I can't help but feel we're going to think of these as the bad old years, and that at some point we'll have migrated off of C to a language with much less UB. It's so easy to express things in C that compile but that the compiler couldn't possibly guess the intent of because C doesn't have a way to express it.

For instance, in Python you can write something like:

  result = [something(value) for value in set_object]

Because Python's set objects are unordered, it's clear that it doesn't matter in which order the items are processed, and that the order of the results doesn't matter. That opens a whole lot of optimizations at the language level that don't rely on brilliant compilers implying what the author meant. Similar code in another language with immutable data can go one step further: since something(value1) can't possibly affect something(value2), it can execute those in parallel with threads or processes or whatever else makes it go fast.

Much of the optimization of C compilers is looking at patterns in the code and trying to find faster ways to do what the author probably meant. Because C lacks the ability to express much intent compared to pretty much any newer language, they have the freedom to guess, but also have to make those kinds of inferences to get decent performance.

On the plus side, this might be a blessing in disguise like when the Hubble telescope needed glasses. We invented brilliant techniques to make it work despite its limitations. Once we fixed its problems, those same techniques made it perform way better than originally expected. All those C compiler optimizations, applied to a language that's not C, may give us superpowers.