[PATCH] D149027: [X86] Add peephole to convert `(Cmp Op32/Op64, Imm8)` -> `(Cmp Op16/Op8, Imm8)`

[Noah Goldstein via Phabricator via llvm-commits]

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This saves a bit of codesize.

This is valid if the sign-flags are not used:

- eq : https://alive2.llvm.org/ce/z/KUtebW
- ne : https://alive2.llvm.org/ce/z/fT0hBt
- ult: https://alive2.llvm.org/ce/z/s5FEYL
- ugt: https://alive2.llvm.org/ce/z/jaq6oS
- uge: https://alive2.llvm.org/ce/z/bYzJ3p
- ule: https://alive2.llvm.org/ce/z/8QXTiC


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D149027

Files:
  llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
  llvm/test/CodeGen/X86/combine-movmsk.ll
  llvm/test/CodeGen/X86/vector-reduce-and-cmp.ll
  llvm/test/CodeGen/X86/vector-reduce-and-scalar.ll

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