Avoid performing replacements when it would unrefine ranges (#117356)
Fixes https://github.com/pytorch/pytorch/issues/117268; check this issue for background.
This PR does the following:
* Do not perform a replacement if the expression we're replacing the symbol with has a less refined value range than the original. There's a little bit of trickiness around the handling for values close to INT64_MAX; when checking if a range refines another, I *only* consider the range representable in 64-bit integers. This is enough to prevent us from doing a substitution like `i0 = 10 - i1`, but it appears to still let us do the other substitutions we like, such as `i0 = i1` or `i0 = 12 * i1`
* The test above is order dependent: if we assert an equality BEFORE we have refined a range, we might be willing to do the replacement because there isn't a meaningful range. This means that it's important to mark things as sizes, before you start doing other error checking. `split_with_sizes` is adjusted accordingly. It would be good to raise an error if you get the ordering wrong, but I leave this to future work.
* It turns out this is not enough to fix AOTAutograd, because we lose the size-ness of unbacked SymInts when AOTAutograd retraces the Dynamo graph. So update deferred runtime assert insertion to also insert size-ness and value ranges annotations. Note that, in principle, it shouldn't be necessary to explicitly do the latter; these should just show up as deferred runtime asserts. That's some extra refactoring for a later day.
Signed-off-by: Edward Z. Yang <ezyang@meta.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/117356
Approved by: https://github.com/lezcano
