Revert "ARM: Remove unnecessary manual ABI lowering for sincos_stret (#166040)" (#166262)

This reverts commit a522ae3.

The ABI handling doesn't account for matching the C ABI, only implicit
sret.

Author: arsenm

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -9869,12 +9869,32 @@ SDValue ARMTargetLowering::LowerFSINCOS(SDValue Op, SelectionDAG &DAG) const {
   assert(Subtarget->isTargetDarwin());
 
   Type *ArgTy = ArgVT.getTypeForEVT(*DAG.getContext());
+  auto PtrVT = getPointerTy(DAG.getDataLayout());
+
+  MachineFrameInfo &MFI = DAG.getMachineFunction().getFrameInfo();
 
   // Pair of floats / doubles used to pass the result.
   Type *RetTy = StructType::get(ArgTy, ArgTy);
   auto &DL = DAG.getDataLayout();
 
   ArgListTy Args;
+  bool ShouldUseSRet = getTM().isAPCS_ABI();
+  SDValue SRet;
+  if (ShouldUseSRet) {
+    // Create stack object for sret.
+    const uint64_t ByteSize = DL.getTypeAllocSize(RetTy);
+    const Align StackAlign = DL.getPrefTypeAlign(RetTy);
+    int FrameIdx = MFI.CreateStackObject(ByteSize, StackAlign, false);
+    SRet = DAG.getFrameIndex(FrameIdx, getPointerTy(DL));
+
+    ArgListEntry Entry(SRet, PointerType::getUnqual(RetTy->getContext()));
+    Entry.IsSExt = false;
+    Entry.IsZExt = false;
+    Entry.IsSRet = true;
+    Args.push_back(Entry);
+    RetTy = Type::getVoidTy(*DAG.getContext());
+  }
+
   Args.emplace_back(Arg, ArgTy);
 
   StringRef LibcallName = getLibcallImplName(SincosStret);
@@ -9884,10 +9904,25 @@ SDValue ARMTargetLowering::LowerFSINCOS(SDValue Op, SelectionDAG &DAG) const {
   TargetLowering::CallLoweringInfo CLI(DAG);
   CLI.setDebugLoc(dl)
       .setChain(DAG.getEntryNode())
-      .setCallee(CC, RetTy, Callee, std::move(Args));
+      .setCallee(CC, RetTy, Callee, std::move(Args))
+      .setDiscardResult(ShouldUseSRet);
   std::pair<SDValue, SDValue> CallResult = LowerCallTo(CLI);
 
-  return CallResult.first;
+  if (!ShouldUseSRet)
+    return CallResult.first;
+
+  SDValue LoadSin =
+      DAG.getLoad(ArgVT, dl, CallResult.second, SRet, MachinePointerInfo());
+
+  // Address of cos field.
+  SDValue Add = DAG.getNode(ISD::ADD, dl, PtrVT, SRet,
+                            DAG.getIntPtrConstant(ArgVT.getStoreSize(), dl));
+  SDValue LoadCos =
+      DAG.getLoad(ArgVT, dl, LoadSin.getValue(1), Add, MachinePointerInfo());
+
+  SDVTList Tys = DAG.getVTList(ArgVT, ArgVT);
+  return DAG.getNode(ISD::MERGE_VALUES, dl, Tys,
+                     LoadSin.getValue(0), LoadCos.getValue(0));
 }
 
 SDValue ARMTargetLowering::LowerWindowsDIVLibCall(SDValue Op, SelectionDAG &DAG,