[llvm] Matched some basic ISD::AVGFLOORU patterns (PR #84903)

[Simon Pilgrim via llvm-commits]

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@@ -2826,6 +2826,36 @@ SDValue DAGCombiner::visitADDLike(SDNode *N) {
   return SDValue();
 }
 
+// Attempt to form ext(avgflooru(A, B)) from add(and(A, B), lshr(xor(A, B), 1))
+static SDValue combineFixedwidthToAVG(SDNode *N, SelectionDAG &DAG) {
+  assert(N->getOpcode() == ISD::ADD && "ADD node is required here");
+  SDValue And = N->getOperand(0);
+  SDValue Lshr = N->getOperand(1);
+  if (And.getOpcode() != ISD::AND || Lshr.getOpcode() != ISD::SRL)
+    return SDValue();
+  SDValue Xor = Lshr.getOperand(0);
+  if (Xor.getOpcode() != ISD::XOR)
+    return SDValue();
+  SDValue And1 = And.getOperand(0);
+  SDValue And2 = And.getOperand(1);
+  SDValue Xor1 = Xor.getOperand(0);
+  SDValue Xor2 = Xor.getOperand(1);
+  if(Xor1 != And1 && Xor2 != And2)
+    return SDValue();
+  // Is the right shift using an immediate value of 1?
+  ConstantSDNode *N1C = isConstOrConstSplat(Lshr.getOperand(1));
+  if (!N1C || N1C->getAPIntValue() != 1)
+    return SDValue();
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RKSimon wrote:

We should be able to vastly simplify this matching code by using the sd_match pattern helper - #84759 will introduce this very soon, but if you're willing to try it you can just add the include and using lines from the patch you should be able to use it here?

https://github.com/llvm/llvm-project/pull/84903