[DAG] Matched Fixedwidth Pattern for ISD::AVGCEILU (llvm#85031)

Fixes: llvm#84753

Author: Sh0g0-1758

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -2529,6 +2529,23 @@ static SDValue foldAddSubBoolOfMaskedVal(SDNode *N, SelectionDAG &DAG) {
   return DAG.getNode(IsAdd ? ISD::SUB : ISD::ADD, DL, VT, C1, LowBit);
 }
 
+// Attempt to form avgceilu(A, B) from (A | B) - ((A ^ B) >> 1)
+static SDValue combineFixedwidthToAVGCEILU(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::AVGCEILU, VT)) {
+    SDValue A, B;
+    if (sd_match(N, m_Sub(m_Or(m_Value(A), m_Value(B)),
+                          m_Srl(m_Xor(m_Deferred(A), m_Deferred(B)),
+                                m_SpecificInt(1))))) {
+      return DAG.getNode(ISD::AVGCEILU, DL, VT, A, B);
+    }
+  }
+  return SDValue();
+}
+
 /// Try to fold a 'not' shifted sign-bit with add/sub with constant operand into
 /// a shift and add with a different constant.
 static SDValue foldAddSubOfSignBit(SDNode *N, SelectionDAG &DAG) {
@@ -3849,6 +3866,10 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
   if (SDValue V = foldAddSubOfSignBit(N, DAG))
     return V;
 
+  // Try to match AVGCEILU fixedwidth pattern
+  if (SDValue V = combineFixedwidthToAVGCEILU(N, DAG))
+    return V;
+
   if (SDValue V = foldAddSubMasked1(false, N0, N1, DAG, SDLoc(N)))
     return V;
 

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

@@ -329,9 +329,17 @@ define <8 x i16> @hadds_i_undef(<8 x i16> %t, <8 x i16> %src1) {
   ret <8 x i16> %result
 }
 
-
-
-
+define <8 x i16> @sub_fixedwidth_v4i32(<8 x i16> %a0, <8 x i16> %a1)  {
+; CHECK-LABEL: sub_fixedwidth_v4i32:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    urhadd v0.8h, v0.8h, v1.8h
+; CHECK-NEXT:    ret
+  %or = or <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 = sub <8 x i16> %or, %srl
+  ret <8 x i16> %res
+}
 
 define <8 x i16> @rhaddu_base(<8 x i16> %src1, <8 x i16> %src2) {
 ; CHECK-LABEL: rhaddu_base: