enhance mangle (#4926)

lib/scope.js

@@ -800,6 +800,7 @@ var base54 = (function() {
     var leading = init("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_");
     var chars, frequency;
     function reset() {
+        chars = null;
         frequency = Object.create(freq);
     }
     base54.consider = function(str, delta) {
@@ -811,19 +812,15 @@ var base54 = (function() {
         return frequency[b] - frequency[a];
     }
     base54.sort = function() {
-        chars = leading.sort(compare).concat(digits.sort(compare));
+        chars = leading.sort(compare).concat(digits).sort(compare);
     };
     base54.reset = reset;
     reset();
     function base54(num) {
-        var ret = "", base = 54;
-        num++;
-        do {
-            num--;
-            ret += chars[num % base];
-            num = Math.floor(num / base);
-            base = 64;
-        } while (num > 0);
+        var ret = leading[num % 54];
+        for (num = Math.floor(num / 54); --num >= 0; num >>= 6) {
+            ret += chars[num & 0x3F];
+        }
         return ret;
     }
     return base54;

test/mocha/let.js

@@ -7,11 +7,11 @@ describe("let", function() {
         // Produce a lot of variables in a function and run it through mangle.
         var s = '"dddddeeeeelllllooooottttt"; function foo() {';
         for (var i = 0; i < 18000; i++) {
-            s += "var v" + i + "=0;";
+            s += "var v" + i + "=[];";
         }
         s += '}';
         var result = UglifyJS.minify(s, {
-            compress: false
+            compress: false,
         }).code;
 
         // Verify that select keywords and reserved keywords not produced