout;
    }
#elif defined(JS_PUNBOX64)
    case INT64_REG: {
      static const RValueAllocation::Layout layout = {PAYLOAD_GPR, PAYLOAD_NONE,
                                                      "unpacked int64"};
      return layout;
    }

    case INT64_STACK: {
      static const RValueAllocation::Layout layout = {
          PAYLOAD_STACK_OFFSET, PAYLOAD_NONE, "unpacked int64"};
      return layout;
    }
#endif

    default: {
      static const RValueAllocation::Layout regLayout = {
          PAYLOAD_PACKED_TAG, PAYLOAD_GPR, "typed value"};

      static const RValueAllocation::Layout stackLayout = {
          PAYLOAD_PACKED_TAG, PAYLOAD_STACK_OFFSET, "typed value"};

      if (mode >= TYPED_REG_MIN && mode <= TYPED_REG_MAX) {
        return regLayout;
      }
      if (mode >= TYPED_STACK_MIN && mode <= TYPED_STACK_MAX) {
        return stackLayout;
      }
    }
  }

  MOZ_CRASH_UNSAFE_PRINTF("Unexpected mode: 0x%x", uint32_t(mode));
}

// Pad serialized RValueAllocations by a multiple of X bytes in the allocation
// buffer.  By padding serialized value allocations, we are building an
// indexable table of elements of X bytes, and thus we can safely divide any
// offset within the buffer by X to obtain an index.
//
// By padding, we are loosing space within the allocation buffer, but we
// multiple by X the number of indexes that we can store on one byte in each
// snapshots.
//
// Some value allocations are taking more than X bytes to be encoded, in which
// case we will pad to a multiple of X, and we are wasting indexes. The choice
// of X should be balanced between the wasted padding of serialized value
// allocation, and the saving made in snapshot indexes.
static const size_t ALLOCATION_TABLE_ALIGNMENT = 2; /* bytes */

void RValueAllocation::readPayload(CompactBufferReader& reader,
                                   PayloadType type, uint8_t* mode,
                                   Payload* p) {
  switch (type) {
    case PAYLOAD_NONE:
      break;
    case PAYLOAD_INDEX:
      p->index = reader.readUnsigned();
      break;
    case PAYLOAD_STACK_OFFSET:
      p->stackOffset = reader.readSigned();
      break;
    case PAYLOAD_GPR:
      p->gpr = Register::FromCode(reader.readByte());
      break;
    case PAYLOAD_FPU:
      p->fpu.data = reader.readByte();
      break;
    case PAYLOAD_PACKED_TAG:
      p->type = JSValueType(*mode & PACKED_TAG_MASK);
      *mode = *mode & ~PACKED_TAG_MASK;
      break;
  }
}

RValueAllocation RValueAllocation::read(CompactBufferReader& reader) {
  uint8_t mode = reader.readByte();
  const Layout& layout = layoutFromMode(Mode(mode & MODE_BITS_MASK));
  Payload arg1, arg2;

  readPayload(reader, layout.type1, &mode, &arg1);
  readPayload(reader, layout.type2, &mode, &arg2);
  return RValueAllocation(Mode(mode), arg1, arg2);
}

void RValueAllocation::writePayload(CompactBufferWriter& writer,
                                    PayloadType type, Payload p) {
  switch (type) {
    case PAYLOAD_NONE:
      break;
    case PAYLOAD_INDEX:
      writer.writeUnsigned(p.index);
      break;
    case PAYLOAD_STACK_OFFSET:
      writer.writeSigned(p.stackOffset);
      break;
    case PAYLOAD_GPR:
      static_assert(Registers::Total <= 0x100,
                    "Not enough bytes to encode all registers.");
      writer.writeByte(p.gpr.code());
      break;
    case PAYLOAD_FPU:
      static_assert(FloatRegisters::Total <= 0x100,
                    "Not enough bytes to encode all float registers.");
      writer.writeByte(p.fpu.code());
      break;
    case PAYLOAD_PACKED_TAG: {
      // This code assumes that the PACKED_TAG payload is following the
      // writeByte of the mode.
      if (!writer.oom()) {
        MOZ_ASSERT(writer.length());
        uint8_t* mode = writer.buffer() + (writer.length() - 1);
        MOZ_ASSERT((*mode & PACKED_TAG_MASK) == 0 &&
                   (p.type & ~PACKED_TAG_MASK) == 0);
        *mode = *mode | p.type;
      }
      break;
    }
  }
}

void RValueAllocation::writePadding(CompactBufferWriter& writer) {
  // Write 0x7f in all padding bytes.
  while (writer.length() % ALLOCATION_TABLE_ALIGNMENT) {
    writer.writeByte(0x7f);
  }
}

void RValueAllocation::write(CompactBufferWriter& writer) const {
  const Layout& layout = layoutFromMode(mode());
  MOZ_ASSERT(layout.type2 != PAYLOAD_PACKED_TAG);
  MOZ_ASSERT(writer.length() % ALLOCATION_TABLE_ALIGNMENT == 0);

  writer.writeByte(mode_);
  writePayload(writer, layout.type1, arg1_);
  writePayload(writer, layout.type2, arg2_);
  writePadding(writer);
}

HashNumber RValueAllocation::hash() const {
  HashNumber res = 0;
  res = HashNumber(mode_);
  res = arg1_.index + (res << 6) + (res << 16) - res;
  res = arg2_.index + (res << 6) + (res << 16) - res;
  return res;
}

#ifdef JS_JITSPEW
void RValueAllocation::dumpPayload(GenericPrinter& out, PayloadType type,
                                   Payload p) {
  switch (type) {
    case PAYLOAD_NONE:
      break;
    case PAYLOAD_INDEX:
      out.printf("index %u", p.index);
      break;
    case PAYLOAD_STACK_OFFSET:
      out.printf("stack %d", p.stackOffset);
      break;
    case PAYLOAD_GPR:
      out.printf("reg %s", p.gpr.name());
      break;
    case PAYLOAD_FPU:
      out.printf("reg %s", p.fpu.name());
      break;
    case PAYLOAD_PACKED_TAG:
      out.printf("%s", ValTypeToString(p.type));
      break;
  }
}

void RValueAllocation::dump(GenericPrinter& out) const {
  const Layout& layout = layoutFromMode(mode());
  out.printf("%s", layout.name);

  if (layout.type1 != PAYLOAD_NONE) {
    out.printf(" (");
  }
  dumpPayload(out, layout.type1, arg1_);
  if (layout.type2 != PAYLOAD_NONE) {
    out.printf(", ");
  }
  dumpPayload(out, layout.type2, arg2_);
  if (layout.type1 != PAYLOAD_NONE) {
    out.printf(")");
  }
}
#endif  // JS_JITSPEW

SnapshotReader::SnapshotReader(const uint8_t* snapshots, uint32_t offset,
                               uint32_t RVATableSize, uint32_t listSize)
    : reader_(snapshots + offset, snapshots + listSize),
      allocReader_(snapshots + listSize, snapshots + listSize + RVATableSize),
      allocTable_(snapshots + listSize),
      allocRead_(0) {
  if (!snapshots) {
    return;
  }
  JitSpew(JitSpew_IonSnapshots, "Creating snapshot reader");
  readSnapshotHeader();
}

#define COMPUTE_SHIFT_AFTER_(name) (name##_BITS + name##_SHIFT)
#define COMPUTE_MASK_(name) ((uint32_t(1 << name##_BITS) - 1) << name##_SHIFT)

// Details of snapshot header packing.
static const uint32_t SNAPSHOT_BAILOUTKIND_SHIFT = 0;
static const uint32_t SNAPSHOT_BAILOUTKIND_BITS = 6;
static const uint32_t SNAPSHOT_BAILOUTKIND_MASK =
    COMPUTE_MASK_(SNAPSHOT_BAILOUTKIND);

static_assert((1 << SNAPSHOT_BAILOUTKIND_BITS) - 1 >=
                  uint8_t(BailoutKind::Limit),
              "Not enough bits for BailoutKinds");

static const uint32_t SNAPSHOT_ROFFSET_SHIFT =
    COMPUTE_SHIFT_AFTER_(SNAPSHOT_BAILOUTKIND);
static const uint32_t SNAPSHOT_ROFFSET_BITS = 32 - SNAPSHOT_ROFFSET_SHIFT;
static const uint32_t SNAPSHOT_ROFFSET_MASK = COMPUTE_MASK_(SNAPSHOT_ROFFSET);

#undef COMPUTE_MASK_
#undef COMPUTE_SHIFT_AFTER_

void SnapshotReader::readSnapshotHeader() {
  uint32_t bits = reader_.readUnsigned();

  bailoutKind_ = BailoutKind((bits & SNAPSHOT_BAILOUTKIND_MASK) >>
                             SNAPSHOT_BAILOUTKIND_SHIFT);
  recoverOffset_ = (bits & SNAPSHOT_ROFFSET_MASK) >> SNAPSHOT_ROFFSET_SHIFT;

  JitSpew(JitSpew_IonSnapshots, "Read snapshot header with bailout kind %u",
          uint32_t(bailoutKind_));

#ifdef TRACK_SNAPSHOTS
  readTrackSnapshot();
#endif
}

#ifdef TRACK_SNAPSHOTS
void SnapshotReader::readTrackSnapshot() {
  pcOpcode_ = reader_.readUnsigned();
  mirOpcode_ = reader_.readUnsigned();
  mirId_ = reader_.readUnsigned();
  lirOpcode_ = reader_.readUnsigned();
  lirId_ = reader_.readUnsigned();
}

void SnapshotReader::spewBailingFrom() const {
#  ifdef JS_JITSPEW
  if (JitSpewEnabled(JitSpew_IonBailouts)) {
    JitSpewHeader(JitSpew_IonBailouts);
    Fprinter& out = JitSpewPrinter();
    out.printf(" bailing from bytecode: %s, MIR: ", CodeName(JSOp(pcOpcode_)));
    MDefinition::PrintOpcodeName(out, MDefinition::Opcode(mirOpcode_));
    out.printf(" [%u], LIR: ", mirId_);
    LInstruction::printName(out, LInstruction::Opcode(lirOpcode_));
    out.printf(" [%u]", lirId_);
    out.printf("\n");
  }
#  endif
}
#endif

uint32_t SnapshotReader::readAllocationIndex() {
  allocRead_++;
  return reader_.readUnsigned();
}

RValueAllocation SnapshotReader::readAllocation() {
  JitSpew(JitSpew_IonSnapshots, "Reading slot %u", allocRead_);
  uint32_t offset = readAllocationIndex() * ALLOCATION_TABLE_ALIGNMENT;
  allocReader_.seek(allocTable_, offset);
  return RValueAllocation::read(allocReader_);
}

SnapshotWriter::SnapshotWriter()
    // Based on the measurements made in Bug 962555 comment 20, this length
    // should be enough to prevent the reallocation of the hash table for at
    // least half of the compilations.
    : allocMap_(32) {}

RecoverReader::RecoverReader(SnapshotReader& snapshot, const uint8_t* recovers,
                             uint32_t size)
    : reader_(nullptr, nullptr), numInstructions_(0), numInstructionsRead_(0) {
  if (!recovers) {
    return;
  }
  reader_ =
      CompactBufferReader(recovers + snapshot.recoverOffset(), recovers + size);
  readRecoverHeader();
  readInstruction();
}

RecoverReader::RecoverReader(const RecoverReader& rr)
    : reader_(rr.reader_),
      numInstructions_(rr.numInstructions_),
      numInstructionsRead_(rr.numInstructionsRead_) {
  if (reader_.currentPosition()) {
    rr.instruction()->cloneInto(&rawData_);
  }
}

RecoverReader& RecoverReader::operator=(const RecoverReader& rr) {
  reader_ = rr.reader_;
  numInstructions_ = rr.numInstructions_;
  numInstructionsRead_ = rr.numInstructionsRead_;
  if (reader_.currentPosition()) {
    rr.instruction()->cloneInto(&rawData_);
  }
  return *this;
}

void RecoverReader::readRecoverHeader() {
  numInstructions_ = reader_.readUnsigned();
  MOZ_ASSERT(numInstructions_);

  JitSpew(JitSpew_IonSnapshots, "Read recover header with instructionCount %u",
          numInstructions_);
}

void RecoverReader::readInstruction() {
  MOZ_ASSERT(moreInstructions());
  RInstruction::readRecoverData(reader_, &rawData_);
  numInstructionsRead_++;
}

SnapshotOffset SnapshotWriter::startSnapshot(RecoverOffset recoverOffset,
                                             BailoutKind kind) {
  lastStart_ = writer_.length();
  allocWritten_ = 0;

  JitSpew(JitSpew_IonSnapshots,
          "starting snapshot with recover offset %u, bailout kind %u",
          recoverOffset, uint32_t(kind));

  MOZ_ASSERT(uint32_t(kind) < (1 << SNAPSHOT_BAILOUTKIND_BITS));
  MOZ_ASSERT(recoverOffset < (1 << SNAPSHOT_ROFFSET_BITS));
  uint32_t bits = (uint32_t(kind) << SNAPSHOT_BAILOUTKIND_SHIFT) |
                  (recoverOffset << SNAPSHOT_ROFFSET_SHIFT);

  writer_.writeUnsigned(bits);
  return lastStart_;
}

#ifdef TRACK_SNAPSHOTS
void SnapshotWriter::trackSnapshot(uint32_t pcOpcode, uint32_t mirOpcode,
                                   uint32_t mirId, uint32_t lirOpcode,
                                   uint32_t lirId) {
  writer_.writeUnsigned(pcOpcode);
  writer_.writeUnsigned(mirOpcode);
  writer_.writeUnsigned(mirId);
  writer_.writeUnsigned(lirOpcode);
  writer_.writeUnsigned(lirId);
}
#endif

bool SnapshotWriter::add(const RValueAllocation& alloc) {
  uint32_t offset;
  RValueAllocMap::AddPtr p = allocMap_.lookupForAdd(alloc);
  if (!p) {
    offset = allocWriter_.length();
    alloc.write(allocWriter_);
    if (!allocMap_.add(p, alloc, offset)) {
      allocWriter_.setOOM();
      return false;
    }
  } else {
    offset = p->value();
  }

#ifdef JS_JITSPEW
  if (JitSpewEnabled(JitSpew_IonSnapshots)) {
    JitSpewHeader(JitSpew_IonSnapshots);
    Fprinter& out = JitSpewPrinter();
    out.printf(" slot %u (%u): ", allocWritten_, offset);
    alloc.dump(out);
    out.printf("\n");
  }
#endif

  allocWritten_++;
  writer_.writeUnsigned(offset / ALLOCATION_TABLE_ALIGNMENT);
  return true;
}

void SnapshotWriter::endSnapshot() {
  // Place a sentinel for asserting on the other end.
#ifdef DEBUG
  writer_.writeSigned(-1);
#endif

  JitSpew(JitSpew_IonSnapshots,
          "ending snapshot total size: %u bytes (start %u)",
          uint32_t(writer_.length() - lastStart_), lastStart_);
}

RecoverOffset RecoverWriter::startRecover(uint32_t instructionCount) {
  MOZ_ASSERT(instructionCount);
  instructionCount_ = instructionCount;
  instructionsWritten_ = 0;

  JitSpew(JitSpew_IonSnapshots, "starting recover with %u instruction(s)",
          instructionCount);

  RecoverOffset recoverOffset = writer_.length();
  writer_.writeUnsigned(instructionCount);
  return recoverOffset;
}

void RecoverWriter::writeInstruction(const MNode* rp) {
  if (!rp->writeRecoverData(writer_)) {
    writer_.setOOM();
  }
  instructionsWritten_++;
}

void RecoverWriter::endRecover() {
  MOZ_ASSERT(instructionCount_ == instructionsWritten_);
}