diff --git a/js/src/frontend/BytecodeEmitter.cpp b/js/src/frontend/BytecodeEmitter.cpp
index 17618b3014d..06847404ad3 100644
--- a/js/src/frontend/BytecodeEmitter.cpp
+++ b/js/src/frontend/BytecodeEmitter.cpp
@@ -2788,7 +2788,8 @@ EmitNameOp(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn, JSBool callContex
     if (op == JSOP_ARGUMENTS || op == JSOP_CALLEE) {
         if (Emit1(cx, bce, op) < 0)
             return JS_FALSE;
-        if (callContext && Emit1(cx, bce, JSOP_PUSH) < 0)
+        /* Need to provide |this| value for call */
+        if (callContext && Emit1(cx, bce, JSOP_UNDEFINED) < 0)
             return JS_FALSE;
     } else {
         if (!pn->pn_cookie.isFree()) {
@@ -6075,7 +6076,8 @@ EmitReturn(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn)
         if (!EmitTree(cx, bce, pn2))
             return false;
     } else {
-        if (Emit1(cx, bce, JSOP_PUSH) < 0)
+        /* No explicit return value provided */
+        if (Emit1(cx, bce, JSOP_UNDEFINED) < 0)
             return false;
     }
 
@@ -6355,9 +6357,9 @@ EmitCallOrNew(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn, ptrdiff_t top)
      * in jsinterp.cpp for JSOP_LAMBDA followed by JSOP_{SET,INIT}PROP.
      *
      * Then (or in a call case that has no explicit reference-base
-     * object) we emit JSOP_PUSH to produce the |this| slot required
-     * for calls (which non-strict mode functions will box into the
-     * global object).
+     * object) we emit JSOP_UNDEFINED to produce the undefined |this| 
+     * value required for calls (which non-strict mode functions 
+     * will box into the global object).
      */
     ParseNode *pn2 = pn->pn_head;
     switch (pn2->getKind()) {
@@ -6379,16 +6381,16 @@ EmitCallOrNew(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn, ptrdiff_t top)
         JS_ASSERT(pn2->isOp(JSOP_XMLNAME));
         if (!EmitXMLName(cx, pn2, JSOP_CALLXMLNAME, bce))
             return false;
-        callop = true;          /* suppress JSOP_PUSH after */
+        callop = true;          /* suppress JSOP_UNDEFINED after */
         break;
 #endif
       default:
         if (!EmitTree(cx, bce, pn2))
             return false;
-        callop = false;             /* trigger JSOP_PUSH after */
+        callop = false;             /* trigger JSOP_UNDEFINED after */
         break;
     }
-    if (!callop && Emit1(cx, bce, JSOP_PUSH) < 0)
+    if (!callop && Emit1(cx, bce, JSOP_UNDEFINED) < 0)
         return false;
 
     /* Remember start of callable-object bytecode for decompilation hint. */
@@ -7027,7 +7029,7 @@ frontend::EmitTree(JSContext *cx, BytecodeEmitter *bce, ParseNode *pn)
             if (!EmitTree(cx, bce, pn->pn_kid))
                 return JS_FALSE;
         } else {
-            if (Emit1(cx, bce, JSOP_PUSH) < 0)
+            if (Emit1(cx, bce, JSOP_UNDEFINED) < 0)
                 return JS_FALSE;
         }
         if (pn->pn_hidden && NewSrcNote(cx, bce, SRC_HIDDEN) < 0)
diff --git a/js/src/jsinfer.cpp b/js/src/jsinfer.cpp
index 355b6d4e06c..99b53dd8063 100644
--- a/js/src/jsinfer.cpp
+++ b/js/src/jsinfer.cpp
@@ -3421,7 +3421,7 @@ ScriptAnalysis::analyzeTypesBytecode(JSContext *cx, unsigned offset,
 
         /* Bytecodes pushing values of known type. */
       case JSOP_VOID:
-      case JSOP_PUSH:
+      case JSOP_UNDEFINED:
         pushed[0].addType(cx, Type::UndefinedType());
         break;
       case JSOP_ZERO:
diff --git a/js/src/jsinterp.cpp b/js/src/jsinterp.cpp
index 6b5f8ca2d98..616f5283af5 100644
--- a/js/src/jsinterp.cpp
+++ b/js/src/jsinterp.cpp
@@ -1995,9 +1995,9 @@ END_CASE(JSOP_LINENO)
 BEGIN_CASE(JSOP_BLOCKCHAIN)
 END_CASE(JSOP_BLOCKCHAIN)
 
-BEGIN_CASE(JSOP_PUSH)
+BEGIN_CASE(JSOP_UNDEFINED)
     PUSH_UNDEFINED();
-END_CASE(JSOP_PUSH)
+END_CASE(JSOP_UNDEFINED)
 
 BEGIN_CASE(JSOP_POP)
     regs.sp--;
diff --git a/js/src/jsopcode.cpp b/js/src/jsopcode.cpp
index e2a74e4b09c..d2008adbab2 100644
--- a/js/src/jsopcode.cpp
+++ b/js/src/jsopcode.cpp
@@ -1917,7 +1917,7 @@ DecompileGroupAssignment(SprintStack *ss, jsbytecode *pc, jsbytecode *endpc,
     const char *rval;
 
     LOAD_OP_DATA(pc);
-    LOCAL_ASSERT(op == JSOP_PUSH || op == JSOP_GETLOCAL);
+    LOCAL_ASSERT(op == JSOP_GETLOCAL);
 
     todo = Sprint(&ss->sprinter, "%s[", VarPrefix(sn));
     if (todo < 0 || !PushOff(ss, todo, JSOP_NOP))
@@ -1934,7 +1934,7 @@ DecompileGroupAssignment(SprintStack *ss, jsbytecode *pc, jsbytecode *endpc,
         if (pc == endpc)
             return pc;
         LOAD_OP_DATA(pc);
-        if (op != JSOP_PUSH && op != JSOP_GETLOCAL)
+        if (op != JSOP_GETLOCAL)
             break;
         if (!hole && SprintPut(&ss->sprinter, ", ", 2) < 0)
             return NULL;
@@ -2548,20 +2548,6 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb)
                 }
                 break;
 
-              case JSOP_PUSH:
-#if JS_HAS_DESTRUCTURING
-                sn = js_GetSrcNote(jp->script, pc);
-                if (sn && SN_TYPE(sn) == SRC_GROUPASSIGN) {
-                    pc = DecompileGroupAssignment(ss, pc, endpc, sn, &todo);
-                    if (!pc)
-                        return NULL;
-                    LOCAL_ASSERT(*pc == JSOP_POPN);
-                    len = oplen = JSOP_POPN_LENGTH;
-                    goto end_groupassignment;
-                }
-#endif
-                /* FALL THROUGH */
-
               case JSOP_BINDNAME:
               case JSOP_BINDGNAME:
                 todo = Sprint(&ss->sprinter, "");
@@ -4193,8 +4179,8 @@ Decompile(SprintStack *ss, jsbytecode *pc, intN nb)
                         LOCAL_ASSERT(*pc == JSOP_NULLBLOCKCHAIN);
                         pc += JSOP_NULLBLOCKCHAIN_LENGTH;
                     }
-                    LOCAL_ASSERT(*pc == JSOP_PUSH);
-                    pc += JSOP_PUSH_LENGTH;
+                    LOCAL_ASSERT(*pc == JSOP_UNDEFINED);
+                    pc += JSOP_UNDEFINED_LENGTH;
                     LOCAL_ASSERT(*pc == JSOP_CALL);
                     LOCAL_ASSERT(GET_ARGC(pc) == 0);
                     len = JSOP_CALL_LENGTH;
@@ -5225,10 +5211,6 @@ DecompileExpression(JSContext *cx, JSScript *script, JSFunction *fun,
     JS_ASSERT(op != JSOP_CASE && op != JSOP_CASEX &&
               op != JSOP_DUP && op != JSOP_DUP2);
 
-    /* JSOP_PUSH is used to generate undefined for group assignment holes. */
-    if (op == JSOP_PUSH)
-        return JS_strdup(cx, js_undefined_str);
-
     /*
      * |this| could convert to a very long object initialiser, so cite it by
      * its keyword name instead.
diff --git a/js/src/jsopcode.tbl b/js/src/jsopcode.tbl
index f99adf415a0..9067f7877c0 100644
--- a/js/src/jsopcode.tbl
+++ b/js/src/jsopcode.tbl
@@ -113,7 +113,7 @@
 OPDEF(JSOP_NOP,       0,  "nop",        NULL,         1,  0,  0,  0,  JOF_BYTE)
 
 /* Long-standing JavaScript bytecodes. */
-OPDEF(JSOP_PUSH,      1,  "push",       NULL,         1,  0,  1,  0,  JOF_BYTE)
+OPDEF(JSOP_UNDEFINED, 1,  js_undefined_str, "",       1,  0,  1,  0,  JOF_BYTE)
 OPDEF(JSOP_POPV,      2,  "popv",       NULL,         1,  1,  0,  2,  JOF_BYTE)
 OPDEF(JSOP_ENTERWITH, 3,  "enterwith",  NULL,         1,  1,  1,  0,  JOF_BYTE|JOF_PARENHEAD)
 OPDEF(JSOP_LEAVEWITH, 4,  "leavewith",  NULL,         1,  1,  0,  0,  JOF_BYTE)
diff --git a/js/src/methodjit/Compiler.cpp b/js/src/methodjit/Compiler.cpp
index 583785363e5..1f806ccfebc 100644
--- a/js/src/methodjit/Compiler.cpp
+++ b/js/src/methodjit/Compiler.cpp
@@ -1681,9 +1681,9 @@ mjit::Compiler::generateMethod()
           BEGIN_CASE(JSOP_NOP)
           END_CASE(JSOP_NOP)
 
-          BEGIN_CASE(JSOP_PUSH)
+          BEGIN_CASE(JSOP_UNDEFINED)
             frame.push(UndefinedValue());
-          END_CASE(JSOP_PUSH)
+          END_CASE(JSOP_UNDEFINED)
 
           BEGIN_CASE(JSOP_POPV)
           BEGIN_CASE(JSOP_SETRVAL)