[PATCH] D146464: [LSR] Fix "new use of poison" problem in lsr-term-fold

[Philip Reames via Phabricator via llvm-commits]

reames created this revision.
reames added reviewers: nikic, eopXD.
Herald added subscribers: StephenFan, bollu, hiraditya, mcrosier.
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This models the approach used in LFTR.  The short summary is that we need to prove the IV is not dead first, and then we have to either prove the poison flag is valid after the new user or delete it.

There is one key differences between this and LFTR, specifically, I allow a non-concrete start to the IV.  The goal of LFTR is to canonicalize and IVs with constant starts are canonical, so the very restrictive definition there is mostly okay.  Here on the other hand, we're explicitly moving *away* from the canonical form, and thus need to handle non-constant starts.

Note that this analysis is quite expensive compile time wise.  I have made no effort to optimize (yet).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D146464

Files:
  llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
  llvm/test/Transforms/LoopStrengthReduce/lsr-term-fold.ll

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