diff -r 000000000000 -r 6474c204b198 js/src/jit/FixedList.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit/FixedList.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,86 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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_FixedList_h
+#define jit_FixedList_h
+
+#include <stddef.h>
+
+#include "jit/Ion.h"
+#include "jit/IonAllocPolicy.h"
+
+namespace js {
+namespace jit {
+
+// List of a fixed length, but the length is unknown until runtime.
+template <typename T>
+class FixedList
+{
+    T *list_;
+    size_t length_;
+
+  private:
+    FixedList(const FixedList&); // no copy definition.
+    void operator= (const FixedList*); // no assignment definition.
+
+  public:
+    FixedList()
+      : list_(nullptr), length_(0)
+    { }
+
+    // Dynamic memory allocation requires the ability to report failure.
+    bool init(TempAllocator &alloc, size_t length) {
+        length_ = length;
+        if (length == 0)
+            return true;
+
+        if (length & mozilla::tl::MulOverflowMask<sizeof(T)>::value)
+            return false;
+        list_ = (T *)alloc.allocate(length * sizeof(T));
+        return list_ != nullptr;
+    }
+
+    size_t length() const {
+        return length_;
+    }
+
+    void shrink(size_t num) {
+        JS_ASSERT(num < length_);
+        length_ -= num;
+    }
+
+    bool growBy(TempAllocator &alloc, size_t num) {
+        size_t newlength = length_ + num;
+        if (newlength < length_)
+            return false;
+        if (newlength & mozilla::tl::MulOverflowMask<sizeof(T)>::value)
+            return false;
+        T *list = (T *)alloc.allocate((length_ + num) * sizeof(T));
+        if (!list)
+            return false;
+
+        for (size_t i = 0; i < length_; i++)
+            list[i] = list_[i];
+
+        length_ += num;
+        list_ = list;
+        return true;
+    }
+
+    T &operator[](size_t index) {
+        JS_ASSERT(index < length_);
+        return list_[index];
+    }
+    const T &operator [](size_t index) const {
+        JS_ASSERT(index < length_);
+        return list_[index];
+    }
+};
+
+} // namespace jit
+} // namespace js
+
+#endif /* jit_FixedList_h */