[llvm] Add SD matchers and unit test coverage for ISD::VECTOR_SHUFFLE (PR #119592)

[Aidan Goldfarb via llvm-commits]

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@@ -540,6 +549,24 @@ struct BinaryOpc_match {
   }
 };
 
+/// Matches shuffle.
+template <typename T0, typename T1, typename T2> struct SDShuffle_match {
+  T0 Op1;
+  T1 Op2;
+  T2 Mask;
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AidanGoldfarb wrote:

Just implemented. I decided to go with the latter, storing the ArrayRef directly in `SDShuffle_match` as it seemed the simplest. I also replaced, in `SDShuffle_match`, the more generic `Mask.match(I->getMask())` with `std::equal(Mask.begin(), Mask.end(), I->getMask().begin())`, which was the same as the test coveraged I added in matchVecShuffle. Please let me know what you think of these changes.

https://github.com/llvm/llvm-project/pull/119592