<i>the Standard imposes no requirements</i> on undefined behaviour. The list you quoted is informative, to give us a basic idea what to possibly expect, not a list of things we may rely upon.<p>Rejecting translation outright aside, undefined behaviour is the strongest language the standard uses for illegal constructs. I do not see it as undefined in the sense of lacking a common definition (eg is 0 a natural number, or not) but something that is undefined the way 0&#x2F;0 is undefined in maths.<p>In a way, the criticized behaviour of aggressively opimizing compilers is a consequence of <i>ignoring the situation completely with unpredictable results</i>. It&#x27;s the same line of reasoning that makes <i>restrict</i> useful, just on steroids.