[PATCH] D145230: [ScalarEvolution] Apply loop guards against min/max for its arguments

[Dmitry Makogon via Phabricator via llvm-commits]

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This adds following rules for rewriting in `ScalarEvolution::applyLoopGuards`:

- `min(a, b) >(=) c   ->   a >(=) c && b >(=) c`
- `max(a, b) <(=) c   ->   a <(=) c && b <(=) c`

This allows us to apply loop guards against min/max calls for its arguments.
For example, imagine there is a loop guard `min(a, b) >= c` and loop IV uses `min(a, zext(b))`.
Previously the guard would give us a rewrite rule `min(a, b) -> max(c, min(a, b))` and it wouldn't allow us to apply it to `min(a, zext(b))`, which is the same as `zext(min(a, b))`.

Now we apply the guards against min/max-s for its arguments and in the above example we would have two rules:

- `a -> max(c, a)` and
- `b -> max(c, b)`.

This way we can apply the rule for `b `in `min(a, zext(b))` and actually make the guard useful.


https://reviews.llvm.org/D145230

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info-rewrite-expressions.ll

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