[llvm] [DAG] Recognise AVGFLOOR (((A >> 1) + (B >> 1)) + (A & B & 1)) patterns (PR #169644)

[Simon Pilgrim via llvm-commits]

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@@ -3154,19 +3154,31 @@ SDValue DAGCombiner::visitADDLike(SDNode *N) {
 }
 
 // Attempt to form avgfloor(A, B) from (A & B) + ((A ^ B) >> 1)
+// Attempt to form avgfloor(A, B) from ((A >> 1) + (B >> 1)) + (A & B & 1)
 SDValue DAGCombiner::foldAddToAvg(SDNode *N, const SDLoc &DL) {
   SDValue N0 = N->getOperand(0);
   EVT VT = N0.getValueType();
   SDValue A, B;
 
+  // FIXME: m_ReassociatableAdd can't handle m_Value/m_Deferred mixing.
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RKSimon wrote:

It looks like @bermondd is working on this at #170061 (new contributors not being able to assign reviewers is REALLY annoying).

https://github.com/llvm/llvm-project/pull/169644