This pass was introduced in 2013 and has not been enabled by default (or even been part of the pass pipeline) since that time. As far as I know, there is no active work on it, and no path towards default enablement. There is a long list of miscompiles reported against this pass (most of https://github.com/llvm/llvm-project/issues?q=is%3Aissue+is%3Aopen+loop-reroll), which have remained unfixed for years.
In the interest of not keeping unused code in tree, this removes the pass entirely. Should interest in default enablement for this pass appear, it would need a from-scratch review anyway.