[llvm] [RISCV] Refactor performCONCAT_VECTORSCombine. NFC (PR #69068)

[Luke Lau via llvm-commits]

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@@ -13867,26 +13844,25 @@ static SDValue performCONCAT_VECTORSCombine(SDNode *N, SelectionDAG &DAG,
   if (!TLI.isLegalStridedLoadStore(WideVecVT, Align))
     return SDValue();
 
+  auto [Stride, Reversed] = *BaseDiff;
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lukel97 wrote:

Yeah that's a better name, will change. (Also open to any other ideas on how we can defer creating the negate node)

https://github.com/llvm/llvm-project/pull/69068