> Because it is not ignoring the undefined behaviour. But it is ignoring the situation? At least, given the broader interpretation of "the situation". I unders

> Because it is not ignoring the undefined behaviour. But it is ignoring the situation? At least, given the broader interpretation of "the situation". I understand there's a narrow interpretation as well. > And sorry, the "situation" is pretty precisely scoped by "Permissible undefined behavior...". Maybe? I think I understand the argument. Will need to think on it some more... > So what can be ignored is this instance of UB, not the fact that UB exists. I think I haven't been clear enough on this - I had been using "ignore the fact that UB exists" to essentially mean "ignore this instance of UB" - i.e., carry on as if there was no UB. I had been using "ignore code paths with UB" for the broader modern-compiler-style interpretation. > Otherwise, if you're going to arbitrarily expand the scope of what the situation is, then how about "the fact that a C spec exist?". That's a situation, after all, and it is the situation you are in. Sure, it's a situation, but I don't think anyone is exactly advocating for an arbitrary expansion of the scope of a situation. "The fact that a C spec exists" is a situation, but it doesn't even pretend to have anything to do with the Standard's permissible UB. > Once again, ignoring something is not generally the same as assuming it doesn't exist. They could be the same if you assume it doesn't exist and then do nothing differently. However, if you use your assumption that it doesn't exist and act differently based on that assumption than if it did exist, then you are not ignoring the situation. I'd agree that proceeding without considering UB at all would count as ignoring something. However, I'd argue that that's not the only way to read "ignore" - dropping something from consideration, to me, certainly sounds like ignoring something. You had to choose to do so, but that doesn't make it not ignoring it. That also depends on framing, though - back to how broadly "the situation" should be read. > I doubt that "just emitting the dereference" qualifies as a documented exception to normal processing of a pointer dereference due to UB. It is exactly the same thing it does when the pointer dereference is UB, so it is just ignoring the UB. Sorry, I don't quite understand what you're trying to say with the first sentence - where did the concept of an exception to normal processing come from? The idea was that emitting a dereference is the characteristic translation behavior, so that phrase in the Standard would cover "ignoring the UB" and doing what may otherwise be expected. > Another misinterpretation that seems to be common is to interpret "the environment" in "characteristic of the environment" to include the (optimising) compiler itself. I had interpreted "the environment" as including semantics; i.e., the translation environment includes these rules for translation/program semantics, so a characteristic behavior could be "normal" semantics. This interpretation doesn't need to include the compiler since the characteristic behavior is derived from the environment, not the compiler. Looking more closely at the Standard, though, I'm not too confident in this interpretation. Perhaps "behaving during [] program execution in a documented manner characteristic of the environment" could work, though it's admittedly not what I originally had in mind, and I'm still not sure it works. ---- I do have to admit, though, that after the discussions I've had with you I'm less confident about my understanding of this. It'd be nice to talk to an actual major compiler dev or some C89 committee members about this. Feel like I had run across such a thing at some point, but I don't remember where or when.