[PATCH] D87832: [IndVars] Remove monotonic checks with unknown exit count

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp:2375
+
+  // The predicate must be monotonic.
+  switch (Pred) {
----------------
reames wrote:
> lebedev.ri wrote:
> > It might be good to hoist that into some ICmp method,
> > this is at least the second such code block.
> It really looks like at least part of this logic can be replaced with SE->isMonotonicPredicate(LHSS, Pred, IncreasingOut).  In particular, I think that covers all your tricky overflow logic and does so more generally.
> 
> If I'm right about that, you can also generalize this.  Consider:
> - If is monotonic, and proven start == proven end (without caring which direction proved), the condition is invariant for the iterations executed.  
> 
> This is starting to look a lot like it might belong in isLoopInvariantPredicate.  It seems to be a generalization of the logic there.
It does not. It requires proved nsw/nuw flags. We are OK if the last iteration actually does overflow, but in this case we exit the loop before our check.


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  https://reviews.llvm.org/D87832/new/

https://reviews.llvm.org/D87832