Sentence:  <WSD>"pessimizing</WSD> 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 optimize the program, but through excessive cleverness is doing the opposite. A few <WSD>pessimizing</WSD> compilers have been written on purpose, however, as pranks or burlesques. 
Meaning of the word marked with <WSD> tags:  To make (something) pessimal or the worst;  to make (something, such as a computer program) less efficient.