//==- WebAssemblyAsmParser.cpp - Assembler for WebAssembly -*- C++ -*-==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file is part of the WebAssembly Assembler.
///
/// It contains code to translate a parsed .s file into MCInsts.
///
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "MCTargetDesc/WebAssemblyTargetStreamer.h"
#include "TargetInfo/WebAssemblyTargetInfo.h"
#include "WebAssembly.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCParser/MCParsedAsmOperand.h"
#include "llvm/MC/MCParser/MCTargetAsmParser.h"
#include "llvm/MC/MCSectionWasm.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCSymbolWasm.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/TargetRegistry.h"

using namespace llvm;

#define DEBUG_TYPE "wasm-asm-parser"

namespace {

/// WebAssemblyOperand - Instances of this class represent the operands in a
/// parsed WASM machine instruction.
struct WebAssemblyOperand : public MCParsedAsmOperand {
  enum KindTy { Token, Integer, Float, Symbol, BrList } Kind;

  SMLoc StartLoc, EndLoc;

  struct TokOp {
    StringRef Tok;
  };

  struct IntOp {
    int64_t Val;
  };

  struct FltOp {
    double Val;
  };

  struct SymOp {
    const MCExpr *Exp;
  };

  struct BrLOp {
    std::vector<unsigned> List;
  };

  union {
    struct TokOp Tok;
    struct IntOp Int;
    struct FltOp Flt;
    struct SymOp Sym;
    struct BrLOp BrL;
  };

  WebAssemblyOperand(KindTy K, SMLoc Start, SMLoc End, TokOp T)
      : Kind(K), StartLoc(Start), EndLoc(End), Tok(T) {}
  WebAssemblyOperand(KindTy K, SMLoc Start, SMLoc End, IntOp I)
      : Kind(K), StartLoc(Start), EndLoc(End), Int(I) {}
  WebAssemblyOperand(KindTy K, SMLoc Start, SMLoc End, FltOp F)
      : Kind(K), StartLoc(Start), EndLoc(End), Flt(F) {}
  WebAssemblyOperand(KindTy K, SMLoc Start, SMLoc End, SymOp S)
      : Kind(K), StartLoc(Start), EndLoc(End), Sym(S) {}
  WebAssemblyOperand(KindTy K, SMLoc Start, SMLoc End)
      : Kind(K), StartLoc(Start), EndLoc(End), BrL() {}

  ~WebAssemblyOperand() {
    if (isBrList())
      BrL.~BrLOp();
  }

  bool isToken() const override { return Kind == Token; }
  bool isImm() const override { return Kind == Integer || Kind == Symbol; }
  bool isFPImm() const { return Kind == Float; }
  bool isMem() const override { return false; }
  bool isReg() const override { return false; }
  bool isBrList() const { return Kind == BrList; }

  unsigned getReg() const override {
    llvm_unreachable("Assembly inspects a register operand");
    return 0;
  }

  StringRef getToken() const {
    assert(isToken());
    return Tok.Tok;
  }

  SMLoc getStartLoc() const override { return StartLoc; }
  SMLoc getEndLoc() const override { return EndLoc; }

  void addRegOperands(MCInst &, unsigned) const {
    // Required by the assembly matcher.
    llvm_unreachable("Assembly matcher creates register operands");
  }

  void addImmOperands(MCInst &Inst, unsigned N) const {
    assert(N == 1 && "Invalid number of operands!");
    if (Kind == Integer)
      Inst.addOperand(MCOperand::createImm(Int.Val));
    else if (Kind == Symbol)
      Inst.addOperand(MCOperand::createExpr(Sym.Exp));
    else
      llvm_unreachable("Should be integer immediate or symbol!");
  }

  void addFPImmOperands(MCInst &Inst, unsigned N) const {
    assert(N == 1 && "Invalid number of operands!");
    if (Kind == Float)
      Inst.addOperand(MCOperand::createFPImm(Flt.Val));
    else
      llvm_unreachable("Should be float immediate!");
  }

  void addBrListOperands(MCInst &Inst, unsigned N) const {
    assert(N == 1 && isBrList() && "Invalid BrList!");
    for (auto Br : BrL.List)
      Inst.addOperand(MCOperand::createImm(Br));
  }

  void print(raw_ostream &OS) const override {
    switch (Kind) {
    case Token:
      OS << "Tok:" << Tok.Tok;
      break;
    case Integer:
      OS << "Int:" << Int.Val;
      break;
    case Float:
      OS << "Flt:" << Flt.Val;
      break;
    case Symbol:
      OS << "Sym:" << Sym.Exp;
      break;
    case BrList:
      OS << "BrList:" << BrL.List.size();
      break;
    }
  }
};

class WebAssemblyAsmParser final : public MCTargetAsmParser {
  MCAsmParser &Parser;
  MCAsmLexer &Lexer;

  // Much like WebAssemblyAsmPrinter in the backend, we have to own these.
  std::vector<std::unique_ptr<wasm::WasmSignature>> Signatures;

  // Order of labels, directives and instructions in a .s file have no
  // syntactical enforcement. This class is a callback from the actual parser,
  // and yet we have to be feeding data to the streamer in a very particular
  // order to ensure a correct binary encoding that matches the regular backend
  // (the streamer does not enforce this). This "state machine" enum helps
  // guarantee that correct order.
  enum ParserState {
    FileStart,
    Label,
    FunctionStart,
    FunctionLocals,
    Instructions,
    EndFunction,
    DataSection,
  } CurrentState = FileStart;

  // For ensuring blocks are properly nested.
  enum NestingType {
    Function,
    Block,
    Loop,
    Try,
    If,
    Else,
    Undefined,
  };
  std::vector<NestingType> NestingStack;

  // We track this to see if a .functype following a label is the same,
  // as this is how we recognize the start of a function.
  MCSymbol *LastLabel = nullptr;
  MCSymbol *LastFunctionLabel = nullptr;

public:
  WebAssemblyAsmParser(const MCSubtargetInfo &STI, MCAsmParser &Parser,
                       const MCInstrInfo &MII, const MCTargetOptions &Options)
      : MCTargetAsmParser(Options, STI, MII), Parser(Parser),
        Lexer(Parser.getLexer()) {
    setAvailableFeatures(ComputeAvailableFeatures(STI.getFeatureBits()));
  }

#define GET_ASSEMBLER_HEADER
#include "WebAssemblyGenAsmMatcher.inc"

  // TODO: This is required to be implemented, but appears unused.
  bool ParseRegister(unsigned & /*RegNo*/, SMLoc & /*StartLoc*/,
                     SMLoc & /*EndLoc*/) override {
    llvm_unreachable("ParseRegister is not implemented.");
  }

  bool error(const Twine &Msg, const AsmToken &Tok) {
    return Parser.Error(Tok.getLoc(), Msg + Tok.getString());
  }

  bool error(const Twine &Msg) {
    return Parser.Error(Lexer.getTok().getLoc(), Msg);
  }

  void addSignature(std::unique_ptr<wasm::WasmSignature> &&Sig) {
    Signatures.push_back(std::move(Sig));
  }

  std::pair<StringRef, StringRef> nestingString(NestingType NT) {
    switch (NT) {
    case Function:
      return {"function", "end_function"};
    case Block:
      return {"block", "end_block"};
    case Loop:
      return {"loop", "end_loop"};
    case Try:
      return {"try", "end_try"};
    case If:
      return {"if", "end_if"};
    case Else:
      return {"else", "end_if"};
    default:
      llvm_unreachable("unknown NestingType");
    }
  }

  void push(NestingType NT) { NestingStack.push_back(NT); }

  bool pop(StringRef Ins, NestingType NT1, NestingType NT2 = Undefined) {
    if (NestingStack.empty())
      return error(Twine("End of block construct with no start: ") + Ins);
    auto Top = NestingStack.back();
    if (Top != NT1 && Top != NT2)
      return error(Twine("Block construct type mismatch, expected: ") +
                   nestingString(Top).second + ", instead got: " + Ins);
    NestingStack.pop_back();
    return false;
  }

  bool ensureEmptyNestingStack() {
    auto Err = !NestingStack.empty();
    while (!NestingStack.empty()) {
      error(Twine("Unmatched block construct(s) at function end: ") +
            nestingString(NestingStack.back()).first);
      NestingStack.pop_back();
    }
    return Err;
  }

  bool isNext(AsmToken::TokenKind Kind) {
    auto Ok = Lexer.is(Kind);
    if (Ok)
      Parser.Lex();
    return Ok;
  }

  bool expect(AsmToken::TokenKind Kind, const char *KindName) {
    if (!isNext(Kind))
      return error(std::string("Expected ") + KindName + ", instead got: ",
                   Lexer.getTok());
    return false;
  }

  StringRef expectIdent() {
    if (!Lexer.is(AsmToken::Identifier)) {
      error("Expected identifier, got: ", Lexer.getTok());
      return StringRef();
    }
    auto Name = Lexer.getTok().getString();
    Parser.Lex();
    return Name;
  }

  Optional<wasm::ValType> parseType(const StringRef &Type) {
    // FIXME: can't use StringSwitch because wasm::ValType doesn't have a
    // "invalid" value.
    if (Type == "i32")
      return wasm::ValType::I32;
    if (Type == "i64")
      return wasm::ValType::I64;
    if (Type == "f32")
      return wasm::ValType::F32;
    if (Type == "f64")
      return wasm::ValType::F64;
    if (Type == "v128" || Type == "i8x16" || Type == "i16x8" ||
        Type == "i32x4" || Type == "i64x2" || Type == "f32x4" ||
        Type == "f64x2")
      return wasm::ValType::V128;
    if (Type == "exnref")
      return wasm::ValType::EXNREF;
    return Optional<wasm::ValType>();
  }

  WebAssembly::BlockType parseBlockType(StringRef ID) {
    // Multivalue block types are handled separately in parseSignature
    return StringSwitch<WebAssembly::BlockType>(ID)
        .Case("i32", WebAssembly::BlockType::I32)
        .Case("i64", WebAssembly::BlockType::I64)
        .Case("f32", WebAssembly::BlockType::F32)
        .Case("f64", WebAssembly::BlockType::F64)
        .Case("v128", WebAssembly::BlockType::V128)
        .Case("exnref", WebAssembly::BlockType::Exnref)
        .Case("void", WebAssembly::BlockType::Void)
        .Default(WebAssembly::BlockType::Invalid);
  }

  bool parseRegTypeList(SmallVectorImpl<wasm::ValType> &Types) {
    while (Lexer.is(AsmToken::Identifier)) {
      auto Type = parseType(Lexer.getTok().getString());
      if (!Type)
        return error("unknown type: ", Lexer.getTok());
      Types.push_back(Type.getValue());
      Parser.Lex();
      if (!isNext(AsmToken::Comma))
        break;
    }
    return false;
  }

  void parseSingleInteger(bool IsNegative, OperandVector &Operands) {
    auto &Int = Lexer.getTok();
    int64_t Val = Int.getIntVal();
    if (IsNegative)
      Val = -Val;
    Operands.push_back(std::make_unique<WebAssemblyOperand>(
        WebAssemblyOperand::Integer, Int.getLoc(), Int.getEndLoc(),
        WebAssemblyOperand::IntOp{Val}));
    Parser.Lex();
  }

  bool parseSingleFloat(bool IsNegative, OperandVector &Operands) {
    auto &Flt = Lexer.getTok();
    double Val;
    if (Flt.getString().getAsDouble(Val, false))
      return error("Cannot parse real: ", Flt);
    if (IsNegative)
      Val = -Val;
    Operands.push_back(std::make_unique<WebAssemblyOperand>(
        WebAssemblyOperand::Float, Flt.getLoc(), Flt.getEndLoc(),
        WebAssemblyOperand::FltOp{Val}));
    Parser.Lex();
    return false;
  }

  bool parseSpecialFloatMaybe(bool IsNegative, OperandVector &Operands) {
    if (Lexer.isNot(AsmToken::Identifier))
      return true;
    auto &Flt = Lexer.getTok();
    auto S = Flt.getString();
    double Val;
    if (S.compare_lower("infinity") == 0) {
      Val = std::numeric_limits<double>::infinity();
    } else if (S.compare_lower("nan") == 0) {
      Val = std::numeric_limits<double>::quiet_NaN();
    } else {
      return true;
    }
    if (IsNegative)
      Val = -Val;
    Operands.push_back(std::make_unique<WebAssemblyOperand>(
        WebAssemblyOperand::Float, Flt.getLoc(), Flt.getEndLoc(),
        WebAssemblyOperand::FltOp{Val}));
    Parser.Lex();
    return false;
  }

  bool checkForP2AlignIfLoadStore(OperandVector &Operands, StringRef InstName) {
    // FIXME: there is probably a cleaner way to do this.
    auto IsLoadStore = InstName.find(".load") != StringRef::npos ||
                       InstName.find(".store") != StringRef::npos;
    auto IsAtomic = InstName.find("atomic.") != StringRef::npos;
    if (IsLoadStore || IsAtomic) {
      // Parse load/store operands of the form: offset:p2align=align
      if (IsLoadStore && isNext(AsmToken::Colon)) {
        auto Id = expectIdent();
        if (Id != "p2align")
          return error("Expected p2align, instead got: " + Id);
        if (expect(AsmToken::Equal, "="))
          return true;
        if (!Lexer.is(AsmToken::Integer))
          return error("Expected integer constant");
        parseSingleInteger(false, Operands);
      } else {
        // Alignment not specified (or atomics, must use default alignment).
        // We can't just call WebAssembly::GetDefaultP2Align since we don't have
        // an opcode until after the assembly matcher, so set a default to fix
        // up later.
        auto Tok = Lexer.getTok();
        Operands.push_back(std::make_unique<WebAssemblyOperand>(
            WebAssemblyOperand::Integer, Tok.getLoc(), Tok.getEndLoc(),
            WebAssemblyOperand::IntOp{-1}));
      }
    }
    return false;
  }

  void addBlockTypeOperand(OperandVector &Operands, SMLoc NameLoc,
                           WebAssembly::BlockType BT) {
    Operands.push_back(std::make_unique<WebAssemblyOperand>(
        WebAssemblyOperand::Integer, NameLoc, NameLoc,
        WebAssemblyOperand::IntOp{static_cast<int64_t>(BT)}));
  }

  bool ParseInstruction(ParseInstructionInfo & /*Info*/, StringRef Name,
                        SMLoc NameLoc, OperandVector &Operands) override {
    // Note: Name does NOT point into the sourcecode, but to a local, so
    // use NameLoc instead.
    Name = StringRef(NameLoc.getPointer(), Name.size());

    // WebAssembly has instructions with / in them, which AsmLexer parses
    // as seperate tokens, so if we find such tokens immediately adjacent (no
    // whitespace), expand the name to include them:
    for (;;) {
      auto &Sep = Lexer.getTok();
      if (Sep.getLoc().getPointer() != Name.end() ||
          Sep.getKind() != AsmToken::Slash)
        break;
      // Extend name with /
      Name = StringRef(Name.begin(), Name.size() + Sep.getString().size());
      Parser.Lex();
      // We must now find another identifier, or error.
      auto &Id = Lexer.getTok();
      if (Id.getKind() != AsmToken::Identifier ||
          Id.getLoc().getPointer() != Name.end())
        return error("Incomplete instruction name: ", Id);
      Name = StringRef(Name.begin(), Name.size() + Id.getString().size());
      Parser.Lex();
    }

    // Now construct the name as first operand.
    Operands.push_back(std::make_unique<WebAssemblyOperand>(
        WebAssemblyOperand::Token, NameLoc, SMLoc::getFromPointer(Name.end()),
        WebAssemblyOperand::TokOp{Name}));

    // If this instruction is part of a control flow structure, ensure
    // proper nesting.
    bool ExpectBlockType = false;
    bool ExpectFuncType = false;
    if (Name == "block") {
      push(Block);
      ExpectBlockType = true;
    } else if (Name == "loop") {
      push(Loop);
      ExpectBlockType = true;
    } else if (Name == "try") {
      push(Try);
      ExpectBlockType = true;
    } else if (Name == "if") {
      push(If);
      ExpectBlockType = true;
    } else if (Name == "else") {
      if (pop(Name, If))
        return true;
      push(Else);
    } else if (Name == "catch") {
      if (pop(Name, Try))
        return true;
      push(Try);
    } else if (Name == "end_if") {
      if (pop(Name, If, Else))
        return true;
    } else if (Name == "end_try") {
      if (pop(Name, Try))
        return true;
    } else if (Name == "end_loop") {
      if (pop(Name, Loop))
        return true;
    } else if (Name == "end_block") {
      if (pop(Name, Block))
        return true;
    } else if (Name == "end_function") {
      ensureLocals(getStreamer());
      CurrentState = EndFunction;
      if (pop(Name, Function) || ensureEmptyNestingStack())
        return true;
    } else if (Name == "call_indirect" || Name == "return_call_indirect") {
      ExpectFuncType = true;
    }

    if (ExpectFuncType || (ExpectBlockType && Lexer.is(AsmToken::LParen))) {
      // This has a special TYPEINDEX operand which in text we
      // represent as a signature, such that we can re-build this signature,
      // attach it to an anonymous symbol, which is what WasmObjectWriter
      // expects to be able to recreate the actual unique-ified type indices.
      auto Loc = Parser.getTok();
      auto Signature = std::make_unique<wasm::WasmSignature>();
      if (parseSignature(Signature.get()))
        return true;
      // Got signature as block type, don't need more
      ExpectBlockType = false;
      auto &Ctx = getStreamer().getContext();
      // The "true" here will cause this to be a nameless symbol.
      MCSymbol *Sym = Ctx.createTempSymbol("typeindex", true);
      auto *WasmSym = cast<MCSymbolWasm>(Sym);
      WasmSym->setSignature(Signature.get());
      addSignature(std::move(Signature));
      WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
      const MCExpr *Expr = MCSymbolRefExpr::create(
          WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, Ctx);
      Operands.push_back(std::make_unique<WebAssemblyOperand>(
          WebAssemblyOperand::Symbol, Loc.getLoc(), Loc.getEndLoc(),
          WebAssemblyOperand::SymOp{Expr}));
    }

    while (Lexer.isNot(AsmToken::EndOfStatement)) {
      auto &Tok = Lexer.getTok();
      switch (Tok.getKind()) {
      case AsmToken::Identifier: {
        if (!parseSpecialFloatMaybe(false, Operands))
          break;
        auto &Id = Lexer.getTok();
        if (ExpectBlockType) {
          // Assume this identifier is a block_type.
          auto BT = parseBlockType(Id.getString());
          if (BT == WebAssembly::BlockType::Invalid)
            return error("Unknown block type: ", Id);
          addBlockTypeOperand(Operands, NameLoc, BT);
          Parser.Lex();
        } else {
          // Assume this identifier is a label.
          const MCExpr *Val;
          SMLoc End;
          if (Parser.parseExpression(Val, End))
            return error("Cannot parse symbol: ", Lexer.getTok());
          Operands.push_back(std::make_unique<WebAssemblyOperand>(
              WebAssemblyOperand::Symbol, Id.getLoc(), Id.getEndLoc(),
              WebAssemblyOperand::SymOp{Val}));
          if (checkForP2AlignIfLoadStore(Operands, Name))
            return true;
        }
        break;
      }
      case AsmToken::Minus:
        Parser.Lex();
        if (Lexer.is(AsmToken::Integer)) {
          parseSingleInteger(true, Operands);
          if (checkForP2AlignIfLoadStore(Operands, Name))
            return true;
        } else if(Lexer.is(AsmToken::Real)) {
          if (parseSingleFloat(true, Operands))
            return true;
        } else if (!parseSpecialFloatMaybe(true, Operands)) {
        } else {
          return error("Expected numeric constant instead got: ",
                       Lexer.getTok());
        }
        break;
      case AsmToken::Integer:
        parseSingleInteger(false, Operands);
        if (checkForP2AlignIfLoadStore(Operands, Name))
          return true;
        break;
      case AsmToken::Real: {
        if (parseSingleFloat(false, Operands))
          return true;
        break;
      }
      case AsmToken::LCurly: {
        Parser.Lex();
        auto Op = std::make_unique<WebAssemblyOperand>(
            WebAssemblyOperand::BrList, Tok.getLoc(), Tok.getEndLoc());
        if (!Lexer.is(AsmToken::RCurly))
          for (;;) {
            Op->BrL.List.push_back(Lexer.getTok().getIntVal());
            expect(AsmToken::Integer, "integer");
            if (!isNext(AsmToken::Comma))
              break;
          }
        expect(AsmToken::RCurly, "}");
        Operands.push_back(std::move(Op));
        break;
      }
      default:
        return error("Unexpected token in operand: ", Tok);
      }
      if (Lexer.isNot(AsmToken::EndOfStatement)) {
        if (expect(AsmToken::Comma, ","))
          return true;
      }
    }
    if (ExpectBlockType && Operands.size() == 1) {
      // Support blocks with no operands as default to void.
      addBlockTypeOperand(Operands, NameLoc, WebAssembly::BlockType::Void);
    }
    Parser.Lex();
    return false;
  }

  void onLabelParsed(MCSymbol *Symbol) override {
    LastLabel = Symbol;
    CurrentState = Label;
  }

  bool parseSignature(wasm::WasmSignature *Signature) {
    if (expect(AsmToken::LParen, "("))
      return true;
    if (parseRegTypeList(Signature->Params))
      return true;
    if (expect(AsmToken::RParen, ")"))
      return true;
    if (expect(AsmToken::MinusGreater, "->"))
      return true;
    if (expect(AsmToken::LParen, "("))
      return true;
    if (parseRegTypeList(Signature->Returns))
      return true;
    if (expect(AsmToken::RParen, ")"))
      return true;
    return false;
  }

  bool CheckDataSection() {
    if (CurrentState != DataSection) {
      auto WS = cast<MCSectionWasm>(getStreamer().getCurrentSection().first);
      if (WS && WS->getKind().isText())
        return error("data directive must occur in a data segment: ",
                     Lexer.getTok());
    }
    CurrentState = DataSection;
    return false;
  }

  // This function processes wasm-specific directives streamed to
  // WebAssemblyTargetStreamer, all others go to the generic parser
  // (see WasmAsmParser).
  bool ParseDirective(AsmToken DirectiveID) override {
    // This function has a really weird return value behavior that is different
    // from all the other parsing functions:
    // - return true && no tokens consumed -> don't know this directive / let
    //   the generic parser handle it.
    // - return true && tokens consumed -> a parsing error occurred.
    // - return false -> processed this directive successfully.
    assert(DirectiveID.getKind() == AsmToken::Identifier);
    auto &Out = getStreamer();
    auto &TOut =
        reinterpret_cast<WebAssemblyTargetStreamer &>(*Out.getTargetStreamer());
    auto &Ctx = Out.getContext();

    // TODO: any time we return an error, at least one token must have been
    // consumed, otherwise this will not signal an error to the caller.
    if (DirectiveID.getString() == ".globaltype") {
      auto SymName = expectIdent();
      if (SymName.empty())
        return true;
      if (expect(AsmToken::Comma, ","))
        return true;
      auto TypeTok = Lexer.getTok();
      auto TypeName = expectIdent();
      if (TypeName.empty())
        return true;
      auto Type = parseType(TypeName);
      if (!Type)
        return error("Unknown type in .globaltype directive: ", TypeTok);
      // Now set this symbol with the correct type.
      auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
      WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
      WasmSym->setGlobalType(
          wasm::WasmGlobalType{uint8_t(Type.getValue()), true});
      // And emit the directive again.
      TOut.emitGlobalType(WasmSym);
      return expect(AsmToken::EndOfStatement, "EOL");
    }

    if (DirectiveID.getString() == ".functype") {
      // This code has to send things to the streamer similar to
      // WebAssemblyAsmPrinter::EmitFunctionBodyStart.
      // TODO: would be good to factor this into a common function, but the
      // assembler and backend really don't share any common code, and this code
      // parses the locals seperately.
      auto SymName = expectIdent();
      if (SymName.empty())
        return true;
      auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
      if (CurrentState == Label && WasmSym == LastLabel) {
        // This .functype indicates a start of a function.
        if (ensureEmptyNestingStack())
          return true;
        CurrentState = FunctionStart;
        LastFunctionLabel = LastLabel;
        push(Function);
      }
      auto Signature = std::make_unique<wasm::WasmSignature>();
      if (parseSignature(Signature.get()))
        return true;
      WasmSym->setSignature(Signature.get());
      addSignature(std::move(Signature));
      WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
      TOut.emitFunctionType(WasmSym);
      // TODO: backend also calls TOut.emitIndIdx, but that is not implemented.
      return expect(AsmToken::EndOfStatement, "EOL");
    }

    if (DirectiveID.getString() == ".export_name") {
      auto SymName = expectIdent();
      if (SymName.empty())
        return true;
      if (expect(AsmToken::Comma, ","))
        return true;
      auto ExportName = expectIdent();
      auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
      WasmSym->setExportName(ExportName);
      TOut.emitExportName(WasmSym, ExportName);
    }

    if (DirectiveID.getString() == ".import_module") {
      auto SymName = expectIdent();
      if (SymName.empty())
        return true;
      if (expect(AsmToken::Comma, ","))
        return true;
      auto ImportModule = expectIdent();
      auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
      WasmSym->setImportModule(ImportModule);
      TOut.emitImportModule(WasmSym, ImportModule);
    }

    if (DirectiveID.getString() == ".import_name") {
      auto SymName = expectIdent();
      if (SymName.empty())
        return true;
      if (expect(AsmToken::Comma, ","))
        return true;
      auto ImportName = expectIdent();
      auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
      WasmSym->setImportName(ImportName);
      TOut.emitImportName(WasmSym, ImportName);
    }

    if (DirectiveID.getString() == ".eventtype") {
      auto SymName = expectIdent();
      if (SymName.empty())
        return true;
      auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
      auto Signature = std::make_unique<wasm::WasmSignature>();
      if (parseRegTypeList(Signature->Params))
        return true;
      WasmSym->setSignature(Signature.get());
      addSignature(std::move(Signature));
      WasmSym->setType(wasm::WASM_SYMBOL_TYPE_EVENT);
      TOut.emitEventType(WasmSym);
      // TODO: backend also calls TOut.emitIndIdx, but that is not implemented.
      return expect(AsmToken::EndOfStatement, "EOL");
    }

    if (DirectiveID.getString() == ".local") {
      if (CurrentState != FunctionStart)
        return error(".local directive should follow the start of a function",
                     Lexer.getTok());
      SmallVector<wasm::ValType, 4> Locals;
      if (parseRegTypeList(Locals))
        return true;
      TOut.emitLocal(Locals);
      CurrentState = FunctionLocals;
      return expect(AsmToken::EndOfStatement, "EOL");
    }

    if (DirectiveID.getString() == ".int8" ||
        DirectiveID.getString() == ".int16" ||
        DirectiveID.getString() == ".int32" ||
        DirectiveID.getString() == ".int64") {
      if (CheckDataSection()) return true;
      const MCExpr *Val;
      SMLoc End;
      if (Parser.parseExpression(Val, End))
        return error("Cannot parse .int expression: ", Lexer.getTok());
      size_t NumBits = 0;
      DirectiveID.getString().drop_front(4).getAsInteger(10, NumBits);
      Out.EmitValue(Val, NumBits / 8, End);
      return expect(AsmToken::EndOfStatement, "EOL");
    }

    if (DirectiveID.getString() == ".asciz") {
      if (CheckDataSection()) return true;
      std::string S;
      if (Parser.parseEscapedString(S))
        return error("Cannot parse string constant: ", Lexer.getTok());
      Out.EmitBytes(StringRef(S.c_str(), S.length() + 1));
      return expect(AsmToken::EndOfStatement, "EOL");
    }

    return true; // We didn't process this directive.
  }

  // Called either when the first instruction is parsed of the function ends.
  void ensureLocals(MCStreamer &Out) {
    if (CurrentState == FunctionStart) {
      // We haven't seen a .local directive yet. The streamer requires locals to
      // be encoded as a prelude to the instructions, so emit an empty list of
      // locals here.
      auto &TOut = reinterpret_cast<WebAssemblyTargetStreamer &>(
          *Out.getTargetStreamer());
      TOut.emitLocal(SmallVector<wasm::ValType, 0>());
      CurrentState = FunctionLocals;
    }
  }

  bool MatchAndEmitInstruction(SMLoc IDLoc, unsigned & /*Opcode*/,
                               OperandVector &Operands, MCStreamer &Out,
                               uint64_t &ErrorInfo,
                               bool MatchingInlineAsm) override {
    MCInst Inst;
    Inst.setLoc(IDLoc);
    unsigned MatchResult =
        MatchInstructionImpl(Operands, Inst, ErrorInfo, MatchingInlineAsm);
    switch (MatchResult) {
    case Match_Success: {
      ensureLocals(Out);
      // Fix unknown p2align operands.
      auto Align = WebAssembly::GetDefaultP2AlignAny(Inst.getOpcode());
      if (Align != -1U) {
        auto &Op0 = Inst.getOperand(0);
        if (Op0.getImm() == -1)
          Op0.setImm(Align);
      }
      Out.EmitInstruction(Inst, getSTI());
      if (CurrentState == EndFunction) {
        onEndOfFunction();
      } else {
        CurrentState = Instructions;
      }
      return false;
    }
    case Match_MissingFeature:
      return Parser.Error(
          IDLoc, "instruction requires a WASM feature not currently enabled");
    case Match_MnemonicFail:
      return Parser.Error(IDLoc, "invalid instruction");
    case Match_NearMisses:
      return Parser.Error(IDLoc, "ambiguous instruction");
    case Match_InvalidTiedOperand:
    case Match_InvalidOperand: {
      SMLoc ErrorLoc = IDLoc;
      if (ErrorInfo != ~0ULL) {
        if (ErrorInfo >= Operands.size())
          return Parser.Error(IDLoc, "too few operands for instruction");
        ErrorLoc = Operands[ErrorInfo]->getStartLoc();
        if (ErrorLoc == SMLoc())
          ErrorLoc = IDLoc;
      }
      return Parser.Error(ErrorLoc, "invalid operand for instruction");
    }
    }
    llvm_unreachable("Implement any new match types added!");
  }

  void doBeforeLabelEmit(MCSymbol *Symbol) override {
    // Start a new section for the next function automatically, since our
    // object writer expects each function to have its own section. This way
    // The user can't forget this "convention".
    auto SymName = Symbol->getName();
    if (SymName.startswith(".L"))
      return; // Local Symbol.
    // Only create a new text section if we're already in one.
    auto CWS = cast<MCSectionWasm>(getStreamer().getCurrentSection().first);
    if (!CWS || !CWS->getKind().isText())
      return;
    auto SecName = ".text." + SymName;
    auto WS = getContext().getWasmSection(SecName, SectionKind::getText());
    getStreamer().SwitchSection(WS);
  }

  void onEndOfFunction() {
    // Automatically output a .size directive, so it becomes optional for the
    // user.
    if (!LastFunctionLabel) return;
    auto TempSym = getContext().createLinkerPrivateTempSymbol();
    getStreamer().EmitLabel(TempSym);
    auto Start = MCSymbolRefExpr::create(LastFunctionLabel, getContext());
    auto End = MCSymbolRefExpr::create(TempSym, getContext());
    auto Expr =
        MCBinaryExpr::create(MCBinaryExpr::Sub, End, Start, getContext());
    getStreamer().emitELFSize(LastFunctionLabel, Expr);
  }

  void onEndOfFile() override { ensureEmptyNestingStack(); }
};
} // end anonymous namespace

// Force static initialization.
extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeWebAssemblyAsmParser() {
  RegisterMCAsmParser<WebAssemblyAsmParser> X(getTheWebAssemblyTarget32());
  RegisterMCAsmParser<WebAssemblyAsmParser> Y(getTheWebAssemblyTarget64());
}

#define GET_REGISTER_MATCHER
#define GET_MATCHER_IMPLEMENTATION
#include "WebAssemblyGenAsmMatcher.inc"