Incorrectly detecting variables as constant

[ben-sb]

There are a few cases where variables are incorrectly detected as constant, and thus incorrectly propagated.

function test() {
  var a = 4;
  var b;
  a == 5 && (b = 10);
  console.log(b);
}

is being converted to

function test() {
  console.log(10); // incorrect constant propagation
}

and

function test(a, b, c) {
  a == 5 && (b = 10);
  console.log(b);
}

is being converted to

function test(a, b, c) {
  if (a == 5) {
    b = 10;
  }
  console.log(10); // incorrect constant propagation
}