• trace 🔒
    This is the heart of the liveness computation. For each variable X that requires a liveness computation, it walks over all the uses of X and does a reverse depth-first search (“trace”) through the MIR. This search stops when we find a definition of that variable. The points visited in this search is the USE-LIVE set for the variable; of those points is added to all the regions that appear in the variable’s type.