[llvm] [VPlan] Impl VPlan-based pattern match for ExtendedRed and MulAccRed (NFCI) (PR #113903)

[David Green via llvm-commits]

davemgreen wrote:

Hello. Let me upload some tests of examples that produce different results with this now. I think it might be that `add(sext(mul(sext, sext))` can be optimized to `add(zext(mul(sext, sext))` nowadays, or that there are multiple uses.

https://github.com/llvm/llvm-project/pull/113903