[PATCH] D112611: [BasicAA] Handle known bits as ranges

[Nikita Popov via Phabricator via llvm-commits]

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BasicAA currently tries to determine that the offset is positive by checking whether all variable indices are positive based on known bits, multiplied by a positive scale. However, this is incorrect if the scale multiplication might overflow. In the modified test case the original value is positive, but may be negative after a left shift.

Fix this by converting known bits into a constant range and reusing the range-based logic, which handles overflow correctly.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D112611

Files:
  llvm/lib/Analysis/BasicAliasAnalysis.cpp
  llvm/test/Analysis/BasicAA/assume-index-positive.ll

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