{"ast_node_type":"other","tokens":[{"end":61,"kind":"keyword","start":0,"text":"involving_tos:"}]}
    involving_tos: IndexVec<BasicBlock, Vec<(usize, usize)>>,
    /// in `opportunities` and the index in `ThreadingOpportunity::chain`.
    /// Cache the number of predecessors for each block, as we clear the basic block cache..