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

[Elvis Wang via llvm-commits]

ElvisWang123 wrote:

> Does this fail for you under aarch64? I didn't look into what might be going on - it was strange that it was trying to do any vectorization with fp128 long doubles. https://godbolt.org/z/hP4eYooTK

Hi @davemgreen 
I am not sure I understood correctly.
Did you mean that the cost model should return InvalidCost or the loop vectorizer should not try to vectorize loop entirely when the type is fp128?

I indeed found an assertion failure on this case because the cost of `fmuladd` from vplan-based cost model  misaligned to the legacy one. Will open other PR or update this PR to fix the cost of `fmuladd` in vplan-based cost model.

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