[llvm] [X86] Narrow vXi32/vXi64 usubsat to vpsubusb/vpsubusw when LHS is known to fit in fewer bits (PR #206592)

[Simon Pilgrim via llvm-commits]

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RKSimon wrote:

You should do everything you can to avoid another TLI call - we are trying to stop their proliferation at the moment.

https://github.com/llvm/llvm-project/pull/206592