The dead store notices for all the DISPATCH calls in ceval.c are false positives.  The "oparg" value is used in many of the case statements.

The dead store notices the clinic generated code all relate to "!--noptargs" which is sometimes used in generated code and sometimes not.  By always making the assignment, the clinic generator code is made less stateful (I would say "simpler" but that part of clinic.py is a mess).