[llvm] [LoopVectorize] Make needsExtract notice scalarized instructions (PR #119720)

[John Brawn via llvm-commits]

john-brawn-arm wrote:

https://github.com/llvm/llvm-project/compare/main...john-brawn-arm:llvm-project:vectorize_osize hopefully shows what I'm talking about in the second paragraph of the description:
https://github.com/llvm/llvm-project/commit/38cadabf6eccbfe9f4c32d323a777886528fa2f8 is a work-in-progress patch to make the vectorizer use the correct cost kind with optsize. X86/small_size.ll gets worse because we incorrectly think scalarizing an instruction would insert extract instructions when it actually doesn't.
https://github.com/llvm/llvm-project/commit/ed66d16dd81e8e1cc570319a9a18fa35e75832f1 is this patch.
https://github.com/llvm/llvm-project/commit/3eae5780be459adf39ea5eebbe0429933ea15624 shows that with this patch the regression is fixed.

https://github.com/llvm/llvm-project/pull/119720