diff --git a/js/src/ds/InlineMap.h b/js/src/ds/InlineMap.h
index 27503060711..68ca36fb397 100644
--- a/js/src/ds/InlineMap.h
+++ b/js/src/ds/InlineMap.h
@@ -89,13 +89,13 @@ class InlineMap
     {
         friend class InlineMap;
         const K &key_;
-        const V &value_;
+        V &value_;
 
-        Entry(const K &key, const V &value) : key_(key), value_(value) {}
+        Entry(const K &key, V &value) : key_(key), value_(value) {}
 
       public:
         const K &key() { return key_; }
-        const V &value() { return value_; }
+        V &value() { return value_; }
     }; /* class Entry */
 
     class Ptr
diff --git a/js/src/frontend/ParseMaps-inl.h b/js/src/frontend/ParseMaps-inl.h
index c371468a8a6..29d18931918 100644
--- a/js/src/frontend/ParseMaps-inl.h
+++ b/js/src/frontend/ParseMaps-inl.h
@@ -31,10 +31,10 @@ ParseMapPool::acquire<AtomIndexMap>()
 }
 
 template <>
-inline AtomDOHMap *
-ParseMapPool::acquire<AtomDOHMap>()
+inline AtomDefnListMap *
+ParseMapPool::acquire<AtomDefnListMap>()
 {
-    return reinterpret_cast<AtomDOHMap *>(allocate());
+    return reinterpret_cast<AtomDefnListMap *>(allocate());
 }
 
 inline void *
@@ -52,41 +52,31 @@ inline Definition *
 AtomDecls::lookupFirst(JSAtom *atom)
 {
     JS_ASSERT(map);
-    AtomDOHPtr p = map->lookup(atom);
+    AtomDefnListPtr p = map->lookup(atom);
     if (!p)
         return NULL;
-    if (p.value().isHeader()) {
-        /* Just return the head defn. */
-        return p.value().header()->defn;
-    }
-    return p.value().defn();
+    return p.value().front();
 }
 
-inline MultiDeclRange
+inline DefinitionList::Range
 AtomDecls::lookupMulti(JSAtom *atom)
 {
     JS_ASSERT(map);
-    AtomDOHPtr p = map->lookup(atom);
-    if (!p)
-        return MultiDeclRange((Definition *) NULL);
-
-    DefnOrHeader &doh = p.value();
-    if (doh.isHeader())
-        return MultiDeclRange(doh.header());
-    return MultiDeclRange(doh.defn());
+    if (AtomDefnListPtr p = map->lookup(atom))
+        return p.value().all();
+    return DefinitionList::Range();
 }
 
 inline bool
 AtomDecls::addUnique(JSAtom *atom, Definition *defn)
 {
     JS_ASSERT(map);
-    AtomDOHAddPtr p = map->lookupForAdd(atom);
-    if (p) {
-        JS_ASSERT(!p.value().isHeader());
-        p.value() = DefnOrHeader(defn);
-        return true;
-    }
-    return map->add(p, atom, DefnOrHeader(defn));
+    AtomDefnListAddPtr p = map->lookupForAdd(atom);
+    if (!p)
+        return map->add(p, atom, DefinitionList(defn));
+    JS_ASSERT(!p.value().isMultiple());
+    p.value() = DefinitionList(defn);
+    return true;
 }
 
 template <class Map>
@@ -112,7 +102,7 @@ AtomThingMapPtr<Map>::releaseMap(JSContext *cx)
 inline bool
 AtomDecls::init()
 {
-    map = cx->parseMapPool().acquire<AtomDOHMap>();
+    map = cx->parseMapPool().acquire<AtomDefnListMap>();
     return map;
 }
 
diff --git a/js/src/frontend/ParseMaps.cpp b/js/src/frontend/ParseMaps.cpp
index 3228fb3f338..773dfbfb29a 100644
--- a/js/src/frontend/ParseMaps.cpp
+++ b/js/src/frontend/ParseMaps.cpp
@@ -6,6 +6,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "ParseMaps-inl.h"
+#include "jscntxt.h"
 #include "jscompartment.h"
 
 using namespace js;
@@ -18,13 +19,13 @@ ParseMapPool::checkInvariants()
      * allocated space for each of the map types.
      */
     JS_STATIC_ASSERT(sizeof(Definition *) == sizeof(jsatomid));
-    JS_STATIC_ASSERT(sizeof(Definition *) == sizeof(DefnOrHeader));
+    JS_STATIC_ASSERT(sizeof(Definition *) == sizeof(DefinitionList));
     JS_STATIC_ASSERT(sizeof(AtomDefnMap::Entry) == sizeof(AtomIndexMap::Entry));
-    JS_STATIC_ASSERT(sizeof(AtomDefnMap::Entry) == sizeof(AtomDOHMap::Entry));
-    JS_STATIC_ASSERT(sizeof(AtomMapT::Entry) == sizeof(AtomDOHMap::Entry));
+    JS_STATIC_ASSERT(sizeof(AtomDefnMap::Entry) == sizeof(AtomDefnListMap::Entry));
+    JS_STATIC_ASSERT(sizeof(AtomMapT::Entry) == sizeof(AtomDefnListMap::Entry));
     /* Ensure that the HasTable::clear goes quickly via memset. */
     JS_STATIC_ASSERT(tl::IsPodType<AtomIndexMap::WordMap::Entry>::result);
-    JS_STATIC_ASSERT(tl::IsPodType<AtomDOHMap::WordMap::Entry>::result);
+    JS_STATIC_ASSERT(tl::IsPodType<AtomDefnListMap::WordMap::Entry>::result);
     JS_STATIC_ASSERT(tl::IsPodType<AtomDefnMap::WordMap::Entry>::result);
 }
 
@@ -53,23 +54,67 @@ ParseMapPool::allocateFresh()
     return (void *) map;
 }
 
+DefinitionList::Node *
+DefinitionList::allocNode(JSContext *cx, Definition *head, Node *tail)
+{
+    Node *result = cx->tempLifoAlloc().new_<Node>(head, tail);
+    if (!result)
+        js_ReportOutOfMemory(cx);
+    return result;
+}
+
+bool
+DefinitionList::pushFront(JSContext *cx, Definition *val)
+{
+    Node *tail;
+    if (isMultiple()) {
+        tail = firstNode();
+    } else {
+        tail = allocNode(cx, defn(), NULL);
+        if (!tail)
+            return false;
+    }
+
+    Node *node = allocNode(cx, val, tail);
+    if (!node)
+        return false;
+    *this = DefinitionList(node);
+    return true;
+}
+
+bool
+DefinitionList::pushBack(JSContext *cx, Definition *val)
+{
+    Node *last;
+    if (isMultiple()) {
+        last = firstNode();
+        while (last->next)
+            last = last->next;
+    } else {
+        last = allocNode(cx, defn(), NULL);
+        if (!last)
+            return false;
+    }
+
+    Node *node = allocNode(cx, val, NULL);
+    if (!node)
+        return false;
+    last->next = node;
+    if (!isMultiple())
+        *this = DefinitionList(last);
+    return true;
+}
+
 #ifdef DEBUG
 void
 AtomDecls::dump()
 {
-    for (AtomDOHRange r = map->all(); !r.empty(); r.popFront()) {
+    for (AtomDefnListRange r = map->all(); !r.empty(); r.popFront()) {
         fprintf(stderr, "atom: ");
         js_DumpAtom(r.front().key());
-        const DefnOrHeader &doh = r.front().value();
-        if (doh.isHeader()) {
-            AtomDeclNode *node = doh.header();
-            do {
-                fprintf(stderr, "  node: %p\n", (void *) node);
-                fprintf(stderr, "    defn: %p\n", (void *) node->defn);
-                node = node->next;
-            } while (node);
-        } else {
-            fprintf(stderr, "  defn: %p\n", (void *) doh.defn());
+        const DefinitionList &dlist = r.front().value();
+        for (DefinitionList::Range dr = dlist.all(); !dr.empty(); dr.popFront()) {
+            fprintf(stderr, "    defn: %p\n", (void *) dr.front());
         }
     }
 }
@@ -90,74 +135,21 @@ DumpAtomDefnMap(const AtomDefnMapPtr &map)
 }
 #endif
 
-AtomDeclNode *
-AtomDecls::allocNode(Definition *defn)
-{
-    AtomDeclNode *p = cx->tempLifoAlloc().new_<AtomDeclNode>(defn);
-    if (!p) {
-        js_ReportOutOfMemory(cx);
-        return NULL;
-    }
-    return p;
-}
-
 bool
 AtomDecls::addShadow(JSAtom *atom, Definition *defn)
 {
-    AtomDeclNode *node = allocNode(defn);
-    if (!node)
-        return false;
-
-    AtomDOHAddPtr p = map->lookupForAdd(atom);
+    AtomDefnListAddPtr p = map->lookupForAdd(atom);
     if (!p)
-        return map->add(p, atom, DefnOrHeader(node));
+        return map->add(p, atom, DefinitionList(defn));
 
-    AtomDeclNode *toShadow;
-    if (p.value().isHeader()) {
-        toShadow = p.value().header();
-    } else {
-        toShadow = allocNode(p.value().defn());
-        if (!toShadow)
-            return false;
-    }
-    node->next = toShadow;
-    p.value() = DefnOrHeader(node);
-    return true;
-}
-
-AtomDeclNode *
-AtomDecls::lastAsNode(DefnOrHeader *doh)
-{
-    if (doh->isHeader()) {
-        AtomDeclNode *last = doh->header();
-        while (last->next)
-            last = last->next;
-        return last;
-    }
-
-    /* Otherwise, we need to turn the existing defn into a node. */
-    AtomDeclNode *node = allocNode(doh->defn());
-    if (!node)
-        return NULL;
-    *doh = DefnOrHeader(node);
-    return node;
+    return p.value().pushFront(cx, defn);
 }
 
 bool
 AtomDecls::addHoist(JSAtom *atom, Definition *defn)
 {
-    AtomDeclNode *node = allocNode(defn);
-    if (!node)
-        return false;
-
-    AtomDOHAddPtr p = map->lookupForAdd(atom);
-    if (p) {
-        AtomDeclNode *last = lastAsNode(&p.value());
-        if (!last)
-            return false;
-        last->next = node;
-        return true;
-    }
-
-    return map->add(p, atom, DefnOrHeader(node));
+    AtomDefnListAddPtr p = map->lookupForAdd(atom);
+    if (p)
+        return p.value().pushBack(cx, defn);
+    return map->add(p, atom, DefinitionList(defn));
 }
diff --git a/js/src/frontend/ParseMaps.h b/js/src/frontend/ParseMaps.h
index 74207aa38d8..dc74c5568ac 100644
--- a/js/src/frontend/ParseMaps.h
+++ b/js/src/frontend/ParseMaps.h
@@ -18,6 +18,8 @@ namespace js {
 
 struct Definition;
 
+typedef InlineMap<JSAtom *, DefinitionList, 24> AtomDefnListMap;
+
 /*
  * A pool that permits the reuse of the backing storage for the defn, index, or
  * defn-or-header (multi) maps.
@@ -91,7 +93,7 @@ class ParseMapPool
         recycle((void *) map);
     }
 
-    void release(AtomDOHMap *map) {
+    void release(AtomDefnListMap *map) {
         recycle((void *) map);
     }
 }; /* ParseMapPool */
@@ -153,59 +155,156 @@ class OwnedAtomThingMapPtr : public AtomThingMapPtrT
 typedef OwnedAtomThingMapPtr<AtomDefnMapPtr> OwnedAtomDefnMapPtr;
 typedef OwnedAtomThingMapPtr<AtomIndexMapPtr> OwnedAtomIndexMapPtr;
 
-/* Node structure for chaining in AtomDecls. */
-struct AtomDeclNode
-{
-    Definition *defn;
-    AtomDeclNode *next;
-
-    explicit AtomDeclNode(Definition *defn)
-      : defn(defn), next(NULL)
-    {}
-};
-
 /*
- * Tagged union of a Definition and an AtomDeclNode, for use in AtomDecl's
- * internal map.
+ * A nonempty list containing one or more pointers to Definitions.
+ *
+ * By far the most common case is that the list contains exactly one
+ * Definition, so the implementation is optimized for that case.
+ *
+ * Nodes for the linked list (if any) are allocated from the tempPool of a
+ * context the caller passes into pushFront and pushBack. This means the
+ * DefinitionList does not own the memory for the nodes: the JSContext does.
+ * As a result, DefinitionList is a POD type; it can be safely and cheaply
+ * copied.
  */
-class DefnOrHeader
+class DefinitionList
 {
+  public:
+    class Range;
+
+  private:
+    friend class Range;
+
+    /* A node in a linked list of Definitions. */
+    struct Node
+    {
+        Definition *defn;
+        Node *next;
+
+        Node(Definition *defn, Node *next) : defn(defn), next(next) {}
+    };
+
     union {
-        Definition    *defn;
-        AtomDeclNode    *head;
-        uintptr_t       bits;
+        Definition *defn;
+        Node *head;
+        uintptr_t bits;
     } u;
 
-  public:
-    DefnOrHeader() {
-        u.bits = 0;
-    }
-
-    explicit DefnOrHeader(Definition *defn) {
-        u.defn = defn;
-        JS_ASSERT(!isHeader());
-    }
-
-    explicit DefnOrHeader(AtomDeclNode *node) {
-        u.head = node;
-        u.bits |= 0x1;
-        JS_ASSERT(isHeader());
-    }
-
-    bool isHeader() const {
-        return u.bits & 0x1;
-    }
-
     Definition *defn() const {
-        JS_ASSERT(!isHeader());
+        JS_ASSERT(!isMultiple());
         return u.defn;
     }
 
-    AtomDeclNode *header() const {
-        JS_ASSERT(isHeader());
-        return (AtomDeclNode *) (u.bits & ~0x1);
+    Node *firstNode() const {
+        JS_ASSERT(isMultiple());
+        return (Node *) (u.bits & ~0x1);
     }
 
+    static Node *
+    allocNode(JSContext *cx, Definition *head, Node *tail);
+            
+  public:
+    class Range
+    {
+        friend class DefinitionList;
+
+        Node *node;
+        Definition *defn;
+
+        explicit Range(const DefinitionList &list) {
+            if (list.isMultiple()) {
+                node = list.firstNode();
+                defn = node->defn;
+            } else {
+                node = NULL;
+                defn = list.defn();
+            }
+        }
+
+      public:
+        /* An empty Range. */
+        Range() : node(NULL), defn(NULL) {}
+
+        void popFront() {
+            JS_ASSERT(!empty());
+            if (!node) {
+                defn = NULL;
+                return;
+            }
+            node = node->next;
+            defn = node ? node->defn : NULL;
+        }
+
+        Definition *front() {
+            JS_ASSERT(!empty());
+            return defn;
+        }
+
+        bool empty() const {
+            JS_ASSERT_IF(!defn, !node);
+            return !defn;
+        }
+    };
+
+    DefinitionList() {
+        u.bits = 0;
+    }
+
+    explicit DefinitionList(Definition *defn) {
+        u.defn = defn;
+        JS_ASSERT(!isMultiple());
+    }
+
+    explicit DefinitionList(Node *node) {
+        u.head = node;
+        u.bits |= 0x1;
+        JS_ASSERT(isMultiple());
+    }
+
+    bool isMultiple() const { return (u.bits & 0x1) != 0; }
+
+    Definition *front() {
+        return isMultiple() ? firstNode()->defn : defn();
+    }
+
+    /*
+     * If there are multiple Definitions in this list, remove the first and
+     * return true. Otherwise there is exactly one Definition in the list; do
+     * nothing and return false.
+     */
+    bool popFront() {
+        if (!isMultiple())
+            return false;
+
+        Node *node = firstNode();
+        Node *next = node->next;
+        if (next->next)
+            *this = DefinitionList(next);
+        else
+            *this = DefinitionList(next->defn);
+        return true;
+    }
+
+    /*
+     * Add a definition to the front of this list.
+     *
+     * Return true on success. On OOM, report on cx and return false.
+     */
+    bool pushFront(JSContext *cx, Definition *val);
+
+    /* Like pushFront, but add the given val to the end of the list. */
+    bool pushBack(JSContext *cx, Definition *val);
+
+    /* Overwrite the first Definition in the list. */
+    void setFront(Definition *val) {
+        if (isMultiple())
+            firstNode()->defn = val;
+        else
+            *this = DefinitionList(val);
+    }
+
+    Range all() const { return Range(*this); }
+
 #ifdef DEBUG
     void dump();
 #endif
@@ -213,7 +312,7 @@ class DefnOrHeader
 
 namespace tl {
 
-template <> struct IsPodType<DefnOrHeader> {
+template <> struct IsPodType<DefinitionList> {
     static const bool result = true;
 };
 
@@ -222,7 +321,7 @@ template <> struct IsPodType<DefnOrHeader> {
 /*
  * Multimap for function-scope atom declarations.
  *
- * Wraps an internal DeclOrHeader map with multi-map functionality.
+ * Wraps an internal DefinitionList map with multi-map functionality.
  *
  * In the common case, no block scoping is used, and atoms have a single
  * associated definition. In the uncommon (block scoping) case, we map the atom
@@ -230,27 +329,17 @@ template <> struct IsPodType<DefnOrHeader> {
  */
 class AtomDecls
 {
-    /* AtomDeclsIter needs to get at the DOHMap directly. */
+    /* AtomDeclsIter needs to get at the DefnListMap directly. */
     friend class AtomDeclsIter;
 
     JSContext   *cx;
-    AtomDOHMap  *map;
+    AtomDefnListMap  *map;
 
     AtomDecls(const AtomDecls &other) MOZ_DELETE;
     void operator=(const AtomDecls &other) MOZ_DELETE;
 
-    AtomDeclNode *allocNode(Definition *defn);
-
-    /*
-     * Fallibly return the value in |doh| as a node.
-     * Update the defn currently occupying |doh| to a node if necessary.
-     */
-    AtomDeclNode *lastAsNode(DefnOrHeader *doh);
-
   public:
-    explicit AtomDecls(JSContext *cx)
-      : cx(cx), map(NULL)
-    {}
+    explicit AtomDecls(JSContext *cx) : cx(cx), map(NULL) {}
 
     ~AtomDecls();
 
@@ -264,7 +353,7 @@ class AtomDecls
     inline Definition *lookupFirst(JSAtom *atom);
 
     /* Perform a lookup that can iterate over the definitions associated with |atom|. */
-    inline MultiDeclRange lookupMulti(JSAtom *atom);
+    inline DefinitionList::Range lookupMulti(JSAtom *atom);
 
     /* Add-or-update a known-unique definition for |atom|. */
     inline bool addUnique(JSAtom *atom, Definition *defn);
@@ -274,40 +363,26 @@ class AtomDecls
     /* Updating the definition for an entry that is known to exist is infallible. */
     void updateFirst(JSAtom *atom, Definition *defn) {
         JS_ASSERT(map);
-        AtomDOHMap::Ptr p = map->lookup(atom);
+        AtomDefnListMap::Ptr p = map->lookup(atom);
         JS_ASSERT(p);
-        if (p.value().isHeader())
-            p.value().header()->defn = defn;
-        else
-            p.value() = DefnOrHeader(defn);
+        p.value().setFront(defn);
     }
 
     /* Remove the node at the head of the chain for |atom|. */
     void remove(JSAtom *atom) {
         JS_ASSERT(map);
-        AtomDOHMap::Ptr p = map->lookup(atom);
+        AtomDefnListMap::Ptr p = map->lookup(atom);
         if (!p)
             return;
 
-        DefnOrHeader &doh = p.value();
-        if (!doh.isHeader()) {
+        DefinitionList &list = p.value();
+        if (!list.popFront()) {
             map->remove(p);
             return;
         }
-
-        AtomDeclNode *node = doh.header();
-        AtomDeclNode *newHead = node->next;
-        if (newHead) {
-            if (newHead->next)
-                p.value() = DefnOrHeader(newHead);
-            else
-                p.value() = DefnOrHeader(newHead->defn);
-        } else {
-            map->remove(p);
-        }
     }
 
-    AtomDOHMap::Range all() {
+    AtomDefnListMap::Range all() {
         JS_ASSERT(map);
         return map->all();
     }
@@ -317,85 +392,14 @@ class AtomDecls
 #endif
 };
 
-/*
- * Lookup state tracker for those situations where the caller wants to traverse
- * multiple definitions associated with a single atom. This occurs due to block
- * scoping.
- */
-class MultiDeclRange
-{
-    friend class AtomDecls;
-
-    AtomDeclNode *node;
-    Definition *defn;
-
-    explicit MultiDeclRange(Definition *defn) : node(NULL), defn(defn) {}
-    explicit MultiDeclRange(AtomDeclNode *node) : node(node), defn(node->defn) {}
-
-  public:
-    void popFront() {
-        JS_ASSERT(!empty());
-        if (!node) {
-            defn = NULL;
-            return;
-        }
-        node = node->next;
-        defn = node ? node->defn : NULL;
-    }
-
-    Definition *front() {
-        JS_ASSERT(!empty());
-        return defn;
-    }
-
-    bool empty() const {
-        JS_ASSERT_IF(!defn, !node);
-        return !defn;
-    }
-};
-
-/* Iterates over all the definitions in an AtomDecls. */
-class AtomDeclsIter
-{
-    AtomDOHMap::Range   r;     /* Range over the map. */
-    AtomDeclNode        *link; /* Optional next node in the current atom's chain. */
-
-  public:
-    explicit AtomDeclsIter(AtomDecls *decls) : r(decls->all()), link(NULL) {}
-
-    Definition *next() {
-        if (link) {
-            JS_ASSERT(link != link->next);
-            Definition *result = link->defn;
-            link = link->next;
-            JS_ASSERT(result);
-            return result;
-        }
-
-        if (r.empty())
-            return NULL;
-
-        const DefnOrHeader &doh = r.front().value();
-        r.popFront();
-
-        if (!doh.isHeader())
-            return doh.defn();
-
-        JS_ASSERT(!link);
-        AtomDeclNode *node = doh.header();
-        link = node->next;
-        return node->defn;
-    }
-};
-
 typedef AtomDefnMap::Range      AtomDefnRange;
 typedef AtomDefnMap::AddPtr     AtomDefnAddPtr;
 typedef AtomDefnMap::Ptr        AtomDefnPtr;
 typedef AtomIndexMap::AddPtr    AtomIndexAddPtr;
 typedef AtomIndexMap::Ptr       AtomIndexPtr;
-typedef AtomDOHMap::Ptr         AtomDOHPtr;
-typedef AtomDOHMap::AddPtr      AtomDOHAddPtr;
-typedef AtomDOHMap::Range       AtomDOHRange;
+typedef AtomDefnListMap::Ptr    AtomDefnListPtr;
+typedef AtomDefnListMap::AddPtr AtomDefnListAddPtr;
+typedef AtomDefnListMap::Range  AtomDefnListRange;
 
 } /* namepsace js */
 
diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index edd6407da77..63f2aa63511 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -706,13 +706,17 @@ Parser::functionBody(FunctionBodyType type)
          * might, in the case of calls to eval) be assigned.
          */
         if (tc->sc->inStrictMode()) {
-            AtomDeclsIter iter(&tc->decls);
-            while (Definition *dn = iter.next()) {
-                if (dn->kind() == Definition::ARG && dn->isAssigned()) {
-                    tc->sc->setFunDefinitelyNeedsArgsObj();
-                    break;
+            for (AtomDefnListMap::Range r = tc->decls.all(); !r.empty(); r.popFront()) {
+                DefinitionList &dlist = r.front().value();
+                for (DefinitionList::Range dr = dlist.all(); !dr.empty(); dr.popFront()) {
+                    Definition *dn = dr.front();
+                    if (dn->kind() == Definition::ARG && dn->isAssigned()) {
+                        tc->sc->setFunDefinitelyNeedsArgsObj();
+                        goto exitLoop;
+                    }
                 }
             }
+          exitLoop: ;
         }
         break;
       case ARGUMENT:
@@ -1570,14 +1574,18 @@ Parser::functionDef(HandlePropertyName funName, FunctionType type, FunctionSynta
      * Parser::functionArguments has returned.
      */
     if (prelude) {
-        AtomDeclsIter iter(&funtc.decls);
-        while (Definition *apn = iter.next()) {
-            /* Filter based on pn_op -- see BindDestructuringArg, above. */
-            if (!apn->isOp(JSOP_SETLOCAL))
-                continue;
+        for (AtomDefnListMap::Range r = tc->decls.all(); !r.empty(); r.popFront()) {
+            DefinitionList &dlist = r.front().value();
+            for (DefinitionList::Range dr = dlist.all(); !dr.empty(); dr.popFront()) {
+                Definition *apn = dr.front();
 
-            if (!BindLocalVariable(context, &funtc, apn, VARIABLE))
-                return NULL;
+                /* Filter based on pn_op -- see BindDestructuringArg, above. */
+                if (!apn->isOp(JSOP_SETLOCAL))
+                    continue;
+
+                if (!BindLocalVariable(context, &funtc, apn, VARIABLE))
+                    return NULL;
+            }
         }
     }
 #endif
@@ -2067,7 +2075,7 @@ OuterLet(TreeContext *tc, StmtInfoTC *stmt, JSAtom *atom)
 }
 
 static bool
-BindFunctionLocal(JSContext *cx, BindData *data, MultiDeclRange &mdl, TreeContext *tc)
+BindFunctionLocal(JSContext *cx, BindData *data, DefinitionList::Range &defs, TreeContext *tc)
 {
     JS_ASSERT(tc->sc->inFunction());
 
@@ -2093,7 +2101,7 @@ BindFunctionLocal(JSContext *cx, BindData *data, MultiDeclRange &mdl, TreeContex
 
     if (kind == ARGUMENT) {
         JS_ASSERT(tc->sc->inFunction());
-        JS_ASSERT(!mdl.empty() && mdl.front()->kind() == Definition::ARG);
+        JS_ASSERT(!defs.empty() && defs.front()->kind() == Definition::ARG);
     } else {
         JS_ASSERT(kind == VARIABLE || kind == CONSTANT);
     }
@@ -2122,11 +2130,11 @@ BindVarOrConst(JSContext *cx, BindData *data, JSAtom *atom, Parser *parser)
         return true;
     }
 
-    MultiDeclRange mdl = tc->decls.lookupMulti(atom);
+    DefinitionList::Range defs = tc->decls.lookupMulti(atom);
     JSOp op = data->op;
 
-    if (stmt || !mdl.empty()) {
-        Definition *dn = mdl.empty() ? NULL : mdl.front();
+    if (stmt || !defs.empty()) {
+        Definition *dn = defs.empty() ? NULL : defs.front();
         Definition::Kind dn_kind = dn ? dn->kind() : Definition::VAR;
 
         if (dn_kind == Definition::ARG) {
@@ -2163,14 +2171,14 @@ BindVarOrConst(JSContext *cx, BindData *data, JSAtom *atom, Parser *parser)
         }
     }
 
-    if (mdl.empty()) {
+    if (defs.empty()) {
         if (!Define(pn, atom, tc))
             return false;
     } else {
         /*
          * A var declaration never recreates an existing binding, it restates
          * it and possibly reinitializes its value. Beware that if pn becomes a
-         * use of |mdl.defn()|, and if we have an initializer for this var or
+         * use of |defs.defn()|, and if we have an initializer for this var or
          * const (typically a const would ;-), then pn must be rewritten into a
          * PNK_ASSIGN node. See js::Parser::variables, further below.
          *
@@ -2178,7 +2186,7 @@ BindVarOrConst(JSContext *cx, BindData *data, JSAtom *atom, Parser *parser)
          * There the x definition is hoisted but the x = 2 assignment mutates
          * the block-local binding of x.
          */
-        Definition *dn = mdl.front();
+        Definition *dn = defs.front();
 
         data->fresh = false;
 
@@ -2198,10 +2206,10 @@ BindVarOrConst(JSContext *cx, BindData *data, JSAtom *atom, Parser *parser)
 
         /* Find the first non-let binding of this atom. */
         while (dn->kind() == Definition::LET) {
-            mdl.popFront();
-            if (mdl.empty())
+            defs.popFront();
+            if (defs.empty())
                 break;
-            dn = mdl.front();
+            dn = defs.front();
         }
 
         if (dn) {
@@ -2240,7 +2248,7 @@ BindVarOrConst(JSContext *cx, BindData *data, JSAtom *atom, Parser *parser)
         pn->pn_dflags |= PND_CONST;
 
     if (tc->sc->inFunction())
-        return BindFunctionLocal(cx, data, mdl, tc);
+        return BindFunctionLocal(cx, data, defs, tc);
 
     return true;
 }
@@ -2305,11 +2313,11 @@ NoteNameUse(ParseNode *pn, Parser *parser)
     PropertyName *name = pn->pn_atom->asPropertyName();
     StmtInfoTC *stmt = LexicalLookup(parser->tc, name, NULL, (StmtInfoTC *)NULL);
 
-    MultiDeclRange mdl = parser->tc->decls.lookupMulti(name);
+    DefinitionList::Range defs = parser->tc->decls.lookupMulti(name);
 
     Definition *dn;
-    if (!mdl.empty()) {
-        dn = mdl.front();
+    if (!defs.empty()) {
+        dn = defs.front();
     } else {
         if (AtomDefnAddPtr p = parser->tc->lexdeps->lookupForAdd(name)) {
             dn = p.value();
diff --git a/js/src/jsprvtd.h b/js/src/jsprvtd.h
index b6b1cb168a3..19b5aef3c2b 100644
--- a/js/src/jsprvtd.h
+++ b/js/src/jsprvtd.h
@@ -174,10 +174,9 @@ struct StackShape;
 
 class MultiDeclRange;
 class ParseMapPool;
-class DefnOrHeader;
+class DefinitionList;
 typedef InlineMap<JSAtom *, Definition *, 24> AtomDefnMap;
 typedef InlineMap<JSAtom *, jsatomid, 24> AtomIndexMap;
-typedef InlineMap<JSAtom *, DefnOrHeader, 24> AtomDOHMap;
 typedef Vector<UpvarCookie, 8> UpvarCookies;
 
 class Breakpoint;