My understanding is that terminating program requires instructions and optimizing program involves removing "useless" instructions. If your code is littered with checks and jumps, it won't be faster than code without these checks and jumps.

In other words: if you write `a[i]` in C, the compiler could either add index checks if its knows the size of `a` with `abort()` calls; or it can just compile it to single access instruction. The latter is faster. The former might be useful for debug build, I guess, but otherwise it's too slow to be acceptable for C usage.