I worked a compiler backend for 5 years. Despite the insane amount of testing, fuzzing, standards tests, etc that we did, there were always bugs coming in, and

I worked a compiler backend for 5 years. Despite the insane amount of testing, fuzzing, standards tests, etc that we did, there were always bugs coming in, and not always in code that looked dodgy. Sometimes an optimization interacts with another in JUST the right way to cause incorrect code to get generated. Honestly, I'm surprised that I haven't run into more of them in the wild.