[llvm] [IR] Add llvm `clmul` intrinsic (PR #140301)

[Craig Topper via llvm-commits]

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@@ -5417,6 +5422,36 @@ void DAGTypeLegalizer::ExpandIntRes_FunnelShift(SDNode *N, SDValue &Lo,
   Hi = DAG.getNode(Opc, DL, HalfVT, Select3, Select2, NewShAmt);
 }
 
+void DAGTypeLegalizer::ExpandIntRes_CLMUL(SDNode *N, SDValue &Lo,
+                                                SDValue &Hi) {
+  // Values numbered from least significant to most significant.
+  SDValue LL, LH, RL, RH;
+  GetExpandedInteger(N->getOperand(0), LL, LH);
+  GetExpandedInteger(N->getOperand(1), RL, RH);
+  EVT HalfVT = LL.getValueType();
+  SDLoc DL(N);
+  
+  // CLMUL is carryless so Lo is computed from the low half
----------------
topperc wrote:

Even regular MUL computes Lo from the low halves. I don't think being carryless is relevant.

https://github.com/llvm/llvm-project/pull/140301