#CReduce is an impressive piece of software. If you're not familiar with it: you give it a C file that exhibits a bug, or some other interesting property (you specify a shell script that returns 0 only if the file is interesting). It then proceeds to shorten the file considerably.

I had a 10 kLOC file on which my analyzer showed buggy behaviour, CReduce shrinked it by 99.6 % 😅 (so far)