[PATCH] D157576: [DAGCombiner] Add fold for `(and/or (icmp ne/eq X,0),(icmp ne/eq X,NegPow2))`

[Noah Goldstein via Phabricator via llvm-commits]

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Add new fold for:

  `(and/or (icmp ne/eq X,0),(icmp ne/eq X,NegPow2))`
      ->
  `(icmp ne/eq (and -X, ~(-NegPow2)), 0)`

This is really an extension of the generic pattern we already support:

  `(and/or (icmp ne/eq X,C0),(icmp ne/eq X,C1))`
      -> iff `absdif(C0, C1).ispow2`
  `(icmp ne/eq (and (sub X, smin(C0, C1)), ~absdif(C0, C1)), 0)`

But negation can be faster than adding a constant, especially for
vectors where creating a zero constant can be meaningfully faster.

Proof: https://alive2.llvm.org/ce/z/edg2N2


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D157576

Files:
  llvm/include/llvm/CodeGen/TargetLowering.h
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/icmp-pow2-diff.ll

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