[PATCH] D149132: [LICM] Reassociate & hoist add expressions

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: anna, nikic, lebedev.ri, skatkov, danilaml, aleksandr.popov.
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This patch allows LICM to reassociate and hoist following expressions:

  loop:
    %sum = add nsw %iv, %C1
    %cmp = icmp <signed pred> %sum, C2

where `C1` and `C2` are loop invariants. The reassociated version looks like

  preheader:
    %inv_sum = C2 - C1
  ...
  loop:
    %cmp = icmp <signed pred> %iv, %inv_sum

In order to prove legality, we need both initial addition and the newly created subtraction
to happen without overflow.


https://reviews.llvm.org/D149132

Files:
  llvm/lib/Transforms/Scalar/LICM.cpp
  llvm/test/Transforms/LICM/hoist-add-sub.ll

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