Pierced bundler: run DCE to a fixpoint

[bakkot]

Consider the following program:

function a() {}
function b() { return a(); }
var c = 0;
var d = 1;
export { d };

If you run bandolier with that as the entrypoint, with default options, you get (an unformatted version of)

(function(w) {
  'use strict';
  function a() {}
  var d = 1;
  var e = { __proto__: null, d: d };
  if (w.Symbol)
    w.Object.defineProperty(e, w.Symbol.toStringTag, { value: 'Module' });
  e = w.Object.freeze(e);
  return e;
})(this);

As you'd expect, b and c are eliminated. But a is not. This is presumably because it's only dead after b has been eliminated.

I think dead code elimination should be run to a fixpoint, so that a is removed as well.