diff -r 000000000000 -r 6474c204b198 js/src/jit/StackSlotAllocator.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit/StackSlotAllocator.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,110 @@
+/* -*- 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_StackSlotAllocator_h
+#define jit_StackSlotAllocator_h
+
+#include "jit/Registers.h"
+
+namespace js {
+namespace jit {
+
+class StackSlotAllocator
+{
+    js::Vector<uint32_t, 4, SystemAllocPolicy> normalSlots;
+    js::Vector<uint32_t, 4, SystemAllocPolicy> doubleSlots;
+    uint32_t height_;
+
+    void freeSlot(uint32_t index) {
+        normalSlots.append(index);
+    }
+    void freeDoubleSlot(uint32_t index) {
+        doubleSlots.append(index);
+    }
+
+    uint32_t allocateDoubleSlot() {
+        if (!doubleSlots.empty())
+            return doubleSlots.popCopy();
+        if (height_ % 8 != 0)
+            normalSlots.append(height_ += 4);
+        return height_ += 8;
+    }
+    uint32_t allocateSlot() {
+        if (!normalSlots.empty())
+            return normalSlots.popCopy();
+        if (!doubleSlots.empty()) {
+            uint32_t index = doubleSlots.popCopy();
+            normalSlots.append(index - 4);
+            return index;
+        }
+        return height_ += 4;
+    }
+
+  public:
+    StackSlotAllocator() : height_(0)
+    { }
+
+    void freeSlot(LDefinition::Type type, uint32_t index) {
+        switch (type) {
+#if JS_BITS_PER_WORD == 32
+          case LDefinition::GENERAL:
+          case LDefinition::OBJECT:
+          case LDefinition::SLOTS:
+#endif
+          case LDefinition::INT32:
+          case LDefinition::FLOAT32: return freeSlot(index);
+#if JS_BITS_PER_WORD == 64
+          case LDefinition::GENERAL:
+          case LDefinition::OBJECT:
+          case LDefinition::SLOTS:
+#endif
+#ifdef JS_PUNBOX64
+          case LDefinition::BOX:
+#endif
+#ifdef JS_NUNBOX32
+          case LDefinition::TYPE:
+          case LDefinition::PAYLOAD:
+#endif
+          case LDefinition::DOUBLE:  return freeDoubleSlot(index);
+          default: MOZ_ASSUME_UNREACHABLE("Unknown slot type");
+        }
+    }
+
+    uint32_t allocateSlot(LDefinition::Type type) {
+        switch (type) {
+#if JS_BITS_PER_WORD == 32
+          case LDefinition::GENERAL:
+          case LDefinition::OBJECT:
+          case LDefinition::SLOTS:
+#endif
+          case LDefinition::INT32:
+          case LDefinition::FLOAT32: return allocateSlot();
+#if JS_BITS_PER_WORD == 64
+          case LDefinition::GENERAL:
+          case LDefinition::OBJECT:
+          case LDefinition::SLOTS:
+#endif
+#ifdef JS_PUNBOX64
+          case LDefinition::BOX:
+#endif
+#ifdef JS_NUNBOX32
+          case LDefinition::TYPE:
+          case LDefinition::PAYLOAD:
+#endif
+          case LDefinition::DOUBLE:  return allocateDoubleSlot();
+          default: MOZ_ASSUME_UNREACHABLE("Unknown slot type");
+        }
+    }
+
+    uint32_t stackHeight() const {
+        return height_;
+    }
+};
+
+} // namespace jit
+} // namespace js
+
+#endif /* jit_StackSlotAllocator_h */