message: Fix block id assignment
  Summary: we can't use `m_blocks.size()` because we may have deleted some blocks from the cfg. Leaving holes and double assigned ids
diff: @@ -1187,7 +1187,10 @@ ControlFlowGraph::~ControlFlowGraph() {
  }
  Block* ControlFlowGraph::create_block() {
  - size_t id = m_blocks.size();
  + const auto& rbegin = m_blocks.rbegin();
  + // Choose the next largest id. Note that we can't use m_block.size() because
  + // we may have deleted some blocks from the cfg.
  + size_t id = (rbegin == m_blocks.rend()) ? 0 : (rbegin->first + 1);
  Block* b = new Block(this, id);
  m_blocks.emplace(id, b);
  return b;
  