// combined "Peeps + ConstProp + GVN" solver (extended version of the one in Combining Analyses, Combining Optimizations 7.3.2)
//
// returns isomorphic node (might be the same node).
Node* peephole_node(Optimizer* opt, Node* n) {
  Node* k;
  bool progress = false;
  
  // potential mutations from ideal() means we need to get rehash.
  hashset_remove(opt->gvn_nodes, n);
  
  // iterative convergence (rewrite peepholes):
  //   we'll settle on a fixpoint and be happy.
  while (k = ideal(n), k) { n = k; }

  // tries to deduce the value of an op based on the
  // types of the inputs, if both inputs were deduced
  // constant we might be constant and if both inputs were
  // ranges we might infer extra data if not a constant.
  Type* t = value(opt, n);
  k = try_as_const(opt, n, t);
  if (k) { return k; }

  // this is ops which replace the node with a direct
  // input (x + 0 => x), because of this we don't need
  // to rerun const prop since they don't change nodes
  // just referenced existing ones (which are either in
  // normal form or waiting on the worklist).
  //
  // identity(opt, n) will always return a node, either n
  // or a direct replacement
  k = identity(opt, n);
  if (k != n) { return k; }

  // GVN, we literally just place nodes into a hash table.
  // no need to rerun it's ruleset if it's just referencing
  // an existing node.
  k = hashset_get(opt->gvn_nodes, n);
  if (k) {
    hashset_put(opt->gvn_nodes, k);
    return k;
  }

  return n;
}