[llvm] [SimpleLoopUnswitch] Don't use BlockFrequencyInfo to skip cold loops (PR #159522)

[Luke Lau via llvm-commits]

lukel97 wrote:

> This only works if the whole function is cold, not if there is a cold loop inside a hot function, right?

Yeah I briefly touched on that in the PR description. I hope that function level granularity is good enough for whatever case motivated the initial patch. At least it seems to be good enough for the test case that was included with it, [llvm/test/Transforms/PhaseOrdering/unswitch-cold-func.ll](https://github.com/llvm/llvm-project/pull/159522#diff-89d1a06d66e24dde89e8d3805d09485fe7691b7dab9d3d924624f252bb5cb7c5)

https://github.com/llvm/llvm-project/pull/159522