// Copyright 2016 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Used for encoding f32 and double constants to bits.
let byte_view = new Uint8Array(8);
let data_view = new DataView(byte_view.buffer);

// The bytes function receives one of
//  - several arguments, each of which is either a number or a string of length
//    1; if it's a string, the charcode of the contained character is used.
//  - a single array argument containing the actual arguments
//  - a single string; the returned buffer will contain the char codes of all
//    contained characters.
function bytes(...input) {
  if (input.length == 1 && typeof input[0] == 'array') input = input[0];
  if (input.length == 1 && typeof input[0] == 'string') {
    let len = input[0].length;
    let view = new Uint8Array(len);
    for (let i = 0; i < len; i++) view[i] = input[0].charCodeAt(i);
    return view.buffer;
  }
  let view = new Uint8Array(input.length);
  for (let i = 0; i < input.length; i++) {
    let val = input[i];
    if (typeof val == 'string') {
      if (val.length != 1) {
        throw new Error('string inputs must have length 1');
      }
      val = val.charCodeAt(0);
    }
    view[i] = val | 0;
  }
  return view.buffer;
}

// Header declaration constants
var kWasmH0 = 0;
var kWasmH1 = 0x61;
var kWasmH2 = 0x73;
var kWasmH3 = 0x6d;

var kWasmV0 = 0x1;
var kWasmV1 = 0;
var kWasmV2 = 0;
var kWasmV3 = 0;

var kHeaderSize = 8;
var kPageSize = 65536;
var kSpecMaxPages = 65536;
var kMaxVarInt32Size = 5;
var kMaxVarInt64Size = 10;

let kDeclNoLocals = 0;

// Section declaration constants
let kUnknownSectionCode = 0;
let kTypeSectionCode = 1;        // Function signature declarations
let kImportSectionCode = 2;      // Import declarations
let kFunctionSectionCode = 3;    // Function declarations
let kTableSectionCode = 4;       // Indirect function table and other tables
let kMemorySectionCode = 5;      // Memory attributes
let kGlobalSectionCode = 6;      // Global declarations
let kExportSectionCode = 7;      // Exports
let kStartSectionCode = 8;       // Start function declaration
let kElementSectionCode = 9;     // Elements section
let kCodeSectionCode = 10;       // Function code
let kDataSectionCode = 11;       // Data segments
let kDataCountSectionCode = 12;  // Data segment count (between Element & Code)
let kTagSectionCode = 13;        // Tag section (between Memory & Global)
let kStringRefSectionCode = 14;  // Stringref literals section (between Tag & Global)
let kLastKnownSectionCode = 14;

// Name section types
let kModuleNameCode = 0;
let kFunctionNamesCode = 1;
let kLocalNamesCode = 2;

let kWasmFunctionTypeForm = 0x60;
let kWasmStructTypeForm = 0x5f;
let kWasmArrayTypeForm = 0x5e;
let kWasmFunctionNominalForm = 0x5d;
let kWasmStructNominalForm = 0x5c;
let kWasmArrayNominalForm = 0x5b;
let kWasmSubtypeForm = 0x50;
let kWasmRecursiveTypeGroupForm = 0x4f;

let kNoSuperType = 0xFFFFFFFF;

let kLimitsNoMaximum = 0x00;
let kLimitsWithMaximum = 0x01;
let kLimitsSharedNoMaximum = 0x02;
let kLimitsSharedWithMaximum = 0x03;
let kLimitsMemory64NoMaximum = 0x04;
let kLimitsMemory64WithMaximum = 0x05;

// Segment flags
let kActiveNoIndex = 0;
let kPassive = 1;
let kActiveWithIndex = 2;
let kDeclarative = 3;
let kPassiveWithElements = 5;
let kDeclarativeWithElements = 7;

// Function declaration flags
let kDeclFunctionName = 0x01;
let kDeclFunctionImport = 0x02;
let kDeclFunctionLocals = 0x04;
let kDeclFunctionExport = 0x08;

// Value types and related
let kWasmVoid = 0x40;
let kWasmI32 = 0x7f;
let kWasmI64 = 0x7e;
let kWasmF32 = 0x7d;
let kWasmF64 = 0x7c;
let kWasmS128 = 0x7b;
let kWasmI8 = 0x7a;
let kWasmI16 = 0x79;

// These are defined as negative integers to distinguish them from positive type
// indices.
let kWasmFuncRef = -0x10;
let kWasmAnyFunc = kWasmFuncRef;  // Alias named as in the JS API spec
let kWasmAnyRef = -0x11;
let kWasmExternRef = kWasmAnyRef;  // Alias for test backwards compatibility.
let kWasmEqRef = -0x13;
let kWasmI31Ref = -0x16;
let kWasmDataRef = -0x19;
let kWasmArrayRef = -0x1a;
let kWasmStringRef = -0x1b;
let kWasmStringViewWtf8 = -0x1c;
let kWasmStringViewWtf16 = -0x1d;
let kWasmStringViewIter = -0x1e;

// Use the positive-byte versions inside function bodies.
let kLeb128Mask = 0x7f;
let kFuncRefCode = kWasmFuncRef & kLeb128Mask;
let kAnyFuncCode = kFuncRefCode;  // Alias named as in the JS API spec
let kExternRefCode = kWasmExternRef & kLeb128Mask;
let kAnyRefCode = kWasmAnyRef & kLeb128Mask;
let kEqRefCode = kWasmEqRef & kLeb128Mask;
let kI31RefCode = kWasmI31Ref & kLeb128Mask;
let kDataRefCode = kWasmDataRef & kLeb128Mask;
let kArrayRefCode = kWasmArrayRef & kLeb128Mask;
let kStringRefCode = kWasmStringRef & kLeb128Mask;
let kStringViewWtf8Code = kWasmStringViewWtf8 & kLeb128Mask;
let kStringViewWtf16Code = kWasmStringViewWtf16 & kLeb128Mask;
let kStringViewIterCode = kWasmStringViewIter & kLeb128Mask;

let kWasmOptRef = 0x6c;
let kWasmRef = 0x6b;
function wasmOptRefType(heap_type) {
  return {opcode: kWasmOptRef, heap_type: heap_type};
}
function wasmRefType(heap_type) {
  return {opcode: kWasmRef, heap_type: heap_type};
}

let kWasmRtt = 0x68;
function wasmRtt(index) {
  if (index < 0) throw new Error("Expecting non-negative type index");
  return {opcode: kWasmRtt, index: index};
}

let kExternalFunction = 0;
let kExternalTable = 1;
let kExternalMemory = 2;
let kExternalGlobal = 3;
let kExternalTag = 4;

let kTableZero = 0;
let kMemoryZero = 0;
let kSegmentZero = 0;

let kExceptionAttribute = 0;

// Useful signatures
let kSig_i_i = makeSig([kWasmI32], [kWasmI32]);
let kSig_l_l = makeSig([kWasmI64], [kWasmI64]);
let kSig_i_l = makeSig([kWasmI64], [kWasmI32]);
let kSig_i_ii = makeSig([kWasmI32, kWasmI32], [kWasmI32]);
let kSig_i_iii = makeSig([kWasmI32, kWasmI32, kWasmI32], [kWasmI32]);
let kSig_v_iiii = makeSig([kWasmI32, kWasmI32, kWasmI32, kWasmI32], []);
let kSig_f_ff = makeSig([kWasmF32, kWasmF32], [kWasmF32]);
let kSig_d_dd = makeSig([kWasmF64, kWasmF64], [kWasmF64]);
let kSig_l_ll = makeSig([kWasmI64, kWasmI64], [kWasmI64]);
let kSig_i_dd = makeSig([kWasmF64, kWasmF64], [kWasmI32]);
let kSig_v_v = makeSig([], []);
let kSig_i_v = makeSig([], [kWasmI32]);
let kSig_l_v = makeSig([], [kWasmI64]);
let kSig_f_v = makeSig([], [kWasmF32]);
let kSig_d_v = makeSig([], [kWasmF64]);
let kSig_v_i = makeSig([kWasmI32], []);
let kSig_v_ii = makeSig([kWasmI32, kWasmI32], []);
let kSig_v_iii = makeSig([kWasmI32, kWasmI32, kWasmI32], []);
let kSig_v_l = makeSig([kWasmI64], []);
let kSig_v_d = makeSig([kWasmF64], []);
let kSig_v_dd = makeSig([kWasmF64, kWasmF64], []);
let kSig_v_ddi = makeSig([kWasmF64, kWasmF64, kWasmI32], []);
let kSig_ii_v = makeSig([], [kWasmI32, kWasmI32]);
let kSig_iii_v = makeSig([], [kWasmI32, kWasmI32, kWasmI32]);
let kSig_ii_i = makeSig([kWasmI32], [kWasmI32, kWasmI32]);
let kSig_iii_i = makeSig([kWasmI32], [kWasmI32, kWasmI32, kWasmI32]);
let kSig_ii_ii = makeSig([kWasmI32, kWasmI32], [kWasmI32, kWasmI32]);
let kSig_iii_ii = makeSig([kWasmI32, kWasmI32], [kWasmI32, kWasmI32, kWasmI32]);

let kSig_v_f = makeSig([kWasmF32], []);
let kSig_f_f = makeSig([kWasmF32], [kWasmF32]);
let kSig_f_d = makeSig([kWasmF64], [kWasmF32]);
let kSig_d_d = makeSig([kWasmF64], [kWasmF64]);
let kSig_r_r = makeSig([kWasmExternRef], [kWasmExternRef]);
let kSig_a_a = makeSig([kWasmAnyFunc], [kWasmAnyFunc]);
let kSig_i_r = makeSig([kWasmExternRef], [kWasmI32]);
let kSig_v_r = makeSig([kWasmExternRef], []);
let kSig_v_a = makeSig([kWasmAnyFunc], []);
let kSig_v_rr = makeSig([kWasmExternRef, kWasmExternRef], []);
let kSig_v_aa = makeSig([kWasmAnyFunc, kWasmAnyFunc], []);
let kSig_r_v = makeSig([], [kWasmExternRef]);
let kSig_a_v = makeSig([], [kWasmAnyFunc]);
let kSig_a_i = makeSig([kWasmI32], [kWasmAnyFunc]);
let kSig_s_i = makeSig([kWasmI32], [kWasmS128]);
let kSig_i_s = makeSig([kWasmS128], [kWasmI32]);

function makeSig(params, results) {
  return {params: params, results: results};
}

function makeSig_v_x(x) {
  return makeSig([x], []);
}

function makeSig_x_v(x) {
  return makeSig([], [x]);
}

function makeSig_v_xx(x) {
  return makeSig([x, x], []);
}

function makeSig_r_v(r) {
  return makeSig([], [r]);
}

function makeSig_r_x(r, x) {
  return makeSig([x], [r]);
}

function makeSig_r_xx(r, x) {
  return makeSig([x, x], [r]);
}

// Opcodes
const kWasmOpcodes = {
  'Unreachable': 0x00,
  'Nop': 0x01,
  'Block': 0x02,
  'Loop': 0x03,
  'If': 0x04,
  'Else': 0x05,
  'Try': 0x06,
  'Catch': 0x07,
  'Throw': 0x08,
  'Rethrow': 0x09,
  'CatchAll': 0x19,
  'End': 0x0b,
  'Br': 0x0c,
  'BrIf': 0x0d,
  'BrTable': 0x0e,
  'Return': 0x0f,
  'CallFunction': 0x10,
  'CallIndirect': 0x11,
  'ReturnCall': 0x12,
  'ReturnCallIndirect': 0x13,
  'CallRef': 0x14,
  'ReturnCallRef': 0x15,
  'Let': 0x17,
  'Delegate': 0x18,
  'Drop': 0x1a,
  'Select': 0x1b,
  'SelectWithType': 0x1c,
  'LocalGet': 0x20,
  'LocalSet': 0x21,
  'LocalTee': 0x22,
  'GlobalGet': 0x23,
  'GlobalSet': 0x24,
  'TableGet': 0x25,
  'TableSet': 0x26,
  'I32LoadMem': 0x28,
  'I64LoadMem': 0x29,
  'F32LoadMem': 0x2a,
  'F64LoadMem': 0x2b,
  'I32LoadMem8S': 0x2c,
  'I32LoadMem8U': 0x2d,
  'I32LoadMem16S': 0x2e,
  'I32LoadMem16U': 0x2f,
  'I64LoadMem8S': 0x30,
  'I64LoadMem8U': 0x31,
  'I64LoadMem16S': 0x32,
  'I64LoadMem16U': 0x33,
  'I64LoadMem32S': 0x34,
  'I64LoadMem32U': 0x35,
  'I32StoreMem': 0x36,
  'I64StoreMem': 0x37,
  'F32StoreMem': 0x38,
  'F64StoreMem': 0x39,
  'I32StoreMem8': 0x3a,
  'I32StoreMem16': 0x3b,
  'I64StoreMem8': 0x3c,
  'I64StoreMem16': 0x3d,
  'I64StoreMem32': 0x3e,
  'MemorySize': 0x3f,
  'MemoryGrow': 0x40,
  'I32Const': 0x41,
  'I64Const': 0x42,
  'F32Const': 0x43,
  'F64Const': 0x44,
  'I32Eqz': 0x45,
  'I32Eq': 0x46,
  'I32Ne': 0x47,
  'I32LtS': 0x48,
  'I32LtU': 0x49,
  'I32GtS': 0x4a,
  'I32GtU': 0x4b,
  'I32LeS': 0x4c,
  'I32LeU': 0x4d,
  'I32GeS': 0x4e,
  'I32GeU': 0x4f,
  'I64Eqz': 0x50,
  'I64Eq': 0x51,
  'I64Ne': 0x52,
  'I64LtS': 0x53,
  'I64LtU': 0x54,
  'I64GtS': 0x55,
  'I64GtU': 0x56,
  'I64LeS': 0x57,
  'I64LeU': 0x58,
  'I64GeS': 0x59,
  'I64GeU': 0x5a,
  'F32Eq': 0x5b,
  'F32Ne': 0x5c,
  'F32Lt': 0x5d,
  'F32Gt': 0x5e,
  'F32Le': 0x5f,
  'F32Ge': 0x60,
  'F64Eq': 0x61,
  'F64Ne': 0x62,
  'F64Lt': 0x63,
  'F64Gt': 0x64,
  'F64Le': 0x65,
  'F64Ge': 0x66,
  'I32Clz': 0x67,
  'I32Ctz': 0x68,
  'I32Popcnt': 0x69,
  'I32Add': 0x6a,
  'I32Sub': 0x6b,
  'I32Mul': 0x6c,
  'I32DivS': 0x6d,
  'I32DivU': 0x6e,
  'I32RemS': 0x6f,
  'I32RemU': 0x70,
  'I32And': 0x71,
  'I32Ior': 0x72,
  'I32Xor': 0x73,
  'I32Shl': 0x74,
  'I32ShrS': 0x75,
  'I32ShrU': 0x76,
  'I32Rol': 0x77,
  'I32Ror': 0x78,
  'I64Clz': 0x79,
  'I64Ctz': 0x7a,
  'I64Popcnt': 0x7b,
  'I64Add': 0x7c,
  'I64Sub': 0x7d,
  'I64Mul': 0x7e,
  'I64DivS': 0x7f,
  'I64DivU': 0x80,
  'I64RemS': 0x81,
  'I64RemU': 0x82,
  'I64And': 0x83,
  'I64Ior': 0x84,
  'I64Xor': 0x85,
  'I64Shl': 0x86,
  'I64ShrS': 0x87,
  'I64ShrU': 0x88,
  'I64Rol': 0x89,
  'I64Ror': 0x8a,
  'F32Abs': 0x8b,
  'F32Neg': 0x8c,
  'F32Ceil': 0x8d,
  'F32Floor': 0x8e,
  'F32Trunc': 0x8f,
  'F32NearestInt': 0x90,
  'F32Sqrt': 0x91,
  'F32Add': 0x92,
  'F32Sub': 0x93,
  'F32Mul': 0x94,
  'F32Div': 0x95,
  'F32Min': 0x96,
  'F32Max': 0x97,
  'F32CopySign': 0x98,
  'F64Abs': 0x99,
  'F64Neg': 0x9a,
  'F64Ceil': 0x9b,
  'F64Floor': 0x9c,
  'F64Trunc': 0x9d,
  'F64NearestInt': 0x9e,
  'F64Sqrt': 0x9f,
  'F64Add': 0xa0,
  'F64Sub': 0xa1,
  'F64Mul': 0xa2,
  'F64Div': 0xa3,
  'F64Min': 0xa4,
  'F64Max': 0xa5,
  'F64CopySign': 0xa6,
  'I32ConvertI64': 0xa7,
  'I32SConvertF32': 0xa8,
  'I32UConvertF32': 0xa9,
  'I32SConvertF64': 0xaa,
  'I32UConvertF64': 0xab,
  'I64SConvertI32': 0xac,
  'I64UConvertI32': 0xad,
  'I64SConvertF32': 0xae,
  'I64UConvertF32': 0xaf,
  'I64SConvertF64': 0xb0,
  'I64UConvertF64': 0xb1,
  'F32SConvertI32': 0xb2,
  'F32UConvertI32': 0xb3,
  'F32SConvertI64': 0xb4,
  'F32UConvertI64': 0xb5,
  'F32ConvertF64': 0xb6,
  'F64SConvertI32': 0xb7,
  'F64UConvertI32': 0xb8,
  'F64SConvertI64': 0xb9,
  'F64UConvertI64': 0xba,
  'F64ConvertF32': 0xbb,
  'I32ReinterpretF32': 0xbc,
  'I64ReinterpretF64': 0xbd,
  'F32ReinterpretI32': 0xbe,
  'F64ReinterpretI64': 0xbf,
  'I32SExtendI8': 0xc0,
  'I32SExtendI16': 0xc1,
  'I64SExtendI8': 0xc2,
  'I64SExtendI16': 0xc3,
  'I64SExtendI32': 0xc4,
  'RefNull': 0xd0,
  'RefIsNull': 0xd1,
  'RefFunc': 0xd2,
  'RefAsNonNull': 0xd3,
  'BrOnNull': 0xd4,
  'RefEq': 0xd5,
  'BrOnNonNull': 0xd6
};

function defineWasmOpcode(name, value) {
  if (globalThis.kWasmOpcodeNames === undefined) {
    globalThis.kWasmOpcodeNames = {};
  }
  Object.defineProperty(globalThis, name, {value: value});
  if (globalThis.kWasmOpcodeNames[value] !== undefined) {
    throw new Error(`Duplicate wasm opcode: ${value}. Previous name: ${
        globalThis.kWasmOpcodeNames[value]}, new name: ${name}`);
  }
  globalThis.kWasmOpcodeNames[value] = name;
}
for (let name in kWasmOpcodes) {
  defineWasmOpcode(`kExpr${name}`, kWasmOpcodes[name]);
}

// Prefix opcodes
const kPrefixOpcodes = {
  'GC': 0xfb,
  'Numeric': 0xfc,
  'Simd': 0xfd,
  'Atomic': 0xfe
};
for (let prefix in kPrefixOpcodes) {
  defineWasmOpcode(`k${prefix}Prefix`, kPrefixOpcodes[prefix]);
}

// GC opcodes
let kExprStructNewWithRtt = 0x01;
let kExprStructNewDefaultWithRtt = 0x02;
let kExprStructGet = 0x03;
let kExprStructGetS = 0x04;
let kExprStructGetU = 0x05;
let kExprStructSet = 0x06;
let kExprStructNew = 0x07;
let kExprStructNewDefault = 0x08;
let kExprArrayNewWithRtt = 0x11;
let kExprArrayNewDefaultWithRtt = 0x12;
let kExprArrayGet = 0x13;
let kExprArrayGetS = 0x14;
let kExprArrayGetU = 0x15;
let kExprArraySet = 0x16;
let kExprArrayLen = 0x17;
let kExprArrayCopy = 0x18;
let kExprArrayInit = 0x19;
let kExprArrayInitStatic = 0x1a;
let kExprArrayNew = 0x1b;
let kExprArrayNewDefault = 0x1c;
let kExprArrayInitFromData = 0x1e;
let kExprArrayInitFromDataStatic = 0x1d;
let kExprI31New = 0x20;
let kExprI31GetS = 0x21;
let kExprI31GetU = 0x22;
let kExprRttCanon = 0x30;
let kExprRttSub = 0x31;
let kExprRttFreshSub = 0x32;
let kExprRefTest = 0x40;
let kExprRefCast = 0x41;
let kExprBrOnCast = 0x42;
let kExprBrOnCastFail = 0x43;
let kExprRefTestStatic = 0x44;
let kExprRefCastStatic = 0x45;
let kExprBrOnCastStatic = 0x46;
let kExprBrOnCastStaticFail = 0x47;
let kExprRefCastNopStatic = 0x48;
let kExprRefIsFunc = 0x50;
let kExprRefIsData = 0x51;
let kExprRefIsI31 = 0x52;
let kExprRefIsArray = 0x53;
let kExprRefAsFunc = 0x58;
let kExprRefAsData = 0x59;
let kExprRefAsI31 = 0x5a;
let kExprRefAsArray = 0x5b;
let kExprBrOnFunc = 0x60;
let kExprBrOnData = 0x61;
let kExprBrOnI31 = 0x62;
let kExprBrOnArray = 0x66;
let kExprBrOnNonFunc = 0x63;
let kExprBrOnNonData = 0x64;
let kExprBrOnNonI31 = 0x65;
let kExprBrOnNonArray = 0x67;
let kExprStringNewWtf8 = 0x80;
let kExprStringNewWtf16 = 0x81;
let kExprStringConst = 0x82;
let kExprStringMeasureUtf8 = 0x83;
let kExprStringMeasureWtf8 = 0x84;
let kExprStringMeasureWtf16 = 0x85;
let kExprStringEncodeWtf8 = 0x86;
let kExprStringEncodeWtf16 = 0x87;
let kExprStringConcat = 0x88;
let kExprStringEq = 0x89;
let kExprStringIsUsvSequence = 0x8a;
let kExprStringAsWtf8 = 0x90;
let kExprStringViewWtf8Advance = 0x91;
let kExprStringViewWtf8Encode = 0x92;
let kExprStringViewWtf8Slice = 0x93;
let kExprStringAsWtf16 = 0x98;
let kExprStringViewWtf16Length = 0x99;
let kExprStringViewWtf16GetCodeunit = 0x9a;
let kExprStringViewWtf16Encode = 0x9b;
let kExprStringViewWtf16Slice = 0x9c;
let kExprStringAsIter = 0xa0;
let kExprStringViewIterCur = 0xa1
let kExprStringViewIterAdvance = 0xa2;
let kExprStringViewIterRewind = 0xa3
let kExprStringViewIterSlice = 0xa4;

// Numeric opcodes.
let kExprI32SConvertSatF32 = 0x00;
let kExprI32UConvertSatF32 = 0x01;
let kExprI32SConvertSatF64 = 0x02;
let kExprI32UConvertSatF64 = 0x03;
let kExprI64SConvertSatF32 = 0x04;
let kExprI64UConvertSatF32 = 0x05;
let kExprI64SConvertSatF64 = 0x06;
let kExprI64UConvertSatF64 = 0x07;
let kExprMemoryInit = 0x08;
let kExprDataDrop = 0x09;
let kExprMemoryCopy = 0x0a;
let kExprMemoryFill = 0x0b;
let kExprTableInit = 0x0c;
let kExprElemDrop = 0x0d;
let kExprTableCopy = 0x0e;
let kExprTableGrow = 0x0f;
let kExprTableSize = 0x10;
let kExprTableFill = 0x11;

// Atomic opcodes.
let kExprAtomicNotify = 0x00;
let kExprI32AtomicWait = 0x01;
let kExprI64AtomicWait = 0x02;
let kExprI32AtomicLoad = 0x10;
let kExprI32AtomicLoad8U = 0x12;
let kExprI32AtomicLoad16U = 0x13;
let kExprI32AtomicStore = 0x17;
let kExprI32AtomicStore8U = 0x19;
let kExprI32AtomicStore16U = 0x1a;
let kExprI32AtomicAdd = 0x1e;
let kExprI32AtomicAdd8U = 0x20;
let kExprI32AtomicAdd16U = 0x21;
let kExprI32AtomicSub = 0x25;
let kExprI32AtomicSub8U = 0x27;
let kExprI32AtomicSub16U = 0x28;
let kExprI32AtomicAnd = 0x2c;
let kExprI32AtomicAnd8U = 0x2e;
let kExprI32AtomicAnd16U = 0x2f;
let kExprI32AtomicOr = 0x33;
let kExprI32AtomicOr8U = 0x35;
let kExprI32AtomicOr16U = 0x36;
let kExprI32AtomicXor = 0x3a;
let kExprI32AtomicXor8U = 0x3c;
let kExprI32AtomicXor16U = 0x3d;
let kExprI32AtomicExchange = 0x41;
let kExprI32AtomicExchange8U = 0x43;
let kExprI32AtomicExchange16U = 0x44;
let kExprI32AtomicCompareExchange = 0x48;
let kExprI32AtomicCompareExchange8U = 0x4a;
let kExprI32AtomicCompareExchange16U = 0x4b;

let kExprI64AtomicLoad = 0x11;
let kExprI64AtomicLoad8U = 0x14;
let kExprI64AtomicLoad16U = 0x15;
let kExprI64AtomicLoad32U = 0x16;
let kExprI64AtomicStore = 0x18;
let kExprI64AtomicStore8U = 0x1b;
let kExprI64AtomicStore16U = 0x1c;
let kExprI64AtomicStore32U = 0x1d;
let kExprI64AtomicAdd = 0x1f;
let kExprI64AtomicAdd8U = 0x22;
let kExprI64AtomicAdd16U = 0x23;
let kExprI64AtomicAdd32U = 0x24;
let kExprI64AtomicSub = 0x26;
let kExprI64AtomicSub8U = 0x29;
let kExprI64AtomicSub16U = 0x2a;
let kExprI64AtomicSub32U = 0x2b;
let kExprI64AtomicAnd = 0x2d;
let kExprI64AtomicAnd8U = 0x30;
let kExprI64AtomicAnd16U = 0x31;
let kExprI64AtomicAnd32U = 0x32;
let kExprI64AtomicOr = 0x34;
let kExprI64AtomicOr8U = 0x37;
let kExprI64AtomicOr16U = 0x38;
let kExprI64AtomicOr32U = 0x39;
let kExprI64AtomicXor = 0x3b;
let kExprI64AtomicXor8U = 0x3e;
let kExprI64AtomicXor16U = 0x3f;
let kExprI64AtomicXor32U = 0x40;
let kExprI64AtomicExchange = 0x42;
let kExprI64AtomicExchange8U = 0x45;
let kExprI64AtomicExchange16U = 0x46;
let kExprI64AtomicExchange32U = 0x47;
let kExprI64AtomicCompareExchange = 0x49
let kExprI64AtomicCompareExchange8U = 0x4c;
let kExprI64AtomicCompareExchange16U = 0x4d;
let kExprI64AtomicCompareExchange32U = 0x4e;

// Simd opcodes.
let kExprS128LoadMem = 0x00;
let kExprS128Load8x8S = 0x01;
let kExprS128Load8x8U = 0x02;
let kExprS128Load16x4S = 0x03;
let kExprS128Load16x4U = 0x04;
let kExprS128Load32x2S = 0x05;
let kExprS128Load32x2U = 0x06;
let kExprS128Load8Splat = 0x07;
let kExprS128Load16Splat = 0x08;
let kExprS128Load32Splat = 0x09;
let kExprS128Load64Splat = 0x0a;
let kExprS128StoreMem = 0x0b;
let kExprS128Const = 0x0c;
let kExprI8x16Shuffle = 0x0d;
let kExprI8x16Swizzle = 0x0e;

let kExprI8x16Splat = 0x0f;
let kExprI16x8Splat = 0x10;
let kExprI32x4Splat = 0x11;
let kExprI64x2Splat = 0x12;
let kExprF32x4Splat = 0x13;
let kExprF64x2Splat = 0x14;
let kExprI8x16ExtractLaneS = 0x15;
let kExprI8x16ExtractLaneU = 0x16;
let kExprI8x16ReplaceLane = 0x17;
let kExprI16x8ExtractLaneS = 0x18;
let kExprI16x8ExtractLaneU = 0x19;
let kExprI16x8ReplaceLane = 0x1a;
let kExprI32x4ExtractLane = 0x1b;
let kExprI32x4ReplaceLane = 0x1c;
let kExprI64x2ExtractLane = 0x1d;
let kExprI64x2ReplaceLane = 0x1e;
let kExprF32x4ExtractLane = 0x1f;
let kExprF32x4ReplaceLane = 0x20;
let kExprF64x2ExtractLane = 0x21;
let kExprF64x2ReplaceLane = 0x22;
let kExprI8x16Eq = 0x23;
let kExprI8x16Ne = 0x24;
let kExprI8x16LtS = 0x25;
let kExprI8x16LtU = 0x26;
let kExprI8x16GtS = 0x27;
let kExprI8x16GtU = 0x28;
let kExprI8x16LeS = 0x29;
let kExprI8x16LeU = 0x2a;
let kExprI8x16GeS = 0x2b;
let kExprI8x16GeU = 0x2c;
let kExprI16x8Eq = 0x2d;
let kExprI16x8Ne = 0x2e;
let kExprI16x8LtS = 0x2f;
let kExprI16x8LtU = 0x30;
let kExprI16x8GtS = 0x31;
let kExprI16x8GtU = 0x32;
let kExprI16x8LeS = 0x33;
let kExprI16x8LeU = 0x34;
let kExprI16x8GeS = 0x35;
let kExprI16x8GeU = 0x36;
let kExprI32x4Eq = 0x37;
let kExprI32x4Ne = 0x38;
let kExprI32x4LtS = 0x39;
let kExprI32x4LtU = 0x3a;
let kExprI32x4GtS = 0x3b;
let kExprI32x4GtU = 0x3c;
let kExprI32x4LeS = 0x3d;
let kExprI32x4LeU = 0x3e;
let kExprI32x4GeS = 0x3f;
let kExprI32x4GeU = 0x40;
let kExprF32x4Eq = 0x41;
let kExprF32x4Ne = 0x42;
let kExprF32x4Lt = 0x43;
let kExprF32x4Gt = 0x44;
let kExprF32x4Le = 0x45;
let kExprF32x4Ge = 0x46;
let kExprF64x2Eq = 0x47;
let kExprF64x2Ne = 0x48;
let kExprF64x2Lt = 0x49;
let kExprF64x2Gt = 0x4a;
let kExprF64x2Le = 0x4b;
let kExprF64x2Ge = 0x4c;
let kExprS128Not = 0x4d;
let kExprS128And = 0x4e;
let kExprS128AndNot = 0x4f;
let kExprS128Or = 0x50;
let kExprS128Xor = 0x51;
let kExprS128Select = 0x52;
let kExprV128AnyTrue = 0x53;
let kExprS128Load8Lane = 0x54;
let kExprS128Load16Lane = 0x55;
let kExprS128Load32Lane = 0x56;
let kExprS128Load64Lane = 0x57;
let kExprS128Store8Lane = 0x58;
let kExprS128Store16Lane = 0x59;
let kExprS128Store32Lane = 0x5a;
let kExprS128Store64Lane = 0x5b;
let kExprS128Load32Zero = 0x5c;
let kExprS128Load64Zero = 0x5d;
let kExprF32x4DemoteF64x2Zero = 0x5e;
let kExprF64x2PromoteLowF32x4 = 0x5f;
let kExprI8x16Abs = 0x60;
let kExprI8x16Neg = 0x61;
let kExprI8x16Popcnt = 0x62;
let kExprI8x16AllTrue = 0x63;
let kExprI8x16BitMask = 0x64;
let kExprI8x16SConvertI16x8 = 0x65;
let kExprI8x16UConvertI16x8 = 0x66;
let kExprF32x4Ceil = 0x67;
let kExprF32x4Floor = 0x68;
let kExprF32x4Trunc = 0x69;
let kExprF32x4NearestInt = 0x6a;
let kExprI8x16Shl = 0x6b;
let kExprI8x16ShrS = 0x6c;
let kExprI8x16ShrU = 0x6d;
let kExprI8x16Add = 0x6e;
let kExprI8x16AddSatS = 0x6f;
let kExprI8x16AddSatU = 0x70;
let kExprI8x16Sub = 0x71;
let kExprI8x16SubSatS = 0x72;
let kExprI8x16SubSatU = 0x73;
let kExprF64x2Ceil = 0x74;
let kExprF64x2Floor = 0x75;
let kExprI8x16MinS = 0x76;
let kExprI8x16MinU = 0x77;
let kExprI8x16MaxS = 0x78;
let kExprI8x16MaxU = 0x79;
let kExprF64x2Trunc = 0x7a;
let kExprI8x16RoundingAverageU = 0x7b;
let kExprI16x8ExtAddPairwiseI8x16S = 0x7c;
let kExprI16x8ExtAddPairwiseI8x16U = 0x7d;
let kExprI32x4ExtAddPairwiseI16x8S = 0x7e;
let kExprI32x4ExtAddPairwiseI16x8U = 0x7f;
let kExprI16x8Abs = 0x80;
let kExprI16x8Neg = 0x81;
let kExprI16x8Q15MulRSatS = 0x82;
let kExprI16x8AllTrue = 0x83;
let kExprI16x8BitMask = 0x84;
let kExprI16x8SConvertI32x4 = 0x85;
let kExprI16x8UConvertI32x4 = 0x86;
let kExprI16x8SConvertI8x16Low = 0x87;
let kExprI16x8SConvertI8x16High = 0x88;
let kExprI16x8UConvertI8x16Low = 0x89;
let kExprI16x8UConvertI8x16High = 0x8a;
let kExprI16x8Shl = 0x8b;
let kExprI16x8ShrS = 0x8c;
let kExprI16x8ShrU = 0x8d;
let kExprI16x8Add = 0x8e;
let kExprI16x8AddSatS = 0x8f;
let kExprI16x8AddSatU = 0x90;
let kExprI16x8Sub = 0x91;
let kExprI16x8SubSatS = 0x92;
let kExprI16x8SubSatU = 0x93;
let kExprF64x2NearestInt = 0x94;
let kExprI16x8Mul = 0x95;
let kExprI16x8MinS = 0x96;
let kExprI16x8MinU = 0x97;
let kExprI16x8MaxS = 0x98;
let kExprI16x8MaxU = 0x99;
let kExprI16x8RoundingAverageU = 0x9b;
let kExprI16x8ExtMulLowI8x16S = 0x9c;
let kExprI16x8ExtMulHighI8x16S = 0x9d;
let kExprI16x8ExtMulLowI8x16U = 0x9e;
let kExprI16x8ExtMulHighI8x16U = 0x9f;
let kExprI32x4Abs = 0xa0;
let kExprI32x4Neg = 0xa1;
let kExprI32x4AllTrue = 0xa3;
let kExprI32x4BitMask = 0xa4;
let kExprI32x4SConvertI16x8Low = 0xa7;
let kExprI32x4SConvertI16x8High = 0xa8;
let kExprI32x4UConvertI16x8Low = 0xa9;
let kExprI32x4UConvertI16x8High = 0xaa;
let kExprI32x4Shl = 0xab;
let kExprI32x4ShrS = 0xac;
let kExprI32x4ShrU = 0xad;
let kExprI32x4Add = 0xae;
let kExprI32x4Sub = 0xb1;
let kExprI32x4Mul = 0xb5;
let kExprI32x4MinS = 0xb6;
let kExprI32x4MinU = 0xb7;
let kExprI32x4MaxS = 0xb8;
let kExprI32x4MaxU = 0xb9;
let kExprI32x4DotI16x8S = 0xba;
let kExprI32x4ExtMulLowI16x8S = 0xbc;
let kExprI32x4ExtMulHighI16x8S = 0xbd;
let kExprI32x4ExtMulLowI16x8U = 0xbe;
let kExprI32x4ExtMulHighI16x8U = 0xbf;
let kExprI64x2Abs = 0xc0;
let kExprI64x2Neg = 0xc1;
let kExprI64x2AllTrue = 0xc3;
let kExprI64x2BitMask = 0xc4;
let kExprI64x2SConvertI32x4Low = 0xc7;
let kExprI64x2SConvertI32x4High = 0xc8;
let kExprI64x2UConvertI32x4Low = 0xc9;
let kExprI64x2UConvertI32x4High = 0xca;
let kExprI64x2Shl = 0xcb;
let kExprI64x2ShrS = 0xcc;
let kExprI64x2ShrU = 0xcd;
let kExprI64x2Add = 0xce;
let kExprI64x2Sub = 0xd1;
let kExprI64x2Mul = 0xd5;
let kExprI64x2Eq = 0xd6;
let kExprI64x2Ne = 0xd7;
let kExprI64x2LtS = 0xd8;
let kExprI64x2GtS = 0xd9;
let kExprI64x2LeS = 0xda;
let kExprI64x2GeS = 0xdb;
let kExprI64x2ExtMulLowI32x4S = 0xdc;
let kExprI64x2ExtMulHighI32x4S = 0xdd;
let kExprI64x2ExtMulLowI32x4U = 0xde;
let kExprI64x2ExtMulHighI32x4U = 0xdf;
let kExprF32x4Abs = 0xe0;
let kExprF32x4Neg = 0xe1;
let kExprF32x4Sqrt = 0xe3;
let kExprF32x4Add = 0xe4;
let kExprF32x4Sub = 0xe5;
let kExprF32x4Mul = 0xe6;
let kExprF32x4Div = 0xe7;
let kExprF32x4Min = 0xe8;
let kExprF32x4Max = 0xe9;
let kExprF32x4Pmin = 0xea;
let kExprF32x4Pmax = 0xeb;
let kExprF64x2Abs = 0xec;
let kExprF64x2Neg = 0xed;
let kExprF64x2Sqrt = 0xef;
let kExprF64x2Add = 0xf0;
let kExprF64x2Sub = 0xf1;
let kExprF64x2Mul = 0xf2;
let kExprF64x2Div = 0xf3;
let kExprF64x2Min = 0xf4;
let kExprF64x2Max = 0xf5;
let kExprF64x2Pmin = 0xf6;
let kExprF64x2Pmax = 0xf7;
let kExprI32x4SConvertF32x4 = 0xf8;
let kExprI32x4UConvertF32x4 = 0xf9;
let kExprF32x4SConvertI32x4 = 0xfa;
let kExprF32x4UConvertI32x4 = 0xfb;
let kExprI32x4TruncSatF64x2SZero = 0xfc;
let kExprI32x4TruncSatF64x2UZero = 0xfd;
let kExprF64x2ConvertLowI32x4S = 0xfe;
let kExprF64x2ConvertLowI32x4U = 0xff;

// Compilation hint constants.
let kCompilationHintStrategyDefault = 0x00;
let kCompilationHintStrategyLazy = 0x01;
let kCompilationHintStrategyEager = 0x02;
let kCompilationHintStrategyLazyBaselineEagerTopTier = 0x03;
let kCompilationHintTierDefault = 0x00;
let kCompilationHintTierBaseline = 0x01;
let kCompilationHintTierOptimized = 0x02;

let kTrapUnreachable = 0;
let kTrapMemOutOfBounds = 1;
let kTrapDivByZero = 2;
let kTrapDivUnrepresentable = 3;
let kTrapRemByZero = 4;
let kTrapFloatUnrepresentable = 5;
let kTrapTableOutOfBounds = 6;
let kTrapFuncSigMismatch = 7;
let kTrapUnalignedAccess = 8;
let kTrapDataSegmentOutOfBounds = 9;
let kTrapElementSegmentOutOfBounds = 10;
let kTrapRethrowNull = 11;
let kTrapArrayTooLarge = 12;

let kTrapMsgs = [
  'unreachable',                                    // --
  'memory access out of bounds',                    // --
  'divide by zero',                                 // --
  'divide result unrepresentable',                  // --
  'remainder by zero',                              // --
  'float unrepresentable in integer range',         // --
  'table index is out of bounds',                   // --
  'null function or function signature mismatch',   // --
  'operation does not support unaligned accesses',  // --
  'data segment out of bounds',                     // --
  'element segment out of bounds',                  // --
  'rethrowing null value',                          // --
  'requested new array is too large'                // --
];

// This requires test/mjsunit/mjsunit.js.
function assertTraps(trap, code) {
  assertThrows(code, WebAssembly.RuntimeError, kTrapMsgs[trap]);
}

class Binary {
  constructor() {
    this.length = 0;
    this.buffer = new Uint8Array(8192);
  }

  ensure_space(needed) {
    if (this.buffer.length - this.length >= needed) return;
    let new_capacity = this.buffer.length * 2;
    while (new_capacity - this.length < needed) new_capacity *= 2;
    let new_buffer = new Uint8Array(new_capacity);
    new_buffer.set(this.buffer);
    this.buffer = new_buffer;
  }

  trunc_buffer() {
    return new Uint8Array(this.buffer.buffer, 0, this.length);
  }

  reset() {
    this.length = 0;
  }

  emit_u8(val) {
    this.ensure_space(1);
    this.buffer[this.length++] = val;
  }

  emit_u16(val) {
    this.ensure_space(2);
    this.buffer[this.length++] = val;
    this.buffer[this.length++] = val >> 8;
  }

  emit_u32(val) {
    this.ensure_space(4);
    this.buffer[this.length++] = val;
    this.buffer[this.length++] = val >> 8;
    this.buffer[this.length++] = val >> 16;
    this.buffer[this.length++] = val >> 24;
  }

  emit_leb_u(val, max_len) {
    this.ensure_space(max_len);
    for (let i = 0; i < max_len; ++i) {
      let v = val & 0xff;
      val = val >>> 7;
      if (val == 0) {
        this.buffer[this.length++] = v;
        return;
      }
      this.buffer[this.length++] = v | 0x80;
    }
    throw new Error('Leb value exceeds maximum length of ' + max_len);
  }

  emit_u32v(val) {
    this.emit_leb_u(val, kMaxVarInt32Size);
  }

  emit_u64v(val) {
    this.emit_leb_u(val, kMaxVarInt64Size);
  }

  emit_bytes(data) {
    this.ensure_space(data.length);
    this.buffer.set(data, this.length);
    this.length += data.length;
  }

  emit_string(string) {
    // When testing illegal names, we pass a byte array directly.
    if (string instanceof Array) {
      this.emit_u32v(string.length);
      this.emit_bytes(string);
      return;
    }

    // This is the hacky way to convert a JavaScript string to a UTF8 encoded
    // string only containing single-byte characters.
    let string_utf8 = unescape(encodeURIComponent(string));
    this.emit_u32v(string_utf8.length);
    for (let i = 0; i < string_utf8.length; i++) {
      this.emit_u8(string_utf8.charCodeAt(i));
    }
  }

  emit_heap_type(heap_type) {
    this.emit_bytes(wasmSignedLeb(heap_type, kMaxVarInt32Size));
  }

  emit_type(type) {
    if ((typeof type) == 'number') {
      this.emit_u8(type >= 0 ? type : type & kLeb128Mask);
    } else {
      this.emit_u8(type.opcode);
      if ('depth' in type) this.emit_u8(type.depth);
      this.emit_heap_type(type.heap_type);
    }
  }

  emit_init_expr_recursive(expr) {
    switch (expr.kind) {
      case kExprGlobalGet:
        this.emit_u8(kExprGlobalGet);
        this.emit_u32v(expr.value);
        break;
      case kExprI32Const:
        this.emit_bytes(wasmI32Const(expr.value));
        break;
      case kExprI64Const:
        this.emit_bytes(wasmI64Const(expr.value));
        break;
      case kExprF32Const:
        this.emit_bytes(wasmF32Const(expr.value));
        break;
      case kExprF64Const:
        this.emit_bytes(wasmF64Const(expr.value));
        break;
      case kSimdPrefix:
        this.emit_bytes(wasmS128Const(expr.value));
        break;
      case kExprI32Add:
      case kExprI32Sub:
      case kExprI32Mul:
      case kExprI64Add:
      case kExprI64Sub:
      case kExprI64Mul:
        this.emit_init_expr_recursive(expr.operands[0]);
        this.emit_init_expr_recursive(expr.operands[1]);
        this.emit_u8(expr.kind);
        break;
      case kExprRefFunc:
        this.emit_u8(kExprRefFunc);
        this.emit_u32v(expr.value);
        break;
      case kExprRefNull:
        this.emit_u8(kExprRefNull);
        this.emit_heap_type(expr.value);
        break;
      case kExprStructNew:
      case kExprStructNewWithRtt:
      case kExprStructNewDefault:
      case kExprStructNewDefaultWithRtt:
        for (let operand of expr.operands) {
          this.emit_init_expr_recursive(operand);
        }
        this.emit_u8(kGCPrefix);
        this.emit_u8(expr.kind);
        this.emit_u32v(expr.value);
        break;
      case kExprArrayInit:
      case kExprArrayInitStatic:
        for (let operand of expr.operands) {
          this.emit_init_expr_recursive(operand);
        }
        this.emit_u8(kGCPrefix);
        this.emit_u8(expr.kind);
        this.emit_u32v(expr.value);
        this.emit_u32v(expr.operands.length - 1);
        break;
      case kExprArrayInitFromData:
      case kExprArrayInitFromDataStatic:
        for (let operand of expr.operands) {
          this.emit_init_expr_recursive(operand);
        }
        this.emit_u8(kGCPrefix);
        this.emit_u8(expr.kind);
        this.emit_u32v(expr.array_index);
        this.emit_u32v(expr.data_segment);
        break;
      case kExprRttCanon:
        this.emit_u8(kGCPrefix);
        this.emit_u8(kExprRttCanon);
        this.emit_u32v(expr.value);
        break;
      case kExprRttSub:
        this.emit_init_expr_recursive(expr.parent);
        this.emit_u8(kGCPrefix);
        this.emit_u8(kExprRttSub);
        this.emit_u32v(expr.value);
        break;
      case kExprRttFreshSub:
        this.emit_init_expr_recursive(expr.parent);
        this.emit_u8(kGCPrefix);
        this.emit_u8(kExprRttFreshSub);
        this.emit_u32v(expr.value);
        break;
      case kExprStringConst:
        this.emit_u8(kGCPrefix);
        this.emit_u8(kExprStringConst);
        this.emit_u32v(expr.index);
        break;
    }
  }

  emit_init_expr(expr) {
    this.emit_init_expr_recursive(expr);
    this.emit_u8(kExprEnd);
  }

  emit_header() {
    this.emit_bytes([
      kWasmH0, kWasmH1, kWasmH2, kWasmH3, kWasmV0, kWasmV1, kWasmV2, kWasmV3
    ]);
  }

  emit_section(section_code, content_generator) {
    // Emit section name.
    this.emit_u8(section_code);
    // Emit the section to a temporary buffer: its full length isn't know yet.
    const section = new Binary;
    content_generator(section);
    // Emit section length.
    this.emit_u32v(section.length);
    // Copy the temporary buffer.
    // Avoid spread because {section} can be huge.
    this.emit_bytes(section.trunc_buffer());
  }
}

class WasmFunctionBuilder {
  // Encoding of local names: a string corresponds to a local name,
  // a number n corresponds to n undefined names.
  constructor(module, name, type_index, arg_names) {
    this.module = module;
    this.name = name;
    this.type_index = type_index;
    this.body = [];
    this.locals = [];
    this.local_names = arg_names;
    this.body_offset = undefined;  // Not valid until module is serialized.
  }

  numLocalNames() {
    let num_local_names = 0;
    for (let loc_name of this.local_names) {
      if (typeof loc_name == 'string') ++num_local_names;
    }
    return num_local_names;
  }

  exportAs(name) {
    this.module.addExport(name, this.index);
    return this;
  }

  exportFunc() {
    this.exportAs(this.name);
    return this;
  }

  setCompilationHint(strategy, baselineTier, topTier) {
    this.module.setCompilationHint(strategy, baselineTier, topTier, this.index);
    return this;
  }

  addBody(body) {
    for (let b of body) {
      if (typeof b !== 'number' || (b & (~0xFF)) !== 0) {
        throw new Error(
            'invalid body (entries must be 8 bit numbers): ' + body);
      }
    }
    this.body = body.slice();
    // Automatically add the end for the function block to the body.
    this.body.push(kExprEnd);
    return this;
  }

  addBodyWithEnd(body) {
    this.body = body;
    return this;
  }

  getNumLocals() {
    let total_locals = 0;
    for (let l of this.locals) {
      total_locals += l.count
    }
    return total_locals;
  }

  addLocals(type, count, names) {
    this.locals.push({type: type, count: count});
    names = names || [];
    if (names.length > count) throw new Error('too many locals names given');
    this.local_names.push(...names);
    if (count > names.length) this.local_names.push(count - names.length);
    return this;
  }

  end() {
    return this.module;
  }
}

class WasmInitExpr {
  static I32Const(value) {
    return {kind: kExprI32Const, value: value};
  }
  static I64Const(value) {
    return {kind: kExprI64Const, value: value};
  }
  static F32Const(value) {
    return {kind: kExprF32Const, value: value};
  }
  static F64Const(value) {
    return {kind: kExprF64Const, value: value};
  }
  static S128Const(value) {
    return {kind: kSimdPrefix, value: value};
  }
  static I32Add(lhs, rhs) {
    return {kind: kExprI32Add, operands: [lhs, rhs]};
  }
  static I32Sub(lhs, rhs) {
    return {kind: kExprI32Sub, operands: [lhs, rhs]};
  }
  static I32Mul(lhs, rhs) {
    return {kind: kExprI32Mul, operands: [lhs, rhs]};
  }
  static I64Add(lhs, rhs) {
    return {kind: kExprI64Add, operands: [lhs, rhs]};
  }
  static I64Sub(lhs, rhs) {
    return {kind: kExprI64Sub, operands: [lhs, rhs]};
  }
  static I64Mul(lhs, rhs) {
    return {kind: kExprI64Mul, operands: [lhs, rhs]};
  }
  static GlobalGet(index) {
    return {kind: kExprGlobalGet, value: index};
  }
  static RefFunc(index) {
    return {kind: kExprRefFunc, value: index};
  }
  static RefNull(type) {
    return {kind: kExprRefNull, value: type};
  }
  static StructNewWithRtt(type, args) {
    return {kind: kExprStructNewWithRtt, value: type, operands: args};
  }
  static StructNew(type, args) {
    return {kind: kExprStructNew, value: type, operands: args};
  }
  static StructNewDefaultWithRtt(type, rtt) {
    return {kind: kExprStructNewDefaultWithRtt, value: type, operands: [rtt]};
  }
  static StructNewDefault(type) {
    return {kind: kExprStructNewDefault, value: type, operands: []};
  }
  static ArrayInit(type, args) {
    return {kind: kExprArrayInit, value: type, operands: args};
  }
  static ArrayInitStatic(type, args) {
    return {kind: kExprArrayInitStatic, value: type, operands: args};
  }
  static ArrayInitFromData(array_index, data_segment, args, builder) {
    // array.init_from_data means we need to pull the data count section before
    // any section that may include init. expressions.
    builder.early_data_count_section = true;
    return {kind: kExprArrayInitFromData, array_index: array_index,
            data_segment: data_segment, operands: args};
  }
  static ArrayInitFromDataStatic(array_index, data_segment, args, builder) {
    // array.init_from_data means we need to pull the data count section before
    // any section that may include init. expressions.
    builder.early_data_count_section = true;
    return {kind: kExprArrayInitFromDataStatic, array_index: array_index,
            data_segment: data_segment, operands: args};
  }
  static RttCanon(type) {
    return {kind: kExprRttCanon, value: type};
  }
  static RttSub(type, parent) {
    return {kind: kExprRttSub, value: type, parent: parent};
  }
  static RttFreshSub(type, parent) {
    return {kind: kExprRttFreshSub, value: type, parent: parent};
  }
  static StringConst(index) {
    return {kind: kExprStringConst, index};
  }

  static defaultFor(type) {
    switch (type) {
      case kWasmI32:
        return this.I32Const(0);
      case kWasmI64:
        return this.I64Const(0);
      case kWasmF32:
        return this.F32Const(0);
      case kWasmF64:
        return this.F64Const(0);
      case kWasmS128:
        return this.S128Const(new Array(16).fill(0));
      default:
        if ((typeof type) != 'number' && type.opcode != kWasmOptRef) {
          throw new Error("Non-defaultable type");
        }
        let heap_type = (typeof type) == 'number' ? type : type.heap_type;
        return this.RefNull(heap_type);
    }
  }
}

class WasmGlobalBuilder {
  // {init} should be constructed with WasmInitExpr.
  constructor(module, type, mutable, init) {
    this.module = module;
    this.type = type;
    this.mutable = mutable;
    this.init = init;
  }

  exportAs(name) {
    this.module.exports.push(
        {name: name, kind: kExternalGlobal, index: this.index});
    return this;
  }
}

class WasmTableBuilder {
  constructor(module, type, initial_size, max_size, init_expr) {
    this.module = module;
    this.type = type;
    this.initial_size = initial_size;
    this.has_max = max_size !== undefined;
    this.max_size = max_size;
    this.init_expr = init_expr;
    this.has_init = init_expr !== undefined;
  }

  exportAs(name) {
    this.module.exports.push(
        {name: name, kind: kExternalTable, index: this.index});
    return this;
  }
}

function makeField(type, mutability) {
  if ((typeof mutability) != 'boolean') {
    throw new Error('field mutability must be boolean');
  }
  return {type: type, mutability: mutability};
}

class WasmStruct {
  constructor(fields, supertype_idx) {
    if (!Array.isArray(fields)) {
      throw new Error('struct fields must be an array');
    }
    this.fields = fields;
    this.type_form = kWasmStructTypeForm;
    this.supertype = supertype_idx;
  }
}

class WasmArray {
  constructor(type, mutability, supertype_idx) {
    this.type = type;
    this.mutability = mutability;
    this.type_form = kWasmArrayTypeForm;
    this.supertype = supertype_idx;
  }
}

class WasmElemSegment {
  constructor(table, offset, type, elements, is_decl) {
    this.table = table;
    this.offset = offset;
    this.type = type;
    this.elements = elements;
    this.is_decl = is_decl;
    // Invariant checks.
    if ((table === undefined) != (offset === undefined)) {
      throw new Error("invalid element segment");
    }
    for (let elem of elements) {
      if (((typeof elem) == 'number') != (type === undefined)) {
        throw new Error("invalid element");
      }
    }
  }

  is_active() {
    return this.table !== undefined;
  }

  is_passive() {
    return this.table === undefined && !this.is_decl;
  }

  is_declarative() {
    return this.table === undefined && this.is_decl;
  }

  expressions_as_elements() {
    return this.type !== undefined;
  }
}

class WasmModuleBuilder {
  constructor() {
    this.types = [];
    this.imports = [];
    this.exports = [];
    this.stringrefs = [];
    this.globals = [];
    this.tables = [];
    this.tags = [];
    this.functions = [];
    this.compilation_hints = [];
    this.element_segments = [];
    this.data_segments = [];
    this.explicit = [];
    this.num_imported_funcs = 0;
    this.num_imported_globals = 0;
    this.num_imported_tables = 0;
    this.num_imported_tags = 0;
    this.nominal = false;  // Controls only how gc-modules are printed.
    this.early_data_count_section = false;
    return this;
  }

  addStart(start_index) {
    this.start_index = start_index;
    return this;
  }

  addMemory(min, max, exported, shared) {
    this.memory = {
      min: min,
      max: max,
      exported: exported,
      shared: shared || false,
      is_memory64: false
    };
    return this;
  }

  addMemory64(min, max, exported) {
    this.memory = {
      min: min,
      max: max,
      exported: exported,
      shared: false,
      is_memory64: true
    };
    return this;
  }

  addExplicitSection(bytes) {
    this.explicit.push(bytes);
    return this;
  }

  stringToBytes(name) {
    var result = new Binary();
    result.emit_u32v(name.length);
    for (var i = 0; i < name.length; i++) {
      result.emit_u8(name.charCodeAt(i));
    }
    return result.trunc_buffer()
  }

  createCustomSection(name, bytes) {
    name = this.stringToBytes(name);
    var section = new Binary();
    section.emit_u8(0);
    section.emit_u32v(name.length + bytes.length);
    section.emit_bytes(name);
    section.emit_bytes(bytes);
    return section.trunc_buffer();
  }

  addCustomSection(name, bytes) {
    this.explicit.push(this.createCustomSection(name, bytes));
  }

  // TODO(7748): Support recursive groups.

  // TODO(7748): Support function supertypes.
  addType(type) {
    this.types.push(type);
    var pl = type.params.length;   // should have params
    var rl = type.results.length;  // should have results
    return this.types.length - 1;
  }

  addLiteralStringRef(str) {
    this.stringrefs.push(str);
    return this.stringrefs.length - 1;
  }

  addStruct(fields, supertype_idx = kNoSuperType) {
    this.types.push(new WasmStruct(fields, supertype_idx));
    return this.types.length - 1;
  }

  addArray(type, mutability, supertype_idx = kNoSuperType) {
    this.types.push(new WasmArray(type, mutability, supertype_idx));
    return this.types.length - 1;
  }

  addGlobal(type, mutable, init) {
    if (init === undefined) init = WasmInitExpr.defaultFor(type);
    let glob = new WasmGlobalBuilder(this, type, mutable, init);
    glob.index = this.globals.length + this.num_imported_globals;
    this.globals.push(glob);
    return glob;
  }

  addTable(
      type, initial_size, max_size = undefined, init_expr = undefined) {
    if (type == kWasmI32 || type == kWasmI64 || type == kWasmF32 ||
        type == kWasmF64 || type == kWasmS128 || type == kWasmVoid) {
      throw new Error('Tables must be of a reference type');
    }
    let table = new WasmTableBuilder(
        this, type, initial_size, max_size, init_expr);
    table.index = this.tables.length + this.num_imported_tables;
    this.tables.push(table);
    return table;
  }

  addTag(type) {
    let type_index = (typeof type) == 'number' ? type : this.addType(type);
    let tag_index = this.tags.length + this.num_imported_tags;
    this.tags.push(type_index);
    return tag_index;
  }

  addFunction(name, type, arg_names) {
    arg_names = arg_names || [];
    let type_index = (typeof type) == 'number' ? type : this.addType(type);
    let num_args = this.types[type_index].params.length;
    if (num_args < arg_names.length)
      throw new Error('too many arg names provided');
    if (num_args > arg_names.length)
      arg_names.push(num_args - arg_names.length);
    let func = new WasmFunctionBuilder(this, name, type_index, arg_names);
    func.index = this.functions.length + this.num_imported_funcs;
    this.functions.push(func);
    return func;
  }

  addImport(module, name, type) {
    if (this.functions.length != 0) {
      throw new Error('Imported functions must be declared before local ones');
    }
    let type_index = (typeof type) == 'number' ? type : this.addType(type);
    this.imports.push({
      module: module,
      name: name,
      kind: kExternalFunction,
      type_index: type_index
    });
    return this.num_imported_funcs++;
  }

  addImportedGlobal(module, name, type, mutable = false) {
    if (this.globals.length != 0) {
      throw new Error('Imported globals must be declared before local ones');
    }
    let o = {
      module: module,
      name: name,
      kind: kExternalGlobal,
      type: type,
      mutable: mutable
    };
    this.imports.push(o);
    return this.num_imported_globals++;
  }

  addImportedMemory(module, name, initial = 0, maximum, shared) {
    let o = {
      module: module,
      name: name,
      kind: kExternalMemory,
      initial: initial,
      maximum: maximum,
      shared: shared
    };
    this.imports.push(o);
    return this;
  }

  addImportedTable(module, name, initial, maximum, type) {
    if (this.tables.length != 0) {
      throw new Error('Imported tables must be declared before local ones');
    }
    let o = {
      module: module,
      name: name,
      kind: kExternalTable,
      initial: initial,
      maximum: maximum,
      type: type || kWasmFuncRef
    };
    this.imports.push(o);
    return this.num_imported_tables++;
  }

  addImportedTag(module, name, type) {
    if (this.tags.length != 0) {
      throw new Error('Imported tags must be declared before local ones');
    }
    let type_index = (typeof type) == 'number' ? type : this.addType(type);
    let o = {
      module: module,
      name: name,
      kind: kExternalTag,
      type_index: type_index
    };
    this.imports.push(o);
    return this.num_imported_tags++;
  }

  addExport(name, index) {
    this.exports.push({name: name, kind: kExternalFunction, index: index});
    return this;
  }

  addExportOfKind(name, kind, index) {
    if (index === undefined && kind != kExternalTable &&
        kind != kExternalMemory) {
      throw new Error(
          'Index for exports other than tables/memories must be provided');
    }
    if (index !== undefined && (typeof index) != 'number') {
      throw new Error('Index for exports must be a number')
    }
    this.exports.push({name: name, kind: kind, index: index});
    return this;
  }

  setCompilationHint(strategy, baselineTier, topTier, index) {
    this.compilation_hints[index] = {
      strategy: strategy,
      baselineTier: baselineTier,
      topTier: topTier
    };
    return this;
  }

  addDataSegment(addr, data, is_global = false) {
    this.data_segments.push(
        {addr: addr, data: data, is_global: is_global, is_active: true});
    return this.data_segments.length - 1;
  }

  addPassiveDataSegment(data) {
    this.data_segments.push({data: data, is_active: false});
    return this.data_segments.length - 1;
  }

  exportMemoryAs(name) {
    this.exports.push({name: name, kind: kExternalMemory, index: 0});
  }

  // {offset} is an initializer expression.
  // If {type} is undefined, then {elements} are function indices. Otherwise,
  // they are initializer expressions.
  addActiveElementSegment(table, offset, elements, type) {
    this.element_segments.push(
        new WasmElemSegment(table, offset, type, elements, false));
    return this.element_segments.length - 1;
  }

  // If {type} is undefined, then {elements} are function indices. Otherwise,
  // they are initializer expressions.
  addPassiveElementSegment(elements, type) {
    this.element_segments.push(
      new WasmElemSegment(undefined, undefined, type, elements, false));
    return this.element_segments.length - 1;
  }

  // If {type} is undefined, then {elements} are function indices. Otherwise,
  // they are initializer expressions.
  addDeclarativeElementSegment(elements, type) {
    this.element_segments.push(
      new WasmElemSegment(undefined, undefined, type, elements, true));
    return this.element_segments.length - 1;
  }

  appendToTable(array) {
    for (let n of array) {
      if (typeof n != 'number')
        throw new Error('invalid table (entries have to be numbers): ' + array);
    }
    if (this.tables.length == 0) {
      this.addTable(kWasmAnyFunc, 0);
    }
    // Adjust the table to the correct size.
    let table = this.tables[0];
    const base = table.initial_size;
    const table_size = base + array.length;
    table.initial_size = table_size;
    if (table.has_max && table_size > table.max_size) {
      table.max_size = table_size;
    }
    return this.addActiveElementSegment(0, WasmInitExpr.I32Const(base), array);
  }

  setTableBounds(min, max = undefined) {
    if (this.tables.length != 0) {
      throw new Error('The table bounds of table \'0\' have already been set.');
    }
    this.addTable(kWasmAnyFunc, min, max);
    return this;
  }

  setNominal() {
    this.nominal = true;
  }

  setName(name) {
    this.name = name;
    return this;
  }

  toBuffer(debug = false) {
    let binary = new Binary;
    let wasm = this;

    // Add header
    binary.emit_header();

    // Add type section
    if (wasm.types.length > 0) {
      if (debug) print('emitting types @ ' + binary.length);
      binary.emit_section(kTypeSectionCode, section => {
        section.emit_u32v(wasm.types.length);
        for (let type of wasm.types) {
          if (type instanceof WasmStruct) {
            if (!this.nominal && type.supertype != kNoSuperType) {
              section.emit_u8(kWasmSubtypeForm);
              section.emit_u8(1);  // supertype count
              section.emit_u32v(type.supertype);
            }
            section.emit_u8(this.nominal ? kWasmStructNominalForm
                                         : kWasmStructTypeForm);
            section.emit_u32v(type.fields.length);
            for (let field of type.fields) {
              section.emit_type(field.type);
              section.emit_u8(field.mutability ? 1 : 0);
            }
            if (this.nominal) {
              if (type.supertype === kNoSuperType) {
                section.emit_u8(kDataRefCode);
              } else {
                section.emit_heap_type(type.supertype);
              }
            }
          } else if (type instanceof WasmArray) {
            if (!this.nominal && type.supertype != kNoSuperType) {
              section.emit_u8(kWasmSubtypeForm);
              section.emit_u8(1);  // supertype count
              section.emit_u32v(type.supertype);
            }
            section.emit_u8(this.nominal ? kWasmArrayNominalForm
                                         : kWasmArrayTypeForm);
            section.emit_type(type.type);
            section.emit_u8(type.mutability ? 1 : 0);
            if (this.nominal) {
              if (type.supertype === kNoSuperType) {
                section.emit_u8(kDataRefCode);
              } else {
                section.emit_heap_type(type.supertype);
              }
            }
          } else {
            /* TODO(7748): Support function supertypes.
            if (!this.nominal && type.supertype != kNoSuperType) {
              section.emit_u8(kWasmSubtypeForm);
              section.emit_u8(1);  // supertype count
              section.emit_u32v(type.supertype);
            } */
            section.emit_u8(this.nominal ? kWasmFunctionNominalForm
                                         : kWasmFunctionTypeForm);
            section.emit_u32v(type.params.length);
            for (let param of type.params) {
              section.emit_type(param);
            }
            section.emit_u32v(type.results.length);
            for (let result of type.results) {
              section.emit_type(result);
            }
            if (this.nominal) {
              /* TODO(7748): Support function supertypes.
              if (type.supertype === kNoSuperType) {
                section.emit_u8(kFuncRefCode);
              } else {
                section.emit_heap_type(type.supertype);
              }*/
              section.emit_u8(kFuncRefCode);
            }
          }
        }
      });
    }

    // Add imports section
    if (wasm.imports.length > 0) {
      if (debug) print('emitting imports @ ' + binary.length);
      binary.emit_section(kImportSectionCode, section => {
        section.emit_u32v(wasm.imports.length);
        for (let imp of wasm.imports) {
          section.emit_string(imp.module);
          section.emit_string(imp.name || '');
          section.emit_u8(imp.kind);
          if (imp.kind == kExternalFunction) {
            section.emit_u32v(imp.type_index);
          } else if (imp.kind == kExternalGlobal) {
            section.emit_type(imp.type);
            section.emit_u8(imp.mutable);
          } else if (imp.kind == kExternalMemory) {
            var has_max = (typeof imp.maximum) != 'undefined';
            var is_shared = (typeof imp.shared) != 'undefined';
            if (is_shared) {
              section.emit_u8(has_max ? 3 : 2);  // flags
            } else {
              section.emit_u8(has_max ? 1 : 0);  // flags
            }
            section.emit_u32v(imp.initial);               // initial
            if (has_max) section.emit_u32v(imp.maximum);  // maximum
          } else if (imp.kind == kExternalTable) {
            section.emit_type(imp.type);
            var has_max = (typeof imp.maximum) != 'undefined';
            section.emit_u8(has_max ? 1 : 0);             // flags
            section.emit_u32v(imp.initial);               // initial
            if (has_max) section.emit_u32v(imp.maximum);  // maximum
          } else if (imp.kind == kExternalTag) {
            section.emit_u32v(kExceptionAttribute);
            section.emit_u32v(imp.type_index);
          } else {
            throw new Error('unknown/unsupported import kind ' + imp.kind);
          }
        }
      });
    }

    // Add functions declarations
    if (wasm.functions.length > 0) {
      if (debug) print('emitting function decls @ ' + binary.length);
      binary.emit_section(kFunctionSectionCode, section => {
        section.emit_u32v(wasm.functions.length);
        for (let func of wasm.functions) {
          section.emit_u32v(func.type_index);
        }
      });
    }

    // If there are any passive data segments, add the DataCount section.
    if (this.early_data_count_section &&
        wasm.data_segments.some(seg => !seg.is_active)) {
      binary.emit_section(kDataCountSectionCode, section => {
        section.emit_u32v(wasm.data_segments.length);
      });
    }

    // Add table section
    if (wasm.tables.length > 0) {
      if (debug) print('emitting tables @ ' + binary.length);
      binary.emit_section(kTableSectionCode, section => {
        section.emit_u32v(wasm.tables.length);
        for (let table of wasm.tables) {
          section.emit_type(table.type);
          section.emit_u8(table.has_max);
          section.emit_u32v(table.initial_size);
          if (table.has_max) section.emit_u32v(table.max_size);
          if (table.has_init) {
            section.emit_init_expr(table.init_expr);
          }
        }
      });
    }

    // Add memory section
    if (wasm.memory !== undefined) {
      if (debug) print('emitting memory @ ' + binary.length);
      binary.emit_section(kMemorySectionCode, section => {
        section.emit_u8(1);  // one memory entry
        const has_max = wasm.memory.max !== undefined;
        if (wasm.memory.is_memory64) {
          if (wasm.memory.shared) {
            throw new Error('sharing memory64 is not supported (yet)');
          }
          section.emit_u8(
              has_max ? kLimitsMemory64WithMaximum : kLimitsMemory64NoMaximum);
          section.emit_u64v(wasm.memory.min);
          if (has_max) section.emit_u64v(wasm.memory.max);
        } else {
          section.emit_u8(
              wasm.memory.shared ?
                  (has_max ? kLimitsSharedWithMaximum :
                             kLimitsSharedNoMaximum) :
                  (has_max ? kLimitsWithMaximum : kLimitsNoMaximum));
          section.emit_u32v(wasm.memory.min);
          if (has_max) section.emit_u32v(wasm.memory.max);
        }
      });
    }

    // Add tag section.
    if (wasm.tags.length > 0) {
      if (debug) print('emitting tags @ ' + binary.length);
      binary.emit_section(kTagSectionCode, section => {
        section.emit_u32v(wasm.tags.length);
        for (let type_index of wasm.tags) {
          section.emit_u32v(kExceptionAttribute);
          section.emit_u32v(type_index);
        }
      });
    }

    // Add stringref section.
    if (wasm.stringrefs.length > 0) {
      if (debug) print('emitting stringrefs @ ' + binary.length);
      binary.emit_section(kStringRefSectionCode, section => {
        section.emit_u32v(0);
        section.emit_u32v(wasm.stringrefs.length);
        for (let str of wasm.stringrefs) {
          section.emit_string(str);
        }
      });
    }

    // Add global section.
    if (wasm.globals.length > 0) {
      if (debug) print('emitting globals @ ' + binary.length);
      binary.emit_section(kGlobalSectionCode, section => {
        section.emit_u32v(wasm.globals.length);
        for (let global of wasm.globals) {
          section.emit_type(global.type);
          section.emit_u8(global.mutable);
          section.emit_init_expr(global.init);
        }
      });
    }

    // Add export table.
    var mem_export = (wasm.memory !== undefined && wasm.memory.exported);
    var exports_count = wasm.exports.length + (mem_export ? 1 : 0);
    if (exports_count > 0) {
      if (debug) print('emitting exports @ ' + binary.length);
      binary.emit_section(kExportSectionCode, section => {
        section.emit_u32v(exports_count);
        for (let exp of wasm.exports) {
          section.emit_string(exp.name);
          section.emit_u8(exp.kind);
          section.emit_u32v(exp.index);
        }
        if (mem_export) {
          section.emit_string('memory');
          section.emit_u8(kExternalMemory);
          section.emit_u8(0);
        }
      });
    }

    // Add start function section.
    if (wasm.start_index !== undefined) {
      if (debug) print('emitting start function @ ' + binary.length);
      binary.emit_section(kStartSectionCode, section => {
        section.emit_u32v(wasm.start_index);
      });
    }

    // Add element segments
    if (wasm.element_segments.length > 0) {
      if (debug) print('emitting element segments @ ' + binary.length);
      binary.emit_section(kElementSectionCode, section => {
        var segments = wasm.element_segments;
        section.emit_u32v(segments.length);

        for (let segment of segments) {
          // Emit flag and header.
          // Each case below corresponds to a flag from
          // https://webassembly.github.io/spec/core/binary/modules.html#element-section
          // (not in increasing order).
          if (segment.is_active()) {
            if (segment.table == 0 && segment.type === undefined) {
              if (segment.expressions_as_elements()) {
                section.emit_u8(0x04);
                section.emit_init_expr(segment.offset);
              } else {
                section.emit_u8(0x00)
                section.emit_init_expr(segment.offset);
              }
            } else {
              if (segment.expressions_as_elements()) {
                section.emit_u8(0x06);
                section.emit_u32v(segment.table);
                section.emit_init_expr(segment.offset);
                section.emit_type(segment.type);
              } else {
                section.emit_u8(0x02);
                section.emit_u32v(segment.table);
                section.emit_init_expr(segment.offset);
                section.emit_u8(kExternalFunction);
              }
            }
          } else {
            if (segment.expressions_as_elements()) {
              if (segment.is_passive()) {
                section.emit_u8(0x05);
              } else {
                section.emit_u8(0x07);
              }
              section.emit_type(segment.type);
            } else {
              if (segment.is_passive()) {
                section.emit_u8(0x01);
              } else {
                section.emit_u8(0x03);
              }
              section.emit_u8(kExternalFunction);
            }
          }

          // Emit elements.
          section.emit_u32v(segment.elements.length);
          for (let element of segment.elements) {
            if (segment.expressions_as_elements()) {
              section.emit_init_expr(element);
            } else {
              section.emit_u32v(element);
            }
          }
        }
      })
    }

    // If there are any passive data segments, add the DataCount section.
    if (!this.early_data_count_section &&
        wasm.data_segments.some(seg => !seg.is_active)) {
      binary.emit_section(kDataCountSectionCode, section => {
        section.emit_u32v(wasm.data_segments.length);
      });
    }

    // If there are compilation hints add a custom section 'compilationHints'
    // after the function section and before the code section.
    if (wasm.compilation_hints.length > 0) {
      if (debug) print('emitting compilation hints @ ' + binary.length);
      // Build custom section payload.
      let payloadBinary = new Binary();
      let implicit_compilation_hints_count = wasm.functions.length;
      payloadBinary.emit_u32v(implicit_compilation_hints_count);

      // Defaults to the compiler's choice if no better hint was given (0x00).
      let defaultHintByte = kCompilationHintStrategyDefault |
          (kCompilationHintTierDefault << 2) |
          (kCompilationHintTierDefault << 4);

      // Emit hint byte for every function defined in this module.
      for (let i = 0; i < implicit_compilation_hints_count; i++) {
        let index = wasm.num_imported_funcs + i;
        var hintByte;
        if (index in wasm.compilation_hints) {
          let hint = wasm.compilation_hints[index];
          hintByte =
              hint.strategy | (hint.baselineTier << 2) | (hint.topTier << 4);
        } else {
          hintByte = defaultHintByte;
        }
        payloadBinary.emit_u8(hintByte);
      }

      // Finalize as custom section.
      let name = 'compilationHints';
      let bytes = this.createCustomSection(name, payloadBinary.trunc_buffer());
      binary.emit_bytes(bytes);
    }

    // Add function bodies.
    if (wasm.functions.length > 0) {
      // emit function bodies
      if (debug) print('emitting code @ ' + binary.length);
      let section_length = 0;
      binary.emit_section(kCodeSectionCode, section => {
        section.emit_u32v(wasm.functions.length);
        let header = new Binary;
        for (let func of wasm.functions) {
          header.reset();
          // Function body length will be patched later.
          let local_decls = func.locals || [];
          header.emit_u32v(local_decls.length);
          for (let decl of local_decls) {
            header.emit_u32v(decl.count);
            header.emit_type(decl.type);
          }
          section.emit_u32v(header.length + func.body.length);
          section.emit_bytes(header.trunc_buffer());
          // Set to section offset for now, will update.
          func.body_offset = section.length;
          section.emit_bytes(func.body);
        }
        section_length = section.length;
      });
      for (let func of wasm.functions) {
        func.body_offset += binary.length - section_length;
      }
    }

    // Add data segments.
    if (wasm.data_segments.length > 0) {
      if (debug) print('emitting data segments @ ' + binary.length);
      binary.emit_section(kDataSectionCode, section => {
        section.emit_u32v(wasm.data_segments.length);
        for (let seg of wasm.data_segments) {
          if (seg.is_active) {
            section.emit_u8(0);  // linear memory index 0 / flags
            if (seg.is_global) {
              // Initializer is a global variable.
              section.emit_u8(kExprGlobalGet);
              section.emit_u32v(seg.addr);
            } else {
              // Initializer is a constant.
              section.emit_bytes(wasmI32Const(seg.addr));
            }
            section.emit_u8(kExprEnd);
          } else {
            section.emit_u8(kPassive);  // flags
          }
          section.emit_u32v(seg.data.length);
          section.emit_bytes(seg.data);
        }
      });
    }

    // Add any explicitly added sections.
    for (let exp of wasm.explicit) {
      if (debug) print('emitting explicit @ ' + binary.length);
      binary.emit_bytes(exp);
    }

    // Add names.
    let num_function_names = 0;
    let num_functions_with_local_names = 0;
    for (let func of wasm.functions) {
      if (func.name !== undefined) ++num_function_names;
      if (func.numLocalNames() > 0) ++num_functions_with_local_names;
    }
    if (num_function_names > 0 || num_functions_with_local_names > 0 ||
        wasm.name !== undefined) {
      if (debug) print('emitting names @ ' + binary.length);
      binary.emit_section(kUnknownSectionCode, section => {
        section.emit_string('name');
        // Emit module name.
        if (wasm.name !== undefined) {
          section.emit_section(kModuleNameCode, name_section => {
            name_section.emit_string(wasm.name);
          });
        }
        // Emit function names.
        if (num_function_names > 0) {
          section.emit_section(kFunctionNamesCode, name_section => {
            name_section.emit_u32v(num_function_names);
            for (let func of wasm.functions) {
              if (func.name === undefined) continue;
              name_section.emit_u32v(func.index);
              name_section.emit_string(func.name);
            }
          });
        }
        // Emit local names.
        if (num_functions_with_local_names > 0) {
          section.emit_section(kLocalNamesCode, name_section => {
            name_section.emit_u32v(num_functions_with_local_names);
            for (let func of wasm.functions) {
              if (func.numLocalNames() == 0) continue;
              name_section.emit_u32v(func.index);
              name_section.emit_u32v(func.numLocalNames());
              let name_index = 0;
              for (let i = 0; i < func.local_names.length; ++i) {
                if (typeof func.local_names[i] == 'string') {
                  name_section.emit_u32v(name_index);
                  name_section.emit_string(func.local_names[i]);
                  name_index++;
                } else {
                  name_index += func.local_names[i];
                }
              }
            }
          });
        }
      });
    }

    return binary.trunc_buffer();
  }

  toArray(debug = false) {
    return Array.from(this.toBuffer(debug));
  }

  instantiate(ffi) {
    let module = this.toModule();
    let instance = new WebAssembly.Instance(module, ffi);
    return instance;
  }

  asyncInstantiate(ffi) {
    return WebAssembly.instantiate(this.toBuffer(), ffi)
        .then(({module, instance}) => instance);
  }

  toModule(debug = false) {
    return new WebAssembly.Module(this.toBuffer(debug));
  }
}

function wasmSignedLeb(val, max_len = 5) {
  let res = [];
  for (let i = 0; i < max_len; ++i) {
    let v = val & 0x7f;
    // If {v} sign-extended from 7 to 32 bits is equal to val, we are done.
    if (((v << 25) >> 25) == val) {
      res.push(v);
      return res;
    }
    res.push(v | 0x80);
    val = val >> 7;
  }
  throw new Error(
      'Leb value <' + val + '> exceeds maximum length of ' + max_len);
}

function wasmUnsignedLeb(val, max_len = 5) {
  let res = [];
  for (let i = 0; i < max_len; ++i) {
    let v = val & 0x7f;
    if (v == val) {
      res.push(v);
      return res;
    }
    res.push(v | 0x80);
    val = val >>> 7;
  }
  throw new Error(
      'Leb value <' + val + '> exceeds maximum length of ' + max_len);
}

function wasmI32Const(val) {
  return [kExprI32Const, ...wasmSignedLeb(val, 5)];
}

// Note: Since {val} is a JS number, the generated constant only has 53 bits of
// precision.
function wasmI64Const(val) {
  return [kExprI64Const, ...wasmSignedLeb(val, 10)];
}

function wasmF32Const(f) {
  // Write in little-endian order at offset 0.
  data_view.setFloat32(0, f, true);
  return [
    kExprF32Const, byte_view[0], byte_view[1], byte_view[2], byte_view[3]
  ];
}

function wasmF64Const(f) {
  // Write in little-endian order at offset 0.
  data_view.setFloat64(0, f, true);
  return [
    kExprF64Const, byte_view[0], byte_view[1], byte_view[2], byte_view[3],
    byte_view[4], byte_view[5], byte_view[6], byte_view[7]
  ];
}

function wasmS128Const(f) {
  // Write in little-endian order at offset 0.
  return [kSimdPrefix, kExprS128Const, ...f];
}

function getOpcodeName(opcode) {
  return globalThis.kWasmOpcodeNames?.[opcode] ?? 'unknown';
}