[llvm] [RISCV] Prefer VLS over VLA if costs are equal (PR #100564)

[Philip Reames via llvm-commits]

preames wrote:

> Looks maybe LSR related? Disabling LSR has the same number of instructions in both loops.

First impression is this is a deficiency in lsr term-folding.  If you want to file a separate bug for this, I can take a look and see if it's easy to fix.  My initial guess is that we're struggling to prove the step non-zero given the slightly complicate expression there.  

https://github.com/llvm/llvm-project/pull/100564