[temac]

I dislike UB, but I do at language level. When LLVM is reached, UB can only have and only be continued to be removed, never added (from a global point of view, applying general as-if rules a compiler can always generate its own boilerplate in which it knows something can not happen, then maybe latter leverage "UB" to e.g. trim impossible paths, that are really impossible in this case -- at least barring other language level "real" UB). So are there really any drawback to internal exploitation of "UB" (maybe we should call it otherwise then) if for example the source language had none?

[pizlonator]

It is true that compilers sometimes have to have operations that have a semantics that are defined only if some conditions hold. But LLVM's and C's interpretation of what happens when the conditions don't hold is extraordinarily liberal and I'm not sure that is either beneficial or sane.

Like, LLVM tries not to add UB, but design choices it made to support optimization with UB do sometimes result in new UB being introduced, like the horror show that happens with `undef` and code versioning.

So, I think that optimizing with UB internally is fine but only if it's some kind of bounded UB where you promise something stronger than nasal demons.