[llvm] [SLP]Fix fmul/fadd fusion costs and retry FMA seeds after all blocks (PR #226117)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> LGTM, I believe it has to be rebased one more time to update checks in a test added in #226609
> 
> Side Q: I was a bit surprised to see, that SLPVectorizer/X86/redux-feed-buildvector.ll didn't require an CHECKs update with this patch. I assume it relates to ttps://github.com/[/pull/225367](https://github.com/llvm/llvm-project/pull/225367) where `fast` got replaced with `reassoc nnan ninf nsz arcp afn`. I expect, that with `fast` current main would still vectorize the sample and with the patch it will stop doing so. Is it desired behaviour for X86?

Yes, updated the test to drop contract attribute to keep testing what it was intended for originally

https://github.com/llvm/llvm-project/pull/226117