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

[Simon Pilgrim via llvm-commits]

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@@ -8837,6 +8837,43 @@ static SDValue visitORCommutative(SelectionDAG &DAG, SDValue N0, SDValue N1,
   return SDValue();
 }
 
+// Fold an OR with a masked destination and a left-shifted
+// source into a shift + double-precision shift (SHRD):
+static SDValue combineOrOnSHLToSHRD(SDNode *N, SDLoc &DL, SelectionDAG &DAG) {
+  EVT VT = N->getValueType(0);
+
+  APInt Mask;
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RKSimon wrote:

```suggestion
  APInt Mask, ShiftAmount;
```

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