[PATCH] D109273: [X86] Fold (and (or (xor X, -1), Y), Z) -> PTERNLOG Z, Y, X, 0xD0

Sun Sep 5 05:29:39 PDT 2021

craig.topper added a comment.

In D109273#2983998 <https://reviews.llvm.org/D109273#2983998>, @pengfei wrote:

> In D109273#2983658 <https://reviews.llvm.org/D109273#2983658>, @RKSimon wrote:
>
>> We do most TERNLOG matching inside X86DAGToDAGISel::tryVPTERNLOG (which has a 'FIXME: Handle inverted inputs?' comment) - might it be possible to handle this there?
>
> As far as I learnt it, it's hard to do so. We have 3 difficulties:
>
> 1. We need a new `ORNP` node for pre-processing and the logic in `tryVPTERNLOG`, but `ORNP` isn't a canonical node like `AND`, `ANDNP` etc. that can be used for permutation;
> 2. Even we have a `ORNP`, we have to change the logic to prioritise `ORNP` over other nodes and ignore the permutation math;
> 3. Even we achieved 1 and 2, we have to change `matchVPTERNLOG`, because it assumes the operands are commutable while it's not true for this combine;

In matchVPTERNLOG, why can’t we just check if each input is a single use xor with -1 after calculating the immediate and then change then change the mask appropriately. No new nodes needed

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https://reviews.llvm.org/D109273