[clang] [llvm] [Arch64][SVE] Lower svrev_* to llvm.vector.reverse and fold svrev(svrev(x)) -> x (PR #116422)

[Benjamin Maxwell via cfe-commits]

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@@ -21962,6 +21962,35 @@ SDValue tryLowerPartialReductionToWideAdd(SDNode *N,
   return DAG.getNode(TopOpcode, DL, AccVT, BottomNode, ExtOp);
 }
 
+static SDValue foldRevInvolution(SDNode *N) {
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MacDue wrote:


Please add a doc comment that explains what this does (I know "Involution" is the mathematical term for this, but it's not a super common term). 


https://github.com/llvm/llvm-project/pull/116422