[llvm] [LoopRotate] Rotate loop if this makes exit count computable (PR #162654)

[Marek Sedláček via llvm-commits]

mark-sed wrote:

@nikic I have enabled the computability check only for LPM2 to avoid the SVEC computation you mentioned. Hopefully this will lower the compile time impact.

https://github.com/llvm/llvm-project/pull/162654