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      1 //===-- WebAssemblyAsmPrinter.cpp - WebAssembly LLVM assembly writer ------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 ///
     10 /// \file
     11 /// \brief This file contains a printer that converts from our internal
     12 /// representation of machine-dependent LLVM code to the WebAssembly assembly
     13 /// language.
     14 ///
     15 //===----------------------------------------------------------------------===//
     16 
     17 #include "WebAssembly.h"
     18 #include "InstPrinter/WebAssemblyInstPrinter.h"
     19 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
     20 #include "WebAssemblyMCInstLower.h"
     21 #include "WebAssemblyMachineFunctionInfo.h"
     22 #include "WebAssemblyRegisterInfo.h"
     23 #include "WebAssemblySubtarget.h"
     24 #include "llvm/ADT/SmallString.h"
     25 #include "llvm/ADT/StringExtras.h"
     26 #include "llvm/CodeGen/Analysis.h"
     27 #include "llvm/CodeGen/AsmPrinter.h"
     28 #include "llvm/CodeGen/MachineConstantPool.h"
     29 #include "llvm/CodeGen/MachineInstr.h"
     30 #include "llvm/IR/DataLayout.h"
     31 #include "llvm/MC/MCContext.h"
     32 #include "llvm/MC/MCStreamer.h"
     33 #include "llvm/MC/MCSymbol.h"
     34 #include "llvm/Support/Debug.h"
     35 #include "llvm/Support/TargetRegistry.h"
     36 #include "llvm/Support/raw_ostream.h"
     37 using namespace llvm;
     38 
     39 #define DEBUG_TYPE "asm-printer"
     40 
     41 namespace {
     42 
     43 class WebAssemblyAsmPrinter final : public AsmPrinter {
     44   const MachineRegisterInfo *MRI;
     45   const WebAssemblyFunctionInfo *MFI;
     46 
     47 public:
     48   WebAssemblyAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
     49       : AsmPrinter(TM, std::move(Streamer)), MRI(nullptr), MFI(nullptr) {}
     50 
     51 private:
     52   const char *getPassName() const override {
     53     return "WebAssembly Assembly Printer";
     54   }
     55 
     56   //===------------------------------------------------------------------===//
     57   // MachineFunctionPass Implementation.
     58   //===------------------------------------------------------------------===//
     59 
     60   bool runOnMachineFunction(MachineFunction &MF) override {
     61     MRI = &MF.getRegInfo();
     62     MFI = MF.getInfo<WebAssemblyFunctionInfo>();
     63     return AsmPrinter::runOnMachineFunction(MF);
     64   }
     65 
     66   //===------------------------------------------------------------------===//
     67   // AsmPrinter Implementation.
     68   //===------------------------------------------------------------------===//
     69 
     70   void EmitJumpTableInfo() override;
     71   void EmitConstantPool() override;
     72   void EmitFunctionBodyStart() override;
     73   void EmitInstruction(const MachineInstr *MI) override;
     74   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
     75                        unsigned AsmVariant, const char *ExtraCode,
     76                        raw_ostream &OS) override;
     77   bool PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNo,
     78                              unsigned AsmVariant, const char *ExtraCode,
     79                              raw_ostream &OS) override;
     80 
     81   MVT getRegType(unsigned RegNo) const;
     82   const char *toString(MVT VT) const;
     83   std::string regToString(const MachineOperand &MO);
     84 };
     85 
     86 } // end anonymous namespace
     87 
     88 //===----------------------------------------------------------------------===//
     89 // Helpers.
     90 //===----------------------------------------------------------------------===//
     91 
     92 MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
     93   const TargetRegisterClass *TRC =
     94       TargetRegisterInfo::isVirtualRegister(RegNo) ?
     95       MRI->getRegClass(RegNo) :
     96       MRI->getTargetRegisterInfo()->getMinimalPhysRegClass(RegNo);
     97   for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64})
     98     if (TRC->hasType(T))
     99       return T;
    100   DEBUG(errs() << "Unknown type for register number: " << RegNo);
    101   llvm_unreachable("Unknown register type");
    102   return MVT::Other;
    103 }
    104 
    105 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
    106   unsigned RegNo = MO.getReg();
    107   assert(TargetRegisterInfo::isVirtualRegister(RegNo) &&
    108          "Unlowered physical register encountered during assembly printing");
    109   assert(!MFI->isVRegStackified(RegNo));
    110   unsigned WAReg = MFI->getWAReg(RegNo);
    111   assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
    112   return '$' + utostr(WAReg);
    113 }
    114 
    115 const char *WebAssemblyAsmPrinter::toString(MVT VT) const {
    116   return WebAssembly::TypeToString(VT);
    117 }
    118 
    119 //===----------------------------------------------------------------------===//
    120 // WebAssemblyAsmPrinter Implementation.
    121 //===----------------------------------------------------------------------===//
    122 
    123 void WebAssemblyAsmPrinter::EmitConstantPool() {
    124   assert(MF->getConstantPool()->getConstants().empty() &&
    125          "WebAssembly disables constant pools");
    126 }
    127 
    128 void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
    129   // Nothing to do; jump tables are incorporated into the instruction stream.
    130 }
    131 
    132 static void ComputeLegalValueVTs(const Function &F, const TargetMachine &TM,
    133                                  Type *Ty, SmallVectorImpl<MVT> &ValueVTs) {
    134   const DataLayout &DL(F.getParent()->getDataLayout());
    135   const WebAssemblyTargetLowering &TLI =
    136       *TM.getSubtarget<WebAssemblySubtarget>(F).getTargetLowering();
    137   SmallVector<EVT, 4> VTs;
    138   ComputeValueVTs(TLI, DL, Ty, VTs);
    139 
    140   for (EVT VT : VTs) {
    141     unsigned NumRegs = TLI.getNumRegisters(F.getContext(), VT);
    142     MVT RegisterVT = TLI.getRegisterType(F.getContext(), VT);
    143     for (unsigned i = 0; i != NumRegs; ++i)
    144       ValueVTs.push_back(RegisterVT);
    145   }
    146 }
    147 
    148 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
    149   if (!MFI->getParams().empty()) {
    150     MCInst Param;
    151     Param.setOpcode(WebAssembly::PARAM);
    152     for (MVT VT : MFI->getParams())
    153       Param.addOperand(MCOperand::createImm(VT.SimpleTy));
    154     EmitToStreamer(*OutStreamer, Param);
    155   }
    156 
    157   SmallVector<MVT, 4> ResultVTs;
    158   const Function &F(*MF->getFunction());
    159   ComputeLegalValueVTs(F, TM, F.getReturnType(), ResultVTs);
    160   // If the return type needs to be legalized it will get converted into
    161   // passing a pointer.
    162   if (ResultVTs.size() == 1) {
    163     MCInst Result;
    164     Result.setOpcode(WebAssembly::RESULT);
    165     Result.addOperand(MCOperand::createImm(ResultVTs.front().SimpleTy));
    166     EmitToStreamer(*OutStreamer, Result);
    167   }
    168 
    169   bool AnyWARegs = false;
    170   MCInst Local;
    171   Local.setOpcode(WebAssembly::LOCAL);
    172   for (unsigned Idx = 0, IdxE = MRI->getNumVirtRegs(); Idx != IdxE; ++Idx) {
    173     unsigned VReg = TargetRegisterInfo::index2VirtReg(Idx);
    174     unsigned WAReg = MFI->getWAReg(VReg);
    175     // Don't declare unused registers.
    176     if (WAReg == WebAssemblyFunctionInfo::UnusedReg)
    177       continue;
    178     // Don't redeclare parameters.
    179     if (WAReg < MFI->getParams().size())
    180       continue;
    181     // Don't declare stackified registers.
    182     if (int(WAReg) < 0)
    183       continue;
    184     Local.addOperand(MCOperand::createImm(getRegType(VReg).SimpleTy));
    185     AnyWARegs = true;
    186   }
    187   auto &PhysRegs = MFI->getPhysRegs();
    188   for (unsigned PReg = 0; PReg < PhysRegs.size(); ++PReg) {
    189     if (PhysRegs[PReg] == -1U)
    190       continue;
    191     Local.addOperand(MCOperand::createImm(getRegType(PReg).SimpleTy));
    192     AnyWARegs = true;
    193   }
    194   if (AnyWARegs)
    195     EmitToStreamer(*OutStreamer, Local);
    196 
    197   AsmPrinter::EmitFunctionBodyStart();
    198 }
    199 
    200 void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
    201   DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
    202 
    203   switch (MI->getOpcode()) {
    204   case WebAssembly::ARGUMENT_I32:
    205   case WebAssembly::ARGUMENT_I64:
    206   case WebAssembly::ARGUMENT_F32:
    207   case WebAssembly::ARGUMENT_F64:
    208     // These represent values which are live into the function entry, so there's
    209     // no instruction to emit.
    210     break;
    211   case WebAssembly::LOOP_END:
    212     // This is a no-op which just exists to tell AsmPrinter.cpp that there's a
    213     // fallthrough which nevertheless requires a label for the destination here.
    214     break;
    215   default: {
    216     WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
    217     MCInst TmpInst;
    218     MCInstLowering.Lower(MI, TmpInst);
    219     EmitToStreamer(*OutStreamer, TmpInst);
    220     break;
    221   }
    222   }
    223 }
    224 
    225 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
    226                                             unsigned OpNo, unsigned AsmVariant,
    227                                             const char *ExtraCode,
    228                                             raw_ostream &OS) {
    229   if (AsmVariant != 0)
    230     report_fatal_error("There are no defined alternate asm variants");
    231 
    232   // First try the generic code, which knows about modifiers like 'c' and 'n'.
    233   if (!AsmPrinter::PrintAsmOperand(MI, OpNo, AsmVariant, ExtraCode, OS))
    234     return false;
    235 
    236   if (!ExtraCode) {
    237     const MachineOperand &MO = MI->getOperand(OpNo);
    238     switch (MO.getType()) {
    239     case MachineOperand::MO_Immediate:
    240       OS << MO.getImm();
    241       return false;
    242     case MachineOperand::MO_Register:
    243       OS << regToString(MO);
    244       return false;
    245     case MachineOperand::MO_GlobalAddress:
    246       getSymbol(MO.getGlobal())->print(OS, MAI);
    247       printOffset(MO.getOffset(), OS);
    248       return false;
    249     case MachineOperand::MO_ExternalSymbol:
    250       GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
    251       printOffset(MO.getOffset(), OS);
    252       return false;
    253     case MachineOperand::MO_MachineBasicBlock:
    254       MO.getMBB()->getSymbol()->print(OS, MAI);
    255       return false;
    256     default:
    257       break;
    258     }
    259   }
    260 
    261   return true;
    262 }
    263 
    264 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
    265                                                   unsigned OpNo,
    266                                                   unsigned AsmVariant,
    267                                                   const char *ExtraCode,
    268                                                   raw_ostream &OS) {
    269   if (AsmVariant != 0)
    270     report_fatal_error("There are no defined alternate asm variants");
    271 
    272   if (!ExtraCode) {
    273     // TODO: For now, we just hard-code 0 as the constant offset; teach
    274     // SelectInlineAsmMemoryOperand how to do address mode matching.
    275     OS << "0(" + regToString(MI->getOperand(OpNo)) + ')';
    276     return false;
    277   }
    278 
    279   return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, AsmVariant, ExtraCode, OS);
    280 }
    281 
    282 // Force static initialization.
    283 extern "C" void LLVMInitializeWebAssemblyAsmPrinter() {
    284   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(TheWebAssemblyTarget32);
    285   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(TheWebAssemblyTarget64);
    286 }
    287