We compile with -Werror, so triple checking compiler warnings isn't required, it won't even compile if there are any warnings.

At one point we were using an older version of GCC, and an older version of clang and both would miscompile different pieces of the code with optimisations turned on. A lot of things have been fixed since then. There were a few cases where the code that was written was undefined in the standard and the compiler could do as they pleased, but there were quite a few cases where that wasn't the case. The places where it was undefined we fixed, the others we never did figure out what was going on. Newer versions of GCC/clang did the right thing, so we finally upgraded, solving a whole lot of the problems.

At this point in time it just doesn't make sense for us to compile with optimisations turned on, so why risk it?