DCE wrong removing var assignment inside for-loop

[garyyeap]

This issue is related to es2015 scoping issue and have been fixed on #713.
Now just open for referring in the test case and it should be closed after the PR#713 has been merged.

Input Code

function test () {
  var arr = ['a', 'b', 'c'];
  var len = arr.length;
  var result = null;

  for (let i = 0; i < len; i++) {
      result = arr[i];
  }

  return result || {};
}

Actual Output

'use strict';function test(){for(var a=['a','b','c'],b=a.length,d=0,;d<b;d++)a[d];return c||{}}

Expected Output

'use strict';function test(){for(var a=['a','b','c'],b=a.length,d=0,c=0;d<b;d++)c=a[d];return c||{}}