[PATCH] D99424: [BasicAA] Be more careful with modulo ops on VariableGEPIndex.

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

Okay, I've finally gotten around to looking into this in more detail. Because thinking about this really fries my brain, I ended up modelling this in alive2 (hopefully correctly...)

https://alive2.llvm.org/ce/z/HYBxGs This is the general case and shows that we only need nsw flags on the arithmetic, rather than both nuw and nsw. This makes sense, as all the arithmetic involved is signed.

https://alive2.llvm.org/ce/z/qXicaB This shows that it is indeed safe to always take the power-of-2 portion of the scale, even if the arithmetic is not nsw.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D99424/new/

https://reviews.llvm.org/D99424