[llvm] [LV] Support multiplies by constants when forming scaled reductions. (PR #161092)

[David Sherwood via llvm-commits]

david-arm wrote:

Does this work when the multiply has `nsw`? I tried modifying `@src2` and `@tgt2` in your alive example by adding `nsw` to the `mul` and the alive seems to fail.

https://github.com/llvm/llvm-project/pull/161092