reduce memory pressure via bit fields (#5203)

lib/scope.js

@@ -44,9 +44,8 @@
 "use strict";
 
 function SymbolDef(id, scope, orig, init) {
+    this._bits = 0;
     this.eliminated = 0;
-    this.exported = false;
-    this.global = false;
     this.id = id;
     this.init = init;
     this.mangled_name = null;
@@ -55,7 +54,6 @@ function SymbolDef(id, scope, orig, init) {
     this.references = [];
     this.replaced = 0;
     this.scope = scope;
-    this.undeclared = false;
 }
 
 SymbolDef.prototype = {
@@ -104,6 +102,15 @@ SymbolDef.prototype = {
     },
 };
 
+DEF_BITPROPS(SymbolDef, [
+    "const_redefs",
+    "cross_loop",
+    "direct_access",
+    "exported",
+    "global",
+    "undeclared",
+]);
+
 var unary_side_effects = makePredicate("delete ++ --");
 
 function is_lhs(node, parent) {