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

[Nikita Popov via llvm-commits]

nikic wrote:

I don't think this change makes sense, even on a temporary basis. If MDA in GVN is slow for some cases, that's because a complexity cutoff is missing or has a too high value. MSSA doesn't really fundamentally change the picture (especially as GVN needs to scan MemoryUses). It still needs to stop at some point, though the cutoffs are going to be different.

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