[PATCH] D147668: [RFC][X86 isel] Remove lane requirement from lowerShuffleAsUNPCKAndPermute

[Han Zhu via Phabricator via llvm-commits]

zhuhan0 added inline comments.


================
Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:13559
+  size_t NumUndefs = 0;
+  SmallSet<int, 32> UniqueMask;
+  for (int Elt : Mask) {
----------------
RKSimon wrote:
> We can probably avoid the SmallSet by using std::optional?
> ``` 
> std::optional<int> UniqueElt;
> for (int Elt : Mask) {
>   if (Elt == SM_SentinelUndef) {
>       NumUndefs++;
>       continue;
>   }
>   if (UniqueElt.has_value() && UniqueElt.value() != Elt)
>     return false;
>   UniqueElt = Elt;
> }
> return NumUndefs <= Mask.size() / 2 && UniqueElt.has_value();
> ```
> (untested)
Sweet. This works!


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D147668/new/

https://reviews.llvm.org/D147668