[llvm] [LoopUnroll] Fix assert fail on zeroed branch weights (PR #165938)

[Joel E. Denny via llvm-commits]

jdenny-ornl wrote:

> @jdenny-ornl It looks like there are other, similar failures reported, including #165998 so a more comprehensive fix may be needed.
> 
> As this has been crashing for a few days now, it may be good to revert back to a known good state

Thanks for suggesting that.  I'm looking now.  If I cannot track this down within a few hours, I will start rolling back the patch series.  Is that reasonable?

https://github.com/llvm/llvm-project/pull/165938