In C it's usually undefined behaviour that causes the compiler to produce code that doesn't behave as expected. So not actually a compiler bug, but indistinguishable from one until you identify the UB.
I’ve found two compiler bugs, both in rustc. One was a hang, so obvious. But the other, I and the people chiming in pretty quickly figured out it was a codegen problem, as it turned out due to enabling noalias before it was ready. Just cut swaths of code until you get it down to no unsafe. It was a pretty good experience.
Delta debugging and C-reduce are your friends there. I dearly miss creduce in my language of choice... Not that compiler bugs are that frequent but when generating so much weird code I tend to trigger them bugs more frequently.
