[PATCH] D140255: [LoopUnrollAndJam] Visit phi operand dependencies in post-order

[Joshua Cao via Phabricator via llvm-commits]

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Fixes https://github.com/llvm/llvm-project/issues/58565

The previous implementation visits operands in pre-order, but this does
not guarantee an instruction is visited before its uses. This can cause
instructions to be copied in the incorrect order. For example:

  a = ...
  b = add a, 1
  c = add a, b
  d = add b, a

Pre-order visits does not guarantee the order in which `a` and `b` are
visited. LoopUnrollAndJam may incorrectly insert `b` before `a`.

This patch implements post-order visits. By visiting dependencies first,
we guarantee that an instruction's dependencies are visited first.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140255

Files:
  llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp
  llvm/test/Transforms/LoopUnrollAndJam/dependencies_visit_order.ll

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