[polly] [InstCombine] Canonicalise SextADD + GEP (PR #69581)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

It's not at all clear to me that this is a generally profitable transform. Just based on the test changes here, loopflatten.ll is an obvious regression (loop no longer flattened), while induction.ll also looks like a regression to me.

This is also a regression on the simple instruction count heuristic, as we go from add+sext+gep to 2*sext+2*gep. Possibly what you want to do is limit this to the case where the RHS of the add is a constant, so the sext folds away?

https://github.com/llvm/llvm-project/pull/69581