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Hi Geoff, Thanks for the detailed reproduction instruction -- they were very helpful, and I can now see the bug. Generally, I think (2) is the better solution. It should be up to SCEVExpander to keep its state consistent. The fact that we're trying to optimize instructions as we insert them makes that trickier, but I still think that is the right invariant to have. I don't see why (2)

Hi All, I've run into what appears to be a bug in ScalarEvolution, but I'm not sure if it is instead caused by me missing an implicit assumption between LSR and SCEV. This issue is caused by the change D18001 <http://reviews.llvm.org/D18001> , which is an attempt to increase SCEV-inserted instruction re-use by picking a more canonical insertion position in the case where a new