[PATCH] D107766: [InstCombine] Get rid of `hasOneUses()` when swapping `lshr` and `zext`

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

Some observations for logical right-shift.
this will have a hard time with variable shift amounts.
You need to avoid creating out-of-bounds shifts, there are two obvious options:

1. https://alive2.llvm.org/ce/z/XShcju <- shift amount needs to be less than target width, and truncation should only drop zeros.
2. https://alive2.llvm.org/ce/z/QiDPV7 <- could saturate the shift amount if you know that `%x` has more leading zeros than the number of bits to be truncated

We might already have this logic somewhere, not sure.


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D107766