[llvm] [SCEV] Fold (C1 * A /u C2) -> A /u (C2 /u C1), if C2 > C1. (PR #157656)

[Mikael Holmen via llvm-commits]

mikaelholmen wrote:

Yes I understand.

I think something breaks in LSR in llc for our out-of-tree target with the patch, but I'm not sure what and even with the reduced C reproducer I have it's hard to understand. And the code diff I see after LSR in llc does not appear if I run LSR alone in opt so there apparently must be some state present from earlier passes for the difference to appear.

We'll continue digging next week but unfortunately the whole team is off Monday-Tuesday so progress from us (if any) will probably not happen until second half of next week.

Hopefully someone else can beat us to it and come up with a reproducer earlier.

https://github.com/llvm/llvm-project/pull/157656