[PATCH] D112108: [InstCombine] Fold `(a & ~b) & ~c` to `a & ~(b | c)`

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec added a comment.

In D112108#3077962 <https://reviews.llvm.org/D112108#3077962>, @spatel wrote:

> I forgot to mention it during the review, but we should always have these kinds of bitwise logic folds apply to the Demorgan'ized sibling form too (and this fold itself is just reassociation + Demorgan):
> 3888de9507c7 <https://reviews.llvm.org/rG3888de9507c78d3d77a4f565f30a3bf1b2fce690>

Thanks Sanjay! I now wander if a next testcase I am looking at needs a pattern as I wanted to add to `visitOr`, because it also looks like a more complex case of reassociation:

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

We currently cannot simplify it.

  define i32 @or_not_and(i32 %a, i32 %b, i32 %c) {
    %or1 = or i32 %a, %b
    %not1 = xor i32 %or1, -1
    %and1 = and i32 %not1, %c
    %or2 = or i32 %a, %c
    %not2 = xor i32 %or2, -1
    %and2 = and i32 %not2, %b
    %or3 = or i32 %and1, %and2
    ret i32 %or3
  }


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https://reviews.llvm.org/D112108