[II2II]

I could be wrong here since I don't develop compilers, but from my understanding many of the undefined behaviours in C are the product of not knowing what the outcome will be for edge cases or due to variations in processor architecture. In these cases, undefined behaviour was intended as a red flag for application developers. Many application developers ended up treating the undefined behaviours as deterministic provided that certain conditions were met. On the other hand, compiler developers took undefined behaviour to mean they could do what they wanted, generating different results in different circumstance, thus violating the expectations of application developers.

[robinsonb5]

I think the problem is that some behaviours are undefined where developers expect them to be implementation-defined (especially in C's largest remaining stronghold, the embedded world) - i.e. do what makes sense on this particular CPU.

Signed overflow is the classic example - making that undefined rather than implementation-defined is a decision that makes less to those of us living in today's exclusively two's-complement world than it would have done when it was taken.

It's become more of an issue in recent years as compilers started doing more advanced optimisations, which some people perceived as the compiler being "lawful evil".

What it reminds me of is that episode of Red Dwarf with Kryten (with his behavioural chip disabled) explaining why he thought it was OK to serve roast human to the crew: "If you eat chicken then obviously you'd eat your own species too, otherwise you'd just be picking on the chickens"!