[llvm] [SLP][REVEC] Make ShuffleCostEstimator and ShuffleInstructionBuilder can vectorize vector instructions. (PR #99606)

[Han-Kuan Chen via llvm-commits]

HanKuanChen wrote:

> > > Need the tests
> > 
> > 
> > This PR and #99499 are trying to solve the same test (test3 in `llvm/test/Transforms/SLPVectorizer/revec.ll`). Do I need to merge this into #99499?
> 
> Probably, the patch is not acceptable without tests

Will merge into #99499 once this PR is good.

https://github.com/llvm/llvm-project/pull/99606