[AArch64] turn extended vecreduce bigger than v16i8 into udot/sdot

We can do this by breaking vecreduce into v16i8 vectors generating udot/sdot and concatenating them.

Differential Revision: https://reviews.llvm.org/D141693

Author: Zain Jaffal

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -14805,6 +14805,9 @@ static SDValue performVecReduceAddCombineWithUADDLP(SDNode *N,
 // Turn a v8i8/v16i8 extended vecreduce into a udot/sdot and vecreduce
 //   vecreduce.add(ext(A)) to vecreduce.add(DOT(zero, A, one))
 //   vecreduce.add(mul(ext(A), ext(B))) to vecreduce.add(DOT(zero, A, B))
+// If we have vectors larger than v16i8 we extract v16i8 vectors,
+// Follow the same steps above to get DOT instructions concatenate them
+// and generate vecreduce.add(concat_vector(DOT, DOT2, ..)).
 static SDValue performVecReduceAddCombine(SDNode *N, SelectionDAG &DAG,
                                           const AArch64Subtarget *ST) {
   if (!ST->hasDotProd())
@@ -14830,7 +14833,9 @@ static SDValue performVecReduceAddCombine(SDNode *N, SelectionDAG &DAG,
     return SDValue();
 
   EVT Op0VT = A.getOperand(0).getValueType();
-  if (Op0VT != MVT::v8i8 && Op0VT != MVT::v16i8)
+  bool IsValidElementCount = Op0VT.getVectorNumElements() % 8 == 0;
+  bool IsValidSize = Op0VT.getScalarSizeInBits() == 8;
+  if (!IsValidElementCount || !IsValidSize)
     return SDValue();
 
   SDLoc DL(Op0);
@@ -14841,13 +14846,65 @@ static SDValue performVecReduceAddCombine(SDNode *N, SelectionDAG &DAG,
   else
     B = B.getOperand(0);
 
-  SDValue Zeros =
-      DAG.getConstant(0, DL, Op0VT == MVT::v8i8 ? MVT::v2i32 : MVT::v4i32);
+  unsigned IsMultipleOf16 = Op0VT.getVectorNumElements() % 16 == 0;
+  unsigned NumOfVecReduce;
+  EVT TargetType;
+  if (IsMultipleOf16) {
+    NumOfVecReduce = Op0VT.getVectorNumElements() / 16;
+    TargetType = MVT::v4i32;
+  } else {
+    NumOfVecReduce = Op0VT.getVectorNumElements() / 8;
+    TargetType = MVT::v2i32;
+  }
   auto DotOpcode =
       (ExtOpcode == ISD::ZERO_EXTEND) ? AArch64ISD::UDOT : AArch64ISD::SDOT;
-  SDValue Dot = DAG.getNode(DotOpcode, DL, Zeros.getValueType(), Zeros,
-                            A.getOperand(0), B);
-  return DAG.getNode(ISD::VECREDUCE_ADD, DL, N->getValueType(0), Dot);
+  // Handle the case where we need to generate only one Dot operation.
+  if (NumOfVecReduce == 1) {
+    SDValue Zeros = DAG.getConstant(0, DL, TargetType);
+    SDValue Dot = DAG.getNode(DotOpcode, DL, Zeros.getValueType(), Zeros,
+                              A.getOperand(0), B);
+    return DAG.getNode(ISD::VECREDUCE_ADD, DL, N->getValueType(0), Dot);
+  }
+  // Generate Dot instructions that are multiple of 16.
+  unsigned VecReduce16Num = Op0VT.getVectorNumElements() / 16;
+  SmallVector<SDValue, 4> SDotVec16;
+  unsigned I = 0;
+  for (; I < VecReduce16Num; I += 1) {
+    SDValue Zeros = DAG.getConstant(0, DL, MVT::v4i32);
+    SDValue Op0 =
+        DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, MVT::v16i8, A.getOperand(0),
+                    DAG.getConstant(I * 16, DL, MVT::i64));
+    SDValue Op1 = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, MVT::v16i8, B,
+                              DAG.getConstant(I * 16, DL, MVT::i64));
+    SDValue Dot =
+        DAG.getNode(DotOpcode, DL, Zeros.getValueType(), Zeros, Op0, Op1);
+    SDotVec16.push_back(Dot);
+  }
+  // Concatenate dot operations.
+  EVT SDot16EVT =
+      EVT::getVectorVT(*DAG.getContext(), MVT::i32, 4 * VecReduce16Num);
+  SDValue ConcatSDot16 =
+      DAG.getNode(ISD::CONCAT_VECTORS, DL, SDot16EVT, SDotVec16);
+  SDValue VecReduceAdd16 =
+      DAG.getNode(ISD::VECREDUCE_ADD, DL, N->getValueType(0), ConcatSDot16);
+  unsigned VecReduce8Num = (Op0VT.getVectorNumElements() % 16) / 8;
+  if (VecReduce8Num == 0)
+    return VecReduceAdd16;
+
+  // Generate the remainder Dot operation that is multiple of 8.
+  SmallVector<SDValue, 4> SDotVec8;
+  SDValue Zeros = DAG.getConstant(0, DL, MVT::v2i32);
+  SDValue Vec8Op0 =
+      DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, MVT::v8i8, A.getOperand(0),
+                  DAG.getConstant(I * 16, DL, MVT::i64));
+  SDValue Vec8Op1 = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, MVT::v8i8, B,
+                                DAG.getConstant(I * 16, DL, MVT::i64));
+  SDValue Dot =
+      DAG.getNode(DotOpcode, DL, Zeros.getValueType(), Zeros, Vec8Op0, Vec8Op1);
+  SDValue VecReudceAdd8 =
+      DAG.getNode(ISD::VECREDUCE_ADD, DL, N->getValueType(0), Dot);
+  return DAG.getNode(ISD::ADD, DL, N->getValueType(0), VecReduceAdd16,
+                     VecReudceAdd8);
 }
 
 // Given an (integer) vecreduce, we know the order of the inputs does not