[llvm] [VP][RISCV] Add llvm.experimental.vp.reverse. (PR #70405)

[Luke Lau via llvm-commits]

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@@ -2857,6 +2860,57 @@ void DAGTypeLegalizer::SplitVecRes_VECTOR_SPLICE(SDNode *N, SDValue &Lo,
                   DAG.getVectorIdxConstant(LoVT.getVectorMinNumElements(), DL));
 }
 
+void DAGTypeLegalizer::SplitVecRes_VP_REVERSE(SDNode *N, SDValue &Lo,
+                                              SDValue &Hi) {
+  EVT VT = N->getValueType(0);
+  SDValue Val = N->getOperand(0);
+  SDValue Mask = N->getOperand(1);
+  SDValue EVL = N->getOperand(2);
+  SDLoc DL(N);
+
+  // Fallback to VP_STRIDED_STORE to stack followed by VP_LOAD.
+  Align Alignment = DAG.getReducedAlign(VT, /*UseABI=*/false);
+
+  EVT MemVT = EVT::getVectorVT(*DAG.getContext(), VT.getVectorElementType(),
+                               VT.getVectorElementCount());
+  SDValue StackPtr = DAG.CreateStackTemporary(MemVT.getStoreSize(), Alignment);
+  EVT PtrVT = StackPtr.getValueType();
+  auto &MF = DAG.getMachineFunction();
+  auto FrameIndex = cast<FrameIndexSDNode>(StackPtr.getNode())->getIndex();
+  auto PtrInfo = MachinePointerInfo::getFixedStack(MF, FrameIndex);
+
+  MachineMemOperand *StoreMMO = DAG.getMachineFunction().getMachineMemOperand(
+      PtrInfo, MachineMemOperand::MOStore, MemoryLocation::UnknownSize,
+      Alignment);
+  MachineMemOperand *LoadMMO = DAG.getMachineFunction().getMachineMemOperand(
+      PtrInfo, MachineMemOperand::MOLoad, MemoryLocation::UnknownSize,
+      Alignment);
+
+  unsigned EltWidth = VT.getScalarSizeInBits() / 8;
+  SDValue NumElemMinus1 =
+      DAG.getNode(ISD::SUB, DL, PtrVT, DAG.getZExtOrTrunc(EVL, DL, PtrVT),
+                  DAG.getConstant(1, DL, PtrVT));
+  SDValue StartOffset = DAG.getNode(ISD::MUL, DL, PtrVT, NumElemMinus1,
+                                    DAG.getConstant(EltWidth, DL, PtrVT));
+  SDValue StorePtr = DAG.getNode(ISD::ADD, DL, PtrVT, StackPtr, StartOffset);
+  SDValue Stride = DAG.getConstant(-(int64_t)EltWidth, DL, PtrVT);
+
+  SDValue TrueMask = DAG.getBoolConstant(true, DL, Mask.getValueType(), VT);
+  SDValue Store = DAG.getStridedStoreVP(DAG.getEntryNode(), DL, Val, StorePtr,
+                                        DAG.getUNDEF(PtrVT), Stride, TrueMask,
+                                        EVL, MemVT, StoreMMO, ISD::UNINDEXED);
+
+  SDValue Load = DAG.getLoadVP(VT, DL, Store, StackPtr, Mask, EVL, LoadMMO);
+
+  EVT LoVT, HiVT;
+  std::tie(LoVT, HiVT) = DAG.GetSplitDestVTs(VT);
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lukel97 wrote:

Could use auto here too

https://github.com/llvm/llvm-project/pull/70405