[llvm] [DAG] Constant fold ISD::FSHL/FSHR nodes (PR #154480)

[Simon Pilgrim via llvm-commits]

================
@@ -8158,6 +8180,12 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
     }
     break;
   }
+  case ISD::FSHL:
+  case ISD::FSHR:
+    // Constant folding.
+    if (SDValue V = FoldConstantArithmetic(Opcode, DL, VT, {N1, N2, N3}))
+      return V;
+    break;
----------------
RKSimon wrote:

How about adding it to the bottom of getNode before memoization - like we do for the 2-op getNode? Keep it in visitFunnelShift as well if you can.

https://github.com/llvm/llvm-project/pull/154480