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diff --git a/js/src/frontend/NameCollections.h b/js/src/frontend/NameCollections.h
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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 frontend_NameCollections_h
+#define frontend_NameCollections_h
+
+#include <type_traits>
+
+#include "ds/InlineTable.h"
+#include "frontend/NameAnalysisTypes.h"
+#include "js/Vector.h"
+
+namespace js {
+namespace frontend {
+
+class FunctionBox;
+
+// A pool of recyclable containers for use in the frontend. The Parser and
+// BytecodeEmitter create many maps for name analysis that are short-lived
+// (i.e., for the duration of parsing or emitting a lexical scope). Making
+// them recyclable cuts down significantly on allocator churn.
+template <typename RepresentativeCollection, typename ConcreteCollectionPool>
+class CollectionPool {
+  using RecyclableCollections = Vector<void*, 32, SystemAllocPolicy>;
+
+  RecyclableCollections all_;
+  RecyclableCollections recyclable_;
+
+  static RepresentativeCollection* asRepresentative(void* p) {
+    return reinterpret_cast<RepresentativeCollection*>(p);
+  }
+
+  RepresentativeCollection* allocate() {
+    size_t newAllLength = all_.length() + 1;
+    if (!all_.reserve(newAllLength) || !recyclable_.reserve(newAllLength)) {
+      return nullptr;
+    }
+
+    RepresentativeCollection* collection = js_new<RepresentativeCollection>();
+    if (collection) {
+      all_.infallibleAppend(collection);
+    }
+    return collection;
+  }
+
+ public:
+  ~CollectionPool() { purgeAll(); }
+
+  void purgeAll() {
+    void** end = all_.end();
+    for (void** it = all_.begin(); it != end; ++it) {
+      js_delete(asRepresentative(*it));
+    }
+
+    all_.clearAndFree();
+    recyclable_.clearAndFree();
+  }
+
+  // Fallibly aquire one of the supported collection types from the pool.
+  template <typename Collection>
+  Collection* acquire(JSContext* cx) {
+    ConcreteCollectionPool::template assertInvariants<Collection>();
+
+    RepresentativeCollection* collection;
+    if (recyclable_.empty()) {
+      collection = allocate();
+      if (!collection) {
+        ReportOutOfMemory(cx);
+      }
+    } else {
+      collection = asRepresentative(recyclable_.popCopy());
+      collection->clear();
+    }
+    return reinterpret_cast<Collection*>(collection);
+  }
+
+  // Release a collection back to the pool.
+  template <typename Collection>
+  void release(Collection** collection) {
+    ConcreteCollectionPool::template assertInvariants<Collection>();
+    MOZ_ASSERT(*collection);
+
+#ifdef DEBUG
+    bool ok = false;
+    // Make sure the collection is in |all_| but not already in |recyclable_|.
+    for (void** it = all_.begin(); it != all_.end(); ++it) {
+      if (*it == *collection) {
+        ok = true;
+        break;
+      }
+    }
+    MOZ_ASSERT(ok);
+    for (void** it = recyclable_.begin(); it != recyclable_.end(); ++it) {
+      MOZ_ASSERT(*it != *collection);
+    }
+#endif
+
+    MOZ_ASSERT(recyclable_.length() < all_.length());
+    // Reserved in allocateFresh.
+    recyclable_.infallibleAppend(*collection);
+    *collection = nullptr;
+  }
+};
+
+template <typename Wrapped>
+struct RecyclableAtomMapValueWrapper {
+  using WrappedType = Wrapped;
+
+  union {
+    Wrapped wrapped;
+    uint64_t dummy;
+  };
+
+  static void assertInvariant() {
+    static_assert(sizeof(Wrapped) <= sizeof(uint64_t),
+                  "Can only recycle atom maps with values smaller than uint64");
+  }
+
+  RecyclableAtomMapValueWrapper() : dummy(0) { assertInvariant(); }
+
+  MOZ_IMPLICIT RecyclableAtomMapValueWrapper(Wrapped w) : wrapped(w) {
+    assertInvariant();
+  }
+
+  MOZ_IMPLICIT operator Wrapped&() { return wrapped; }
+
+  MOZ_IMPLICIT operator Wrapped&() const { return wrapped; }
+
+  Wrapped* operator->() { return &wrapped; }
+
+  const Wrapped* operator->() const { return &wrapped; }
+};
+
+struct NameMapHasher : public DefaultHasher<const ParserAtom*> {
+  static inline HashNumber hash(const Lookup& l) {
+    // Name maps use the atom's precomputed hash code, which is based on
+    // the atom's contents rather than its pointer value. This is necessary
+    // to preserve iteration order while recording/replaying: iteration can
+    // affect generated script bytecode and the order in which e.g. lookup
+    // property hooks are performed on the associated global.
+    return l->hash();
+  }
+};
+
+template <typename MapValue>
+using RecyclableNameMap =
+    InlineMap<const ParserAtom*, RecyclableAtomMapValueWrapper<MapValue>, 24,
+              NameMapHasher, SystemAllocPolicy>;
+
+using DeclaredNameMap = RecyclableNameMap<DeclaredNameInfo>;
+using NameLocationMap = RecyclableNameMap<NameLocation>;
+// Cannot use GCThingIndex here because it's not trivial type.
+using AtomIndexMap = RecyclableNameMap<uint32_t>;
+
+template <typename RepresentativeTable>
+class InlineTablePool
+    : public CollectionPool<RepresentativeTable,
+                            InlineTablePool<RepresentativeTable>> {
+  template <typename>
+  struct IsRecyclableAtomMapValueWrapper : std::false_type {};
+
+  template <typename T>
+  struct IsRecyclableAtomMapValueWrapper<RecyclableAtomMapValueWrapper<T>>
+      : std::true_type {};
+
+ public:
+  template <typename Table>
+  static void assertInvariants() {
+    static_assert(
+        Table::SizeOfInlineEntries == RepresentativeTable::SizeOfInlineEntries,
+        "Only tables with the same size for inline entries are usable in the "
+        "pool.");
+
+    using EntryType = typename Table::Table::Entry;
+    using KeyType = typename EntryType::KeyType;
+    using ValueType = typename EntryType::ValueType;
+
+    static_assert(IsRecyclableAtomMapValueWrapper<ValueType>::value,
+                  "Please adjust the static assertions below if you need to "
+                  "support other types than RecyclableAtomMapValueWrapper");
+
+    using WrappedType = typename ValueType::WrappedType;
+
+    // We can't directly check |std::is_trivial<EntryType>|, because neither
+    // mozilla::HashMapEntry nor IsRecyclableAtomMapValueWrapper are trivially
+    // default constructible. Instead we check that the key and the unwrapped
+    // value are trivial and additionally ensure that the entry itself is
+    // trivially copyable and destructible.
+
+    static_assert(std::is_trivial_v<KeyType>,
+                  "Only tables with trivial keys are usable in the pool.");
+    static_assert(std::is_trivial_v<WrappedType>,
+                  "Only tables with trivial values are usable in the pool.");
+
+    static_assert(
+        std::is_trivially_copyable_v<EntryType>,
+        "Only tables with trivially copyable entries are usable in the pool.");
+    static_assert(std::is_trivially_destructible_v<EntryType>,
+                  "Only tables with trivially destructible entries are usable "
+                  "in the pool.");
+  }
+};
+
+template <typename RepresentativeVector>
+class VectorPool : public CollectionPool<RepresentativeVector,
+                                         VectorPool<RepresentativeVector>> {
+ public:
+  template <typename Vector>
+  static void assertInvariants() {
+    static_assert(
+        Vector::sMaxInlineStorage == RepresentativeVector::sMaxInlineStorage,
+        "Only vectors with the same size for inline entries are usable in the "
+        "pool.");
+
+    using ElementType = typename Vector::ElementType;
+
+    static_assert(std::is_trivial_v<ElementType>,
+                  "Only vectors of trivial values are usable in the pool.");
+    static_assert(std::is_trivially_destructible_v<ElementType>,
+                  "Only vectors of trivially destructible values are usable in "
+                  "the pool.");
+
+    static_assert(
+        sizeof(ElementType) ==
+            sizeof(typename RepresentativeVector::ElementType),
+        "Only vectors with same-sized elements are usable in the pool.");
+  }
+};
+
+class NameCollectionPool {
+  InlineTablePool<AtomIndexMap> mapPool_;
+  VectorPool<AtomVector> vectorPool_;
+  uint32_t activeCompilations_;
+
+ public:
+  NameCollectionPool() : activeCompilations_(0) {}
+
+  bool hasActiveCompilation() const { return activeCompilations_ != 0; }
+
+  void addActiveCompilation() { activeCompilations_++; }
+
+  void removeActiveCompilation() {
+    MOZ_ASSERT(hasActiveCompilation());
+    activeCompilations_--;
+  }
+
+  template <typename Map>
+  Map* acquireMap(JSContext* cx) {
+    MOZ_ASSERT(hasActiveCompilation());
+    return mapPool_.acquire<Map>(cx);
+  }
+
+  template <typename Map>
+  void releaseMap(Map** map) {
+    MOZ_ASSERT(hasActiveCompilation());
+    MOZ_ASSERT(map);
+    if (*map) {
+      mapPool_.release(map);
+    }
+  }
+
+  template <typename Vector>
+  Vector* acquireVector(JSContext* cx) {
+    MOZ_ASSERT(hasActiveCompilation());
+    return vectorPool_.acquire<Vector>(cx);
+  }
+
+  template <typename Vector>
+  void releaseVector(Vector** vec) {
+    MOZ_ASSERT(hasActiveCompilation());
+    MOZ_ASSERT(vec);
+    if (*vec) {
+      vectorPool_.release(vec);
+    }
+  }
+
+  void purge() {
+    if (!hasActiveCompilation()) {
+      mapPool_.purgeAll();
+      vectorPool_.purgeAll();
+    }
+  }
+};
+
+template <typename T, template <typename> typename Impl>
+class PooledCollectionPtr {
+  NameCollectionPool& pool_;
+  T* collection_ = nullptr;
+
+ protected:
+  ~PooledCollectionPtr() { Impl<T>::releaseCollection(pool_, &collection_); }
+
+  T& collection() {
+    MOZ_ASSERT(collection_);
+    return *collection_;
+  }
+
+  const T& collection() const {
+    MOZ_ASSERT(collection_);
+    return *collection_;
+  }
+
+ public:
+  explicit PooledCollectionPtr(NameCollectionPool& pool) : pool_(pool) {}
+
+  bool acquire(JSContext* cx) {
+    MOZ_ASSERT(!collection_);
+    collection_ = Impl<T>::acquireCollection(cx, pool_);
+    return !!collection_;
+  }
+
+  explicit operator bool() const { return !!collection_; }
+
+  T* operator->() { return &collection(); }
+
+  const T* operator->() const { return &collection(); }
+
+  T& operator*() { return collection(); }
+
+  const T& operator*() const { return collection(); }
+};
+
+template <typename Map>
+class PooledMapPtr : public PooledCollectionPtr<Map, PooledMapPtr> {
+  friend class PooledCollectionPtr<Map, PooledMapPtr>;
+
+  static Map* acquireCollection(JSContext* cx, NameCollectionPool& pool) {
+    return pool.acquireMap<Map>(cx);
+  }
+
+  static void releaseCollection(NameCollectionPool& pool, Map** ptr) {
+    pool.releaseMap(ptr);
+  }
+
+  using Base = PooledCollectionPtr<Map, PooledMapPtr>;
+
+ public:
+  using Base::Base;
+
+  ~PooledMapPtr() = default;
+};
+
+template <typename Vector>
+class PooledVectorPtr : public PooledCollectionPtr<Vector, PooledVectorPtr> {
+  friend class PooledCollectionPtr<Vector, PooledVectorPtr>;
+
+  static Vector* acquireCollection(JSContext* cx, NameCollectionPool& pool) {
+    return pool.acquireVector<Vector>(cx);
+  }
+
+  static void releaseCollection(NameCollectionPool& pool, Vector** ptr) {
+    pool.releaseVector(ptr);
+  }
+
+  using Base = PooledCollectionPtr<Vector, PooledVectorPtr>;
+  using Base::collection;
+
+ public:
+  using Base::Base;
+
+  ~PooledVectorPtr() = default;
+
+  typename Vector::ElementType& operator[](size_t index) {
+    return collection()[index];
+  }
+
+  const typename Vector::ElementType& operator[](size_t index) const {
+    return collection()[index];
+  }
+};
+
+}  // namespace frontend
+}  // namespace js
+
+#endif  // frontend_NameCollections_h