[llvm] [LoopPredication] Fix division by zero in case of zero branch weights (PR #66506)

[Duncan P. N. Exon Smith via llvm-commits]

https://github.com/dexonsmith commented:

It looks to me like the test case could probably be reduced. E.g., is the call to `@llvm.experimental.guard` necessary to trigger the bug? Do you need all of the attributes? Can you reduce the number of basic blocks?

I can't add comments to most of the file though because you've already committed an `XFAIL`ed version. (Since this is an assertion failure, does it even fail consistently when assertions are off? I could imagine it XPASS-ing on a non-assertion bot.)

https://github.com/llvm/llvm-project/pull/66506