[PATCH] D152116: [X86] Transform `(icmp eq/ne (and X, C0), (shift X, C1))` to get better constants.

[Noah Goldstein via Phabricator via llvm-commits]

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If `C0` is a mask and `C1` shifts out all the masked bits (to
essentially compare two subsets of `X`), we can arbitrarily re-order
shift as `srl` or `shl`.

We can use this re-ordering to:

1. get better `and` constants for `C0` (zero extended moves or avoid imm64).
2. covert `srl` to `shl` if `shl` will be implementable with `lea` or `add` (both of which can be preferable).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D152116

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/cmp-shiftX-maskX.ll

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