Function cleanup_kinds 

pub(crate) fn cleanup_kinds(
    mir: &Body<'_>,
    nop_landing_pads: &DenseBitSet<BasicBlock>,
) -> IndexVec<BasicBlock, CleanupKind>

MSVC requires unwinding code to be split to a tree of funclets, where each funclet can only branch to itself or to its parent. Luckily, the code we generates matches this pattern. Recover that structure in an analyze pass.