[PATCH] D92069: [NFC] [TargetRegisterInfo] add one use check to lookThruCopyLike.

[Nemanja Ivanovic via Phabricator via llvm-commits]

nemanjai added a comment.

I don't see an issue in providing two functions to achieve the two different goals:

  lookThruCopyLike()           // Look through a chain of copies.
  lookThruSingleUseCopyChain() // Look through a chain of copies, checking that each def has a single use.

Also, I am a little curious about what this change is meant to accomplish. The name of the introduced `bool` parameter is `AllDefHaveOneUser` yet we don't actually check all defs - we only check the final one that we are returning. So it is presumably possible to have something like this (all regs virtual):

  %1 = ...
  %2 = SUBREG_TO_REG %1, ...
  %3 = COPY %2
  %4 = SUBREG_TO_REG %2
  %5 = COPY %4
  %6 = COPY %4
  %7 = <some use of %4>
  %8 = <some use of %5>
  %9 = <some use of %6>

Running `lookThruCopyLike()` on `%9` will presumably correctly return `%1` and if a `bool` argument is passed, it will be set to `true`. I would argue that this is a surprising result since I would expect `AllDefHaveOneUser` to mean that all the definitions traversed (`%9, %6, %4, %2, %1`) have a single use. But this is clearly not the case. Am I just missing something?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D92069/new/

https://reviews.llvm.org/D92069