I'm not really convinced the author is correct in claiming that a one-word change opened the floodgates to optimizations on undefined behavior. In particular I

I'm not really convinced the author is correct in claiming that a one-word change opened the floodgates to optimizations on undefined behavior. In particular I think: > Careful reading will reveal that the word “Permissible” has been exchanged to “Possible”. In my opinion this change has lead C to go in a very problematic direction. is a red herring. In my opinion, the actual problematic phrase is this: > ignoring the situation completely with unpredictable results which didn't change between C89 and C99. It all comes down to what "ignoring the situation" should mean. Compiler vendors appear to interpret this to mean "ignore situations that invoke undefined behavior". Programmers who dislike optimizations based on undefined behavior appear to interpret this to mean "ignore the violation that leads to undefined behavior and treat it like conforming code". Who's right? It's ambiguous. > C compilers have taken the concept of undefined behavior even further by doing the mental acrobatics of thinking that “If undefined behavior happens, I can do want I want, So therefor I can assume that it will never happen”. I think this description is a bit uncharitable. I think a better description might be "If undefined behavior happens, there are no constraints on program behavior. Thus, if I assume that undefined behavior never happens, optimize the program based on that assumption, and that assumption is violated, the resulting program behavior is still OK because the standard imposes no rules on what the program must do when undefined behavior is invoked." > Lets take a look at signed integer overflow: Wasn't this useful for loop counters? I think this gist had more info: https://gist.github.com/rygorous/e0f055bfb74e3d5f0af20690759de5a7 https://gist.github.com/rygorous/e0f055bfb74e3d5f0af20690759... In addition, this bit: > In C89, undefined behavior is interpreted as, “The C standard doesn’t have requirements for the behavior, so you must define what the behavior is in your implementation, and there are a few permissible options”. is implementation-defined behavior, not undefined behavior. As the C89 standard notes, defining the implementation's behavior is only one of the things an implementation may do, not something it must do.