[llvm] [GVN] Support rnflow pattern matching and transform (PR #162259)

[Madhur Amilkanthwar via llvm-commits]

madhur13490 wrote:

Hi @fhahn  and @nikic,
This patch requires some cosmetic changes. My concern is this is to understand if this what GVN should do?

The patch is functionally correct as the rnflow application passes. However, compared to trunk this patch **regresses** the app by ~10-12% as the new select instruction the pass is generating is more constly than hoisting the load. I played around `SelectOptimize.cpp` by turning on --disable-loop-level-heuristics. That helps a bit but still ~10% regression persists.


https://github.com/llvm/llvm-project/pull/162259