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diff --git a/js/src/jit/JitAllocPolicy.h b/js/src/jit/JitAllocPolicy.h
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+++ b/js/src/jit/JitAllocPolicy.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 jit_JitAllocPolicy_h
+#define jit_JitAllocPolicy_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Likely.h"
+#include "mozilla/OperatorNewExtensions.h"
+#include "mozilla/TemplateLib.h"
+
+#include <algorithm>
+#include <stddef.h>
+#include <string.h>
+#include <type_traits>
+#include <utility>
+
+#include "ds/LifoAlloc.h"
+#include "jit/InlineList.h"
+#include "js/Utility.h"
+
+namespace js {
+namespace jit {
+
+class TempAllocator {
+  LifoAllocScope lifoScope_;
+
+ public:
+  // Most infallible JIT allocations are small, so we use a ballast of 16
+  // KiB. And with a ballast of 16 KiB, a chunk size of 32 KiB works well,
+  // because TempAllocators with a peak allocation size of less than 16 KiB
+  // (which is most of them) only have to allocate a single chunk.
+  static const size_t BallastSize;             // 16 KiB
+  static const size_t PreferredLifoChunkSize;  // 32 KiB
+
+  explicit TempAllocator(LifoAlloc* lifoAlloc) : lifoScope_(lifoAlloc) {
+    lifoAlloc->setAsInfallibleByDefault();
+  }
+
+  void* allocateInfallible(size_t bytes) {
+    return lifoScope_.alloc().allocInfallible(bytes);
+  }
+
+  [[nodiscard]] void* allocate(size_t bytes) {
+    LifoAlloc::AutoFallibleScope fallibleAllocator(lifoAlloc());
+    return lifoScope_.alloc().allocEnsureUnused(bytes, BallastSize);
+  }
+
+  template <typename T>
+  [[nodiscard]] T* allocateArray(size_t n) {
+    LifoAlloc::AutoFallibleScope fallibleAllocator(lifoAlloc());
+    size_t bytes;
+    if (MOZ_UNLIKELY(!CalculateAllocSize<T>(n, &bytes))) {
+      return nullptr;
+    }
+    return static_cast<T*>(
+        lifoScope_.alloc().allocEnsureUnused(bytes, BallastSize));
+  }
+
+  // View this allocator as a fallible allocator.
+  struct Fallible {
+    TempAllocator& alloc;
+  };
+  Fallible fallible() { return {*this}; }
+
+  LifoAlloc* lifoAlloc() { return &lifoScope_.alloc(); }
+
+  [[nodiscard]] bool ensureBallast() {
+    JS_OOM_POSSIBLY_FAIL_BOOL();
+    return lifoScope_.alloc().ensureUnusedApproximate(BallastSize);
+  }
+};
+
+class JitAllocPolicy {
+  TempAllocator& alloc_;
+
+ public:
+  MOZ_IMPLICIT JitAllocPolicy(TempAllocator& alloc) : alloc_(alloc) {}
+  template <typename T>
+  T* maybe_pod_malloc(size_t numElems) {
+    size_t bytes;
+    if (MOZ_UNLIKELY(!CalculateAllocSize<T>(numElems, &bytes))) {
+      return nullptr;
+    }
+    return static_cast<T*>(alloc_.allocate(bytes));
+  }
+  template <typename T>
+  T* maybe_pod_calloc(size_t numElems) {
+    T* p = maybe_pod_malloc<T>(numElems);
+    if (MOZ_LIKELY(p)) {
+      memset(p, 0, numElems * sizeof(T));
+    }
+    return p;
+  }
+  template <typename T>
+  T* maybe_pod_realloc(T* p, size_t oldSize, size_t newSize) {
+    T* n = pod_malloc<T>(newSize);
+    if (MOZ_UNLIKELY(!n)) {
+      return n;
+    }
+    MOZ_ASSERT(!(oldSize & mozilla::tl::MulOverflowMask<sizeof(T)>::value));
+    memcpy(n, p, std::min(oldSize * sizeof(T), newSize * sizeof(T)));
+    return n;
+  }
+  template <typename T>
+  T* pod_malloc(size_t numElems) {
+    return maybe_pod_malloc<T>(numElems);
+  }
+  template <typename T>
+  T* pod_calloc(size_t numElems) {
+    return maybe_pod_calloc<T>(numElems);
+  }
+  template <typename T>
+  T* pod_realloc(T* ptr, size_t oldSize, size_t newSize) {
+    return maybe_pod_realloc<T>(ptr, oldSize, newSize);
+  }
+  template <typename T>
+  void free_(T* p, size_t numElems = 0) {}
+  void reportAllocOverflow() const {}
+  [[nodiscard]] bool checkSimulatedOOM() const {
+    return !js::oom::ShouldFailWithOOM();
+  }
+};
+
+struct TempObject {
+  inline void* operator new(size_t nbytes,
+                            TempAllocator::Fallible view) noexcept(true) {
+    return view.alloc.allocate(nbytes);
+  }
+  inline void* operator new(size_t nbytes, TempAllocator& alloc) {
+    return alloc.allocateInfallible(nbytes);
+  }
+  template <class T>
+  inline void* operator new(size_t nbytes, T* pos) {
+    static_assert(std::is_convertible_v<T*, TempObject*>,
+                  "Placement new argument type must inherit from TempObject");
+    return pos;
+  }
+  template <class T>
+  inline void* operator new(size_t nbytes, mozilla::NotNullTag, T* pos) {
+    static_assert(std::is_convertible_v<T*, TempObject*>,
+                  "Placement new argument type must inherit from TempObject");
+    MOZ_ASSERT(pos);
+    return pos;
+  }
+};
+
+template <typename T>
+class TempObjectPool {
+  TempAllocator* alloc_;
+  InlineForwardList<T> freed_;
+
+ public:
+  TempObjectPool() : alloc_(nullptr) {}
+  void setAllocator(TempAllocator& alloc) {
+    MOZ_ASSERT(freed_.empty());
+    alloc_ = &alloc;
+  }
+  template <typename... Args>
+  T* allocate(Args&&... args) {
+    MOZ_ASSERT(alloc_);
+    if (freed_.empty()) {
+      return new (alloc_->fallible()) T(std::forward<Args>(args)...);
+    }
+    T* res = freed_.popFront();
+    return new (res) T(std::forward<Args>(args)...);
+  }
+  void free(T* obj) { freed_.pushFront(obj); }
+  void clear() { freed_.clear(); }
+};
+
+}  // namespace jit
+}  // namespace js
+
+#endif /* jit_JitAllocPolicy_h */