[llvm] [GVN][PGO] Skip GVN if entry BlockFreq is 0 (PR #166336)

[Mircea Trofin via llvm-commits]

https://github.com/mtrofin approved this pull request.

LGTM because it sounds like the problem is understood, and the mitigation is interim and opt-in. I don't know if there's more background to this, though, so I'd wait for others to lgtm.

https://github.com/llvm/llvm-project/pull/166336