[llvm] [ISel] Introduce llvm.clmul[rh] intrinsics (PR #168731)

[Craig Topper via llvm-commits]

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@@ -8301,6 +8301,46 @@ SDValue TargetLowering::expandFunnelShift(SDNode *Node,
   return DAG.getNode(ISD::OR, DL, VT, ShX, ShY);
 }
 
+SDValue TargetLowering::expandCLMUL(SDNode *Node, SelectionDAG &DAG) const {
+  SDLoc DL(Node);
+  EVT VT = Node->getValueType(0);
+  SDValue X = Node->getOperand(0);
+  SDValue Y = Node->getOperand(1);
+  unsigned BW = VT.getScalarSizeInBits();
+
+  if (VT.isVector() && (isOperationLegalOrCustomOrPromote(
+                            Node->getOpcode(), VT.getVectorElementType()) ||
+                        !isOperationLegalOrCustom(ISD::VSELECT, VT)))
+    return DAG.UnrollVectorOp(Node);
+
+  SDValue Res = DAG.getConstant(0, DL, VT);
+  switch (Node->getOpcode()) {
+  case ISD::CLMUL: {
+    for (unsigned I = 0; I < BW; ++I) {
+      SDValue SignMask = DAG.getConstant(APInt::getOneBitSet(BW, I), DL, VT);
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topperc wrote:

SignMask is not a good name

https://github.com/llvm/llvm-project/pull/168731