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

[David Sherwood via llvm-commits]

david-arm wrote:

> 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.

In the test you've added the original IR seems to already have a select instruction - do you also see a select in rnflow prior to GVN?

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