The Free On-line Dictionary of Computing (30 December 2018):

pessimising compiler

   /pes'*-mi:z"ing k*m-pi:l"r/ (Antonym of "optimising
   compiler") A compiler that produces object code that is
   worse than the straightforward or obvious hand translation.
   The implication is that the compiler is actually trying to
   optimise the program, but through excessive cleverness is
   doing the opposite.  A few pessimizing compilers have been
   written on purpose, however, as pranks or burlesques.

   (1995-02-01)