potential simple loop optimization assistance strategy?

[Paul Schlie <schlie at comcast dot net>]

As in general it seems that as the compiler knows what it needs to know to
enable ideal loop optimization, why not simply have it assert: if it knew x,
then it could do y?  For example, if given something like:

  for (i = x; i < y; i++){ ... }

Where it may not be known statically if x < y, or what (y - x) % N may be;
therefore possibly difficult to ideally optimize.  Where then instead of
assuming something that may not be factual by default, it could generate a
warning indicating that the loop may be further optimized if it knew that
x < y, and/or (y - x) % N == 0.  Where then the programmer could then choose
to warrant it by preconditioning the loop:

  assert((x < y) && ((y - x) % 4)); // which could throw an exception.

  for ((i = x; i < y; i++){ ... }

Where although it would require run-time code, it's overhead should be
insignificant if the benefit of the optimization were truly significant;
thereby enabling the programmer to help the compiler help himself, without
the introducing potentially arbitrary behaviors, by explicitly trapping them
instead.

Where if the programmer didn't add an assertion, or explicitly enable a
potentially unsafe optimization, then the compiler should not presume
anything other than what it truly factually knows, which may include
optimizations based on whether the target traps or wraps overflow, etc.

(it may even be reasonable for the compiler to optionally insert run-time
assertions automatically to enable the deterministic trapping of conditions
which may be inconsistent with the optimizations assumptions?)