[DAG] Matched FixedWidth pattern for ISD::AVGFLOORU (#84903)

Fixes: #84749

Author: Sh0g0-1758

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -2820,6 +2820,23 @@ SDValue DAGCombiner::visitADDLike(SDNode *N) {
   return SDValue();
 }
 
+// Attempt to form avgflooru(A, B) from (A & B) + ((A ^ B) >> 1)
+static SDValue combineFixedwidthToAVGFLOORU(SDNode *N, SelectionDAG &DAG) {
+  const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+  SDValue N0 = N->getOperand(0);
+  EVT VT = N0.getValueType();
+  SDLoc DL(N);
+  if (TLI.isOperationLegal(ISD::AVGFLOORU, VT)) {
+    SDValue A, B;
+    if (sd_match(N, m_Add(m_And(m_Value(A), m_Value(B)),
+                          m_Srl(m_Xor(m_Deferred(A), m_Deferred(B)),
+                                m_SpecificInt(1))))) {
+      return DAG.getNode(ISD::AVGFLOORU, DL, VT, A, B);
+    }
+  }
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitADD(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
@@ -2835,6 +2852,10 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
   if (SDValue V = foldAddSubOfSignBit(N, DAG))
     return V;
 
+  // Try to match AVGFLOORU fixedwidth pattern
+  if (SDValue V = combineFixedwidthToAVGFLOORU(N, DAG))
+    return V;
+
   // fold (a+b) -> (a|b) iff a and b share no bits.
   if ((!LegalOperations || TLI.isOperationLegal(ISD::OR, VT)) &&
       DAG.haveNoCommonBitsSet(N0, N1))

llvm/test/CodeGen/AArch64/hadd-combine.ll

@@ -859,6 +859,18 @@ define <4 x i32> @urhadd_v4i32(<4 x i32> %x) {
   ret <4 x i32> %r
 }
 
+define <8 x i16> @uhadd_fixedwidth_v4i32(<8 x i16> %a0, <8 x i16> %a1)  {
+; CHECK-LABEL: uhadd_fixedwidth_v4i32:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    uhadd v0.8h, v0.8h, v1.8h
+; CHECK-NEXT:    ret
+  %and = and <8 x i16> %a0, %a1
+  %xor = xor <8 x i16> %a0, %a1
+  %srl = lshr <8 x i16> %xor, <i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1>
+  %res = add <8 x i16> %and, %srl
+  ret <8 x i16> %res
+}
+
 declare <8 x i8> @llvm.aarch64.neon.shadd.v8i8(<8 x i8>, <8 x i8>)
 declare <4 x i16> @llvm.aarch64.neon.shadd.v4i16(<4 x i16>, <4 x i16>)
 declare <2 x i32> @llvm.aarch64.neon.shadd.v2i32(<2 x i32>, <2 x i32>)