[llvm] [DAG][X86] Bitfield insertion can combine into SHL + SHRD (PR #220182)

[Simon Pilgrim via llvm-commits]

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@@ -32285,8 +32285,44 @@ static SDValue LowerFunnelShift(SDValue Op, const X86Subtarget &Subtarget,
     return DAG.getZExtOrTrunc(Res, DL, VT);
   }
 
-  if (VT == MVT::i8 || ExpandFunnel)
+  // If expanding the funnel shift is required OR the value type is unsupported
+  if (VT == MVT::i8 || ExpandFunnel) {
+    // Proceed if one operand is the result of an ISD::SHL or the node is
+    // MVT::i8
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RKSimon wrote:

This comment would be better describing the fold below

https://github.com/llvm/llvm-project/pull/220182