DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

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/* -*- 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_JitcodeMap_h
#define jit_JitcodeMap_h

#include "jit/CompactBuffer.h"
#include "jit/CompileInfo.h"
#include "jit/ExecutableAllocator.h"
#include "jit/OptimizationTracking.h"

namespace js {
namespace jit {

/*
 * The Ion jitcode map implements tables to allow mapping from addresses in ion
 * jitcode to the list of (JSScript*, jsbytecode*) pairs that are implicitly
 * active in the frame at that point in the native code.
 *
 * To represent this information efficiently, a multi-level table is used.
 *
 * At the top level, a global splay-tree of JitcodeGlobalEntry describings the
 * mapping for each individual IonCode script generated by compiles.  The
 * entries are ordered by their nativeStartAddr.
 *
 * Every entry in the table is of fixed size, but there are different entry
 * types, distinguished by the kind field.
 */

class JitcodeGlobalTable;
class JitcodeIonTable;
class JitcodeRegionEntry;

class JitcodeGlobalEntry;

struct NativeToBytecode {
  CodeOffset nativeOffset;
  InlineScriptTree* tree;
  jsbytecode* pc;
};

class JitcodeSkiplistTower {
 public:
  static const unsigned MAX_HEIGHT = 32;

 private:
  uint8_t height_;
  bool isFree_;
  JitcodeGlobalEntry* ptrs_[1];

 public:
  explicit JitcodeSkiplistTower(unsigned height)
      : height_(height), isFree_(false) {
    MOZ_ASSERT(height >= 1 && height <= MAX_HEIGHT);
    clearPtrs();
  }

  unsigned height() const { return height_; }

  JitcodeGlobalEntry** ptrs(unsigned level) { return ptrs_; }

  JitcodeGlobalEntry* next(unsigned level) const {
    MOZ_ASSERT(!isFree_);
    MOZ_ASSERT(level < height());
    return ptrs_[level];
  }
  void setNext(unsigned level, JitcodeGlobalEntry* entry) {
    MOZ_ASSERT(!isFree_);
    MOZ_ASSERT(level < height());
    ptrs_[level] = entry;
  }

  //
  // When stored in a free-list, towers use 'ptrs_[0]' to store a
  // pointer to the next tower.  In this context only, 'ptrs_[0]'
  // may refer to a |JitcodeSkiplistTower*| instead of a
  // |JitcodeGlobalEntry*|.
  //

  void addToFreeList(JitcodeSkiplistTower** freeList) {
    JitcodeSkiplistTower* nextFreeTower = *freeList;
    MOZ_ASSERT_IF(nextFreeTower,
                  nextFreeTower->isFree_ && nextFreeTower->height() == height_);
    ptrs_[0] = (JitcodeGlobalEntry*)nextFreeTower;
    isFree_ = true;
    *freeList = this;
  }

  static JitcodeSkiplistTower* PopFromFreeList(
      JitcodeSkiplistTower** freeList) {
    if (!*freeList) {
      return nullptr;
    }

    JitcodeSkiplistTower* tower = *freeList;
    MOZ_ASSERT(tower->isFree_);
    JitcodeSkiplistTower* nextFreeTower =
        (JitcodeSkiplistTower*)tower->ptrs_[0];
    tower->clearPtrs();
    tower->isFree_ = false;
    *freeList = nextFreeTower;
    return tower;
  }

  static size_t CalculateSize(unsigned height) {
    MOZ_ASSERT(height >= 1);
    return sizeof(JitcodeSkiplistTower) +
           (sizeof(JitcodeGlobalEntry*) * (height - 1));
  }

 private:
  void clearPtrs() {
    for (unsigned i = 0; i < height_; i++) {
      ptrs_[0] = nullptr;
    }
  }
};

class JitcodeGlobalEntry {
  friend class JitcodeGlobalTable;

 public:
  enum Kind {
    INVALID = 0,
    Ion,
    Baseline,
    BaselineInterpreter,
    IonCache,
    Dummy,
    Query,
    LIMIT
  };
  JS_STATIC_ASSERT(LIMIT <= 8);

  struct BytecodeLocation {
    JSScript* script;
    jsbytecode* pc;
    BytecodeLocation(JSScript* script, jsbytecode* pc)
        : script(script), pc(pc) {}
  };
  typedef Vector<BytecodeLocation, 0, SystemAllocPolicy> BytecodeLocationVector;

  struct BaseEntry {
    static const uint64_t kNoSampleInBuffer = UINT64_MAX;

    JitCode* jitcode_;
    void* nativeStartAddr_;
    void* nativeEndAddr_;
    // If this entry is referenced from the profiler buffer, this is the
    // position where the most recent sample that references it starts.
    // Otherwise set to kNoSampleInBuffer.
    uint64_t samplePositionInBuffer_;
    Kind kind_ : 7;

    void init() {
      jitcode_ = nullptr;
      nativeStartAddr_ = nullptr;
      nativeEndAddr_ = nullptr;
      samplePositionInBuffer_ = kNoSampleInBuffer;
      kind_ = INVALID;
    }

    void init(Kind kind, JitCode* code, void* nativeStartAddr,
              void* nativeEndAddr) {
      MOZ_ASSERT_IF(kind != Query, code);
      MOZ_ASSERT(nativeStartAddr);
      MOZ_ASSERT(nativeEndAddr);
      MOZ_ASSERT(kind > INVALID && kind < LIMIT);
      jitcode_ = code;
      nativeStartAddr_ = nativeStartAddr;
      nativeEndAddr_ = nativeEndAddr;
      samplePositionInBuffer_ = kNoSampleInBuffer;
      kind_ = kind;
    }

    void setSamplePositionInBuffer(uint64_t bufferWritePos) {
      samplePositionInBuffer_ = bufferWritePos;
    }
    void setAsExpired() { samplePositionInBuffer_ = kNoSampleInBuffer; }
    bool isSampled(uint64_t bufferRangeStart) {
      if (samplePositionInBuffer_ == kNoSampleInBuffer) {
        return false;
      }
      return bufferRangeStart <= samplePositionInBuffer_;
    }

    Kind kind() const { return kind_; }
    JitCode* jitcode() const { return jitcode_; }
    void* nativeStartAddr() const { return nativeStartAddr_; }
    void* nativeEndAddr() const { return nativeEndAddr_; }

    bool startsBelowPointer(void* ptr) const {
      return ((uint8_t*)nativeStartAddr()) <= ((uint8_t*)ptr);
    }
    bool endsAbovePointer(void* ptr) const {
      return ((uint8_t*)nativeEndAddr()) > ((uint8_t*)ptr);
    }
    bool containsPointer(void* ptr) const {
      return startsBelowPointer(ptr) && endsAbovePointer(ptr);
    }

    template <class ShouldTraceProvider>
    bool traceJitcode(JSTracer* trc);
    bool isJitcodeMarkedFromAnyThread(JSRuntime* rt);
    bool isJitcodeAboutToBeFinalized();
  };

  struct IonEntry : public BaseEntry {
    // regionTable_ points to the start of the region table within the
    // packed map for compile represented by this entry.  Since the
    // region table occurs at the tail of the memory region, this pointer
    // points somewhere inside the region memory space, and not to the start
    // of the memory space.
    JitcodeIonTable* regionTable_;

    // optsRegionTable_ points to the table within the compact
    // optimizations map indexing all regions that have tracked
    // optimization attempts. optsTypesTable_ is the tracked typed info
    // associated with the attempts vectors; it is the same length as the
    // attempts table. optsAttemptsTable_ is the table indexing those
    // attempts vectors.
    //
    // All pointers point into the same block of memory; the beginning of
    // the block is optRegionTable_->payloadStart().
    const IonTrackedOptimizationsRegionTable* optsRegionTable_;
    const IonTrackedOptimizationsTypesTable* optsTypesTable_;
    const IonTrackedOptimizationsAttemptsTable* optsAttemptsTable_;

    // The types table above records type sets, which have been gathered
    // into one vector here.
    IonTrackedTypeVector* optsAllTypes_;

    // Linked list pointers to allow traversing through all entries that
    // could possibly contain nursery pointers. Note that the contained
    // pointers can be mutated into nursery pointers at any time.
    IonEntry* prevNursery_;
    IonEntry* nextNursery_;

    struct ScriptNamePair {
      JSScript* script;
      char* str;
    };

    struct SizedScriptList {
      uint32_t size;
      ScriptNamePair pairs[1];
      SizedScriptList(uint32_t sz, JSScript** scrs, char** strs) : size(sz) {
        for (uint32_t i = 0; i < size; i++) {
          pairs[i].script = scrs[i];
          pairs[i].str = strs[i];
        }
      }

      static uint32_t AllocSizeFor(uint32_t nscripts) {
        return sizeof(SizedScriptList) +
               ((nscripts - 1) * sizeof(ScriptNamePair));
      }
    };

    SizedScriptList* scriptList_;

    void init(JitCode* code, void* nativeStartAddr, void* nativeEndAddr,
              SizedScriptList* scriptList, JitcodeIonTable* regionTable) {
      MOZ_ASSERT(scriptList);
      MOZ_ASSERT(regionTable);
      BaseEntry::init(Ion, code, nativeStartAddr, nativeEndAddr);
      regionTable_ = regionTable;
      scriptList_ = scriptList;
      optsRegionTable_ = nullptr;
      optsTypesTable_ = nullptr;
      optsAllTypes_ = nullptr;
      optsAttemptsTable_ = nullptr;
      prevNursery_ = nextNursery_ = nullptr;
    }

    void initTrackedOptimizations(
        const IonTrackedOptimizationsRegionTable* regionTable,
        const IonTrackedOptimizationsTypesTable* typesTable,
        const IonTrackedOptimizationsAttemptsTable* attemptsTable,
        IonTrackedTypeVector* allTypes) {
      optsRegionTable_ = regionTable;
      optsTypesTable_ = typesTable;
      optsAttemptsTable_ = attemptsTable;
      optsAllTypes_ = allTypes;
    }

    SizedScriptList* sizedScriptList() const { return scriptList_; }

    unsigned numScripts() const { return scriptList_->size; }

    JSScript* getScript(unsigned idx) const {
      MOZ_ASSERT(idx < numScripts());
      return sizedScriptList()->pairs[idx].script;
    }

    const char* getStr(unsigned idx) const {
      MOZ_ASSERT(idx < numScripts());
      return sizedScriptList()->pairs[idx].str;
    }

    void destroy();

    JitcodeIonTable* regionTable() const { return regionTable_; }

    int scriptIndex(JSScript* script) const {
      unsigned count = numScripts();
      for (unsigned i = 0; i < count; i++) {
        if (getScript(i) == script) {
          return i;
        }
      }
      return -1;
    }

    void* canonicalNativeAddrFor(void* ptr) const;

    MOZ_MUST_USE bool callStackAtAddr(void* ptr,
                                      BytecodeLocationVector& results,
                                      uint32_t* depth) const;

    uint32_t callStackAtAddr(void* ptr, const char** results,
                             uint32_t maxResults) const;

    void youngestFrameLocationAtAddr(void* ptr, JSScript** script,
                                     jsbytecode** pc) const;

    bool hasTrackedOptimizations() const { return !!optsRegionTable_; }

    const IonTrackedOptimizationsRegionTable* trackedOptimizationsRegionTable()
        const {
      MOZ_ASSERT(hasTrackedOptimizations());
      return optsRegionTable_;
    }

    uint8_t numOptimizationAttempts() const {
      MOZ_ASSERT(hasTrackedOptimizations());
      return optsAttemptsTable_->numEntries();
    }

    IonTrackedOptimizationsAttempts trackedOptimizationAttempts(uint8_t index) {
      MOZ_ASSERT(hasTrackedOptimizations());
      return optsAttemptsTable_->entry(index);
    }

    IonTrackedOptimizationsTypeInfo trackedOptimizationTypeInfo(uint8_t index) {
      MOZ_ASSERT(hasTrackedOptimizations());
      return optsTypesTable_->entry(index);
    }

    const IonTrackedTypeVector* allTrackedTypes() {
      MOZ_ASSERT(hasTrackedOptimizations());
      return optsAllTypes_;
    }

    mozilla::Maybe<uint8_t> trackedOptimizationIndexAtAddr(
        void* ptr, uint32_t* entryOffsetOut);

    void forEachOptimizationAttempt(
        uint8_t index, JS::ForEachTrackedOptimizationAttemptOp& op);
    void forEachOptimizationTypeInfo(
        uint8_t index, IonTrackedOptimizationsTypeInfo::ForEachOpAdapter& op);

    template <class ShouldTraceProvider>
    bool trace(JSTracer* trc);
    void sweepChildren();
    bool isMarkedFromAnyThread(JSRuntime* rt);
  };

  struct BaselineEntry : public BaseEntry {
    JSScript* script_;
    const char* str_;

    // Last location that caused Ion to abort compilation and the reason
    // therein, if any. Only actionable aborts are tracked. Internal
    // errors like OOMs are not.
    jsbytecode* ionAbortPc_;
    const char* ionAbortMessage_;

    void init(JitCode* code, void* nativeStartAddr, void* nativeEndAddr,
              JSScript* script, const char* str) {
      MOZ_ASSERT(script != nullptr);
      BaseEntry::init(Baseline, code, nativeStartAddr, nativeEndAddr);
      script_ = script;
      str_ = str;
    }

    JSScript* script() const { return script_; }

    const char* str() const { return str_; }

    void trackIonAbort(jsbytecode* pc, const char* message) {
      MOZ_ASSERT(script_->containsPC(pc));
      MOZ_ASSERT(message);
      ionAbortPc_ = pc;
      ionAbortMessage_ = message;
    }

    bool hadIonAbort() const {
      MOZ_ASSERT(!ionAbortPc_ || ionAbortMessage_);
      return ionAbortPc_ != nullptr;
    }

    void destroy();

    void* canonicalNativeAddrFor(void* ptr) const;

    MOZ_MUST_USE bool callStackAtAddr(void* ptr,
                                      BytecodeLocationVector& results,
                                      uint32_t* depth) const;

    uint32_t callStackAtAddr(void* ptr, const char** results,
                             uint32_t maxResults) const;

    void youngestFrameLocationAtAddr(void* ptr, JSScript** script,
                                     jsbytecode** pc) const;

    template <class ShouldTraceProvider>
    bool trace(JSTracer* trc);
    void sweepChildren();
    bool isMarkedFromAnyThread(JSRuntime* rt);
  };

  struct BaselineInterpreterEntry : public BaseEntry {
    void init(JitCode* code, void* nativeStartAddr, void* nativeEndAddr) {
      BaseEntry::init(BaselineInterpreter, code, nativeStartAddr,
                      nativeEndAddr);
    }

    void destroy() {}

    void* canonicalNativeAddrFor(void* ptr) const;

    MOZ_MUST_USE bool callStackAtAddr(void* ptr,
                                      BytecodeLocationVector& results,
                                      uint32_t* depth) const;

    uint32_t callStackAtAddr(void* ptr, const char** results,
                             uint32_t maxResults) const;

    void youngestFrameLocationAtAddr(void* ptr, JSScript** script,
                                     jsbytecode** pc) const;
  };

  struct IonCacheEntry : public BaseEntry {
    void* rejoinAddr_;
    JS::TrackedOutcome trackedOutcome_;

    void init(JitCode* code, void* nativeStartAddr, void* nativeEndAddr,
              void* rejoinAddr, JS::TrackedOutcome trackedOutcome) {
      MOZ_ASSERT(rejoinAddr != nullptr);
      BaseEntry::init(IonCache, code, nativeStartAddr, nativeEndAddr);
      rejoinAddr_ = rejoinAddr;
      trackedOutcome_ = trackedOutcome;
    }

    void* rejoinAddr() const { return rejoinAddr_; }
    JS::TrackedOutcome trackedOutcome() const { return trackedOutcome_; }

    void destroy() {}

    void* canonicalNativeAddrFor() const;

    MOZ_MUST_USE bool callStackAtAddr(JSRuntime* rt, void* ptr,
                                      BytecodeLocationVector& results,
                                      uint32_t* depth) const;

    uint32_t callStackAtAddr(JSRuntime* rt, void* ptr, const char** results,
                             uint32_t maxResults) const;

    void youngestFrameLocationAtAddr(JSRuntime* rt, void* ptr,
                                     JSScript** script, jsbytecode** pc) const;

    bool hasTrackedOptimizations() const { return true; }
    mozilla::Maybe<uint8_t> trackedOptimizationIndexAtAddr(
        JSRuntime* rt, void* ptr, uint32_t* entryOffsetOut);
    void forEachOptimizationAttempt(
        JSRuntime* rt, uint8_t index,
        JS::ForEachTrackedOptimizationAttemptOp& op);
    void forEachOptimizationTypeInfo(
        JSRuntime* rt, uint8_t index,
        IonTrackedOptimizationsTypeInfo::ForEachOpAdapter& op);

    template <class ShouldTraceProvider>
    bool trace(JSTracer* trc);
    void sweepChildren(JSRuntime* rt);
    bool isMarkedFromAnyThread(JSRuntime* rt);
  };

  // Dummy entries are created for jitcode generated when profiling is not
  // turned on, so that they have representation in the global table if they are
  // on the stack when profiling is enabled.
  struct DummyEntry : public BaseEntry {
    void init(JitCode* code, void* nativeStartAddr, void* nativeEndAddr) {
      BaseEntry::init(Dummy, code, nativeStartAddr, nativeEndAddr);
    }

    void destroy() {}

    void* canonicalNativeAddrFor(JSRuntime* rt, void* ptr) const {
      return nullptr;
    }

    MOZ_MUST_USE bool callStackAtAddr(JSRuntime* rt, void* ptr,
                                      BytecodeLocationVector& results,
                                      uint32_t* depth) const {
      return true;
    }

    uint32_t callStackAtAddr(JSRuntime* rt, void* ptr, const char** results,
                             uint32_t maxResults) const {
      return 0;
    }

    void youngestFrameLocationAtAddr(JSRuntime* rt, void* ptr,
                                     JSScript** script, jsbytecode** pc) const {
      *script = nullptr;
      *pc = nullptr;
    }
  };

  // QueryEntry is never stored in the table, just used for queries
  // where an instance of JitcodeGlobalEntry is required to do tree
  // lookups.
  struct QueryEntry : public BaseEntry {
    void init(void* addr) { BaseEntry::init(Query, nullptr, addr, addr); }
    uint8_t* addr() const {
      return reinterpret_cast<uint8_t*>(nativeStartAddr());
    }
    void destroy() {}
  };

 private:
  JitcodeSkiplistTower* tower_;

  union {
    // Shadowing BaseEntry instance to allow access to base fields
    // and type extraction.
    BaseEntry base_;

    // The most common entry type: describing jitcode generated by
    // Ion main-line code.
    IonEntry ion_;

    // Baseline jitcode.
    BaselineEntry baseline_;

    // BaselineInterpreter code.
    BaselineInterpreterEntry baselineInterpreter_;

    // IonCache stubs.
    IonCacheEntry ionCache_;

    // Dummy entries.
    DummyEntry dummy_;

    // When doing queries on the SplayTree for particular addresses,
    // the query addresses are representd using a QueryEntry.
    QueryEntry query_;
  };

 public:
  JitcodeGlobalEntry() : tower_(nullptr) { base_.init(); }

  explicit JitcodeGlobalEntry(const IonEntry& ion) : JitcodeGlobalEntry() {
    ion_ = ion;
  }

  explicit JitcodeGlobalEntry(const BaselineEntry& baseline)
      : JitcodeGlobalEntry() {
    baseline_ = baseline;
  }

  explicit JitcodeGlobalEntry(const BaselineInterpreterEntry& baselineInterp)
      : JitcodeGlobalEntry() {
    baselineInterpreter_ = baselineInterp;
  }

  explicit JitcodeGlobalEntry(const IonCacheEntry& ionCache)
      : JitcodeGlobalEntry() {
    ionCache_ = ionCache;
  }

  explicit JitcodeGlobalEntry(const DummyEntry& dummy) : JitcodeGlobalEntry() {
    dummy_ = dummy;
  }

  explicit JitcodeGlobalEntry(const QueryEntry& query) : JitcodeGlobalEntry() {
    query_ = query;
  }

  static JitcodeGlobalEntry MakeQuery(void* ptr) {
    QueryEntry query;
    query.init(ptr);
    return JitcodeGlobalEntry(query);
  }

  void destroy() {
    switch (kind()) {
      case Ion:
        ionEntry().destroy();
        break;
      case Baseline:
        baselineEntry().destroy();
        break;
      case BaselineInterpreter:
        baselineInterpreterEntry().destroy();
        break;
      case IonCache:
        ionCacheEntry().destroy();
        break;
      case Dummy:
        dummyEntry().destroy();
        break;
      case Query:
        queryEntry().destroy();
        break;
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
  }

  JitCode* jitcode() const { return baseEntry().jitcode(); }
  void* nativeStartAddr() const { return base_.nativeStartAddr(); }
  void* nativeEndAddr() const { return base_.nativeEndAddr(); }

  void setSamplePositionInBuffer(uint64_t samplePositionInBuffer) {
    baseEntry().setSamplePositionInBuffer(samplePositionInBuffer);
  }
  void setAsExpired() { baseEntry().setAsExpired(); }
  bool isSampled(uint64_t bufferRangeStart) {
    return baseEntry().isSampled(bufferRangeStart);
  }

  bool startsBelowPointer(void* ptr) const {
    return base_.startsBelowPointer(ptr);
  }
  bool endsAbovePointer(void* ptr) const { return base_.endsAbovePointer(ptr); }
  bool containsPointer(void* ptr) const { return base_.containsPointer(ptr); }

  bool overlapsWith(const JitcodeGlobalEntry& entry) const {
    // Catch full containment of |entry| within |this|, and partial overlaps.
    if (containsPointer(entry.nativeStartAddr()) ||
        containsPointer(entry.nativeEndAddr())) {
      return true;
    }

    // Catch full containment of |this| within |entry|.
    if (startsBelowPointer(entry.nativeEndAddr()) &&
        endsAbovePointer(entry.nativeStartAddr())) {
      return true;
    }

    return false;
  }

  Kind kind() const { return base_.kind(); }

  bool isValid() const { return (kind() > INVALID) && (kind() < LIMIT); }
  bool isIon() const { return kind() == Ion; }
  bool isBaseline() const { return kind() == Baseline; }
  bool isBaselineInterpreter() const { return kind() == BaselineInterpreter; }
  bool isIonCache() const { return kind() == IonCache; }
  bool isDummy() const { return kind() == Dummy; }
  bool isQuery() const { return kind() == Query; }

  BaseEntry& baseEntry() {
    MOZ_ASSERT(isValid());
    return base_;
  }
  IonEntry& ionEntry() {
    MOZ_ASSERT(isIon());
    return ion_;
  }
  BaselineEntry& baselineEntry() {
    MOZ_ASSERT(isBaseline());
    return baseline_;
  }
  BaselineInterpreterEntry& baselineInterpreterEntry() {
    MOZ_ASSERT(isBaselineInterpreter());
    return baselineInterpreter_;
  }
  IonCacheEntry& ionCacheEntry() {
    MOZ_ASSERT(isIonCache());
    return ionCache_;
  }
  DummyEntry& dummyEntry() {
    MOZ_ASSERT(isDummy());
    return dummy_;
  }
  QueryEntry& queryEntry() {
    MOZ_ASSERT(isQuery());
    return query_;
  }

  const BaseEntry& baseEntry() const {
    MOZ_ASSERT(isValid());
    return base_;
  }
  const IonEntry& ionEntry() const {
    MOZ_ASSERT(isIon());
    return ion_;
  }
  const BaselineEntry& baselineEntry() const {
    MOZ_ASSERT(isBaseline());
    return baseline_;
  }
  const BaselineInterpreterEntry& baselineInterpreterEntry() const {
    MOZ_ASSERT(isBaselineInterpreter());
    return baselineInterpreter_;
  }
  const IonCacheEntry& ionCacheEntry() const {
    MOZ_ASSERT(isIonCache());
    return ionCache_;
  }
  const DummyEntry& dummyEntry() const {
    MOZ_ASSERT(isDummy());
    return dummy_;
  }
  const QueryEntry& queryEntry() const {
    MOZ_ASSERT(isQuery());
    return query_;
  }

  void* canonicalNativeAddrFor(JSRuntime* rt, void* ptr) const {
    switch (kind()) {
      case Ion:
        return ionEntry().canonicalNativeAddrFor(ptr);
      case Baseline:
        return baselineEntry().canonicalNativeAddrFor(ptr);
      case IonCache:
        return ionCacheEntry().canonicalNativeAddrFor();
      case Dummy:
        return dummyEntry().canonicalNativeAddrFor(rt, ptr);
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
    return nullptr;
  }

  // Read the inline call stack at a given point in the native code and append
  // into the given vector.  Innermost (script,pc) pair will be appended first,
  // and outermost appended last.
  //
  // Returns false on memory failure.
  MOZ_MUST_USE bool callStackAtAddr(JSRuntime* rt, void* ptr,
                                    BytecodeLocationVector& results,
                                    uint32_t* depth) const {
    switch (kind()) {
      case Ion:
        return ionEntry().callStackAtAddr(ptr, results, depth);
      case Baseline:
        return baselineEntry().callStackAtAddr(ptr, results, depth);
      case BaselineInterpreter:
        return baselineInterpreterEntry().callStackAtAddr(ptr, results, depth);
      case IonCache:
        return ionCacheEntry().callStackAtAddr(rt, ptr, results, depth);
      case Dummy:
        return dummyEntry().callStackAtAddr(rt, ptr, results, depth);
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
    return false;
  }

  uint32_t callStackAtAddr(JSRuntime* rt, void* ptr, const char** results,
                           uint32_t maxResults) const {
    switch (kind()) {
      case Ion:
        return ionEntry().callStackAtAddr(ptr, results, maxResults);
      case Baseline:
        return baselineEntry().callStackAtAddr(ptr, results, maxResults);
      case BaselineInterpreter:
        return baselineInterpreterEntry().callStackAtAddr(ptr, results,
                                                          maxResults);
      case IonCache:
        return ionCacheEntry().callStackAtAddr(rt, ptr, results, maxResults);
      case Dummy:
        return dummyEntry().callStackAtAddr(rt, ptr, results, maxResults);
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
    return false;
  }

  void youngestFrameLocationAtAddr(JSRuntime* rt, void* ptr, JSScript** script,
                                   jsbytecode** pc) const {
    switch (kind()) {
      case Ion:
        return ionEntry().youngestFrameLocationAtAddr(ptr, script, pc);
      case Baseline:
        return baselineEntry().youngestFrameLocationAtAddr(ptr, script, pc);
      case IonCache:
        return ionCacheEntry().youngestFrameLocationAtAddr(rt, ptr, script, pc);
      case Dummy:
        return dummyEntry().youngestFrameLocationAtAddr(rt, ptr, script, pc);
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
  }

  // Figure out the number of the (JSScript*, jsbytecode*) pairs that are active
  // at this location.
  uint32_t lookupInlineCallDepth(void* ptr);

  // Compare two global entries.
  static int compare(const JitcodeGlobalEntry& ent1,
                     const JitcodeGlobalEntry& ent2);
  int compareTo(const JitcodeGlobalEntry& other) {
    return compare(*this, other);
  }

  bool hasTrackedOptimizations() const {
    switch (kind()) {
      case Ion:
        return ionEntry().hasTrackedOptimizations();
      case IonCache:
        return ionCacheEntry().hasTrackedOptimizations();
      case Baseline:
      case Dummy:
        break;
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
    return false;
  }

  bool canHoldNurseryPointers() const {
    return isIon() && ionEntry().hasTrackedOptimizations();
  }

  mozilla::Maybe<uint8_t> trackedOptimizationIndexAtAddr(
      JSRuntime* rt, void* addr, uint32_t* entryOffsetOut) {
    switch (kind()) {
      case Ion:
        return ionEntry().trackedOptimizationIndexAtAddr(addr, entryOffsetOut);
      case IonCache:
        return ionCacheEntry().trackedOptimizationIndexAtAddr(rt, addr,
                                                              entryOffsetOut);
      case Baseline:
      case Dummy:
        break;
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
    return mozilla::Nothing();
  }

  void forEachOptimizationAttempt(JSRuntime* rt, uint8_t index,
                                  JS::ForEachTrackedOptimizationAttemptOp& op) {
    switch (kind()) {
      case Ion:
        ionEntry().forEachOptimizationAttempt(index, op);
        return;
      case IonCache:
        ionCacheEntry().forEachOptimizationAttempt(rt, index, op);
        return;
      case Baseline:
      case Dummy:
        break;
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
  }

  void forEachOptimizationTypeInfo(
      JSRuntime* rt, uint8_t index,
      IonTrackedOptimizationsTypeInfo::ForEachOpAdapter& op) {
    switch (kind()) {
      case Ion:
        ionEntry().forEachOptimizationTypeInfo(index, op);
        return;
      case IonCache:
        ionCacheEntry().forEachOptimizationTypeInfo(rt, index, op);
        return;
      case Baseline:
      case Dummy:
        break;
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
  }

  IonTrackedOptimizationsAttempts trackedOptimizationAttempts(uint8_t index) {
    return ionEntry().trackedOptimizationAttempts(index);
  }

  IonTrackedOptimizationsTypeInfo trackedOptimizationTypeInfo(uint8_t index) {
    return ionEntry().trackedOptimizationTypeInfo(index);
  }

  const IonTrackedTypeVector* allTrackedTypes() {
    return ionEntry().allTrackedTypes();
  }

  Zone* zone() { return baseEntry().jitcode()->zone(); }

  template <class ShouldTraceProvider>
  bool trace(JSTracer* trc) {
    bool tracedAny = baseEntry().traceJitcode<ShouldTraceProvider>(trc);
    switch (kind()) {
      case Ion:
        tracedAny |= ionEntry().trace<ShouldTraceProvider>(trc);
        break;
      case Baseline:
        tracedAny |= baselineEntry().trace<ShouldTraceProvider>(trc);
        break;
      case IonCache:
        tracedAny |= ionCacheEntry().trace<ShouldTraceProvider>(trc);
        break;
      case BaselineInterpreter:
      case Dummy:
        break;
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
    return tracedAny;
  }

  void sweepChildren(JSRuntime* rt) {
    switch (kind()) {
      case Ion:
        ionEntry().sweepChildren();
        break;
      case Baseline:
        baselineEntry().sweepChildren();
        break;
      case IonCache:
        ionCacheEntry().sweepChildren(rt);
        break;
      case BaselineInterpreter:
      case Dummy:
        break;
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
  }

  bool isMarkedFromAnyThread(JSRuntime* rt) {
    if (!baseEntry().isJitcodeMarkedFromAnyThread(rt)) {
      return false;
    }
    switch (kind()) {
      case Ion:
        return ionEntry().isMarkedFromAnyThread(rt);
      case Baseline:
        return baselineEntry().isMarkedFromAnyThread(rt);
      case IonCache:
        return ionCacheEntry().isMarkedFromAnyThread(rt);
      case Dummy:
        break;
      default:
        MOZ_CRASH("Invalid JitcodeGlobalEntry kind.");
    }
    return true;
  }

  //
  // When stored in a free-list, entries use 'tower_' to store a
  // pointer to the next entry.  In this context only, 'tower_'
  // may refer to a |JitcodeGlobalEntry*| instead of a
  // |JitcodeSkiplistTower*|.
  //

  void addToFreeList(JitcodeGlobalEntry** freeList) {
    MOZ_ASSERT(!isValid());

    JitcodeGlobalEntry* nextFreeEntry = *freeList;
    MOZ_ASSERT_IF(nextFreeEntry, !nextFreeEntry->isValid());

    tower_ = (JitcodeSkiplistTower*)nextFreeEntry;
    *freeList = this;
  }

  static JitcodeGlobalEntry* PopFromFreeList(JitcodeGlobalEntry** freeList) {
    if (!*freeList) {
      return nullptr;
    }

    JitcodeGlobalEntry* entry = *freeList;
    MOZ_ASSERT(!entry->isValid());
    JitcodeGlobalEntry* nextFreeEntry = (JitcodeGlobalEntry*)entry->tower_;
    entry->tower_ = nullptr;
    *freeList = nextFreeEntry;
    return entry;
  }
};

/*
 * Global table of JitcodeGlobalEntry values sorted by native address range.
 */
class JitcodeGlobalTable {
 private:
  static const size_t LIFO_CHUNK_SIZE = 16 * 1024;

  LifoAlloc alloc_;
  JitcodeGlobalEntry* freeEntries_;
  uint32_t rand_;
  uint32_t skiplistSize_;
  JitcodeGlobalEntry::IonEntry* nurseryEntries_;

  JitcodeGlobalEntry* startTower_[JitcodeSkiplistTower::MAX_HEIGHT];
  JitcodeSkiplistTower* freeTowers_[JitcodeSkiplistTower::MAX_HEIGHT];

 public:
  JitcodeGlobalTable()
      : alloc_(LIFO_CHUNK_SIZE),
        freeEntries_(nullptr),
        rand_(0),
        skiplistSize_(0),
        nurseryEntries_(nullptr) {
    for (unsigned i = 0; i < JitcodeSkiplistTower::MAX_HEIGHT; i++) {
      startTower_[i] = nullptr;
    }
    for (unsigned i = 0; i < JitcodeSkiplistTower::MAX_HEIGHT; i++) {
      freeTowers_[i] = nullptr;
    }
  }
  ~JitcodeGlobalTable() {}

  bool empty() const { return skiplistSize_ == 0; }

  JitcodeGlobalEntry* lookup(void* ptr) { return lookupInternal(ptr); }

  JitcodeGlobalEntry& lookupInfallible(void* ptr) {
    JitcodeGlobalEntry* entry = lookupInternal(ptr);
    MOZ_ASSERT(entry);
    return *entry;
  }

  const JitcodeGlobalEntry& lookupForSamplerInfallible(
      void* ptr, JSRuntime* rt, uint64_t samplePosInBuffer);

  MOZ_MUST_USE bool addEntry(const JitcodeGlobalEntry::IonEntry& entry) {
    return addEntry(JitcodeGlobalEntry(entry));
  }
  MOZ_MUST_USE bool addEntry(const JitcodeGlobalEntry::BaselineEntry& entry) {
    return addEntry(JitcodeGlobalEntry(entry));
  }
  MOZ_MUST_USE bool addEntry(
      const JitcodeGlobalEntry::BaselineInterpreterEntry& entry) {
    return addEntry(JitcodeGlobalEntry(entry));
  }
  MOZ_MUST_USE bool addEntry(const JitcodeGlobalEntry::IonCacheEntry& entry) {
    return addEntry(JitcodeGlobalEntry(entry));
  }
  MOZ_MUST_USE bool addEntry(const JitcodeGlobalEntry::DummyEntry& entry) {
    return addEntry(JitcodeGlobalEntry(entry));
  }

  void removeEntry(JitcodeGlobalEntry& entry, JitcodeGlobalEntry** prevTower);
  void releaseEntry(JitcodeGlobalEntry& entry, JitcodeGlobalEntry** prevTower,
                    JSRuntime* rt);

  void setAllEntriesAsExpired();
  void traceForMinorGC(JSTracer* trc);
  MOZ_MUST_USE bool markIteratively(GCMarker* marker);
  void sweep(JSRuntime* rt);

 private:
  MOZ_MUST_USE bool addEntry(const JitcodeGlobalEntry& entry);

  JitcodeGlobalEntry* lookupInternal(void* ptr);

  // Initialize towerOut such that towerOut[i] (for i in [0, MAX_HEIGHT-1])
  // is a JitcodeGlobalEntry that is sorted to be <query, whose successor at
  // level i is either null, or sorted to be >= query.
  //
  // If entry with the given properties does not exist for level i, then
  // towerOut[i] is initialized to nullptr.
  void searchInternal(const JitcodeGlobalEntry& query,
                      JitcodeGlobalEntry** towerOut);

  JitcodeGlobalEntry* searchAtHeight(unsigned level, JitcodeGlobalEntry* start,
                                     const JitcodeGlobalEntry& query);

  // Calculate next random tower height.
  unsigned generateTowerHeight();

  JitcodeSkiplistTower* allocateTower(unsigned height);
  JitcodeGlobalEntry* allocateEntry();

#ifdef DEBUG
  void verifySkiplist();
#else
  void verifySkiplist() {}
#endif

  void addToNurseryList(JitcodeGlobalEntry::IonEntry* entry) {
    MOZ_ASSERT(entry->prevNursery_ == nullptr);
    MOZ_ASSERT(entry->nextNursery_ == nullptr);

    entry->nextNursery_ = nurseryEntries_;
    if (nurseryEntries_) {
      nurseryEntries_->prevNursery_ = entry;
    }
    nurseryEntries_ = entry;
  }

  void removeFromNurseryList(JitcodeGlobalEntry::IonEntry* entry) {
    // Splice out of list to be scanned on a minor GC.
    if (entry->prevNursery_) {
      entry->prevNursery_->nextNursery_ = entry->nextNursery_;
    }
    if (entry->nextNursery_) {
      entry->nextNursery_->prevNursery_ = entry->prevNursery_;
    }

    if (nurseryEntries_ == entry) {
      nurseryEntries_ = entry->nextNursery_;
    }

    entry->prevNursery_ = entry->nextNursery_ = nullptr;
  }

 public:
  class Range {
   protected:
    JitcodeGlobalTable& table_;
    JitcodeGlobalEntry* cur_;

   public:
    explicit Range(JitcodeGlobalTable& table)
        : table_(table), cur_(table.startTower_[0]) {}

    JitcodeGlobalEntry* front() const {
      MOZ_ASSERT(!empty());
      return cur_;
    }

    bool empty() const { return !cur_; }

    void popFront() {
      MOZ_ASSERT(!empty());
      cur_ = cur_->tower_->next(0);
    }
  };

  // An enumerator class that can remove entries as it enumerates. If this
  // functionality is not needed, use Range instead.
  class Enum : public Range {
    JSRuntime* rt_;
    JitcodeGlobalEntry* next_;
    JitcodeGlobalEntry* prevTower_[JitcodeSkiplistTower::MAX_HEIGHT];

   public:
    Enum(JitcodeGlobalTable& table, JSRuntime* rt);

    void popFront();
    void removeFront();
  };
};

// clang-format off
/*
 * Container class for main jitcode table.
 * The Region table's memory is structured as follows:
 *
 *      +------------------------------------------------+   |
 *      |  Region 1 Run                                  |   |
 *      |------------------------------------------------|   |
 *      |  Region 2 Run                                  |   |
 *      |                                                |   |
 *      |                                                |   |
 *      |------------------------------------------------|   |
 *      |  Region 3 Run                                  |   |
 *      |                                                |   |
 *      |------------------------------------------------|   |-- Payload
 *      |                                                |   |
 *      |               ...                              |   |
 *      |                                                |   |
 *      |------------------------------------------------|   |
 *      |  Region M Run                                  |   |
 *      |                                                |   |
 *      +================================================+ <- RegionTable pointer points here
 *      | uint23_t numRegions = M                        |   |
 *      +------------------------------------------------+   |
 *      | Region 1                                       |   |
 *      |   uint32_t entryOffset = size(Payload)         |   |
 *      +------------------------------------------------+   |
 *      |                                                |   |-- Table
 *      |   ...                                          |   |
 *      |                                                |   |
 *      +------------------------------------------------+   |
 *      | Region M                                       |   |
 *      |   uint32_t entryOffset                         |   |
 *      +------------------------------------------------+   |
 *
 * The region table is composed of two sections: a tail section that contains a table of
 * fixed-size entries containing offsets into the the head section, and a head section that
 * holds a sequence of variable-sized runs.  The table in the tail section serves to
 * locate the variable-length encoded structures in the head section.
 *
 * The entryOffsets in the table indicate the bytes offset to subtract from the regionTable
 * pointer to arrive at the encoded region in the payload.
 *
 *
 * Variable-length entries in payload
 * ----------------------------------
 * The entryOffsets in the region table's fixed-sized entries refer to a location within the
 * variable-length payload section.  This location contains a compactly encoded "run" of
 * mappings.
 *
 * Each run starts by describing the offset within the native code it starts at, and the
 * sequence of (JSScript*, jsbytecode*) pairs active at that site.  Following that, there
 * are a number of variable-length entries encoding (nativeOffsetDelta, bytecodeOffsetDelta)
 * pairs for the run.
 *
 *      VarUint32 nativeOffset;
 *          - The offset from nativeStartAddr in the global table entry at which
 *            the jitcode for this region starts.
 *
 *      Uint8_t scriptDepth;
 *          - The depth of inlined scripts for this region.
 *
 *      List<VarUint32> inlineScriptPcStack;
 *          - We encode (2 * scriptDepth) VarUint32s here.  Each pair of uint32s are taken
 *            as an index into the scriptList in the global table entry, and a pcOffset
 *            respectively.
 *
 *      List<NativeAndBytecodeDelta> deltaRun;
 *          - The rest of the entry is a deltaRun that stores a series of variable-length
 *            encoded NativeAndBytecodeDelta datums.
 */
// clang-format on
class JitcodeRegionEntry {
 private:
  static const unsigned MAX_RUN_LENGTH = 100;

 public:
  static void WriteHead(CompactBufferWriter& writer, uint32_t nativeOffset,
                        uint8_t scriptDepth);
  static void ReadHead(CompactBufferReader& reader, uint32_t* nativeOffset,
                       uint8_t* scriptDepth);

  static void WriteScriptPc(CompactBufferWriter& writer, uint32_t scriptIdx,
                            uint32_t pcOffset);
  static void ReadScriptPc(CompactBufferReader& reader, uint32_t* scriptIdx,
                           uint32_t* pcOffset);

  static void WriteDelta(CompactBufferWriter& writer, uint32_t nativeDelta,
                         int32_t pcDelta);
  static void ReadDelta(CompactBufferReader& reader, uint32_t* nativeDelta,
                        int32_t* pcDelta);

  // Given a pointer into an array of NativeToBytecode (and a pointer to the end
  // of the array), compute the number of entries that would be consume by
  // outputting a run starting at this one.
  static uint32_t ExpectedRunLength(const NativeToBytecode* entry,
                                    const NativeToBytecode* end);

  // Write a run, starting at the given NativeToBytecode entry, into the given
  // buffer writer.
  static MOZ_MUST_USE bool WriteRun(CompactBufferWriter& writer,
                                    JSScript** scriptList,
                                    uint32_t scriptListSize, uint32_t runLength,
                                    const NativeToBytecode* entry);

  // Delta Run entry formats are encoded little-endian:
  //
  //  byte 0
  //  NNNN-BBB0
  //      Single byte format.  nativeDelta in [0, 15], pcDelta in [0, 7]
  //
  static const uint32_t ENC1_MASK = 0x1;
  static const uint32_t ENC1_MASK_VAL = 0x0;

  static const uint32_t ENC1_NATIVE_DELTA_MAX = 0xf;
  static const unsigned ENC1_NATIVE_DELTA_SHIFT = 4;

  static const uint32_t ENC1_PC_DELTA_MASK = 0x0e;
  static const int32_t ENC1_PC_DELTA_MAX = 0x7;
  static const unsigned ENC1_PC_DELTA_SHIFT = 1;

  //  byte 1    byte 0
  //  NNNN-NNNN BBBB-BB01
  //      Two-byte format.  nativeDelta in [0, 255], pcDelta in [0, 63]
  //
  static const uint32_t ENC2_MASK = 0x3;
  static const uint32_t ENC2_MASK_VAL = 0x1;

  static const uint32_t ENC2_NATIVE_DELTA_MAX = 0xff;
  static const unsigned ENC2_NATIVE_DELTA_SHIFT = 8;

  static const uint32_t ENC2_PC_DELTA_MASK = 0x00fc;
  static const int32_t ENC2_PC_DELTA_MAX = 0x3f;
  static const unsigned ENC2_PC_DELTA_SHIFT = 2;

  //  byte 2    byte 1    byte 0
  //  NNNN-NNNN NNNB-BBBB BBBB-B011
  //      Three-byte format.  nativeDelta in [0, 2047], pcDelta in [-512, 511]
  //
  static const uint32_t ENC3_MASK = 0x7;
  static const uint32_t ENC3_MASK_VAL = 0x3;

  static const uint32_t ENC3_NATIVE_DELTA_MAX = 0x7ff;
  static const unsigned ENC3_NATIVE_DELTA_SHIFT = 13;

  static const uint32_t ENC3_PC_DELTA_MASK = 0x001ff8;
  static const int32_t ENC3_PC_DELTA_MAX = 0x1ff;
  static const int32_t ENC3_PC_DELTA_MIN = -ENC3_PC_DELTA_MAX - 1;
  static const unsigned ENC3_PC_DELTA_SHIFT = 3;

  //  byte 3    byte 2    byte 1    byte 0
  //  NNNN-NNNN NNNN-NNNN BBBB-BBBB BBBB-B111
  //      Three-byte format.  nativeDelta in [0, 65535],
  //                          pcDelta in [-4096, 4095]
  static const uint32_t ENC4_MASK = 0x7;
  static const uint32_t ENC4_MASK_VAL = 0x7;

  static const uint32_t ENC4_NATIVE_DELTA_MAX = 0xffff;
  static const unsigned ENC4_NATIVE_DELTA_SHIFT = 16;

  static const uint32_t ENC4_PC_DELTA_MASK = 0x0000fff8;
  static const int32_t ENC4_PC_DELTA_MAX = 0xfff;
  static const int32_t ENC4_PC_DELTA_MIN = -ENC4_PC_DELTA_MAX - 1;
  static const unsigned ENC4_PC_DELTA_SHIFT = 3;

  static bool IsDeltaEncodeable(uint32_t nativeDelta, int32_t pcDelta) {
    return (nativeDelta <= ENC4_NATIVE_DELTA_MAX) &&
           (pcDelta >= ENC4_PC_DELTA_MIN) && (pcDelta <= ENC4_PC_DELTA_MAX);
  }

 private:
  const uint8_t* data_;
  const uint8_t* end_;

  // Unpacked state from jitcode entry.
  uint32_t nativeOffset_;
  uint8_t scriptDepth_;
  const uint8_t* scriptPcStack_;
  const uint8_t* deltaRun_;

  void unpack();

 public:
  JitcodeRegionEntry(const uint8_t* data, const uint8_t* end)
      : data_(data),
        end_(end),
        nativeOffset_(0),
        scriptDepth_(0),
        scriptPcStack_(nullptr),
        deltaRun_(nullptr) {
    MOZ_ASSERT(data_ < end_);
    unpack();
    MOZ_ASSERT(scriptPcStack_ < end_);
    MOZ_ASSERT(deltaRun_ <= end_);
  }

  uint32_t nativeOffset() const { return nativeOffset_; }
  uint32_t scriptDepth() const { return scriptDepth_; }

  class ScriptPcIterator {
   private:
    const uint8_t* start_;
    const uint8_t* end_;
#ifdef DEBUG
    uint32_t count_;
#endif
    uint32_t idx_;
    const uint8_t* cur_;

   public:
    ScriptPcIterator(const uint8_t* start, const uint8_t* end, uint32_t count)
        : start_(start),
          end_(end),
#ifdef DEBUG
          count_(count),
#endif
          idx_(0),
          cur_(start_) {
    }

    bool hasMore() const {
      MOZ_ASSERT((idx_ == count_) == (cur_ == end_));
      MOZ_ASSERT((idx_ < count_) == (cur_ < end_));
      return cur_ < end_;
    }

    void readNext(uint32_t* scriptIdxOut, uint32_t* pcOffsetOut) {
      MOZ_ASSERT(scriptIdxOut);
      MOZ_ASSERT(pcOffsetOut);
      MOZ_ASSERT(hasMore());

      CompactBufferReader reader(cur_, end_);
      ReadScriptPc(reader, scriptIdxOut, pcOffsetOut);

      cur_ = reader.currentPosition();
      MOZ_ASSERT(cur_ <= end_);

      idx_++;
      MOZ_ASSERT_IF(idx_ == count_, cur_ == end_);
    }

    void reset() {
      idx_ = 0;
      cur_ = start_;
    }
  };

  ScriptPcIterator scriptPcIterator() const {
    // End of script+pc sequence is the start of the delta run.
    return ScriptPcIterator(scriptPcStack_, deltaRun_, scriptDepth_);
  }

  class DeltaIterator {
   private:
    const uint8_t* start_;
    const uint8_t* end_;
    const uint8_t* cur_;

   public:
    DeltaIterator(const uint8_t* start, const uint8_t* end)
        : start_(start), end_(end), cur_(start) {}

    bool hasMore() const {
      MOZ_ASSERT(cur_ <= end_);
      return cur_ < end_;
    }

    void readNext(uint32_t* nativeDeltaOut, int32_t* pcDeltaOut) {
      MOZ_ASSERT(nativeDeltaOut != nullptr);
      MOZ_ASSERT(pcDeltaOut != nullptr);

      MOZ_ASSERT(hasMore());

      CompactBufferReader reader(cur_, end_);
      ReadDelta(reader, nativeDeltaOut, pcDeltaOut);

      cur_ = reader.currentPosition();
      MOZ_ASSERT(cur_ <= end_);
    }

    void reset() { cur_ = start_; }
  };
  DeltaIterator deltaIterator() const { return DeltaIterator(deltaRun_, end_); }

  uint32_t findPcOffset(uint32_t queryNativeOffset,
                        uint32_t startPcOffset) const;
};

class JitcodeIonTable {
 private:
  /* Variable length payload section "below" here. */
  uint32_t numRegions_;
  uint32_t regionOffsets_[1];

  const uint8_t* payloadEnd() const {
    return reinterpret_cast<const uint8_t*>(this);
  }

 public:
  explicit JitcodeIonTable(uint32_t numRegions) : numRegions_(numRegions) {
    for (uint32_t i = 0; i < numRegions; i++) {
      regionOffsets_[i] = 0;
    }
  }

  MOZ_MUST_USE bool makeIonEntry(JSContext* cx, JitCode* code,
                                 uint32_t numScripts, JSScript** scripts,
                                 JitcodeGlobalEntry::IonEntry& out);

  uint32_t numRegions() const { return numRegions_; }

  uint32_t regionOffset(uint32_t regionIndex) const {
    MOZ_ASSERT(regionIndex < numRegions());
    return regionOffsets_[regionIndex];
  }

  JitcodeRegionEntry regionEntry(uint32_t regionIndex) const {
    const uint8_t* regionStart = payloadEnd() - regionOffset(regionIndex);
    const uint8_t* regionEnd = payloadEnd();
    if (regionIndex < numRegions_ - 1) {
      regionEnd -= regionOffset(regionIndex + 1);
    }
    return JitcodeRegionEntry(regionStart, regionEnd);
  }

  bool regionContainsOffset(uint32_t regionIndex, uint32_t nativeOffset) {
    MOZ_ASSERT(regionIndex < numRegions());

    JitcodeRegionEntry ent = regionEntry(regionIndex);
    if (nativeOffset < ent.nativeOffset()) {
      return false;
    }

    if (regionIndex == numRegions_ - 1) {
      return true;
    }

    return nativeOffset < regionEntry(regionIndex + 1).nativeOffset();
  }

  uint32_t findRegionEntry(uint32_t offset) const;

  const uint8_t* payloadStart() const {
    // The beginning of the payload the beginning of the first region are the
    // same.
    return payloadEnd() - regionOffset(0);
  }

  static MOZ_MUST_USE bool WriteIonTable(CompactBufferWriter& writer,
                                         JSScript** scriptList,
                                         uint32_t scriptListSize,
                                         const NativeToBytecode* start,
                                         const NativeToBytecode* end,
                                         uint32_t* tableOffsetOut,
                                         uint32_t* numRegionsOut);
};

}  // namespace jit
}  // namespace js

#endif /* jit_JitcodeMap_h */