[RISCV 14/n] Support for function calls

[asb]

Summary

No support for varargs, but simple function call examples will generate something sensible.

[asb]

Updates:

• Error when encountering a byval argument (support added in a later patch)
• Make better use of range-based for loops
• Reflect upstream changes to ADJCALLSTACKDOWN in rL302527

[majnemer]

lib/Target/RISCV/RISCVISelLowering.cpp

170

report_fatal_error

186

report_fatal_error

207–210

Please consistently brace.

212

report_fatal_error

227

report_fatal_error

[asb]

Address review comments from @majnemer (thanks!).

[asb]

Instruction definitions and patterns have been split, as discussed in http://lists.llvm.org/pipermail/llvm-dev/2017-August/116635.html

[apazos]

lib/Target/RISCV/RISCVInstrInfo.cpp

31

Code width standard is 80 columns.

[asb]

Fix line that was over 80 columns (thanks @apazos).

[kparzysz]

lib/Target/RISCV/RISCVInstrInfo.td

316

Please add spaces between Defs and [].

lib/Target/RISCV/RISCVFrameLowering.h

explicit RISCVFrameLowering(const RISCVSubtarget &STI)
       : TargetFrameLowering(StackGrowsDown,
                             /*StackAlignment=*/8,
                             /*LocalAreaOffset=*/0) {}
 
   void emitPrologue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
   void emitEpilogue(MachineFunction &MF, MachineBasicBlock &MBB) const override;
 
   bool hasFP(const MachineFunction &MF) const override;
+
+  MachineBasicBlock::iterator
+  eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
+                                MachineBasicBlock::iterator MI) const override {
+    return MBB.erase(MI);
+  }
 };
 }
 #endif

lib/Target/RISCV/RISCVISelLowering.h

 #include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/Target/TargetLowering.h"
 
 namespace llvm {
 class RISCVSubtarget;
 namespace RISCVISD {
 enum NodeType : unsigned {
   FIRST_NUMBER = ISD::BUILTIN_OP_END,
-  RET_FLAG
+  RET_FLAG,
+  CALL
 };
 }
 
 class RISCVTargetLowering : public TargetLowering {
   const RISCVSubtarget *Subtarget;
 
 public:
   explicit RISCVTargetLowering(const TargetMachine &TM,
SDValue LowerFormalArguments(SDValue Chain, CallingConv::ID CallConv,
                                bool IsVarArg,
                                const SmallVectorImpl<ISD::InputArg> &Ins,
                                const SDLoc &DL, SelectionDAG &DAG,
                                SmallVectorImpl<SDValue> &InVals) const override;
   SDValue LowerReturn(SDValue Chain, CallingConv::ID CallConv, bool IsVarArg,
                       const SmallVectorImpl<ISD::OutputArg> &Outs,
                       const SmallVectorImpl<SDValue> &OutVals, const SDLoc &DL,
                       SelectionDAG &DAG) const override;
+  SDValue LowerCall(TargetLowering::CallLoweringInfo &CLI,
+                    SmallVectorImpl<SDValue> &InVals) const override;
   bool shouldConvertConstantLoadToIntImm(const APInt &Imm,
                                          Type *Ty) const override {
     return true;
   }
   SDValue lowerGlobalAddress(SDValue Op, SelectionDAG &DAG) const;
 };
 }
 
 #endif

lib/Target/RISCV/RISCVISelLowering.cpp

if (VA.isRegLoc()) {
       }
     } else {
       llvm_unreachable("Defined with too many args");
     }
   }
   return Chain;
 }
 
+// Lower a call to a callseq_start + CALL + callseq_end chain, and add input 
+// and output parameter nodes.
+SDValue RISCVTargetLowering::LowerCall(CallLoweringInfo &CLI,
+                                       SmallVectorImpl<SDValue> &InVals) const {
+  SelectionDAG &DAG = CLI.DAG;
+  SDLoc &DL = CLI.DL;
+  SmallVectorImpl<ISD::OutputArg> &Outs = CLI.Outs;
+  SmallVectorImpl<SDValue> &OutVals = CLI.OutVals;
+  SmallVectorImpl<ISD::InputArg> &Ins = CLI.Ins;
+  SDValue Chain = CLI.Chain;
+  SDValue Callee = CLI.Callee;
+  CLI.IsTailCall = false;
+  CallingConv::ID CallConv = CLI.CallConv;
+  bool IsVarArg = CLI.IsVarArg;
+  EVT PtrVT = getPointerTy(DAG.getDataLayout());
+
+  if (IsVarArg) {
+    llvm_unreachable("LowerCall with varargs not implemented");
+  }
+
+  MachineFunction &MF = DAG.getMachineFunction();
+
+  // Analyze the operands of the call, assigning locations to each operand.
+  SmallVector<CCValAssign, 16> ArgLocs;
+  CCState ArgCCInfo(CallConv, IsVarArg, MF, ArgLocs, *DAG.getContext());
+  ArgCCInfo.AnalyzeCallOperands(Outs, CC_RISCV32);
+
+  // Get a count of how many bytes are to be pushed on the stack.
+  unsigned NumBytes = ArgCCInfo.getNextStackOffset();
+
+  for (auto &Arg : Outs) {
+    if (!Arg.Flags.isByVal())
+      continue;
+    llvm_unreachable("Passing arguments byval not yet implemented");
+  }
+
+  Chain = DAG.getCALLSEQ_START(Chain, NumBytes, 0, CLI.DL);
+
+  // Copy argument values to their designated locations.
+  SmallVector<std::pair<unsigned, SDValue>, 8> RegsToPass;
+  SDValue StackPtr;
+  for (unsigned I = 0, E = ArgLocs.size(); I != E; ++I) {
+    CCValAssign &VA = ArgLocs[I];
+    SDValue ArgValue = OutVals[I];
+
+    // Promote the value if needed.
+    // For now, only handle fully promoted arguments.
+    switch (VA.getLocInfo()) {
+    case CCValAssign::Full:
+      break;
+    default:
+      llvm_unreachable("Unknown loc info!");
+    }
+
+    if (VA.isRegLoc())
+      // Queue up the argument copies and emit them at the end.
+      RegsToPass.push_back(std::make_pair(VA.getLocReg(), ArgValue));
+    else {
+      assert(VA.isMemLoc() && "Argument not register or memory");
+      llvm_unreachable("Passing arguments via the stack not yet implemented");
+    }
+  }
+
+  SDValue Glue;
+
+  // Build a sequence of copy-to-reg nodes, chained and glued together.
+  for (auto &Reg : RegsToPass) {
+    Chain = DAG.getCopyToReg(Chain, DL, Reg.first, Reg.second, Glue);
+    Glue = Chain.getValue(1);
+  }
+
+  if (isa<GlobalAddressSDNode>(Callee)) {
+    Callee = lowerGlobalAddress(Callee, DAG);
+  } else if (isa<ExternalSymbolSDNode>(Callee)) {
+    llvm_unreachable(
+        "lowerExternalSymbol, needed for lowerCall, not yet handled");
+  }
+
+  // The first call operand is the chain and the second is the target address.
+  SmallVector<SDValue, 8> Ops;
+  Ops.push_back(Chain);
+  Ops.push_back(Callee);
+
+  // Add argument registers to the end of the list so that they are
+  // known live into the call.
+  for (auto &Reg : RegsToPass)
+    Ops.push_back(DAG.getRegister(Reg.first, Reg.second.getValueType()));
+
+  // Add a register mask operand representing the call-preserved registers.
+  const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
+  const uint32_t *Mask = TRI->getCallPreservedMask(MF, CallConv);
+  assert(Mask && "Missing call preserved mask for calling convention");
+  Ops.push_back(DAG.getRegisterMask(Mask));
+
+  // Glue the call to the argument copies, if any.
+  if (Glue.getNode())
+    Ops.push_back(Glue);
+
+  // Emit the call.
+  SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
+  Chain = DAG.getNode(RISCVISD::CALL, DL, NodeTys, Ops);
+  Glue = Chain.getValue(1);
+
+  // Mark the end of the call, which is glued to the call itself.
+  Chain = DAG.getCALLSEQ_END(Chain,
+                             DAG.getConstant(NumBytes, DL, PtrVT, true),
+                             DAG.getConstant(0, DL, PtrVT, true),
+                             Glue, DL);
+  Glue = Chain.getValue(1);
+
+  // Assign locations to each value returned by this call.
+  SmallVector<CCValAssign, 16> RVLocs;
+  CCState RetCCInfo(CallConv, IsVarArg, MF, RVLocs, *DAG.getContext());
+  RetCCInfo.AnalyzeCallResult(Ins, RetCC_RISCV32);
+
+  // Copy all of the result registers out of their specified physreg.
+  for (auto &VA : RVLocs) {
+    // Copy the value out, gluing the copy to the end of the call sequence.
+    SDValue RetValue = DAG.getCopyFromReg(Chain, DL, VA.getLocReg(),
+                                          VA.getLocVT(), Glue);
+    Chain = RetValue.getValue(1);
+    Glue = RetValue.getValue(2);
+
+    InVals.push_back(Chain.getValue(0));
+  }
+
+  return Chain;
+}
+
 SDValue
 RISCVTargetLowering::LowerReturn(SDValue Chain, CallingConv::ID CallConv,
                                  bool IsVarArg,
                                  const SmallVectorImpl<ISD::OutputArg> &Outs,
                                  const SmallVectorImpl<SDValue> &OutVals,
                                  const SDLoc &DL, SelectionDAG &DAG) const {
   if (IsVarArg) {
     report_fatal_error("VarArg not supported");

 }
 
 const char *RISCVTargetLowering::getTargetNodeName(unsigned Opcode) const {
   switch ((RISCVISD::NodeType)Opcode) {
   case RISCVISD::FIRST_NUMBER:
     break;
   case RISCVISD::RET_FLAG:
     return "RISCVISD::RET_FLAG";
+  case RISCVISD::CALL:
+    return "RISCVISD::CALL";
   }
   return nullptr;
 }

lib/Target/RISCV/RISCVInstrInfo.cpp

 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TargetRegistry.h"
 
 #define GET_INSTRINFO_CTOR_DTOR
 #include "RISCVGenInstrInfo.inc"
 
 using namespace llvm;
 
-RISCVInstrInfo::RISCVInstrInfo() : RISCVGenInstrInfo() {}
+RISCVInstrInfo::RISCVInstrInfo() : RISCVGenInstrInfo(RISCV::ADJCALLSTACKDOWN, RISCV::ADJCALLSTACKUP) {}
 
 void RISCVInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
                                  MachineBasicBlock::iterator Position,
                                  const DebugLoc &DL,
                                  unsigned DestinationRegister,
                                  unsigned SourceRegister,
                                  bool KillSource) const {
   if (!RISCV::GPRRegClass.contains(DestinationRegister, SourceRegister)) {

lib/Target/RISCV/RISCVInstrInfo.td

 //===-- RISCVInstrInfo.td - Target Description for RISCV ---*- tablegen -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file describes the RISC-V instructions in TableGen format.
 //
 //===----------------------------------------------------------------------===//
 
 include "RISCVInstrFormats.td"
 
+def SDT_RISCVCallSeqStart : SDCallSeqStart<[SDTCisVT<0, i32>,
+                                            SDTCisVT<1, i32>]>;
+def SDT_RISCVCallSeqEnd   : SDCallSeqEnd<[SDTCisVT<0, i32>,
+                                         SDTCisVT<1, i32>]>;
+def SDT_RISCVCall         : SDTypeProfile<0, -1, [SDTCisVT<0, i32>]>;
+
+
+def Call             : SDNode<"RISCVISD::CALL", SDT_RISCVCall,
+                              [SDNPHasChain, SDNPOptInGlue, SDNPOutGlue,
+                               SDNPVariadic]>;
 def RetFlag : SDNode<"RISCVISD::RET_FLAG", SDTNone,
                      [SDNPHasChain, SDNPOptInGlue, SDNPVariadic]>;
+def CallSeqStart     : SDNode<"ISD::CALLSEQ_START", SDT_RISCVCallSeqStart,
+                              [SDNPHasChain, SDNPOutGlue]>;
+def CallSeqEnd       : SDNode<"ISD::CALLSEQ_END", SDT_RISCVCallSeqEnd,
+                              [SDNPHasChain, SDNPOptInGlue, SDNPOutGlue]>;
 
 // Operands
 class ImmAsmOperand<string prefix, int width, string suffix> : AsmOperandClass {
   let Name = prefix # "Imm" # width # suffix;
   let RenderMethod = "addImmOperands";
   let DiagnosticType = !strconcat("Invalid", Name);
 }
 

 // is adopted.
 
 def LUI : FU<0b0110111, (outs GPR:$rd), (ins uimm20:$imm20),
              "lui\t$rd, $imm20", []>;
 
 def AUIPC : FU<0b0010111, (outs GPR:$rd), (ins uimm20:$imm20),
              "auipc\t$rd, $imm20", []>;
 
+let isCall=1 in {
 def JAL : FUJ<0b1101111, (outs GPR:$rd), (ins simm21_lsb0:$imm20),
               "jal\t$rd, $imm20", []>;
+}
 
 let isTerminator=1, isBarrier=1 in {
 def PseudoBR : Pseudo<(outs), (ins simm21_lsb0:$imm20), [(br bb:$imm20)]>,
                PseudoInstExpansion<(JAL X0_32, simm21_lsb0:$imm20)>;
 }
 
+let isCall=1 in {
 def JALR : FI<0b000, 0b1100111, (outs GPR:$rd), (ins GPR:$rs1, simm12:$imm12),
               "jalr\t$rd, $rs1, $imm12", []>;
+}
+
+let isCall=1, Defs=[X1_32] in {
+  def PseudoCALL : Pseudo<(outs), (ins GPR:$rs1), [(Call GPR:$rs1)]>,
+                   PseudoInstExpansion<(JALR X1_32, GPR:$rs1, 0)>;
+}
 
 let isReturn=1, isTerminator=1, isBarrier=1 in {
   def PseudoRET : Pseudo<(outs), (ins), [(RetFlag)]>,
                   PseudoInstExpansion<(JALR X0_32, X1_32, 0)>;
 }
 
+// Pessimistically assume the stack pointer will be clobbered
+let Defs = [X2_32], Uses = [X2_32] in {
+  def ADJCALLSTACKDOWN : Pseudo<(outs), (ins i32imm:$amt1, i32imm:$amt2),
+                                [(CallSeqStart timm:$amt1, timm:$amt2)]>;
+  def ADJCALLSTACKUP   : Pseudo<(outs), (ins i32imm:$amt1, i32imm:$amt2),
+                                [(CallSeqEnd timm:$amt1, timm:$amt2)]>;
+}
+
 class Bcc<bits<3> funct3, string OpcodeStr, PatFrag CondOp> :
       FSB<funct3, 0b1100011, (outs), (ins GPR:$rs1, GPR:$rs2, simm13_lsb0:$imm12),
          OpcodeStr#"\t$rs1, $rs2, $imm12", [(brcond (i32 (CondOp GPR:$rs1, GPR:$rs2)), bb:$imm12)]> {
   let isBranch = 1;
   let isTerminator = 1;
 }
 
 def BEQ   : Bcc<0b000, "beq", seteq>;

 def CSRRWI : CSR_ri<0b101, "csrrwi">;
 def CSRRSI : CSR_ri<0b110, "csrrsi">;
 def CSRRCI : CSR_ri<0b111, "csrrci">;
 
 
 // signed 12-bit immediate
 def : Pat<(simm12:$imm), (ADDI X0_32, simm12:$imm)>;
 
 // 32-bit immediate
 def : Pat<(i32 imm:$imm), (ADDI (LUI (HI20 imm:$imm)), (LO12Sext imm:$imm))>;

lib/Target/RISCV/RISCVMCInstLower.cpp

bool llvm::LowerRISCVMachineOperandToMCOperand(const MachineOperand &MO,
     default:
       llvm_unreachable("unknown operand type");
     case MachineOperand::MO_Register:
       // Ignore all implicit register operands.
       if (MO.isImplicit())
         return false;
       MCOp = MCOperand::createReg(MO.getReg());
       break;
+    case MachineOperand::MO_RegisterMask:
+      // Regmasks are like implicit defs.
+      return false;
     case MachineOperand::MO_Immediate:
       MCOp = MCOperand::createImm(MO.getImm());
       break;
     case MachineOperand::MO_MachineBasicBlock:
       MCOp = MCOperand::createExpr(
           MCSymbolRefExpr::create(MO.getMBB()->getSymbol(), AP.OutContext));
       break;
     case MachineOperand::MO_GlobalAddress:

lib/Target/RISCV/RISCVRegisterInfo.h

 #include "RISCVGenRegisterInfo.inc"
 
 namespace llvm {
 
 struct RISCVRegisterInfo : public RISCVGenRegisterInfo {
 
   RISCVRegisterInfo();
 
+  const uint32_t *getCallPreservedMask(const MachineFunction &MF,
+                                       CallingConv::ID) const override;
+
   const MCPhysReg *getCalleeSavedRegs(const MachineFunction *MF) const override;
 
   BitVector getReservedRegs(const MachineFunction &MF) const override;
 
   const uint32_t *getNoPreservedMask() const override;
 
   void eliminateFrameIndex(MachineBasicBlock::iterator MI, int SPAdj,
                            unsigned FIOperandNum,
                            RegScavenger *RS = nullptr) const override;
 
   unsigned getFrameRegister(const MachineFunction &MF) const override;
 };
 }
 
 #endif

lib/Target/RISCV/RISCVRegisterInfo.cpp

if (isInt<12>(Offset)) {
     llvm_unreachable(
         "Frame offsets outside of the signed 12-bit range not supported");
   }
 }
 
 unsigned RISCVRegisterInfo::getFrameRegister(const MachineFunction &MF) const {
   return RISCV::X8_32;
 }
+
+const uint32_t *
+RISCVRegisterInfo::getCallPreservedMask(const MachineFunction & /*MF*/,
+                                        CallingConv::ID /*CC*/) const {
+  return CSR_RegMask;
+}

test/CodeGen/RISCV/calls.ll

+; RUN: llc -mtriple=riscv32 -verify-machineinstrs < %s | FileCheck %s
+
+declare i32 @external_function(i32) nounwind
+
+define i32 @test_call_external(i32 %a) {
+; CHECK-LABEL: test_call_external:
+; CHECK: lui a1, %hi(external_function)
+; CHECK: addi a1, a1, %lo(external_function)
+; CHECK: jalr ra, a1, 0
+  %1 = call i32 @external_function(i32 %a) nounwind
+  ret i32 %1
+}
+
+define i32 @defined_function(i32 %a) nounwind noinline {
+  %1 = add i32 %a, 1
+  ret i32 %1
+}
+
+define i32 @test_call_defined(i32 %a) {
+; CHECK-LABEL: test_call_defined:
+; CHECK: lui a1, %hi(defined_function)
+; CHECK: addi a1, a1, %lo(defined_function)
+; CHECK: jalr ra, a1, 0
+  %1 = call i32 @defined_function(i32 %a) nounwind
+  ret i32 %1
+}
+
+define i32 @test_call_indirect(i32 (i32)* %a, i32 %b) {
+; CHECK-LABEL: test_call_indirect:
+; CHECK: addi a2, a0, 0
+; CHECK: addi a0, a1, 0
+; CHECK: jalr ra, a2, 0
+  %1 = call i32 %a(i32 %b)
+  ret i32 %1
+}