[llvm] [RISCV] Undo unprofitable zext of icmp combine (PR #134306)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Can this be done in DAGCombine or does it need something that only codegen prepare can do?

It can be done in DAGCombine, I can move it over if that's preferred

https://github.com/llvm/llvm-project/pull/134306