improve general performance (#3104)

lib/scope.js

@@ -55,7 +55,7 @@ function SymbolDef(scope, orig, init) {
     this.mangled_name = null;
     this.undeclared = false;
     this.id = SymbolDef.next_id++;
-};
+}
 
 SymbolDef.next_id = 1;
 
@@ -556,17 +556,21 @@ AST_Toplevel.DEFMETHOD("compute_char_frequency", function(options){
 });
 
 var base54 = (function() {
-    var leading = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_".split("");
-    var digits = "0123456789".split("");
+    var freq = Object.create(null);
+    function init(chars) {
+        var array = [];
+        for (var i = 0, len = chars.length; i < len; i++) {
+            var ch = chars[i];
+            array.push(ch);
+            freq[ch] = -1e-2 * i;
+        }
+        return array;
+    }
+    var digits = init("0123456789");
+    var leading = init("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_");
     var chars, frequency;
     function reset() {
-        frequency = Object.create(null);
-        leading.forEach(function(ch) {
-            frequency[ch] = 0;
-        });
-        digits.forEach(function(ch) {
-            frequency[ch] = 0;
-        });
+        frequency = Object.create(freq);
     }
     base54.consider = function(str, delta) {
         for (var i = str.length; --i >= 0;) {
@@ -577,7 +581,7 @@ var base54 = (function() {
         return frequency[b] - frequency[a];
     }
     base54.sort = function() {
-        chars = mergeSort(leading, compare).concat(mergeSort(digits, compare));
+        chars = leading.sort(compare).concat(digits.sort(compare));
     };
     base54.reset = reset;
     reset();
@@ -591,6 +595,6 @@ var base54 = (function() {
             base = 64;
         } while (num > 0);
         return ret;
-    };
+    }
     return base54;
 })();