[llvm] [X86] Enforce strict pre-legalization to combine in scalarizeExtEltFP (PR #117681)

[Phoebe Wang via llvm-commits]

https://github.com/phoebewang commented:

This looks better than https://github.com/llvm/llvm-project/pull/117682

Please add the example as regression test.

https://github.com/llvm/llvm-project/pull/117681