'Insert del statements for each variable.
Returns a 2-tuple of (variable definition map, variable deletion map)
which indicates variables defined and deleted in each block.
The algorithm avoids relying on explicit knowledge on loops and
distinguish between variables that are defined locally vs variables that
come from incoming blocks.
We start with simple usage (variable reference) and definition (variable
creation) maps on each block. Propagate the liveness info to predecessor
blocks until it stabilize, at which point we know which variables must
exist before entering each block. Then, we compute the end of variable
lives and insert del statements accordingly. Variables are deleted after
the last use. Variable referenced by terminators (e.g. conditional
branch and return) are deleted by the successors or the caller.'

def _insert_var_dels(self):

    vlt = self.func_ir.variable_lifetime
    self._patch_var_dels(vlt.deadmaps.internal, vlt.deadmaps.escaping)
