The folds the two steps into a new opcode.  In the case
of store_name/load_name, it saves one three byte
instruction, a trip around the eval-loop, two stack
mutations, a incref/decref pair, a dictionary lookup,
and an error check (for the lookup).  While it acts
like a dup followed by a store, it is implemented more
simply as a store that doesn’t pop the stack.  The
transformation is broadly applicable and occurs
thousands of times in the standard library and test suite.