Re: Computer architects leaving Intel...

Undefined behaviour is something that is exercised at run-time.
That's why the "undefined behaviour sanitizers" insert run-time
checks.  And of course they only detect the behaviour when it is
actually exercised.

IIUC the way the run-time checks need to *prevent* undefined behavior
rather than merely detecting it, because if you do

    if (would_UB_here())
      fprintf (stderr, ...);
    maybe_do_UB_here();

the compiler is allowed to skip the `fprintf` if `maybe_do_UB_here`
does UB.  IOW the UB effect can be "retroactive".


        Stefan