[llvm] [DFAJumpThreading] Avoid exploring the paths that never come back (PR #85505)

[Usman Nadeem via llvm-commits]

https://github.com/UsmanNadeem approved this pull request.

This patch preserves loop info while unfolding, for use in paths(...), which looks okay to me.

I don't have an knowledgeable opinion on whether the pass should preserve the loop analysis as a whole or not. I searched a little and it looks like only loop passes are required to preserve it and (even though it operates on loops) DFAJumpThreading is a function pass. Considering that this pass does transformations in a very small number of functions I would assume that the total cost to recreate the loop analysis would be reasonable.

https://github.com/llvm/llvm-project/pull/85505