[RISCV] Use separate CCValAssign for both parts of f64 with ilp32. (#69129)

Mark any registers as CustomReg and any stack slot as CustomMem.
    
This allows us to more directly emit the register or memory access for
the high part. Previously we needed a memory access if the low register
was X17 and we assumed the stack offset was 0. If the low part wasn't
X17, we assumed the high register was the next register after the low
register.
    
This is another part of supporting FP arguments with GISel.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -16452,9 +16452,16 @@ bool RISCV::CC_RISCV(const DataLayout &DL, RISCVABI::ABI ABI, unsigned ValNo,
       return false;
     }
     LocVT = MVT::i32;
-    if (!State.AllocateReg(ArgGPRs))
-      State.AllocateStack(4, Align(4));
-    State.addLoc(CCValAssign::getReg(ValNo, ValVT, Reg, LocVT, LocInfo));
+    State.addLoc(CCValAssign::getCustomReg(ValNo, ValVT, Reg, LocVT, LocInfo));
+    Register HiReg = State.AllocateReg(ArgGPRs);
+    if (HiReg) {
+      State.addLoc(
+          CCValAssign::getCustomReg(ValNo, ValVT, HiReg, LocVT, LocInfo));
+    } else {
+      unsigned StackOffset = State.AllocateStack(4, Align(4));
+      State.addLoc(
+          CCValAssign::getCustomMem(ValNo, ValVT, StackOffset, LocVT, LocInfo));
+    }
     return false;
   }
 
@@ -16763,7 +16770,9 @@ static SDValue unpackFromMemLoc(SelectionDAG &DAG, SDValue Chain,
 }
 
 static SDValue unpackF64OnRV32DSoftABI(SelectionDAG &DAG, SDValue Chain,
-                                       const CCValAssign &VA, const SDLoc &DL) {
+                                       const CCValAssign &VA,
+                                       const CCValAssign &HiVA,
+                                       const SDLoc &DL) {
   assert(VA.getLocVT() == MVT::i32 && VA.getValVT() == MVT::f64 &&
          "Unexpected VA");
   MachineFunction &MF = DAG.getMachineFunction();
@@ -16776,16 +16785,17 @@ static SDValue unpackF64OnRV32DSoftABI(SelectionDAG &DAG, SDValue Chain,
   RegInfo.addLiveIn(VA.getLocReg(), LoVReg);
   SDValue Lo = DAG.getCopyFromReg(Chain, DL, LoVReg, MVT::i32);
   SDValue Hi;
-  if (VA.getLocReg() == RISCV::X17) {
+  if (HiVA.isMemLoc()) {
     // Second half of f64 is passed on the stack.
-    int FI = MFI.CreateFixedObject(4, 0, /*IsImmutable=*/true);
+    int FI = MFI.CreateFixedObject(4, HiVA.getLocMemOffset(),
+                                   /*IsImmutable=*/true);
     SDValue FIN = DAG.getFrameIndex(FI, MVT::i32);
     Hi = DAG.getLoad(MVT::i32, DL, Chain, FIN,
                      MachinePointerInfo::getFixedStack(MF, FI));
   } else {
     // Second half of f64 is passed in another GPR.
     Register HiVReg = RegInfo.createVirtualRegister(&RISCV::GPRRegClass);
-    RegInfo.addLiveIn(VA.getLocReg() + 1, HiVReg);
+    RegInfo.addLiveIn(HiVA.getLocReg(), HiVReg);
     Hi = DAG.getCopyFromReg(Chain, DL, HiVReg, MVT::i32);
   }
   return DAG.getNode(RISCVISD::BuildPairF64, DL, MVT::f64, Lo, Hi);
@@ -17028,15 +17038,16 @@ SDValue RISCVTargetLowering::LowerFormalArguments(
                      CallConv == CallingConv::Fast ? RISCV::CC_RISCV_FastCC
                                                    : RISCV::CC_RISCV);
 
-  for (unsigned i = 0, e = ArgLocs.size(); i != e; ++i) {
+  for (unsigned i = 0, e = ArgLocs.size(), InsIdx = 0; i != e; ++i, ++InsIdx) {
     CCValAssign &VA = ArgLocs[i];
     SDValue ArgValue;
     // Passing f64 on RV32D with a soft float ABI must be handled as a special
     // case.
-    if (VA.getLocVT() == MVT::i32 && VA.getValVT() == MVT::f64)
-      ArgValue = unpackF64OnRV32DSoftABI(DAG, Chain, VA, DL);
-    else if (VA.isRegLoc())
-      ArgValue = unpackFromRegLoc(DAG, Chain, VA, DL, Ins[i], *this);
+    if (VA.getLocVT() == MVT::i32 && VA.getValVT() == MVT::f64) {
+      assert(VA.needsCustom());
+      ArgValue = unpackF64OnRV32DSoftABI(DAG, Chain, VA, ArgLocs[++i], DL);
+    } else if (VA.isRegLoc())
+      ArgValue = unpackFromRegLoc(DAG, Chain, VA, DL, Ins[InsIdx], *this);
     else
       ArgValue = unpackFromMemLoc(DAG, Chain, VA, DL);
 
@@ -17048,19 +17059,20 @@ SDValue RISCVTargetLowering::LowerFormalArguments(
       // stores are relative to that.
       InVals.push_back(DAG.getLoad(VA.getValVT(), DL, Chain, ArgValue,
                                    MachinePointerInfo()));
-      unsigned ArgIndex = Ins[i].OrigArgIndex;
-      unsigned ArgPartOffset = Ins[i].PartOffset;
+      unsigned ArgIndex = Ins[InsIdx].OrigArgIndex;
+      unsigned ArgPartOffset = Ins[InsIdx].PartOffset;
       assert(VA.getValVT().isVector() || ArgPartOffset == 0);
-      while (i + 1 != e && Ins[i + 1].OrigArgIndex == ArgIndex) {
+      while (i + 1 != e && Ins[InsIdx + 1].OrigArgIndex == ArgIndex) {
         CCValAssign &PartVA = ArgLocs[i + 1];
-        unsigned PartOffset = Ins[i + 1].PartOffset - ArgPartOffset;
+        unsigned PartOffset = Ins[InsIdx + 1].PartOffset - ArgPartOffset;
         SDValue Offset = DAG.getIntPtrConstant(PartOffset, DL);
         if (PartVA.getValVT().isScalableVector())
           Offset = DAG.getNode(ISD::VSCALE, DL, XLenVT, Offset);
         SDValue Address = DAG.getNode(ISD::ADD, DL, PtrVT, ArgValue, Offset);
         InVals.push_back(DAG.getLoad(PartVA.getValVT(), DL, Chain, Address,
                                      MachinePointerInfo()));
         ++i;
+        ++InsIdx;
       }
       continue;
     }
@@ -17276,14 +17288,16 @@ SDValue RISCVTargetLowering::LowerCall(CallLoweringInfo &CLI,
   SmallVector<std::pair<Register, SDValue>, 8> RegsToPass;
   SmallVector<SDValue, 8> MemOpChains;
   SDValue StackPtr;
-  for (unsigned i = 0, j = 0, e = ArgLocs.size(); i != e; ++i) {
+  for (unsigned i = 0, j = 0, e = ArgLocs.size(), OutIdx = 0; i != e;
+       ++i, ++OutIdx) {
     CCValAssign &VA = ArgLocs[i];
-    SDValue ArgValue = OutVals[i];
-    ISD::ArgFlagsTy Flags = Outs[i].Flags;
+    SDValue ArgValue = OutVals[OutIdx];
+    ISD::ArgFlagsTy Flags = Outs[OutIdx].Flags;
 
     // Handle passing f64 on RV32D with a soft float ABI as a special case.
     if (VA.getLocVT() == MVT::i32 && VA.getValVT() == MVT::f64) {
       assert(VA.isRegLoc() && "Expected register VA assignment");
+      assert(VA.needsCustom());
       SDValue SplitF64 = DAG.getNode(
           RISCVISD::SplitF64, DL, DAG.getVTList(MVT::i32, MVT::i32), ArgValue);
       SDValue Lo = SplitF64.getValue(0);
@@ -17292,18 +17306,22 @@ SDValue RISCVTargetLowering::LowerCall(CallLoweringInfo &CLI,
       Register RegLo = VA.getLocReg();
       RegsToPass.push_back(std::make_pair(RegLo, Lo));
 
-      if (RegLo == RISCV::X17) {
+      // Get the CCValAssign for the Hi part.
+      CCValAssign &HiVA = ArgLocs[++i];
+
+      if (HiVA.isMemLoc()) {
         // Second half of f64 is passed on the stack.
-        // Work out the address of the stack slot.
         if (!StackPtr.getNode())
           StackPtr = DAG.getCopyFromReg(Chain, DL, RISCV::X2, PtrVT);
+        SDValue Address =
+            DAG.getNode(ISD::ADD, DL, PtrVT, StackPtr,
+                        DAG.getIntPtrConstant(HiVA.getLocMemOffset(), DL));
         // Emit the store.
         MemOpChains.push_back(
-            DAG.getStore(Chain, DL, Hi, StackPtr, MachinePointerInfo()));
+            DAG.getStore(Chain, DL, Hi, Address, MachinePointerInfo()));
       } else {
         // Second half of f64 is passed in another GPR.
-        assert(RegLo < RISCV::X31 && "Invalid register pair");
-        Register RegHigh = RegLo + 1;
+        Register RegHigh = HiVA.getLocReg();
         RegsToPass.push_back(std::make_pair(RegHigh, Hi));
       }
       continue;
@@ -17314,24 +17332,24 @@ SDValue RISCVTargetLowering::LowerCall(CallLoweringInfo &CLI,
     if (VA.getLocInfo() == CCValAssign::Indirect) {
       // Store the argument in a stack slot and pass its address.
       Align StackAlign =
-          std::max(getPrefTypeAlign(Outs[i].ArgVT, DAG),
+          std::max(getPrefTypeAlign(Outs[OutIdx].ArgVT, DAG),
                    getPrefTypeAlign(ArgValue.getValueType(), DAG));
       TypeSize StoredSize = ArgValue.getValueType().getStoreSize();
       // If the original argument was split (e.g. i128), we need
       // to store the required parts of it here (and pass just one address).
       // Vectors may be partly split to registers and partly to the stack, in
       // which case the base address is partly offset and subsequent stores are
       // relative to that.
-      unsigned ArgIndex = Outs[i].OrigArgIndex;
-      unsigned ArgPartOffset = Outs[i].PartOffset;
+      unsigned ArgIndex = Outs[OutIdx].OrigArgIndex;
+      unsigned ArgPartOffset = Outs[OutIdx].PartOffset;
       assert(VA.getValVT().isVector() || ArgPartOffset == 0);
       // Calculate the total size to store. We don't have access to what we're
       // actually storing other than performing the loop and collecting the
       // info.
       SmallVector<std::pair<SDValue, SDValue>> Parts;
-      while (i + 1 != e && Outs[i + 1].OrigArgIndex == ArgIndex) {
-        SDValue PartValue = OutVals[i + 1];
-        unsigned PartOffset = Outs[i + 1].PartOffset - ArgPartOffset;
+      while (i + 1 != e && Outs[OutIdx + 1].OrigArgIndex == ArgIndex) {
+        SDValue PartValue = OutVals[OutIdx + 1];
+        unsigned PartOffset = Outs[OutIdx + 1].PartOffset - ArgPartOffset;
         SDValue Offset = DAG.getIntPtrConstant(PartOffset, DL);
         EVT PartVT = PartValue.getValueType();
         if (PartVT.isScalableVector())
@@ -17340,6 +17358,7 @@ SDValue RISCVTargetLowering::LowerCall(CallLoweringInfo &CLI,
         StackAlign = std::max(StackAlign, getPrefTypeAlign(PartVT, DAG));
         Parts.push_back(std::make_pair(PartValue, Offset));
         ++i;
+        ++OutIdx;
       }
       SDValue SpillSlot = DAG.CreateStackTemporary(StoredSize, StackAlign);
       int FI = cast<FrameIndexSDNode>(SpillSlot)->getIndex();
@@ -17481,7 +17500,8 @@ SDValue RISCVTargetLowering::LowerCall(CallLoweringInfo &CLI,
   analyzeInputArgs(MF, RetCCInfo, Ins, /*IsRet=*/true, RISCV::CC_RISCV);
 
   // Copy all of the result registers out of their specified physreg.
-  for (auto &VA : RVLocs) {
+  for (unsigned i = 0, e = RVLocs.size(); i != e; ++i) {
+    auto &VA = RVLocs[i];
     // Copy the value out
     SDValue RetValue =
         DAG.getCopyFromReg(Chain, DL, VA.getLocReg(), VA.getLocVT(), Glue);
@@ -17490,9 +17510,9 @@ SDValue RISCVTargetLowering::LowerCall(CallLoweringInfo &CLI,
     Glue = RetValue.getValue(2);
 
     if (VA.getLocVT() == MVT::i32 && VA.getValVT() == MVT::f64) {
-      assert(VA.getLocReg() == ArgGPRs[0] && "Unexpected reg assignment");
-      SDValue RetValue2 =
-          DAG.getCopyFromReg(Chain, DL, ArgGPRs[1], MVT::i32, Glue);
+      assert(VA.needsCustom());
+      SDValue RetValue2 = DAG.getCopyFromReg(Chain, DL, RVLocs[++i].getLocReg(),
+                                             MVT::i32, Glue);
       Chain = RetValue2.getValue(1);
       Glue = RetValue2.getValue(2);
       RetValue = DAG.getNode(RISCVISD::BuildPairF64, DL, MVT::f64, RetValue,
@@ -17555,21 +17575,21 @@ RISCVTargetLowering::LowerReturn(SDValue Chain, CallingConv::ID CallConv,
   SmallVector<SDValue, 4> RetOps(1, Chain);
 
   // Copy the result values into the output registers.
-  for (unsigned i = 0, e = RVLocs.size(); i < e; ++i) {
-    SDValue Val = OutVals[i];
+  for (unsigned i = 0, e = RVLocs.size(), OutIdx = 0; i < e; ++i, ++OutIdx) {
+    SDValue Val = OutVals[OutIdx];
     CCValAssign &VA = RVLocs[i];
     assert(VA.isRegLoc() && "Can only return in registers!");
 
     if (VA.getLocVT() == MVT::i32 && VA.getValVT() == MVT::f64) {
       // Handle returning f64 on RV32D with a soft float ABI.
       assert(VA.isRegLoc() && "Expected return via registers");
+      assert(VA.needsCustom());
       SDValue SplitF64 = DAG.getNode(RISCVISD::SplitF64, DL,
                                      DAG.getVTList(MVT::i32, MVT::i32), Val);
       SDValue Lo = SplitF64.getValue(0);
       SDValue Hi = SplitF64.getValue(1);
       Register RegLo = VA.getLocReg();
-      assert(RegLo < RISCV::X31 && "Invalid register pair");
-      Register RegHi = RegLo + 1;
+      Register RegHi = RVLocs[++i].getLocReg();
 
       if (STI.isRegisterReservedByUser(RegLo) ||
           STI.isRegisterReservedByUser(RegHi))