[PATCH] D55935: [X86][SSE] Canonicalize OR(AND(X, C), AND(Y, ~C)) -> OR(AND(X, C), ANDNP(C, Y))

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

Would we better off doing a generic DAGCombine into the optimal xor-and-xor (aka, masked merge) pattern?
(x & C) | (y & ~C) --> ((x ^ y) & C) ^ y

That should allow load folding of the constant, so it never burns a register to hold the constant.

We weren't allowed to do that transform with a variable mask in D46814 <https://reviews.llvm.org/D46814> because:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20180528/556578.html

But I think that's ok with a constant mask. We can't accidentally dynamically access an undef value when the mask is a constant.


Repository:
  rL LLVM

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  https://reviews.llvm.org/D55935/new/

https://reviews.llvm.org/D55935