diff -r ce072f38628c -r fb3cd08bc7fb src/Stack.h
--- a/src/Stack.h	Sat Dec 22 16:42:20 2012 -0800
+++ b/src/Stack.h	Sat Dec 22 18:22:14 2012 -0800
@@ -66,7 +66,14 @@
         Object *callee_;
     };
     Code *code_;
+
+    // Position of the LIFO stack at function entry.
     Address lifoPosition_;
+    
+    // Loop nesting level, for LIFO stack balancing. LIFO stack balancing
+    // is not strictly required, but it helps to avoid unnecessary waste,
+    // since once the LIFO stack is depleted, we must use the heap instead.
+    unsigned loopDepth_;
 
   public:
     Frame(Frame *prev, bytecode *prevpc, Function *fun, Code *code, Address lifoPosition)
@@ -74,7 +81,8 @@
         prevpc_(prevpc),
         fun_(fun),
         code_(code),
-        lifoPosition_(lifoPosition)
+        lifoPosition_(lifoPosition),
+        loopDepth_(0)
     {
     }
 
@@ -87,8 +95,11 @@
     {
     }
 
+    Address *loopStack() {
+        return reinterpret_cast<Address *>(this + 1);
+    }
     LocalSlot *locals() {
-        return reinterpret_cast<LocalSlot *>(this + 1);
+        return reinterpret_cast<LocalSlot *>(loopStack() + code_->maxLoopDepth());
     }
     LocalSlot *stackBase() {
         return locals() + code_->nlocals();
@@ -124,6 +135,8 @@
         assert(slot < fun()->nargs());
         return *(reinterpret_cast<LocalSlot *>(this) - slot - 1);
     }
+    void enterLoop(Zone *zone);
+    void leaveLoop(Zone *zone);
     void accept(VirtualObjectVisitor *visitor);
 };