pub fn postorder<'a, 'tcx>(
    body: &'a Body<'tcx>,
) -> impl Iterator<Item = (BasicBlock, &'a BasicBlockData<'tcx>)> + ExactSizeIterator + DoubleEndedIteratorExpand description
Postorder traversal of a graph.
This function creates an iterator over the Body’s basic blocks, that:
- returns basic blocks in a postorder,
 - traverses the 
BasicBlocksCFG cache’s reverse postorder backwards, and does not cache the postorder itself. 
See Postorder’s docs to learn what is postorder traversal.