[PATCH] D113216: [InstCombine] (~(a | b) & c) | ~(a | b | c) -> ~(a | b)

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec created this revision.
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This handles expressions:

`(~(a | b) & c) | ~(a | (b | c))` -> `~(a | b)`
`(~(a | b) & c) | ~(b | (a | c))` -> `~(a | b)`

The expression `(~(a | b) & c) | ~((a | b) | c)` is just an
`(~x & c) | ~(x | c)` and will be simplified without this
patch but two cases above need reassociation.

  ----------------------------------------
  define i4 @src(i4 %a, i4 %b, i4 %c) {
  %0:
    %or1 = or i4 %c, %a
    %or2 = or i4 %or1, %b
    %not1 = xor i4 %or2, 15
    %or3 = or i4 %a, %b
    %not2 = xor i4 %or3, 15
    %and2 = and i4 %not2, %c
    %or4 = or i4 %and2, %not1
    ret i4 %or4
  }
  =>
  define i4 @tgt(i4 %a, i4 %b, i4 %c) {
  %0:
    %or = or i4 %a, %b
    %not = xor i4 %or, 15
    ret i4 %not
  }
  Transformation seems to be correct!


https://reviews.llvm.org/D113216

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  llvm/test/Transforms/InstCombine/and-xor-or.ll

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