[llvm] [DAGCombiner][LegalizeTypes] Fuse i128 sdiv+srem / udiv+urem into single __divmodti4 / __udivmodti4 call (PR #187908)

[Craig Topper via llvm-commits]

================
@@ -30640,6 +30613,72 @@ SDValue X86TargetLowering::LowerWin64_i128OP(SDValue Op, SelectionDAG &DAG) cons
   return DAG.getBitcast(VT, CallInfo.first);
 }
 
+void X86TargetLowering::LowerWin64_i128DIVREM(SDNode *N, SelectionDAG &DAG,
+                                              SDValue &Quot,
+                                              SDValue &Rem) const {
+  assert(Subtarget.isTargetWin64() && "Unexpected target");
+  EVT VT = N->getValueType(0);
+  assert(VT == MVT::i128 && "Unexpected type");
+
+  bool isSigned = N->getOpcode() == ISD::SDIVREM;
+  RTLIB::Libcall LC = isSigned ? RTLIB::SDIVREM_I128 : RTLIB::UDIVREM_I128;
+  RTLIB::LibcallImpl LCImpl = DAG.getLibcalls().getLibcallImpl(LC);
+
+  SDLoc dl(N);
+
+  // If no fused divrem libcall is available, fall back to separate div and rem.
+  // This goes through LowerWin64_i128OP with the correct pointer-arg ABI.
+  if (LCImpl == RTLIB::Unsupported) {
+    unsigned DivOp = isSigned ? ISD::SDIV : ISD::UDIV;
+    unsigned RemOp = isSigned ? ISD::SREM : ISD::UREM;
+    Quot = DAG.getNode(DivOp, dl, VT, N->getOperand(0), N->getOperand(1));
+    Rem = DAG.getNode(RemOp, dl, VT, N->getOperand(0), N->getOperand(1));
+    return;
+  }
+  SDValue InChain = DAG.getEntryNode();
+
+  TargetLowering::ArgListTy Args;
+
+  // Spill both i128 inputs to stack temporaries and pass as pointers as per
+  // Win64 CC (Win64 has no calling convention for passing i128 by value).
+  for (unsigned i = 0; i < 2; ++i) {
+    EVT ArgVT = N->getOperand(i).getValueType();
+    assert(ArgVT == MVT::i128 && "Unexpected argument type");
+    SDValue StackPtr = DAG.CreateStackTemporary(ArgVT, 16);
+    int SPFI = cast<FrameIndexSDNode>(StackPtr.getNode())->getIndex();
+    MachinePointerInfo MPI =
+        MachinePointerInfo::getFixedStack(DAG.getMachineFunction(), SPFI);
+    InChain =
+        DAG.getStore(InChain, dl, N->getOperand(i), StackPtr, MPI, Align(16));
+    Args.emplace_back(StackPtr, PointerType::get(*DAG.getContext(), 0));
+  }
+
+  // Allocate a stack slot for the remainder output pointer.
+  MachineFunction &MF = DAG.getMachineFunction();
+  int RemFI = MF.getFrameInfo().CreateStackObject(16, Align(16), false);
+  SDValue RemPtr = DAG.getFrameIndex(RemFI, getPointerTy(DAG.getDataLayout()));
+  Args.emplace_back(RemPtr, PointerType::get(*DAG.getContext(), 0));
+
+  SDValue Callee =
+      DAG.getExternalSymbol(LCImpl, getPointerTy(DAG.getDataLayout()));
+
+  TargetLowering::CallLoweringInfo CLI(DAG);
+  CLI.setDebugLoc(dl)
+      .setChain(InChain)
+      .setLibCallee(
+          DAG.getLibcalls().getLibcallImplCallingConv(LCImpl),
+          static_cast<EVT>(MVT::v2i64).getTypeForEVT(*DAG.getContext()), Callee,
----------------
topperc wrote:

This `static_cast<EVT>(MVT::v2i64)` looks really weird to me. Is that invoking the EVT constructor?

https://github.com/llvm/llvm-project/pull/187908