In my experience, there is no such thing as "this cannot happen" in any program with more than 100 SLOC. UB is fine as long as it's treated as "anything may hap

In my experience, there is no such thing as "this cannot happen" in any program with more than 100 SLOC. UB is fine as long as it's treated as "anything may happen", but definitely not as "cannot happen". There's other ways compilers can wring out more performance from current CPUs, than by pretending certain bit patterns will never occur as input to certain operations, and with ever-increasing SIMD widths, optimising code that definitely will happen, will become even more important.