xref: /dports/www/node10/node-v10.24.1/deps/v8/src/wasm/wasm-interpreter.cc

// 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.

#include <atomic>
#include <type_traits>

#include "src/wasm/wasm-interpreter.h"

#include "src/assembler-inl.h"
#include "src/boxed-float.h"
#include "src/compiler/wasm-compiler.h"
#include "src/conversions.h"
#include "src/identity-map.h"
#include "src/objects-inl.h"
#include "src/trap-handler/trap-handler.h"
#include "src/utils.h"
#include "src/wasm/decoder.h"
#include "src/wasm/function-body-decoder-impl.h"
#include "src/wasm/function-body-decoder.h"
#include "src/wasm/memory-tracing.h"
#include "src/wasm/wasm-engine.h"
#include "src/wasm/wasm-external-refs.h"
#include "src/wasm/wasm-limits.h"
#include "src/wasm/wasm-module.h"
#include "src/wasm/wasm-objects-inl.h"

#include "src/zone/accounting-allocator.h"
#include "src/zone/zone-containers.h"

namespace v8 {
namespace internal {
namespace wasm {

#define TRACE(...)                                        \
  do {                                                    \
    if (FLAG_trace_wasm_interpreter) PrintF(__VA_ARGS__); \
  } while (false)

#define FOREACH_INTERNAL_OPCODE(V) V(Breakpoint, 0xFF)

#define WASM_CTYPES(V) \
  V(I32, int32_t) V(I64, int64_t) V(F32, float) V(F64, double) V(S128, Simd128)

#define FOREACH_SIMPLE_BINOP(V) \
  V(I32Add, uint32_t, +)        \
  V(I32Sub, uint32_t, -)        \
  V(I32Mul, uint32_t, *)        \
  V(I32And, uint32_t, &)        \
  V(I32Ior, uint32_t, |)        \
  V(I32Xor, uint32_t, ^)        \
  V(I32Eq, uint32_t, ==)        \
  V(I32Ne, uint32_t, !=)        \
  V(I32LtU, uint32_t, <)        \
  V(I32LeU, uint32_t, <=)       \
  V(I32GtU, uint32_t, >)        \
  V(I32GeU, uint32_t, >=)       \
  V(I32LtS, int32_t, <)         \
  V(I32LeS, int32_t, <=)        \
  V(I32GtS, int32_t, >)         \
  V(I32GeS, int32_t, >=)        \
  V(I64Add, uint64_t, +)        \
  V(I64Sub, uint64_t, -)        \
  V(I64Mul, uint64_t, *)        \
  V(I64And, uint64_t, &)        \
  V(I64Ior, uint64_t, |)        \
  V(I64Xor, uint64_t, ^)        \
  V(I64Eq, uint64_t, ==)        \
  V(I64Ne, uint64_t, !=)        \
  V(I64LtU, uint64_t, <)        \
  V(I64LeU, uint64_t, <=)       \
  V(I64GtU, uint64_t, >)        \
  V(I64GeU, uint64_t, >=)       \
  V(I64LtS, int64_t, <)         \
  V(I64LeS, int64_t, <=)        \
  V(I64GtS, int64_t, >)         \
  V(I64GeS, int64_t, >=)        \
  V(F32Add, float, +)           \
  V(F32Sub, float, -)           \
  V(F32Eq, float, ==)           \
  V(F32Ne, float, !=)           \
  V(F32Lt, float, <)            \
  V(F32Le, float, <=)           \
  V(F32Gt, float, >)            \
  V(F32Ge, float, >=)           \
  V(F64Add, double, +)          \
  V(F64Sub, double, -)          \
  V(F64Eq, double, ==)          \
  V(F64Ne, double, !=)          \
  V(F64Lt, double, <)           \
  V(F64Le, double, <=)          \
  V(F64Gt, double, >)           \
  V(F64Ge, double, >=)          \
  V(F32Mul, float, *)           \
  V(F64Mul, double, *)          \
  V(F32Div, float, /)           \
  V(F64Div, double, /)

#define FOREACH_OTHER_BINOP(V) \
  V(I32DivS, int32_t)          \
  V(I32DivU, uint32_t)         \
  V(I32RemS, int32_t)          \
  V(I32RemU, uint32_t)         \
  V(I32Shl, uint32_t)          \
  V(I32ShrU, uint32_t)         \
  V(I32ShrS, int32_t)          \
  V(I64DivS, int64_t)          \
  V(I64DivU, uint64_t)         \
  V(I64RemS, int64_t)          \
  V(I64RemU, uint64_t)         \
  V(I64Shl, uint64_t)          \
  V(I64ShrU, uint64_t)         \
  V(I64ShrS, int64_t)          \
  V(I32Ror, int32_t)           \
  V(I32Rol, int32_t)           \
  V(I64Ror, int64_t)           \
  V(I64Rol, int64_t)           \
  V(F32Min, float)             \
  V(F32Max, float)             \
  V(F64Min, double)            \
  V(F64Max, double)            \
  V(I32AsmjsDivS, int32_t)     \
  V(I32AsmjsDivU, uint32_t)    \
  V(I32AsmjsRemS, int32_t)     \
  V(I32AsmjsRemU, uint32_t)    \
  V(F32CopySign, Float32)      \
  V(F64CopySign, Float64)

#define FOREACH_I32CONV_FLOATOP(V)   \
  V(I32SConvertF32, int32_t, float)  \
  V(I32SConvertF64, int32_t, double) \
  V(I32UConvertF32, uint32_t, float) \
  V(I32UConvertF64, uint32_t, double)

#define FOREACH_OTHER_UNOP(V)    \
  V(I32Clz, uint32_t)            \
  V(I32Ctz, uint32_t)            \
  V(I32Popcnt, uint32_t)         \
  V(I32Eqz, uint32_t)            \
  V(I64Clz, uint64_t)            \
  V(I64Ctz, uint64_t)            \
  V(I64Popcnt, uint64_t)         \
  V(I64Eqz, uint64_t)            \
  V(F32Abs, Float32)             \
  V(F32Neg, Float32)             \
  V(F32Ceil, float)              \
  V(F32Floor, float)             \
  V(F32Trunc, float)             \
  V(F32NearestInt, float)        \
  V(F64Abs, Float64)             \
  V(F64Neg, Float64)             \
  V(F64Ceil, double)             \
  V(F64Floor, double)            \
  V(F64Trunc, double)            \
  V(F64NearestInt, double)       \
  V(I32ConvertI64, int64_t)      \
  V(I64SConvertF32, float)       \
  V(I64SConvertF64, double)      \
  V(I64UConvertF32, float)       \
  V(I64UConvertF64, double)      \
  V(I64SConvertI32, int32_t)     \
  V(I64UConvertI32, uint32_t)    \
  V(F32SConvertI32, int32_t)     \
  V(F32UConvertI32, uint32_t)    \
  V(F32SConvertI64, int64_t)     \
  V(F32UConvertI64, uint64_t)    \
  V(F32ConvertF64, double)       \
  V(F32ReinterpretI32, int32_t)  \
  V(F64SConvertI32, int32_t)     \
  V(F64UConvertI32, uint32_t)    \
  V(F64SConvertI64, int64_t)     \
  V(F64UConvertI64, uint64_t)    \
  V(F64ConvertF32, float)        \
  V(F64ReinterpretI64, int64_t)  \
  V(I32AsmjsSConvertF32, float)  \
  V(I32AsmjsUConvertF32, float)  \
  V(I32AsmjsSConvertF64, double) \
  V(I32AsmjsUConvertF64, double) \
  V(F32Sqrt, float)              \
  V(F64Sqrt, double)

namespace {

constexpr uint32_t kFloat32SignBitMask = uint32_t{1} << 31;
constexpr uint64_t kFloat64SignBitMask = uint64_t{1} << 63;

inline int32_t ExecuteI32DivS(int32_t a, int32_t b, TrapReason* trap) {
  if (b == 0) {
    *trap = kTrapDivByZero;
    return 0;
  }
  if (b == -1 && a == std::numeric_limits<int32_t>::min()) {
    *trap = kTrapDivUnrepresentable;
    return 0;
  }
  return a / b;
}

inline uint32_t ExecuteI32DivU(uint32_t a, uint32_t b, TrapReason* trap) {
  if (b == 0) {
    *trap = kTrapDivByZero;
    return 0;
  }
  return a / b;
}

inline int32_t ExecuteI32RemS(int32_t a, int32_t b, TrapReason* trap) {
  if (b == 0) {
    *trap = kTrapRemByZero;
    return 0;
  }
  if (b == -1) return 0;
  return a % b;
}

inline uint32_t ExecuteI32RemU(uint32_t a, uint32_t b, TrapReason* trap) {
  if (b == 0) {
    *trap = kTrapRemByZero;
    return 0;
  }
  return a % b;
}

inline uint32_t ExecuteI32Shl(uint32_t a, uint32_t b, TrapReason* trap) {
  return a << (b & 0x1F);
}

inline uint32_t ExecuteI32ShrU(uint32_t a, uint32_t b, TrapReason* trap) {
  return a >> (b & 0x1F);
}

inline int32_t ExecuteI32ShrS(int32_t a, int32_t b, TrapReason* trap) {
  return a >> (b & 0x1F);
}

inline int64_t ExecuteI64DivS(int64_t a, int64_t b, TrapReason* trap) {
  if (b == 0) {
    *trap = kTrapDivByZero;
    return 0;
  }
  if (b == -1 && a == std::numeric_limits<int64_t>::min()) {
    *trap = kTrapDivUnrepresentable;
    return 0;
  }
  return a / b;
}

inline uint64_t ExecuteI64DivU(uint64_t a, uint64_t b, TrapReason* trap) {
  if (b == 0) {
    *trap = kTrapDivByZero;
    return 0;
  }
  return a / b;
}

inline int64_t ExecuteI64RemS(int64_t a, int64_t b, TrapReason* trap) {
  if (b == 0) {
    *trap = kTrapRemByZero;
    return 0;
  }
  if (b == -1) return 0;
  return a % b;
}

inline uint64_t ExecuteI64RemU(uint64_t a, uint64_t b, TrapReason* trap) {
  if (b == 0) {
    *trap = kTrapRemByZero;
    return 0;
  }
  return a % b;
}

inline uint64_t ExecuteI64Shl(uint64_t a, uint64_t b, TrapReason* trap) {
  return a << (b & 0x3F);
}

inline uint64_t ExecuteI64ShrU(uint64_t a, uint64_t b, TrapReason* trap) {
  return a >> (b & 0x3F);
}

inline int64_t ExecuteI64ShrS(int64_t a, int64_t b, TrapReason* trap) {
  return a >> (b & 0x3F);
}

inline uint32_t ExecuteI32Ror(uint32_t a, uint32_t b, TrapReason* trap) {
  uint32_t shift = (b & 0x1F);
  return (a >> shift) | (a << (32 - shift));
}

inline uint32_t ExecuteI32Rol(uint32_t a, uint32_t b, TrapReason* trap) {
  uint32_t shift = (b & 0x1F);
  return (a << shift) | (a >> (32 - shift));
}

inline uint64_t ExecuteI64Ror(uint64_t a, uint64_t b, TrapReason* trap) {
  uint32_t shift = (b & 0x3F);
  return (a >> shift) | (a << (64 - shift));
}

inline uint64_t ExecuteI64Rol(uint64_t a, uint64_t b, TrapReason* trap) {
  uint32_t shift = (b & 0x3F);
  return (a << shift) | (a >> (64 - shift));
}

inline float ExecuteF32Min(float a, float b, TrapReason* trap) {
  return JSMin(a, b);
}

inline float ExecuteF32Max(float a, float b, TrapReason* trap) {
  return JSMax(a, b);
}

inline Float32 ExecuteF32CopySign(Float32 a, Float32 b, TrapReason* trap) {
  return Float32::FromBits((a.get_bits() & ~kFloat32SignBitMask) |
                           (b.get_bits() & kFloat32SignBitMask));
}

inline double ExecuteF64Min(double a, double b, TrapReason* trap) {
  return JSMin(a, b);
}

inline double ExecuteF64Max(double a, double b, TrapReason* trap) {
  return JSMax(a, b);
}

inline Float64 ExecuteF64CopySign(Float64 a, Float64 b, TrapReason* trap) {
  return Float64::FromBits((a.get_bits() & ~kFloat64SignBitMask) |
                           (b.get_bits() & kFloat64SignBitMask));
}

inline int32_t ExecuteI32AsmjsDivS(int32_t a, int32_t b, TrapReason* trap) {
  if (b == 0) return 0;
  if (b == -1 && a == std::numeric_limits<int32_t>::min()) {
    return std::numeric_limits<int32_t>::min();
  }
  return a / b;
}

inline uint32_t ExecuteI32AsmjsDivU(uint32_t a, uint32_t b, TrapReason* trap) {
  if (b == 0) return 0;
  return a / b;
}

inline int32_t ExecuteI32AsmjsRemS(int32_t a, int32_t b, TrapReason* trap) {
  if (b == 0) return 0;
  if (b == -1) return 0;
  return a % b;
}

inline uint32_t ExecuteI32AsmjsRemU(uint32_t a, uint32_t b, TrapReason* trap) {
  if (b == 0) return 0;
  return a % b;
}

inline int32_t ExecuteI32AsmjsSConvertF32(float a, TrapReason* trap) {
  return DoubleToInt32(a);
}

inline uint32_t ExecuteI32AsmjsUConvertF32(float a, TrapReason* trap) {
  return DoubleToUint32(a);
}

inline int32_t ExecuteI32AsmjsSConvertF64(double a, TrapReason* trap) {
  return DoubleToInt32(a);
}

inline uint32_t ExecuteI32AsmjsUConvertF64(double a, TrapReason* trap) {
  return DoubleToUint32(a);
}

int32_t ExecuteI32Clz(uint32_t val, TrapReason* trap) {
  return base::bits::CountLeadingZeros(val);
}

uint32_t ExecuteI32Ctz(uint32_t val, TrapReason* trap) {
  return base::bits::CountTrailingZeros(val);
}

uint32_t ExecuteI32Popcnt(uint32_t val, TrapReason* trap) {
  return base::bits::CountPopulation(val);
}

inline uint32_t ExecuteI32Eqz(uint32_t val, TrapReason* trap) {
  return val == 0 ? 1 : 0;
}

int64_t ExecuteI64Clz(uint64_t val, TrapReason* trap) {
  return base::bits::CountLeadingZeros(val);
}

inline uint64_t ExecuteI64Ctz(uint64_t val, TrapReason* trap) {
  return base::bits::CountTrailingZeros(val);
}

inline int64_t ExecuteI64Popcnt(uint64_t val, TrapReason* trap) {
  return base::bits::CountPopulation(val);
}

inline int32_t ExecuteI64Eqz(uint64_t val, TrapReason* trap) {
  return val == 0 ? 1 : 0;
}

inline Float32 ExecuteF32Abs(Float32 a, TrapReason* trap) {
  return Float32::FromBits(a.get_bits() & ~kFloat32SignBitMask);
}

inline Float32 ExecuteF32Neg(Float32 a, TrapReason* trap) {
  return Float32::FromBits(a.get_bits() ^ kFloat32SignBitMask);
}

inline float ExecuteF32Ceil(float a, TrapReason* trap) { return ceilf(a); }

inline float ExecuteF32Floor(float a, TrapReason* trap) { return floorf(a); }

inline float ExecuteF32Trunc(float a, TrapReason* trap) { return truncf(a); }

inline float ExecuteF32NearestInt(float a, TrapReason* trap) {
  return nearbyintf(a);
}

inline float ExecuteF32Sqrt(float a, TrapReason* trap) {
  float result = sqrtf(a);
  return result;
}

inline Float64 ExecuteF64Abs(Float64 a, TrapReason* trap) {
  return Float64::FromBits(a.get_bits() & ~kFloat64SignBitMask);
}

inline Float64 ExecuteF64Neg(Float64 a, TrapReason* trap) {
  return Float64::FromBits(a.get_bits() ^ kFloat64SignBitMask);
}

inline double ExecuteF64Ceil(double a, TrapReason* trap) { return ceil(a); }

inline double ExecuteF64Floor(double a, TrapReason* trap) { return floor(a); }

inline double ExecuteF64Trunc(double a, TrapReason* trap) { return trunc(a); }

inline double ExecuteF64NearestInt(double a, TrapReason* trap) {
  return nearbyint(a);
}

inline double ExecuteF64Sqrt(double a, TrapReason* trap) { return sqrt(a); }

template <typename int_type, typename float_type>
int_type ExecuteConvert(float_type a, TrapReason* trap) {
  if (is_inbounds<int_type>(a)) {
    return static_cast<int_type>(a);
  }
  *trap = kTrapFloatUnrepresentable;
  return 0;
}

template <typename int_type, typename float_type>
int_type ExecuteConvertSaturate(float_type a) {
  TrapReason base_trap = kTrapCount;
  int32_t val = ExecuteConvert<int_type>(a, &base_trap);
  if (base_trap == kTrapCount) {
    return val;
  }
  return std::isnan(a) ? 0
                       : (a < static_cast<float_type>(0.0)
                              ? std::numeric_limits<int_type>::min()
                              : std::numeric_limits<int_type>::max());
}

template <typename dst_type, typename src_type, void (*fn)(Address)>
inline dst_type CallExternalIntToFloatFunction(src_type input) {
  uint8_t data[std::max(sizeof(dst_type), sizeof(src_type))];
  Address data_addr = reinterpret_cast<Address>(data);
  WriteUnalignedValue<src_type>(data_addr, input);
  fn(data_addr);
  return ReadUnalignedValue<dst_type>(data_addr);
}

template <typename dst_type, typename src_type, int32_t (*fn)(Address)>
inline dst_type CallExternalFloatToIntFunction(src_type input,
                                               TrapReason* trap) {
  uint8_t data[std::max(sizeof(dst_type), sizeof(src_type))];
  Address data_addr = reinterpret_cast<Address>(data);
  WriteUnalignedValue<src_type>(data_addr, input);
  if (!fn(data_addr)) *trap = kTrapFloatUnrepresentable;
  return ReadUnalignedValue<dst_type>(data_addr);
}

inline uint32_t ExecuteI32ConvertI64(int64_t a, TrapReason* trap) {
  return static_cast<uint32_t>(a & 0xFFFFFFFF);
}

int64_t ExecuteI64SConvertF32(float a, TrapReason* trap) {
  return CallExternalFloatToIntFunction<int64_t, float,
                                        float32_to_int64_wrapper>(a, trap);
}

int64_t ExecuteI64SConvertSatF32(float a) {
  TrapReason base_trap = kTrapCount;
  int64_t val = ExecuteI64SConvertF32(a, &base_trap);
  if (base_trap == kTrapCount) {
    return val;
  }
  return std::isnan(a) ? 0
                       : (a < 0.0 ? std::numeric_limits<int64_t>::min()
                                  : std::numeric_limits<int64_t>::max());
}

int64_t ExecuteI64SConvertF64(double a, TrapReason* trap) {
  return CallExternalFloatToIntFunction<int64_t, double,
                                        float64_to_int64_wrapper>(a, trap);
}

int64_t ExecuteI64SConvertSatF64(double a) {
  TrapReason base_trap = kTrapCount;
  int64_t val = ExecuteI64SConvertF64(a, &base_trap);
  if (base_trap == kTrapCount) {
    return val;
  }
  return std::isnan(a) ? 0
                       : (a < 0.0 ? std::numeric_limits<int64_t>::min()
                                  : std::numeric_limits<int64_t>::max());
}

uint64_t ExecuteI64UConvertF32(float a, TrapReason* trap) {
  return CallExternalFloatToIntFunction<uint64_t, float,
                                        float32_to_uint64_wrapper>(a, trap);
}

uint64_t ExecuteI64UConvertSatF32(float a) {
  TrapReason base_trap = kTrapCount;
  uint64_t val = ExecuteI64UConvertF32(a, &base_trap);
  if (base_trap == kTrapCount) {
    return val;
  }
  return std::isnan(a) ? 0
                       : (a < 0.0 ? std::numeric_limits<uint64_t>::min()
                                  : std::numeric_limits<uint64_t>::max());
}

uint64_t ExecuteI64UConvertF64(double a, TrapReason* trap) {
  return CallExternalFloatToIntFunction<uint64_t, double,
                                        float64_to_uint64_wrapper>(a, trap);
}

uint64_t ExecuteI64UConvertSatF64(double a) {
  TrapReason base_trap = kTrapCount;
  int64_t val = ExecuteI64UConvertF64(a, &base_trap);
  if (base_trap == kTrapCount) {
    return val;
  }
  return std::isnan(a) ? 0
                       : (a < 0.0 ? std::numeric_limits<uint64_t>::min()
                                  : std::numeric_limits<uint64_t>::max());
}

inline int64_t ExecuteI64SConvertI32(int32_t a, TrapReason* trap) {
  return static_cast<int64_t>(a);
}

inline int64_t ExecuteI64UConvertI32(uint32_t a, TrapReason* trap) {
  return static_cast<uint64_t>(a);
}

inline float ExecuteF32SConvertI32(int32_t a, TrapReason* trap) {
  return static_cast<float>(a);
}

inline float ExecuteF32UConvertI32(uint32_t a, TrapReason* trap) {
  return static_cast<float>(a);
}

inline float ExecuteF32SConvertI64(int64_t a, TrapReason* trap) {
  return static_cast<float>(a);
}

inline float ExecuteF32UConvertI64(uint64_t a, TrapReason* trap) {
  return CallExternalIntToFloatFunction<float, uint64_t,
                                        uint64_to_float32_wrapper>(a);
}

inline float ExecuteF32ConvertF64(double a, TrapReason* trap) {
  return static_cast<float>(a);
}

inline Float32 ExecuteF32ReinterpretI32(int32_t a, TrapReason* trap) {
  return Float32::FromBits(a);
}

inline double ExecuteF64SConvertI32(int32_t a, TrapReason* trap) {
  return static_cast<double>(a);
}

inline double ExecuteF64UConvertI32(uint32_t a, TrapReason* trap) {
  return static_cast<double>(a);
}

inline double ExecuteF64SConvertI64(int64_t a, TrapReason* trap) {
  return static_cast<double>(a);
}

inline double ExecuteF64UConvertI64(uint64_t a, TrapReason* trap) {
  return CallExternalIntToFloatFunction<double, uint64_t,
                                        uint64_to_float64_wrapper>(a);
}

inline double ExecuteF64ConvertF32(float a, TrapReason* trap) {
  return static_cast<double>(a);
}

inline Float64 ExecuteF64ReinterpretI64(int64_t a, TrapReason* trap) {
  return Float64::FromBits(a);
}

inline int32_t ExecuteI32ReinterpretF32(WasmValue a) {
  return a.to_f32_boxed().get_bits();
}

inline int64_t ExecuteI64ReinterpretF64(WasmValue a) {
  return a.to_f64_boxed().get_bits();
}

enum InternalOpcode {
#define DECL_INTERNAL_ENUM(name, value) kInternal##name = value,
  FOREACH_INTERNAL_OPCODE(DECL_INTERNAL_ENUM)
#undef DECL_INTERNAL_ENUM
};

const char* OpcodeName(uint32_t val) {
  switch (val) {
#define DECL_INTERNAL_CASE(name, value) \
  case kInternal##name:                 \
    return "Internal" #name;
    FOREACH_INTERNAL_OPCODE(DECL_INTERNAL_CASE)
#undef DECL_INTERNAL_CASE
  }
  return WasmOpcodes::OpcodeName(static_cast<WasmOpcode>(val));
}

class SideTable;

// Code and metadata needed to execute a function.
struct InterpreterCode {
  const WasmFunction* function;  // wasm function
  BodyLocalDecls locals;         // local declarations
  const byte* orig_start;        // start of original code
  const byte* orig_end;          // end of original code
  byte* start;                   // start of (maybe altered) code
  byte* end;                     // end of (maybe altered) code
  SideTable* side_table;         // precomputed side table for control flow.

  const byte* at(pc_t pc) { return start + pc; }
};

// A helper class to compute the control transfers for each bytecode offset.
// Control transfers allow Br, BrIf, BrTable, If, Else, and End bytecodes to
// be directly executed without the need to dynamically track blocks.
class SideTable : public ZoneObject {
 public:
  ControlTransferMap map_;
  uint32_t max_stack_height_ = 0;

  SideTable(Zone* zone, const WasmModule* module, InterpreterCode* code)
      : map_(zone) {
    // Create a zone for all temporary objects.
    Zone control_transfer_zone(zone->allocator(), ZONE_NAME);

    // Represents a control flow label.
    class CLabel : public ZoneObject {
      explicit CLabel(Zone* zone, uint32_t target_stack_height, uint32_t arity)
          : target_stack_height(target_stack_height),
            arity(arity),
            refs(zone) {}

     public:
      struct Ref {
        const byte* from_pc;
        const uint32_t stack_height;
      };
      const byte* target = nullptr;
      uint32_t target_stack_height;
      // Arity when branching to this label.
      const uint32_t arity;
      ZoneVector<Ref> refs;

      static CLabel* New(Zone* zone, uint32_t stack_height, uint32_t arity) {
        return new (zone) CLabel(zone, stack_height, arity);
      }

      // Bind this label to the given PC.
      void Bind(const byte* pc) {
        DCHECK_NULL(target);
        target = pc;
      }

      // Reference this label from the given location.
      void Ref(const byte* from_pc, uint32_t stack_height) {
        // Target being bound before a reference means this is a loop.
        DCHECK_IMPLIES(target, *target == kExprLoop);
        refs.push_back({from_pc, stack_height});
      }

      void Finish(ControlTransferMap* map, const byte* start) {
        DCHECK_NOT_NULL(target);
        for (auto ref : refs) {
          size_t offset = static_cast<size_t>(ref.from_pc - start);
          auto pcdiff = static_cast<pcdiff_t>(target - ref.from_pc);
          DCHECK_GE(ref.stack_height, target_stack_height);
          spdiff_t spdiff =
              static_cast<spdiff_t>(ref.stack_height - target_stack_height);
          TRACE("control transfer @%zu: Δpc %d, stack %u->%u = -%u\n", offset,
                pcdiff, ref.stack_height, target_stack_height, spdiff);
          ControlTransferEntry& entry = (*map)[offset];
          entry.pc_diff = pcdiff;
          entry.sp_diff = spdiff;
          entry.target_arity = arity;
        }
      }
    };

    // An entry in the control stack.
    struct Control {
      const byte* pc;
      CLabel* end_label;
      CLabel* else_label;
      // Arity (number of values on the stack) when exiting this control
      // structure via |end|.
      uint32_t exit_arity;
      // Track whether this block was already left, i.e. all further
      // instructions are unreachable.
      bool unreachable = false;

      Control(const byte* pc, CLabel* end_label, CLabel* else_label,
              uint32_t exit_arity)
          : pc(pc),
            end_label(end_label),
            else_label(else_label),
            exit_arity(exit_arity) {}
      Control(const byte* pc, CLabel* end_label, uint32_t exit_arity)
          : Control(pc, end_label, nullptr, exit_arity) {}

      void Finish(ControlTransferMap* map, const byte* start) {
        end_label->Finish(map, start);
        if (else_label) else_label->Finish(map, start);
      }
    };

    // Compute the ControlTransfer map.
    // This algorithm maintains a stack of control constructs similar to the
    // AST decoder. The {control_stack} allows matching {br,br_if,br_table}
    // bytecodes with their target, as well as determining whether the current
    // bytecodes are within the true or false block of an else.
    ZoneVector<Control> control_stack(&control_transfer_zone);
    uint32_t stack_height = 0;
    uint32_t func_arity =
        static_cast<uint32_t>(code->function->sig->return_count());
    CLabel* func_label =
        CLabel::New(&control_transfer_zone, stack_height, func_arity);
    control_stack.emplace_back(code->orig_start, func_label, func_arity);
    auto control_parent = [&]() -> Control& {
      DCHECK_LE(2, control_stack.size());
      return control_stack[control_stack.size() - 2];
    };
    auto copy_unreachable = [&] {
      control_stack.back().unreachable = control_parent().unreachable;
    };
    for (BytecodeIterator i(code->orig_start, code->orig_end, &code->locals);
         i.has_next(); i.next()) {
      WasmOpcode opcode = i.current();
      if (WasmOpcodes::IsPrefixOpcode(opcode)) opcode = i.prefixed_opcode();
      bool unreachable = control_stack.back().unreachable;
      if (unreachable) {
        TRACE("@%u: %s (is unreachable)\n", i.pc_offset(),
              WasmOpcodes::OpcodeName(opcode));
      } else {
        auto stack_effect =
            StackEffect(module, code->function->sig, i.pc(), i.end());
        TRACE("@%u: %s (sp %d - %d + %d)\n", i.pc_offset(),
              WasmOpcodes::OpcodeName(opcode), stack_height, stack_effect.first,
              stack_effect.second);
        DCHECK_GE(stack_height, stack_effect.first);
        DCHECK_GE(kMaxUInt32, static_cast<uint64_t>(stack_height) -
                                  stack_effect.first + stack_effect.second);
        stack_height = stack_height - stack_effect.first + stack_effect.second;
        if (stack_height > max_stack_height_) max_stack_height_ = stack_height;
      }
      switch (opcode) {
        case kExprBlock:
        case kExprLoop: {
          bool is_loop = opcode == kExprLoop;
          BlockTypeImmediate<Decoder::kNoValidate> imm(&i, i.pc());
          if (imm.type == kWasmVar) {
            imm.sig = module->signatures[imm.sig_index];
          }
          TRACE("control @%u: %s, arity %d->%d\n", i.pc_offset(),
                is_loop ? "Loop" : "Block", imm.in_arity(), imm.out_arity());
          CLabel* label =
              CLabel::New(&control_transfer_zone, stack_height,
                          is_loop ? imm.in_arity() : imm.out_arity());
          control_stack.emplace_back(i.pc(), label, imm.out_arity());
          copy_unreachable();
          if (is_loop) label->Bind(i.pc());
          break;
        }
        case kExprIf: {
          BlockTypeImmediate<Decoder::kNoValidate> imm(&i, i.pc());
          if (imm.type == kWasmVar) {
            imm.sig = module->signatures[imm.sig_index];
          }
          TRACE("control @%u: If, arity %d->%d\n", i.pc_offset(),
                imm.in_arity(), imm.out_arity());
          CLabel* end_label = CLabel::New(&control_transfer_zone, stack_height,
                                          imm.out_arity());
          CLabel* else_label =
              CLabel::New(&control_transfer_zone, stack_height, 0);
          control_stack.emplace_back(i.pc(), end_label, else_label,
                                     imm.out_arity());
          copy_unreachable();
          if (!unreachable) else_label->Ref(i.pc(), stack_height);
          break;
        }
        case kExprElse: {
          Control* c = &control_stack.back();
          copy_unreachable();
          TRACE("control @%u: Else\n", i.pc_offset());
          if (!control_parent().unreachable) {
            c->end_label->Ref(i.pc(), stack_height);
          }
          DCHECK_NOT_NULL(c->else_label);
          c->else_label->Bind(i.pc() + 1);
          c->else_label->Finish(&map_, code->orig_start);
          c->else_label = nullptr;
          DCHECK_GE(stack_height, c->end_label->target_stack_height);
          stack_height = c->end_label->target_stack_height;
          break;
        }
        case kExprEnd: {
          Control* c = &control_stack.back();
          TRACE("control @%u: End\n", i.pc_offset());
          // Only loops have bound labels.
          DCHECK_IMPLIES(c->end_label->target, *c->pc == kExprLoop);
          if (!c->end_label->target) {
            if (c->else_label) c->else_label->Bind(i.pc());
            c->end_label->Bind(i.pc() + 1);
          }
          c->Finish(&map_, code->orig_start);
          DCHECK_GE(stack_height, c->end_label->target_stack_height);
          stack_height = c->end_label->target_stack_height + c->exit_arity;
          control_stack.pop_back();
          break;
        }
        case kExprBr: {
          BreakDepthImmediate<Decoder::kNoValidate> imm(&i, i.pc());
          TRACE("control @%u: Br[depth=%u]\n", i.pc_offset(), imm.depth);
          Control* c = &control_stack[control_stack.size() - imm.depth - 1];
          if (!unreachable) c->end_label->Ref(i.pc(), stack_height);
          break;
        }
        case kExprBrIf: {
          BreakDepthImmediate<Decoder::kNoValidate> imm(&i, i.pc());
          TRACE("control @%u: BrIf[depth=%u]\n", i.pc_offset(), imm.depth);
          Control* c = &control_stack[control_stack.size() - imm.depth - 1];
          if (!unreachable) c->end_label->Ref(i.pc(), stack_height);
          break;
        }
        case kExprBrTable: {
          BranchTableImmediate<Decoder::kNoValidate> imm(&i, i.pc());
          BranchTableIterator<Decoder::kNoValidate> iterator(&i, imm);
          TRACE("control @%u: BrTable[count=%u]\n", i.pc_offset(),
                imm.table_count);
          if (!unreachable) {
            while (iterator.has_next()) {
              uint32_t j = iterator.cur_index();
              uint32_t target = iterator.next();
              Control* c = &control_stack[control_stack.size() - target - 1];
              c->end_label->Ref(i.pc() + j, stack_height);
            }
          }
          break;
        }
        default:
          break;
      }
      if (WasmOpcodes::IsUnconditionalJump(opcode)) {
        control_stack.back().unreachable = true;
      }
    }
    DCHECK_EQ(0, control_stack.size());
    DCHECK_EQ(func_arity, stack_height);
  }

  ControlTransferEntry& Lookup(pc_t from) {
    auto result = map_.find(from);
    DCHECK(result != map_.end());
    return result->second;
  }
};

struct ExternalCallResult {
  enum Type {
    // The function should be executed inside this interpreter.
    INTERNAL,
    // For indirect calls: Table or function does not exist.
    INVALID_FUNC,
    // For indirect calls: Signature does not match expected signature.
    SIGNATURE_MISMATCH,
    // The function was executed and returned normally.
    EXTERNAL_RETURNED,
    // The function was executed, threw an exception, and the stack was unwound.
    EXTERNAL_UNWOUND
  };
  Type type;
  // If type is INTERNAL, this field holds the function to call internally.
  InterpreterCode* interpreter_code;

  ExternalCallResult(Type type) : type(type) {  // NOLINT
    DCHECK_NE(INTERNAL, type);
  }
  ExternalCallResult(Type type, InterpreterCode* code)
      : type(type), interpreter_code(code) {
    DCHECK_EQ(INTERNAL, type);
  }
};

// The main storage for interpreter code. It maps {WasmFunction} to the
// metadata needed to execute each function.
class CodeMap {
  Zone* zone_;
  const WasmModule* module_;
  ZoneVector<InterpreterCode> interpreter_code_;
  // TODO(wasm): Remove this testing wart. It is needed because interpreter
  // entry stubs are not generated in testing the interpreter in cctests.
  bool call_indirect_through_module_ = false;

 public:
  CodeMap(Isolate* isolate, const WasmModule* module,
          const uint8_t* module_start, Zone* zone)
      : zone_(zone), module_(module), interpreter_code_(zone) {
    if (module == nullptr) return;
    interpreter_code_.reserve(module->functions.size());
    for (const WasmFunction& function : module->functions) {
      if (function.imported) {
        DCHECK(!function.code.is_set());
        AddFunction(&function, nullptr, nullptr);
      } else {
        AddFunction(&function, module_start + function.code.offset(),
                    module_start + function.code.end_offset());
      }
    }
  }

  bool call_indirect_through_module() { return call_indirect_through_module_; }

  void set_call_indirect_through_module(bool val) {
    call_indirect_through_module_ = val;
  }

  const WasmModule* module() const { return module_; }

  InterpreterCode* GetCode(const WasmFunction* function) {
    InterpreterCode* code = GetCode(function->func_index);
    DCHECK_EQ(function, code->function);
    return code;
  }

  InterpreterCode* GetCode(uint32_t function_index) {
    DCHECK_LT(function_index, interpreter_code_.size());
    return Preprocess(&interpreter_code_[function_index]);
  }

  InterpreterCode* GetIndirectCode(uint32_t table_index, uint32_t entry_index) {
    uint32_t saved_index;
    USE(saved_index);
    if (table_index >= module_->function_tables.size()) return nullptr;
    // Mask table index for SSCA mitigation.
    saved_index = table_index;
    table_index &=
        static_cast<int32_t>((table_index - module_->function_tables.size()) &
                             ~static_cast<int32_t>(table_index)) >>
        31;
    DCHECK_EQ(table_index, saved_index);
    const WasmIndirectFunctionTable* table =
        &module_->function_tables[table_index];
    if (entry_index >= table->values.size()) return nullptr;
    // Mask entry_index for SSCA mitigation.
    saved_index = entry_index;
    entry_index &= static_cast<int32_t>((entry_index - table->values.size()) &
                                        ~static_cast<int32_t>(entry_index)) >>
                   31;
    DCHECK_EQ(entry_index, saved_index);
    uint32_t index = table->values[entry_index];
    if (index >= interpreter_code_.size()) return nullptr;
    // Mask index for SSCA mitigation.
    saved_index = index;
    index &= static_cast<int32_t>((index - interpreter_code_.size()) &
                                  ~static_cast<int32_t>(index)) >>
             31;
    DCHECK_EQ(index, saved_index);

    return GetCode(index);
  }

  InterpreterCode* Preprocess(InterpreterCode* code) {
    DCHECK_EQ(code->function->imported, code->start == nullptr);
    if (!code->side_table && code->start) {
      // Compute the control targets map and the local declarations.
      code->side_table = new (zone_) SideTable(zone_, module_, code);
    }
    return code;
  }

  void AddFunction(const WasmFunction* function, const byte* code_start,
                   const byte* code_end) {
    InterpreterCode code = {
        function, BodyLocalDecls(zone_),         code_start,
        code_end, const_cast<byte*>(code_start), const_cast<byte*>(code_end),
        nullptr};

    DCHECK_EQ(interpreter_code_.size(), function->func_index);
    interpreter_code_.push_back(code);
  }

  void SetFunctionCode(const WasmFunction* function, const byte* start,
                       const byte* end) {
    DCHECK_LT(function->func_index, interpreter_code_.size());
    InterpreterCode* code = &interpreter_code_[function->func_index];
    DCHECK_EQ(function, code->function);
    code->orig_start = start;
    code->orig_end = end;
    code->start = const_cast<byte*>(start);
    code->end = const_cast<byte*>(end);
    code->side_table = nullptr;
    Preprocess(code);
  }
};

// Like a static_cast from src to dst, but specialized for boxed floats.
template <typename dst, typename src>
struct converter {
  dst operator()(src val) const { return static_cast<dst>(val); }
};
template <>
struct converter<Float64, uint64_t> {
  Float64 operator()(uint64_t val) const { return Float64::FromBits(val); }
};
template <>
struct converter<Float32, uint32_t> {
  Float32 operator()(uint32_t val) const { return Float32::FromBits(val); }
};
template <>
struct converter<uint64_t, Float64> {
  uint64_t operator()(Float64 val) const { return val.get_bits(); }
};
template <>
struct converter<uint32_t, Float32> {
  uint32_t operator()(Float32 val) const { return val.get_bits(); }
};

template <typename T>
V8_INLINE bool has_nondeterminism(T val) {
  static_assert(!std::is_floating_point<T>::value, "missing specialization");
  return false;
}
template <>
V8_INLINE bool has_nondeterminism<float>(float val) {
  return std::isnan(val);
}
template <>
V8_INLINE bool has_nondeterminism<double>(double val) {
  return std::isnan(val);
}

// Responsible for executing code directly.
class ThreadImpl {
  struct Activation {
    uint32_t fp;
    sp_t sp;
    Activation(uint32_t fp, sp_t sp) : fp(fp), sp(sp) {}
  };

 public:
  ThreadImpl(Zone* zone, CodeMap* codemap,
             Handle<WasmInstanceObject> instance_object)
      : codemap_(codemap),
        instance_object_(instance_object),
        zone_(zone),
        frames_(zone),
        activations_(zone) {}

  //==========================================================================
  // Implementation of public interface for WasmInterpreter::Thread.
  //==========================================================================

  WasmInterpreter::State state() { return state_; }

  void InitFrame(const WasmFunction* function, WasmValue* args) {
    DCHECK_EQ(current_activation().fp, frames_.size());
    InterpreterCode* code = codemap()->GetCode(function);
    size_t num_params = function->sig->parameter_count();
    EnsureStackSpace(num_params);
    Push(args, num_params);
    PushFrame(code);
  }

  WasmInterpreter::State Run(int num_steps = -1) {
    DCHECK(state_ == WasmInterpreter::STOPPED ||
           state_ == WasmInterpreter::PAUSED);
    DCHECK(num_steps == -1 || num_steps > 0);
    if (num_steps == -1) {
      TRACE("  => Run()\n");
    } else if (num_steps == 1) {
      TRACE("  => Step()\n");
    } else {
      TRACE("  => Run(%d)\n", num_steps);
    }
    state_ = WasmInterpreter::RUNNING;
    Execute(frames_.back().code, frames_.back().pc, num_steps);
    // If state_ is STOPPED, the current activation must be fully unwound.
    DCHECK_IMPLIES(state_ == WasmInterpreter::STOPPED,
                   current_activation().fp == frames_.size());
    return state_;
  }

  void Pause() { UNIMPLEMENTED(); }

  void Reset() {
    TRACE("----- RESET -----\n");
    sp_ = stack_start_;
    frames_.clear();
    state_ = WasmInterpreter::STOPPED;
    trap_reason_ = kTrapCount;
    possible_nondeterminism_ = false;
  }

  int GetFrameCount() {
    DCHECK_GE(kMaxInt, frames_.size());
    return static_cast<int>(frames_.size());
  }

  WasmValue GetReturnValue(uint32_t index) {
    if (state_ == WasmInterpreter::TRAPPED) return WasmValue(0xDEADBEEF);
    DCHECK_EQ(WasmInterpreter::FINISHED, state_);
    Activation act = current_activation();
    // Current activation must be finished.
    DCHECK_EQ(act.fp, frames_.size());
    return GetStackValue(act.sp + index);
  }

  WasmValue GetStackValue(sp_t index) {
    DCHECK_GT(StackHeight(), index);
    return stack_start_[index];
  }

  void SetStackValue(sp_t index, WasmValue value) {
    DCHECK_GT(StackHeight(), index);
    stack_start_[index] = value;
  }

  TrapReason GetTrapReason() { return trap_reason_; }

  pc_t GetBreakpointPc() { return break_pc_; }

  bool PossibleNondeterminism() { return possible_nondeterminism_; }

  uint64_t NumInterpretedCalls() { return num_interpreted_calls_; }

  void AddBreakFlags(uint8_t flags) { break_flags_ |= flags; }

  void ClearBreakFlags() { break_flags_ = WasmInterpreter::BreakFlag::None; }

  uint32_t NumActivations() {
    return static_cast<uint32_t>(activations_.size());
  }

  uint32_t StartActivation() {
    TRACE("----- START ACTIVATION %zu -----\n", activations_.size());
    // If you use activations, use them consistently:
    DCHECK_IMPLIES(activations_.empty(), frames_.empty());
    DCHECK_IMPLIES(activations_.empty(), StackHeight() == 0);
    uint32_t activation_id = static_cast<uint32_t>(activations_.size());
    activations_.emplace_back(static_cast<uint32_t>(frames_.size()),
                              StackHeight());
    state_ = WasmInterpreter::STOPPED;
    return activation_id;
  }

  void FinishActivation(uint32_t id) {
    TRACE("----- FINISH ACTIVATION %zu -----\n", activations_.size() - 1);
    DCHECK_LT(0, activations_.size());
    DCHECK_EQ(activations_.size() - 1, id);
    // Stack height must match the start of this activation (otherwise unwind
    // first).
    DCHECK_EQ(activations_.back().fp, frames_.size());
    DCHECK_LE(activations_.back().sp, StackHeight());
    sp_ = stack_start_ + activations_.back().sp;
    activations_.pop_back();
  }

  uint32_t ActivationFrameBase(uint32_t id) {
    DCHECK_GT(activations_.size(), id);
    return activations_[id].fp;
  }

  // Handle a thrown exception. Returns whether the exception was handled inside
  // the current activation. Unwinds the interpreted stack accordingly.
  WasmInterpreter::Thread::ExceptionHandlingResult HandleException(
      Isolate* isolate) {
    DCHECK(isolate->has_pending_exception());
    // TODO(wasm): Add wasm exception handling (would return HANDLED).
    USE(isolate->pending_exception());
    TRACE("----- UNWIND -----\n");
    DCHECK_LT(0, activations_.size());
    Activation& act = activations_.back();
    DCHECK_LE(act.fp, frames_.size());
    frames_.resize(act.fp);
    DCHECK_LE(act.sp, StackHeight());
    sp_ = stack_start_ + act.sp;
    state_ = WasmInterpreter::STOPPED;
    return WasmInterpreter::Thread::UNWOUND;
  }

 private:
  // Entries on the stack of functions being evaluated.
  struct Frame {
    InterpreterCode* code;
    pc_t pc;
    sp_t sp;

    // Limit of parameters.
    sp_t plimit() { return sp + code->function->sig->parameter_count(); }
    // Limit of locals.
    sp_t llimit() { return plimit() + code->locals.type_list.size(); }
  };

  struct Block {
    pc_t pc;
    sp_t sp;
    size_t fp;
    unsigned arity;
  };

  friend class InterpretedFrameImpl;

  CodeMap* codemap_;
  Handle<WasmInstanceObject> instance_object_;
  Zone* zone_;
  WasmValue* stack_start_ = nullptr;  // Start of allocated stack space.
  WasmValue* stack_limit_ = nullptr;  // End of allocated stack space.
  WasmValue* sp_ = nullptr;           // Current stack pointer.
  ZoneVector<Frame> frames_;
  WasmInterpreter::State state_ = WasmInterpreter::STOPPED;
  pc_t break_pc_ = kInvalidPc;
  TrapReason trap_reason_ = kTrapCount;
  bool possible_nondeterminism_ = false;
  uint8_t break_flags_ = 0;  // a combination of WasmInterpreter::BreakFlag
  uint64_t num_interpreted_calls_ = 0;
  // Store the stack height of each activation (for unwind and frame
  // inspection).
  ZoneVector<Activation> activations_;

  CodeMap* codemap() const { return codemap_; }
  const WasmModule* module() const { return codemap_->module(); }

  void DoTrap(TrapReason trap, pc_t pc) {
    state_ = WasmInterpreter::TRAPPED;
    trap_reason_ = trap;
    CommitPc(pc);
  }

  // Push a frame with arguments already on the stack.
  void PushFrame(InterpreterCode* code) {
    DCHECK_NOT_NULL(code);
    DCHECK_NOT_NULL(code->side_table);
    EnsureStackSpace(code->side_table->max_stack_height_ +
                     code->locals.type_list.size());

    ++num_interpreted_calls_;
    size_t arity = code->function->sig->parameter_count();
    // The parameters will overlap the arguments already on the stack.
    DCHECK_GE(StackHeight(), arity);
    frames_.push_back({code, 0, StackHeight() - arity});
    frames_.back().pc = InitLocals(code);
    TRACE("  => PushFrame #%zu (#%u @%zu)\n", frames_.size() - 1,
          code->function->func_index, frames_.back().pc);
  }

  pc_t InitLocals(InterpreterCode* code) {
    for (auto p : code->locals.type_list) {
      WasmValue val;
      switch (p) {
#define CASE_TYPE(wasm, ctype) \
  case kWasm##wasm:            \
    val = WasmValue(ctype{});  \
    break;
        WASM_CTYPES(CASE_TYPE)
#undef CASE_TYPE
        default:
          UNREACHABLE();
          break;
      }
      Push(val);
    }
    return code->locals.encoded_size;
  }

  void CommitPc(pc_t pc) {
    DCHECK(!frames_.empty());
    frames_.back().pc = pc;
  }

  bool SkipBreakpoint(InterpreterCode* code, pc_t pc) {
    if (pc == break_pc_) {
      // Skip the previously hit breakpoint when resuming.
      break_pc_ = kInvalidPc;
      return true;
    }
    return false;
  }

  int LookupTargetDelta(InterpreterCode* code, pc_t pc) {
    return static_cast<int>(code->side_table->Lookup(pc).pc_diff);
  }

  int DoBreak(InterpreterCode* code, pc_t pc, size_t depth) {
    ControlTransferEntry& control_transfer_entry = code->side_table->Lookup(pc);
    DoStackTransfer(sp_ - control_transfer_entry.sp_diff,
                    control_transfer_entry.target_arity);
    return control_transfer_entry.pc_diff;
  }

  pc_t ReturnPc(Decoder* decoder, InterpreterCode* code, pc_t pc) {
    switch (code->orig_start[pc]) {
      case kExprCallFunction: {
        CallFunctionImmediate<Decoder::kNoValidate> imm(decoder, code->at(pc));
        return pc + 1 + imm.length;
      }
      case kExprCallIndirect: {
        CallIndirectImmediate<Decoder::kNoValidate> imm(decoder, code->at(pc));
        return pc + 1 + imm.length;
      }
      default:
        UNREACHABLE();
    }
  }

  bool DoReturn(Decoder* decoder, InterpreterCode** code, pc_t* pc, pc_t* limit,
                size_t arity) {
    DCHECK_GT(frames_.size(), 0);
    WasmValue* sp_dest = stack_start_ + frames_.back().sp;
    frames_.pop_back();
    if (frames_.size() == current_activation().fp) {
      // A return from the last frame terminates the execution.
      state_ = WasmInterpreter::FINISHED;
      DoStackTransfer(sp_dest, arity);
      TRACE("  => finish\n");
      return false;
    } else {
      // Return to caller frame.
      Frame* top = &frames_.back();
      *code = top->code;
      decoder->Reset((*code)->start, (*code)->end);
      *pc = ReturnPc(decoder, *code, top->pc);
      *limit = top->code->end - top->code->start;
      TRACE("  => Return to #%zu (#%u @%zu)\n", frames_.size() - 1,
            (*code)->function->func_index, *pc);
      DoStackTransfer(sp_dest, arity);
      return true;
    }
  }

  // Returns true if the call was successful, false if the stack check failed
  // and the current activation was fully unwound.
  bool DoCall(Decoder* decoder, InterpreterCode* target, pc_t* pc,
              pc_t* limit) V8_WARN_UNUSED_RESULT {
    frames_.back().pc = *pc;
    PushFrame(target);
    if (!DoStackCheck()) return false;
    *pc = frames_.back().pc;
    *limit = target->end - target->start;
    decoder->Reset(target->start, target->end);
    return true;
  }

  // Copies {arity} values on the top of the stack down the stack to {dest},
  // dropping the values in-between.
  void DoStackTransfer(WasmValue* dest, size_t arity) {
    // before: |---------------| pop_count | arity |
    //         ^ 0             ^ dest              ^ sp_
    //
    // after:  |---------------| arity |
    //         ^ 0                     ^ sp_
    DCHECK_LE(dest, sp_);
    DCHECK_LE(dest + arity, sp_);
    if (arity) memmove(dest, sp_ - arity, arity * sizeof(*sp_));
    sp_ = dest + arity;
  }

  template <typename mtype>
  inline Address BoundsCheckMem(uint32_t offset, uint32_t index) {
    size_t mem_size = instance_object_->memory_size();
    if (sizeof(mtype) > mem_size) return kNullAddress;
    if (offset > (mem_size - sizeof(mtype))) return kNullAddress;
    if (index > (mem_size - sizeof(mtype) - offset)) return kNullAddress;
    // Compute the effective address of the access, making sure to condition
    // the index even in the in-bounds case.
    return reinterpret_cast<Address>(instance_object_->memory_start()) +
           offset + (index & instance_object_->memory_mask());
  }

  template <typename ctype, typename mtype>
  bool ExecuteLoad(Decoder* decoder, InterpreterCode* code, pc_t pc, int& len,
                   MachineRepresentation rep) {
    MemoryAccessImmediate<Decoder::kNoValidate> imm(decoder, code->at(pc),
                                                    sizeof(ctype));
    uint32_t index = Pop().to<uint32_t>();
    Address addr = BoundsCheckMem<mtype>(imm.offset, index);
    if (!addr) {
      DoTrap(kTrapMemOutOfBounds, pc);
      return false;
    }
    WasmValue result(
        converter<ctype, mtype>{}(ReadLittleEndianValue<mtype>(addr)));

    Push(result);
    len = 1 + imm.length;

    if (FLAG_wasm_trace_memory) {
      wasm::MemoryTracingInfo info(imm.offset + index, false, rep);
      TraceMemoryOperation(ExecutionEngine::kInterpreter, &info,
                           code->function->func_index, static_cast<int>(pc),
                           instance_object_->memory_start());
    }

    return true;
  }

  template <typename ctype, typename mtype>
  bool ExecuteStore(Decoder* decoder, InterpreterCode* code, pc_t pc, int& len,
                    MachineRepresentation rep) {
    MemoryAccessImmediate<Decoder::kNoValidate> imm(decoder, code->at(pc),
                                                    sizeof(ctype));
    ctype val = Pop().to<ctype>();

    uint32_t index = Pop().to<uint32_t>();
    Address addr = BoundsCheckMem<mtype>(imm.offset, index);
    if (!addr) {
      DoTrap(kTrapMemOutOfBounds, pc);
      return false;
    }
    WriteLittleEndianValue<mtype>(addr, converter<mtype, ctype>{}(val));
    len = 1 + imm.length;

    if (FLAG_wasm_trace_memory) {
      wasm::MemoryTracingInfo info(imm.offset + index, true, rep);
      TraceMemoryOperation(ExecutionEngine::kInterpreter, &info,
                           code->function->func_index, static_cast<int>(pc),
                           instance_object_->memory_start());
    }

    return true;
  }

  template <typename type>
  bool ExtractAtomicOpParams(Decoder* decoder, InterpreterCode* code,
                             Address& address, pc_t pc, int& len,
                             type* val = nullptr, type* val2 = nullptr) {
    MemoryAccessImmediate<Decoder::kNoValidate> imm(decoder, code->at(pc + 1),
                                                    sizeof(type));
    if (val2) *val2 = Pop().to<uint32_t>();
    if (val) *val = Pop().to<uint32_t>();
    uint32_t index = Pop().to<uint32_t>();
    address = BoundsCheckMem<type>(imm.offset, index);
    if (!address) {
      DoTrap(kTrapMemOutOfBounds, pc);
      return false;
    }
    len = 2 + imm.length;
    return true;
  }

  bool ExecuteNumericOp(WasmOpcode opcode, Decoder* decoder,
                        InterpreterCode* code, pc_t pc, int& len) {
    switch (opcode) {
      case kExprI32SConvertSatF32:
        Push(WasmValue(ExecuteConvertSaturate<int32_t>(Pop().to<float>())));
        return true;
      case kExprI32UConvertSatF32:
        Push(WasmValue(ExecuteConvertSaturate<uint32_t>(Pop().to<float>())));
        return true;
      case kExprI32SConvertSatF64:
        Push(WasmValue(ExecuteConvertSaturate<int32_t>(Pop().to<double>())));
        return true;
      case kExprI32UConvertSatF64:
        Push(WasmValue(ExecuteConvertSaturate<uint32_t>(Pop().to<double>())));
        return true;
      case kExprI64SConvertSatF32:
        Push(WasmValue(ExecuteI64SConvertSatF32(Pop().to<float>())));
        return true;
      case kExprI64UConvertSatF32:
        Push(WasmValue(ExecuteI64UConvertSatF32(Pop().to<float>())));
        return true;
      case kExprI64SConvertSatF64:
        Push(WasmValue(ExecuteI64SConvertSatF64(Pop().to<double>())));
        return true;
      case kExprI64UConvertSatF64:
        Push(WasmValue(ExecuteI64UConvertSatF64(Pop().to<double>())));
        return true;
      default:
        FATAL("Unknown or unimplemented opcode #%d:%s", code->start[pc],
              OpcodeName(code->start[pc]));
        UNREACHABLE();
    }
    return false;
  }

  bool ExecuteAtomicOp(WasmOpcode opcode, Decoder* decoder,
                       InterpreterCode* code, pc_t pc, int& len) {
    WasmValue result;
    switch (opcode) {
#define ATOMIC_BINOP_CASE(name, type, operation)                            \
  case kExpr##name: {                                                       \
    type val;                                                               \
    Address addr;                                                           \
    if (!ExtractAtomicOpParams<type>(decoder, code, addr, pc, len, &val)) { \
      return false;                                                         \
    }                                                                       \
    static_assert(sizeof(std::atomic<type>) == sizeof(type),                \
                  "Size mismatch for types std::atomic<" #type              \
                  ">, and " #type);                                         \
    result = WasmValue(                                                     \
        std::operation(reinterpret_cast<std::atomic<type>*>(addr), val));   \
    Push(result);                                                           \
    break;                                                                  \
  }
      ATOMIC_BINOP_CASE(I32AtomicAdd, uint32_t, atomic_fetch_add);
      ATOMIC_BINOP_CASE(I32AtomicAdd8U, uint8_t, atomic_fetch_add);
      ATOMIC_BINOP_CASE(I32AtomicAdd16U, uint16_t, atomic_fetch_add);
      ATOMIC_BINOP_CASE(I32AtomicSub, uint32_t, atomic_fetch_sub);
      ATOMIC_BINOP_CASE(I32AtomicSub8U, uint8_t, atomic_fetch_sub);
      ATOMIC_BINOP_CASE(I32AtomicSub16U, uint16_t, atomic_fetch_sub);
      ATOMIC_BINOP_CASE(I32AtomicAnd, uint32_t, atomic_fetch_and);
      ATOMIC_BINOP_CASE(I32AtomicAnd8U, uint8_t, atomic_fetch_and);
      ATOMIC_BINOP_CASE(I32AtomicAnd16U, uint16_t, atomic_fetch_and);
      ATOMIC_BINOP_CASE(I32AtomicOr, uint32_t, atomic_fetch_or);
      ATOMIC_BINOP_CASE(I32AtomicOr8U, uint8_t, atomic_fetch_or);
      ATOMIC_BINOP_CASE(I32AtomicOr16U, uint16_t, atomic_fetch_or);
      ATOMIC_BINOP_CASE(I32AtomicXor, uint32_t, atomic_fetch_xor);
      ATOMIC_BINOP_CASE(I32AtomicXor8U, uint8_t, atomic_fetch_xor);
      ATOMIC_BINOP_CASE(I32AtomicXor16U, uint16_t, atomic_fetch_xor);
      ATOMIC_BINOP_CASE(I32AtomicExchange, uint32_t, atomic_exchange);
      ATOMIC_BINOP_CASE(I32AtomicExchange8U, uint8_t, atomic_exchange);
      ATOMIC_BINOP_CASE(I32AtomicExchange16U, uint16_t, atomic_exchange);
#undef ATOMIC_BINOP_CASE
#define ATOMIC_COMPARE_EXCHANGE_CASE(name, type)                         \
  case kExpr##name: {                                                    \
    type val;                                                            \
    type val2;                                                           \
    Address addr;                                                        \
    if (!ExtractAtomicOpParams<type>(decoder, code, addr, pc, len, &val, \
                                     &val2)) {                           \
      return false;                                                      \
    }                                                                    \
    static_assert(sizeof(std::atomic<type>) == sizeof(type),             \
                  "Size mismatch for types std::atomic<" #type           \
                  ">, and " #type);                                      \
    std::atomic_compare_exchange_strong(                                 \
        reinterpret_cast<std::atomic<type>*>(addr), &val, val2);         \
    Push(WasmValue(val));                                                \
    break;                                                               \
  }
      ATOMIC_COMPARE_EXCHANGE_CASE(I32AtomicCompareExchange, uint32_t);
      ATOMIC_COMPARE_EXCHANGE_CASE(I32AtomicCompareExchange8U, uint8_t);
      ATOMIC_COMPARE_EXCHANGE_CASE(I32AtomicCompareExchange16U, uint16_t);
#undef ATOMIC_COMPARE_EXCHANGE_CASE
#define ATOMIC_LOAD_CASE(name, type, operation)                                \
  case kExpr##name: {                                                          \
    Address addr;                                                              \
    if (!ExtractAtomicOpParams<type>(decoder, code, addr, pc, len)) {          \
      return false;                                                            \
    }                                                                          \
    static_assert(sizeof(std::atomic<type>) == sizeof(type),                   \
                  "Size mismatch for types std::atomic<" #type                 \
                  ">, and " #type);                                            \
    result =                                                                   \
        WasmValue(std::operation(reinterpret_cast<std::atomic<type>*>(addr))); \
    Push(result);                                                              \
    break;                                                                     \
  }
      ATOMIC_LOAD_CASE(I32AtomicLoad, uint32_t, atomic_load);
      ATOMIC_LOAD_CASE(I32AtomicLoad8U, uint8_t, atomic_load);
      ATOMIC_LOAD_CASE(I32AtomicLoad16U, uint16_t, atomic_load);
#undef ATOMIC_LOAD_CASE
#define ATOMIC_STORE_CASE(name, type, operation)                            \
  case kExpr##name: {                                                       \
    type val;                                                               \
    Address addr;                                                           \
    if (!ExtractAtomicOpParams<type>(decoder, code, addr, pc, len, &val)) { \
      return false;                                                         \
    }                                                                       \
    static_assert(sizeof(std::atomic<type>) == sizeof(type),                \
                  "Size mismatch for types std::atomic<" #type              \
                  ">, and " #type);                                         \
    std::operation(reinterpret_cast<std::atomic<type>*>(addr), val);        \
    break;                                                                  \
  }
      ATOMIC_STORE_CASE(I32AtomicStore, uint32_t, atomic_store);
      ATOMIC_STORE_CASE(I32AtomicStore8U, uint8_t, atomic_store);
      ATOMIC_STORE_CASE(I32AtomicStore16U, uint16_t, atomic_store);
#undef ATOMIC_STORE_CASE
      default:
        UNREACHABLE();
        return false;
    }
    return true;
  }

  byte* GetGlobalPtr(const WasmGlobal* global) {
    if (global->mutability && global->imported) {
      DCHECK(FLAG_experimental_wasm_mut_global);
      return reinterpret_cast<byte*>(
          instance_object_->imported_mutable_globals()[global->index]);
    } else {
      return instance_object_->globals_start() + global->offset;
    }
  }

  bool ExecuteSimdOp(WasmOpcode opcode, Decoder* decoder, InterpreterCode* code,
                     pc_t pc, int& len) {
    switch (opcode) {
#define SPLAT_CASE(format, sType, valType, num) \
  case kExpr##format##Splat: {                  \
    WasmValue val = Pop();                      \
    valType v = val.to<valType>();              \
    sType s;                                    \
    for (int i = 0; i < num; i++) s.val[i] = v; \
    Push(WasmValue(Simd128(s)));                \
    return true;                                \
  }
      SPLAT_CASE(I32x4, int4, int32_t, 4)
      SPLAT_CASE(F32x4, float4, float, 4)
      SPLAT_CASE(I16x8, int8, int32_t, 8)
      SPLAT_CASE(I8x16, int16, int32_t, 16)
#undef SPLAT_CASE
#define EXTRACT_LANE_CASE(format, name)                                 \
  case kExpr##format##ExtractLane: {                                    \
    SimdLaneImmediate<Decoder::kNoValidate> imm(decoder, code->at(pc)); \
    ++len;                                                              \
    WasmValue val = Pop();                                              \
    Simd128 s = val.to_s128();                                          \
    Push(WasmValue(s.to_##name().val[imm.lane]));                       \
    return true;                                                        \
  }
      EXTRACT_LANE_CASE(I32x4, i32x4)
      EXTRACT_LANE_CASE(F32x4, f32x4)
      EXTRACT_LANE_CASE(I16x8, i16x8)
      EXTRACT_LANE_CASE(I8x16, i8x16)
#undef EXTRACT_LANE_CASE
      default:
        return false;
    }
  }

  // Check if our control stack (frames_) exceeds the limit. Trigger stack
  // overflow if it does, and unwinding the current frame.
  // Returns true if execution can continue, false if the current activation was
  // fully unwound.
  // Do call this function immediately *after* pushing a new frame. The pc of
  // the top frame will be reset to 0 if the stack check fails.
  bool DoStackCheck() V8_WARN_UNUSED_RESULT {
    // The goal of this stack check is not to prevent actual stack overflows,
    // but to simulate stack overflows during the execution of compiled code.
    // That is why this function uses FLAG_stack_size, even though the value
    // stack actually lies in zone memory.
    const size_t stack_size_limit = FLAG_stack_size * KB;
    // Sum up the value stack size and the control stack size.
    const size_t current_stack_size =
        (sp_ - stack_start_) + frames_.size() * sizeof(Frame);
    if (V8_LIKELY(current_stack_size <= stack_size_limit)) {
      return true;
    }
    // The pc of the top frame is initialized to the first instruction. We reset
    // it to 0 here such that we report the same position as in compiled code.
    frames_.back().pc = 0;
    Isolate* isolate = instance_object_->GetIsolate();
    HandleScope handle_scope(isolate);
    isolate->StackOverflow();
    return HandleException(isolate) == WasmInterpreter::Thread::HANDLED;
  }

  void Execute(InterpreterCode* code, pc_t pc, int max) {
    DCHECK_NOT_NULL(code->side_table);
    DCHECK(!frames_.empty());
    // There must be enough space on the stack to hold the arguments, locals,
    // and the value stack.
    DCHECK_LE(code->function->sig->parameter_count() +
                  code->locals.type_list.size() +
                  code->side_table->max_stack_height_,
              stack_limit_ - stack_start_ - frames_.back().sp);

    Decoder decoder(code->start, code->end);
    pc_t limit = code->end - code->start;
    bool hit_break = false;

    while (true) {
#define PAUSE_IF_BREAK_FLAG(flag)                                     \
  if (V8_UNLIKELY(break_flags_ & WasmInterpreter::BreakFlag::flag)) { \
    hit_break = true;                                                 \
    max = 0;                                                          \
  }

      DCHECK_GT(limit, pc);
      DCHECK_NOT_NULL(code->start);

      // Do first check for a breakpoint, in order to set hit_break correctly.
      const char* skip = "        ";
      int len = 1;
      byte orig = code->start[pc];
      WasmOpcode opcode = static_cast<WasmOpcode>(orig);
      if (WasmOpcodes::IsPrefixOpcode(opcode)) {
        opcode = static_cast<WasmOpcode>(opcode << 8 | code->start[pc + 1]);
      }
      if (V8_UNLIKELY(orig == kInternalBreakpoint)) {
        orig = code->orig_start[pc];
        if (WasmOpcodes::IsPrefixOpcode(static_cast<WasmOpcode>(orig))) {
          opcode =
              static_cast<WasmOpcode>(orig << 8 | code->orig_start[pc + 1]);
        }
        if (SkipBreakpoint(code, pc)) {
          // skip breakpoint by switching on original code.
          skip = "[skip]  ";
        } else {
          TRACE("@%-3zu: [break] %-24s:", pc, WasmOpcodes::OpcodeName(opcode));
          TraceValueStack();
          TRACE("\n");
          hit_break = true;
          break;
        }
      }

      // If max is 0, break. If max is positive (a limit is set), decrement it.
      if (max == 0) break;
      if (max > 0) --max;

      USE(skip);
      TRACE("@%-3zu: %s%-24s:", pc, skip, WasmOpcodes::OpcodeName(opcode));
      TraceValueStack();
      TRACE("\n");

#ifdef DEBUG
      // Compute the stack effect of this opcode, and verify later that the
      // stack was modified accordingly.
      std::pair<uint32_t, uint32_t> stack_effect = wasm::StackEffect(
          codemap_->module(), frames_.back().code->function->sig,
          code->orig_start + pc, code->orig_end);
      sp_t expected_new_stack_height =
          StackHeight() - stack_effect.first + stack_effect.second;
#endif

      switch (orig) {
        case kExprNop:
          break;
        case kExprBlock: {
          BlockTypeImmediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          len = 1 + imm.length;
          break;
        }
        case kExprLoop: {
          BlockTypeImmediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          len = 1 + imm.length;
          break;
        }
        case kExprIf: {
          BlockTypeImmediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          WasmValue cond = Pop();
          bool is_true = cond.to<uint32_t>() != 0;
          if (is_true) {
            // fall through to the true block.
            len = 1 + imm.length;
            TRACE("  true => fallthrough\n");
          } else {
            len = LookupTargetDelta(code, pc);
            TRACE("  false => @%zu\n", pc + len);
          }
          break;
        }
        case kExprElse: {
          len = LookupTargetDelta(code, pc);
          TRACE("  end => @%zu\n", pc + len);
          break;
        }
        case kExprSelect: {
          WasmValue cond = Pop();
          WasmValue fval = Pop();
          WasmValue tval = Pop();
          Push(cond.to<int32_t>() != 0 ? tval : fval);
          break;
        }
        case kExprBr: {
          BreakDepthImmediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          len = DoBreak(code, pc, imm.depth);
          TRACE("  br => @%zu\n", pc + len);
          break;
        }
        case kExprBrIf: {
          BreakDepthImmediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          WasmValue cond = Pop();
          bool is_true = cond.to<uint32_t>() != 0;
          if (is_true) {
            len = DoBreak(code, pc, imm.depth);
            TRACE("  br_if => @%zu\n", pc + len);
          } else {
            TRACE("  false => fallthrough\n");
            len = 1 + imm.length;
          }
          break;
        }
        case kExprBrTable: {
          BranchTableImmediate<Decoder::kNoValidate> imm(&decoder,
                                                         code->at(pc));
          BranchTableIterator<Decoder::kNoValidate> iterator(&decoder, imm);
          uint32_t key = Pop().to<uint32_t>();
          uint32_t depth = 0;
          if (key >= imm.table_count) key = imm.table_count;
          for (uint32_t i = 0; i <= key; i++) {
            DCHECK(iterator.has_next());
            depth = iterator.next();
          }
          len = key + DoBreak(code, pc + key, static_cast<size_t>(depth));
          TRACE("  br[%u] => @%zu\n", key, pc + key + len);
          break;
        }
        case kExprReturn: {
          size_t arity = code->function->sig->return_count();
          if (!DoReturn(&decoder, &code, &pc, &limit, arity)) return;
          PAUSE_IF_BREAK_FLAG(AfterReturn);
          continue;
        }
        case kExprUnreachable: {
          return DoTrap(kTrapUnreachable, pc);
        }
        case kExprEnd: {
          break;
        }
        case kExprI32Const: {
          ImmI32Immediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          Push(WasmValue(imm.value));
          len = 1 + imm.length;
          break;
        }
        case kExprI64Const: {
          ImmI64Immediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          Push(WasmValue(imm.value));
          len = 1 + imm.length;
          break;
        }
        case kExprF32Const: {
          ImmF32Immediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          Push(WasmValue(imm.value));
          len = 1 + imm.length;
          break;
        }
        case kExprF64Const: {
          ImmF64Immediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          Push(WasmValue(imm.value));
          len = 1 + imm.length;
          break;
        }
        case kExprGetLocal: {
          LocalIndexImmediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          Push(GetStackValue(frames_.back().sp + imm.index));
          len = 1 + imm.length;
          break;
        }
        case kExprSetLocal: {
          LocalIndexImmediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          WasmValue val = Pop();
          SetStackValue(frames_.back().sp + imm.index, val);
          len = 1 + imm.length;
          break;
        }
        case kExprTeeLocal: {
          LocalIndexImmediate<Decoder::kNoValidate> imm(&decoder, code->at(pc));
          WasmValue val = Pop();
          SetStackValue(frames_.back().sp + imm.index, val);
          Push(val);
          len = 1 + imm.length;
          break;
        }
        case kExprDrop: {
          Pop();
          break;
        }
        case kExprCallFunction: {
          CallFunctionImmediate<Decoder::kNoValidate> imm(&decoder,
                                                          code->at(pc));
          InterpreterCode* target = codemap()->GetCode(imm.index);
          if (target->function->imported) {
            CommitPc(pc);
            ExternalCallResult result =
                CallImportedFunction(target->function->func_index);
            switch (result.type) {
              case ExternalCallResult::INTERNAL:
                // The import is a function of this instance. Call it directly.
                target = result.interpreter_code;
                DCHECK(!target->function->imported);
                break;
              case ExternalCallResult::INVALID_FUNC:
              case ExternalCallResult::SIGNATURE_MISMATCH:
                // Direct calls are checked statically.
                UNREACHABLE();
              case ExternalCallResult::EXTERNAL_RETURNED:
                PAUSE_IF_BREAK_FLAG(AfterCall);
                len = 1 + imm.length;
                break;
              case ExternalCallResult::EXTERNAL_UNWOUND:
                return;
            }
            if (result.type != ExternalCallResult::INTERNAL) break;
          }
          // Execute an internal call.
          if (!DoCall(&decoder, target, &pc, &limit)) return;
          code = target;
          PAUSE_IF_BREAK_FLAG(AfterCall);
          continue;  // don't bump pc
        } break;
        case kExprCallIndirect: {
          CallIndirectImmediate<Decoder::kNoValidate> imm(&decoder,
                                                          code->at(pc));
          uint32_t entry_index = Pop().to<uint32_t>();
          // Assume only one table for now.
          DCHECK_LE(module()->function_tables.size(), 1u);
          ExternalCallResult result =
              CallIndirectFunction(0, entry_index, imm.sig_index);
          switch (result.type) {
            case ExternalCallResult::INTERNAL:
              // The import is a function of this instance. Call it directly.
              if (!DoCall(&decoder, result.interpreter_code, &pc, &limit))
                return;
              code = result.interpreter_code;
              PAUSE_IF_BREAK_FLAG(AfterCall);
              continue;  // don't bump pc
            case ExternalCallResult::INVALID_FUNC:
              return DoTrap(kTrapFuncInvalid, pc);
            case ExternalCallResult::SIGNATURE_MISMATCH:
              return DoTrap(kTrapFuncSigMismatch, pc);
            case ExternalCallResult::EXTERNAL_RETURNED:
              PAUSE_IF_BREAK_FLAG(AfterCall);
              len = 1 + imm.length;
              break;
            case ExternalCallResult::EXTERNAL_UNWOUND:
              return;
          }
        } break;
        case kExprGetGlobal: {
          GlobalIndexImmediate<Decoder::kNoValidate> imm(&decoder,
                                                         code->at(pc));
          const WasmGlobal* global = &module()->globals[imm.index];
          byte* ptr = GetGlobalPtr(global);
          WasmValue val;
          switch (global->type) {
#define CASE_TYPE(wasm, ctype)                       \
  case kWasm##wasm:                                  \
    val = WasmValue(*reinterpret_cast<ctype*>(ptr)); \
    break;
            WASM_CTYPES(CASE_TYPE)
#undef CASE_TYPE
            default:
              UNREACHABLE();
          }
          Push(val);
          len = 1 + imm.length;
          break;
        }
        case kExprSetGlobal: {
          GlobalIndexImmediate<Decoder::kNoValidate> imm(&decoder,
                                                         code->at(pc));
          const WasmGlobal* global = &module()->globals[imm.index];
          byte* ptr = GetGlobalPtr(global);
          WasmValue val = Pop();
          switch (global->type) {
#define CASE_TYPE(wasm, ctype)                        \
  case kWasm##wasm:                                   \
    *reinterpret_cast<ctype*>(ptr) = val.to<ctype>(); \
    break;
            WASM_CTYPES(CASE_TYPE)
#undef CASE_TYPE
            default:
              UNREACHABLE();
          }
          len = 1 + imm.length;
          break;
        }

#define LOAD_CASE(name, ctype, mtype, rep)                      \
  case kExpr##name: {                                           \
    if (!ExecuteLoad<ctype, mtype>(&decoder, code, pc, len,     \
                                   MachineRepresentation::rep)) \
      return;                                                   \
    break;                                                      \
  }

          LOAD_CASE(I32LoadMem8S, int32_t, int8_t, kWord8);
          LOAD_CASE(I32LoadMem8U, int32_t, uint8_t, kWord8);
          LOAD_CASE(I32LoadMem16S, int32_t, int16_t, kWord16);
          LOAD_CASE(I32LoadMem16U, int32_t, uint16_t, kWord16);
          LOAD_CASE(I64LoadMem8S, int64_t, int8_t, kWord8);
          LOAD_CASE(I64LoadMem8U, int64_t, uint8_t, kWord16);
          LOAD_CASE(I64LoadMem16S, int64_t, int16_t, kWord16);
          LOAD_CASE(I64LoadMem16U, int64_t, uint16_t, kWord16);
          LOAD_CASE(I64LoadMem32S, int64_t, int32_t, kWord32);
          LOAD_CASE(I64LoadMem32U, int64_t, uint32_t, kWord32);
          LOAD_CASE(I32LoadMem, int32_t, int32_t, kWord32);
          LOAD_CASE(I64LoadMem, int64_t, int64_t, kWord64);
          LOAD_CASE(F32LoadMem, Float32, uint32_t, kFloat32);
          LOAD_CASE(F64LoadMem, Float64, uint64_t, kFloat64);
#undef LOAD_CASE

#define STORE_CASE(name, ctype, mtype, rep)                      \
  case kExpr##name: {                                            \
    if (!ExecuteStore<ctype, mtype>(&decoder, code, pc, len,     \
                                    MachineRepresentation::rep)) \
      return;                                                    \
    break;                                                       \
  }

          STORE_CASE(I32StoreMem8, int32_t, int8_t, kWord8);
          STORE_CASE(I32StoreMem16, int32_t, int16_t, kWord16);
          STORE_CASE(I64StoreMem8, int64_t, int8_t, kWord8);
          STORE_CASE(I64StoreMem16, int64_t, int16_t, kWord16);
          STORE_CASE(I64StoreMem32, int64_t, int32_t, kWord32);
          STORE_CASE(I32StoreMem, int32_t, int32_t, kWord32);
          STORE_CASE(I64StoreMem, int64_t, int64_t, kWord64);
          STORE_CASE(F32StoreMem, Float32, uint32_t, kFloat32);
          STORE_CASE(F64StoreMem, Float64, uint64_t, kFloat64);
#undef STORE_CASE

#define ASMJS_LOAD_CASE(name, ctype, mtype, defval)                 \
  case kExpr##name: {                                               \
    uint32_t index = Pop().to<uint32_t>();                          \
    ctype result;                                                   \
    Address addr = BoundsCheckMem<mtype>(0, index);                 \
    if (!addr) {                                                    \
      result = defval;                                              \
    } else {                                                        \
      /* TODO(titzer): alignment for asmjs load mem? */             \
      result = static_cast<ctype>(*reinterpret_cast<mtype*>(addr)); \
    }                                                               \
    Push(WasmValue(result));                                        \
    break;                                                          \
  }
          ASMJS_LOAD_CASE(I32AsmjsLoadMem8S, int32_t, int8_t, 0);
          ASMJS_LOAD_CASE(I32AsmjsLoadMem8U, int32_t, uint8_t, 0);
          ASMJS_LOAD_CASE(I32AsmjsLoadMem16S, int32_t, int16_t, 0);
          ASMJS_LOAD_CASE(I32AsmjsLoadMem16U, int32_t, uint16_t, 0);
          ASMJS_LOAD_CASE(I32AsmjsLoadMem, int32_t, int32_t, 0);
          ASMJS_LOAD_CASE(F32AsmjsLoadMem, float, float,
                          std::numeric_limits<float>::quiet_NaN());
          ASMJS_LOAD_CASE(F64AsmjsLoadMem, double, double,
                          std::numeric_limits<double>::quiet_NaN());
#undef ASMJS_LOAD_CASE

#define ASMJS_STORE_CASE(name, ctype, mtype)                                   \
  case kExpr##name: {                                                          \
    WasmValue val = Pop();                                                     \
    uint32_t index = Pop().to<uint32_t>();                                     \
    Address addr = BoundsCheckMem<mtype>(0, index);                            \
    if (addr) {                                                                \
      *(reinterpret_cast<mtype*>(addr)) = static_cast<mtype>(val.to<ctype>()); \
    }                                                                          \
    Push(val);                                                                 \
    break;                                                                     \
  }

          ASMJS_STORE_CASE(I32AsmjsStoreMem8, int32_t, int8_t);
          ASMJS_STORE_CASE(I32AsmjsStoreMem16, int32_t, int16_t);
          ASMJS_STORE_CASE(I32AsmjsStoreMem, int32_t, int32_t);
          ASMJS_STORE_CASE(F32AsmjsStoreMem, float, float);
          ASMJS_STORE_CASE(F64AsmjsStoreMem, double, double);
#undef ASMJS_STORE_CASE
        case kExprGrowMemory: {
          MemoryIndexImmediate<Decoder::kNoValidate> imm(&decoder,
                                                         code->at(pc));
          uint32_t delta_pages = Pop().to<uint32_t>();
          Handle<WasmMemoryObject> memory(instance_object_->memory_object());
          Isolate* isolate = memory->GetIsolate();
          int32_t result = WasmMemoryObject::Grow(isolate, memory, delta_pages);
          Push(WasmValue(result));
          len = 1 + imm.length;
          // Treat one grow_memory instruction like 1000 other instructions,
          // because it is a really expensive operation.
          if (max > 0) max = std::max(0, max - 1000);
          break;
        }
        case kExprMemorySize: {
          MemoryIndexImmediate<Decoder::kNoValidate> imm(&decoder,
                                                         code->at(pc));
          Push(WasmValue(static_cast<uint32_t>(instance_object_->memory_size() /
                                               kWasmPageSize)));
          len = 1 + imm.length;
          break;
        }
        // We need to treat kExprI32ReinterpretF32 and kExprI64ReinterpretF64
        // specially to guarantee that the quiet bit of a NaN is preserved on
        // ia32 by the reinterpret casts.
        case kExprI32ReinterpretF32: {
          WasmValue val = Pop();
          Push(WasmValue(ExecuteI32ReinterpretF32(val)));
          break;
        }
        case kExprI64ReinterpretF64: {
          WasmValue val = Pop();
          Push(WasmValue(ExecuteI64ReinterpretF64(val)));
          break;
        }
        case kNumericPrefix: {
          ++len;
          if (!ExecuteNumericOp(opcode, &decoder, code, pc, len)) return;
          break;
        }
        case kAtomicPrefix: {
          if (!ExecuteAtomicOp(opcode, &decoder, code, pc, len)) return;
          break;
        }
        case kSimdPrefix: {
          ++len;
          if (!ExecuteSimdOp(opcode, &decoder, code, pc, len)) return;
          break;
        }

#define EXECUTE_SIMPLE_BINOP(name, ctype, op)               \
  case kExpr##name: {                                       \
    WasmValue rval = Pop();                                 \
    WasmValue lval = Pop();                                 \
    auto result = lval.to<ctype>() op rval.to<ctype>();     \
    possible_nondeterminism_ |= has_nondeterminism(result); \
    Push(WasmValue(result));                                \
    break;                                                  \
  }
          FOREACH_SIMPLE_BINOP(EXECUTE_SIMPLE_BINOP)
#undef EXECUTE_SIMPLE_BINOP

#define EXECUTE_OTHER_BINOP(name, ctype)                    \
  case kExpr##name: {                                       \
    TrapReason trap = kTrapCount;                           \
    ctype rval = Pop().to<ctype>();                         \
    ctype lval = Pop().to<ctype>();                         \
    auto result = Execute##name(lval, rval, &trap);         \
    possible_nondeterminism_ |= has_nondeterminism(result); \
    if (trap != kTrapCount) return DoTrap(trap, pc);        \
    Push(WasmValue(result));                                \
    break;                                                  \
  }
          FOREACH_OTHER_BINOP(EXECUTE_OTHER_BINOP)
#undef EXECUTE_OTHER_BINOP

#define EXECUTE_UNOP(name, ctype, exec_fn)                  \
  case kExpr##name: {                                       \
    TrapReason trap = kTrapCount;                           \
    ctype val = Pop().to<ctype>();                          \
    auto result = exec_fn(val, &trap);                      \
    possible_nondeterminism_ |= has_nondeterminism(result); \
    if (trap != kTrapCount) return DoTrap(trap, pc);        \
    Push(WasmValue(result));                                \
    break;                                                  \
  }

#define EXECUTE_OTHER_UNOP(name, ctype) EXECUTE_UNOP(name, ctype, Execute##name)
          FOREACH_OTHER_UNOP(EXECUTE_OTHER_UNOP)
#undef EXECUTE_OTHER_UNOP

#define EXECUTE_I32CONV_FLOATOP(name, out_type, in_type) \
  EXECUTE_UNOP(name, in_type, ExecuteConvert<out_type>)
          FOREACH_I32CONV_FLOATOP(EXECUTE_I32CONV_FLOATOP)
#undef EXECUTE_I32CONV_FLOATOP
#undef EXECUTE_UNOP

        default:
          FATAL("Unknown or unimplemented opcode #%d:%s", code->start[pc],
                OpcodeName(code->start[pc]));
          UNREACHABLE();
      }

#ifdef DEBUG
      if (!WasmOpcodes::IsControlOpcode(opcode)) {
        DCHECK_EQ(expected_new_stack_height, StackHeight());
      }
#endif

      pc += len;
      if (pc == limit) {
        // Fell off end of code; do an implicit return.
        TRACE("@%-3zu: ImplicitReturn\n", pc);
        if (!DoReturn(&decoder, &code, &pc, &limit,
                      code->function->sig->return_count()))
          return;
        PAUSE_IF_BREAK_FLAG(AfterReturn);
      }
#undef PAUSE_IF_BREAK_FLAG
    }

    state_ = WasmInterpreter::PAUSED;
    break_pc_ = hit_break ? pc : kInvalidPc;
    CommitPc(pc);
  }

  WasmValue Pop() {
    DCHECK_GT(frames_.size(), 0);
    DCHECK_GT(StackHeight(), frames_.back().llimit());  // can't pop into locals
    return *--sp_;
  }

  void PopN(int n) {
    DCHECK_GE(StackHeight(), n);
    DCHECK_GT(frames_.size(), 0);
    // Check that we don't pop into locals.
    DCHECK_GE(StackHeight() - n, frames_.back().llimit());
    sp_ -= n;
  }

  WasmValue PopArity(size_t arity) {
    if (arity == 0) return WasmValue();
    CHECK_EQ(1, arity);
    return Pop();
  }

  void Push(WasmValue val) {
    DCHECK_NE(kWasmStmt, val.type());
    DCHECK_LE(1, stack_limit_ - sp_);
    *sp_++ = val;
  }

  void Push(WasmValue* vals, size_t arity) {
    DCHECK_LE(arity, stack_limit_ - sp_);
    for (WasmValue *val = vals, *end = vals + arity; val != end; ++val) {
      DCHECK_NE(kWasmStmt, val->type());
    }
    memcpy(sp_, vals, arity * sizeof(*sp_));
    sp_ += arity;
  }

  void EnsureStackSpace(size_t size) {
    if (V8_LIKELY(static_cast<size_t>(stack_limit_ - sp_) >= size)) return;
    size_t old_size = stack_limit_ - stack_start_;
    size_t requested_size =
        base::bits::RoundUpToPowerOfTwo64((sp_ - stack_start_) + size);
    size_t new_size = Max(size_t{8}, Max(2 * old_size, requested_size));
    WasmValue* new_stack = zone_->NewArray<WasmValue>(new_size);
    memcpy(new_stack, stack_start_, old_size * sizeof(*sp_));
    sp_ = new_stack + (sp_ - stack_start_);
    stack_start_ = new_stack;
    stack_limit_ = new_stack + new_size;
  }

  sp_t StackHeight() { return sp_ - stack_start_; }

  void TraceValueStack() {
#ifdef DEBUG
    if (!FLAG_trace_wasm_interpreter) return;
    Frame* top = frames_.size() > 0 ? &frames_.back() : nullptr;
    sp_t sp = top ? top->sp : 0;
    sp_t plimit = top ? top->plimit() : 0;
    sp_t llimit = top ? top->llimit() : 0;
    for (size_t i = sp; i < StackHeight(); ++i) {
      if (i < plimit)
        PrintF(" p%zu:", i);
      else if (i < llimit)
        PrintF(" l%zu:", i);
      else
        PrintF(" s%zu:", i);
      WasmValue val = GetStackValue(i);
      switch (val.type()) {
        case kWasmI32:
          PrintF("i32:%d", val.to<int32_t>());
          break;
        case kWasmI64:
          PrintF("i64:%" PRId64 "", val.to<int64_t>());
          break;
        case kWasmF32:
          PrintF("f32:%f", val.to<float>());
          break;
        case kWasmF64:
          PrintF("f64:%lf", val.to<double>());
          break;
        case kWasmStmt:
          PrintF("void");
          break;
        default:
          UNREACHABLE();
          break;
      }
    }
#endif  // DEBUG
  }

  ExternalCallResult TryHandleException(Isolate* isolate) {
    if (HandleException(isolate) == WasmInterpreter::Thread::UNWOUND) {
      return {ExternalCallResult::EXTERNAL_UNWOUND};
    }
    return {ExternalCallResult::EXTERNAL_RETURNED};
  }

  ExternalCallResult CallExternalWasmFunction(
      Isolate* isolate, Handle<WasmInstanceObject> instance,
      const wasm::WasmCode* code, FunctionSig* sig) {
    if (code->kind() == wasm::WasmCode::kWasmToJsWrapper &&
        !IsJSCompatibleSignature(sig)) {
      isolate->Throw(*isolate->factory()->NewTypeError(
          MessageTemplate::kWasmTrapTypeError));
      return TryHandleException(isolate);
    }

    Handle<WasmDebugInfo> debug_info(instance_object_->debug_info(), isolate);
    Handle<JSFunction> wasm_entry =
        WasmDebugInfo::GetCWasmEntry(debug_info, sig);

    TRACE("  => Calling external wasm function\n");

    // Copy the arguments to one buffer.
    // TODO(clemensh): Introduce a helper for all argument buffer
    // con-/destruction.
    int num_args = static_cast<int>(sig->parameter_count());
    std::vector<uint8_t> arg_buffer(num_args * 8);
    size_t offset = 0;
    WasmValue* wasm_args = sp_ - num_args;
    for (int i = 0; i < num_args; ++i) {
      int param_size = ValueTypes::ElementSizeInBytes(sig->GetParam(i));
      if (arg_buffer.size() < offset + param_size) {
        arg_buffer.resize(std::max(2 * arg_buffer.size(), offset + param_size));
      }
      Address address = reinterpret_cast<Address>(arg_buffer.data()) + offset;
      switch (sig->GetParam(i)) {
        case kWasmI32:
          WriteUnalignedValue(address, wasm_args[i].to<uint32_t>());
          break;
        case kWasmI64:
          WriteUnalignedValue(address, wasm_args[i].to<uint64_t>());
          break;
        case kWasmF32:
          WriteUnalignedValue(address, wasm_args[i].to<float>());
          break;
        case kWasmF64:
          WriteUnalignedValue(address, wasm_args[i].to<double>());
          break;
        default:
          UNIMPLEMENTED();
      }
      offset += param_size;
    }

    // Ensure that there is enough space in the arg_buffer to hold the return
    // value(s).
    size_t return_size = 0;
    for (ValueType t : sig->returns()) {
      return_size += ValueTypes::ElementSizeInBytes(t);
    }
    if (arg_buffer.size() < return_size) {
      arg_buffer.resize(return_size);
    }

    // Wrap the arg_buffer data pointer in a handle. As
    // this is an aligned pointer, to the GC it will look like a Smi.
    Handle<Object> arg_buffer_obj(reinterpret_cast<Object*>(arg_buffer.data()),
                                  isolate);
    DCHECK(!arg_buffer_obj->IsHeapObject());

    static_assert(compiler::CWasmEntryParameters::kNumParameters == 3,
                  "code below needs adaption");
    Handle<Object> args[compiler::CWasmEntryParameters::kNumParameters];
    args[compiler::CWasmEntryParameters::kCodeObject] = Handle<Object>::cast(
        isolate->factory()->NewForeign(code->instruction_start(), TENURED));
    args[compiler::CWasmEntryParameters::kWasmInstance] = instance;
    args[compiler::CWasmEntryParameters::kArgumentsBuffer] = arg_buffer_obj;

    Handle<Object> receiver = isolate->factory()->undefined_value();
    trap_handler::SetThreadInWasm();
    MaybeHandle<Object> maybe_retval =
        Execution::Call(isolate, wasm_entry, receiver, arraysize(args), args);
    TRACE("  => External wasm function returned%s\n",
          maybe_retval.is_null() ? " with exception" : "");

    if (maybe_retval.is_null()) {
      // JSEntryStub may through a stack overflow before we actually get to wasm
      // code or back to the interpreter, meaning the thread-in-wasm flag won't
      // be cleared.
      if (trap_handler::IsThreadInWasm()) {
        trap_handler::ClearThreadInWasm();
      }
      return TryHandleException(isolate);
    }

    trap_handler::ClearThreadInWasm();

    // Pop arguments off the stack.
    sp_ -= num_args;
    // Push return values.
    if (sig->return_count() > 0) {
      // TODO(wasm): Handle multiple returns.
      DCHECK_EQ(1, sig->return_count());
      Address address = reinterpret_cast<Address>(arg_buffer.data());
      switch (sig->GetReturn()) {
        case kWasmI32:
          Push(WasmValue(ReadUnalignedValue<uint32_t>(address)));
          break;
        case kWasmI64:
          Push(WasmValue(ReadUnalignedValue<uint64_t>(address)));
          break;
        case kWasmF32:
          Push(WasmValue(ReadUnalignedValue<float>(address)));
          break;
        case kWasmF64:
          Push(WasmValue(ReadUnalignedValue<double>(address)));
          break;
        default:
          UNIMPLEMENTED();
      }
    }
    return {ExternalCallResult::EXTERNAL_RETURNED};
  }

  ExternalCallResult CallImportedFunction(uint32_t function_index) {
    // Use a new HandleScope to avoid leaking / accumulating handles in the
    // outer scope.
    Isolate* isolate = instance_object_->GetIsolate();
    HandleScope handle_scope(isolate);

    DCHECK_GT(module()->num_imported_functions, function_index);
    Handle<WasmInstanceObject> instance;
    WasmCode* code;
    {
      ImportedFunctionEntry entry(instance_object_, function_index);
      instance = handle(entry.instance(), isolate);
      code = isolate->wasm_engine()->code_manager()->GetCodeFromStartAddress(
          entry.target());
    }
    FunctionSig* sig = codemap()->module()->functions[function_index].sig;
    return CallExternalWasmFunction(isolate, instance, code, sig);
  }

  ExternalCallResult CallIndirectFunction(uint32_t table_index,
                                          uint32_t entry_index,
                                          uint32_t sig_index) {
    if (codemap()->call_indirect_through_module()) {
      // Rely on the information stored in the WasmModule.
      InterpreterCode* code =
          codemap()->GetIndirectCode(table_index, entry_index);
      if (!code) return {ExternalCallResult::INVALID_FUNC};
      if (code->function->sig_index != sig_index) {
        // If not an exact match, we have to do a canonical check.
        int function_canonical_id =
            module()->signature_ids[code->function->sig_index];
        int expected_canonical_id = module()->signature_ids[sig_index];
        DCHECK_EQ(function_canonical_id,
                  module()->signature_map.Find(code->function->sig));
        if (function_canonical_id != expected_canonical_id) {
          return {ExternalCallResult::SIGNATURE_MISMATCH};
        }
      }
      return {ExternalCallResult::INTERNAL, code};
    }

    Isolate* isolate = instance_object_->GetIsolate();
    uint32_t expected_sig_id = module()->signature_ids[sig_index];
    DCHECK_EQ(expected_sig_id,
              module()->signature_map.Find(module()->signatures[sig_index]));

    // The function table is stored in the instance.
    // TODO(wasm): the wasm interpreter currently supports only one table.
    CHECK_EQ(0, table_index);
    // Bounds check against table size.
    if (entry_index >= instance_object_->indirect_function_table_size()) {
      return {ExternalCallResult::INVALID_FUNC};
    }

    WasmCode* code;
    Handle<WasmInstanceObject> instance;
    {
      IndirectFunctionTableEntry entry(instance_object_, entry_index);
      // Signature check.
      if (entry.sig_id() != static_cast<int32_t>(expected_sig_id)) {
        return {ExternalCallResult::SIGNATURE_MISMATCH};
      }

      instance = handle(entry.instance(), isolate);
      code = isolate->wasm_engine()->code_manager()->GetCodeFromStartAddress(
          entry.target());
    }

    // Call either an internal or external WASM function.
    HandleScope scope(isolate);
    FunctionSig* signature = module()->signatures[sig_index];

    if (code->kind() == wasm::WasmCode::kFunction) {
      if (!instance_object_.is_identical_to(instance)) {
        // Cross instance call.
        return CallExternalWasmFunction(isolate, instance, code, signature);
      }
      return {ExternalCallResult::INTERNAL, codemap()->GetCode(code->index())};
    }

    // Call to external function.
    if (code->kind() == wasm::WasmCode::kInterpreterEntry ||
        code->kind() == wasm::WasmCode::kWasmToJsWrapper) {
      return CallExternalWasmFunction(isolate, instance, code, signature);
    }
    return {ExternalCallResult::INVALID_FUNC};
  }

  inline Activation current_activation() {
    return activations_.empty() ? Activation(0, 0) : activations_.back();
  }
};

class InterpretedFrameImpl {
 public:
  InterpretedFrameImpl(ThreadImpl* thread, int index)
      : thread_(thread), index_(index) {
    DCHECK_LE(0, index);
  }

  const WasmFunction* function() const { return frame()->code->function; }

  int pc() const {
    DCHECK_LE(0, frame()->pc);
    DCHECK_GE(kMaxInt, frame()->pc);
    return static_cast<int>(frame()->pc);
  }

  int GetParameterCount() const {
    DCHECK_GE(kMaxInt, function()->sig->parameter_count());
    return static_cast<int>(function()->sig->parameter_count());
  }

  int GetLocalCount() const {
    size_t num_locals = function()->sig->parameter_count() +
                        frame()->code->locals.type_list.size();
    DCHECK_GE(kMaxInt, num_locals);
    return static_cast<int>(num_locals);
  }

  int GetStackHeight() const {
    bool is_top_frame =
        static_cast<size_t>(index_) + 1 == thread_->frames_.size();
    size_t stack_limit =
        is_top_frame ? thread_->StackHeight() : thread_->frames_[index_ + 1].sp;
    DCHECK_LE(frame()->sp, stack_limit);
    size_t frame_size = stack_limit - frame()->sp;
    DCHECK_LE(GetLocalCount(), frame_size);
    return static_cast<int>(frame_size) - GetLocalCount();
  }

  WasmValue GetLocalValue(int index) const {
    DCHECK_LE(0, index);
    DCHECK_GT(GetLocalCount(), index);
    return thread_->GetStackValue(static_cast<int>(frame()->sp) + index);
  }

  WasmValue GetStackValue(int index) const {
    DCHECK_LE(0, index);
    // Index must be within the number of stack values of this frame.
    DCHECK_GT(GetStackHeight(), index);
    return thread_->GetStackValue(static_cast<int>(frame()->sp) +
                                  GetLocalCount() + index);
  }

 private:
  ThreadImpl* thread_;
  int index_;

  ThreadImpl::Frame* frame() const {
    DCHECK_GT(thread_->frames_.size(), index_);
    return &thread_->frames_[index_];
  }
};

// Converters between WasmInterpreter::Thread and WasmInterpreter::ThreadImpl.
// Thread* is the public interface, without knowledge of the object layout.
// This cast is potentially risky, but as long as we always cast it back before
// accessing any data, it should be fine. UBSan is not complaining.
WasmInterpreter::Thread* ToThread(ThreadImpl* impl) {
  return reinterpret_cast<WasmInterpreter::Thread*>(impl);
}
ThreadImpl* ToImpl(WasmInterpreter::Thread* thread) {
  return reinterpret_cast<ThreadImpl*>(thread);
}

// Same conversion for InterpretedFrame and InterpretedFrameImpl.
InterpretedFrame* ToFrame(InterpretedFrameImpl* impl) {
  return reinterpret_cast<InterpretedFrame*>(impl);
}
const InterpretedFrameImpl* ToImpl(const InterpretedFrame* frame) {
  return reinterpret_cast<const InterpretedFrameImpl*>(frame);
}

}  // namespace

//============================================================================
// Implementation of the pimpl idiom for WasmInterpreter::Thread.
// Instead of placing a pointer to the ThreadImpl inside of the Thread object,
// we just reinterpret_cast them. ThreadImpls are only allocated inside this
// translation unit anyway.
//============================================================================
WasmInterpreter::State WasmInterpreter::Thread::state() {
  return ToImpl(this)->state();
}
void WasmInterpreter::Thread::InitFrame(const WasmFunction* function,
                                        WasmValue* args) {
  ToImpl(this)->InitFrame(function, args);
}
WasmInterpreter::State WasmInterpreter::Thread::Run(int num_steps) {
  return ToImpl(this)->Run(num_steps);
}
void WasmInterpreter::Thread::Pause() { return ToImpl(this)->Pause(); }
void WasmInterpreter::Thread::Reset() { return ToImpl(this)->Reset(); }
WasmInterpreter::Thread::ExceptionHandlingResult
WasmInterpreter::Thread::HandleException(Isolate* isolate) {
  return ToImpl(this)->HandleException(isolate);
}
pc_t WasmInterpreter::Thread::GetBreakpointPc() {
  return ToImpl(this)->GetBreakpointPc();
}
int WasmInterpreter::Thread::GetFrameCount() {
  return ToImpl(this)->GetFrameCount();
}
WasmInterpreter::FramePtr WasmInterpreter::Thread::GetFrame(int index) {
  DCHECK_LE(0, index);
  DCHECK_GT(GetFrameCount(), index);
  return FramePtr(ToFrame(new InterpretedFrameImpl(ToImpl(this), index)));
}
WasmValue WasmInterpreter::Thread::GetReturnValue(int index) {
  return ToImpl(this)->GetReturnValue(index);
}
TrapReason WasmInterpreter::Thread::GetTrapReason() {
  return ToImpl(this)->GetTrapReason();
}
bool WasmInterpreter::Thread::PossibleNondeterminism() {
  return ToImpl(this)->PossibleNondeterminism();
}
uint64_t WasmInterpreter::Thread::NumInterpretedCalls() {
  return ToImpl(this)->NumInterpretedCalls();
}
void WasmInterpreter::Thread::AddBreakFlags(uint8_t flags) {
  ToImpl(this)->AddBreakFlags(flags);
}
void WasmInterpreter::Thread::ClearBreakFlags() {
  ToImpl(this)->ClearBreakFlags();
}
uint32_t WasmInterpreter::Thread::NumActivations() {
  return ToImpl(this)->NumActivations();
}
uint32_t WasmInterpreter::Thread::StartActivation() {
  return ToImpl(this)->StartActivation();
}
void WasmInterpreter::Thread::FinishActivation(uint32_t id) {
  ToImpl(this)->FinishActivation(id);
}
uint32_t WasmInterpreter::Thread::ActivationFrameBase(uint32_t id) {
  return ToImpl(this)->ActivationFrameBase(id);
}

//============================================================================
// The implementation details of the interpreter.
//============================================================================
class WasmInterpreterInternals : public ZoneObject {
 public:
  // Create a copy of the module bytes for the interpreter, since the passed
  // pointer might be invalidated after constructing the interpreter.
  const ZoneVector<uint8_t> module_bytes_;
  CodeMap codemap_;
  ZoneVector<ThreadImpl> threads_;

  WasmInterpreterInternals(Isolate* isolate, Zone* zone,
                           const WasmModule* module,
                           const ModuleWireBytes& wire_bytes,
                           Handle<WasmInstanceObject> instance_object)
      : module_bytes_(wire_bytes.start(), wire_bytes.end(), zone),
        codemap_(isolate, module, module_bytes_.data(), zone),
        threads_(zone) {
    threads_.emplace_back(zone, &codemap_, instance_object);
  }
};

namespace {
// TODO(wasm): a finalizer is only required to delete the global handle.
void GlobalHandleDeleter(const v8::WeakCallbackInfo<void>& data) {
  GlobalHandles::Destroy(reinterpret_cast<Object**>(
      reinterpret_cast<JSObject**>(data.GetParameter())));
}

Handle<WasmInstanceObject> MakeWeak(
    Isolate* isolate, Handle<WasmInstanceObject> instance_object) {
  Handle<Object> handle = isolate->global_handles()->Create(*instance_object);
  // TODO(wasm): use a phantom handle in the WasmInterpreter.
  GlobalHandles::MakeWeak(handle.location(), handle.location(),
                          &GlobalHandleDeleter,
                          v8::WeakCallbackType::kFinalizer);
  return Handle<WasmInstanceObject>::cast(handle);
}
}  // namespace

//============================================================================
// Implementation of the public interface of the interpreter.
//============================================================================
WasmInterpreter::WasmInterpreter(Isolate* isolate, const WasmModule* module,
                                 const ModuleWireBytes& wire_bytes,
                                 Handle<WasmInstanceObject> instance_object)
    : zone_(isolate->allocator(), ZONE_NAME),
      internals_(new (&zone_) WasmInterpreterInternals(
          isolate, &zone_, module, wire_bytes,
          MakeWeak(isolate, instance_object))) {}

WasmInterpreter::~WasmInterpreter() { internals_->~WasmInterpreterInternals(); }

void WasmInterpreter::Run() { internals_->threads_[0].Run(); }

void WasmInterpreter::Pause() { internals_->threads_[0].Pause(); }

bool WasmInterpreter::SetBreakpoint(const WasmFunction* function, pc_t pc,
                                    bool enabled) {
  InterpreterCode* code = internals_->codemap_.GetCode(function);
  size_t size = static_cast<size_t>(code->end - code->start);
  // Check bounds for {pc}.
  if (pc < code->locals.encoded_size || pc >= size) return false;
  // Make a copy of the code before enabling a breakpoint.
  if (enabled && code->orig_start == code->start) {
    code->start = reinterpret_cast<byte*>(zone_.New(size));
    memcpy(code->start, code->orig_start, size);
    code->end = code->start + size;
  }
  bool prev = code->start[pc] == kInternalBreakpoint;
  if (enabled) {
    code->start[pc] = kInternalBreakpoint;
  } else {
    code->start[pc] = code->orig_start[pc];
  }
  return prev;
}

bool WasmInterpreter::GetBreakpoint(const WasmFunction* function, pc_t pc) {
  InterpreterCode* code = internals_->codemap_.GetCode(function);
  size_t size = static_cast<size_t>(code->end - code->start);
  // Check bounds for {pc}.
  if (pc < code->locals.encoded_size || pc >= size) return false;
  // Check if a breakpoint is present at that place in the code.
  return code->start[pc] == kInternalBreakpoint;
}

bool WasmInterpreter::SetTracing(const WasmFunction* function, bool enabled) {
  UNIMPLEMENTED();
  return false;
}

int WasmInterpreter::GetThreadCount() {
  return 1;  // only one thread for now.
}

WasmInterpreter::Thread* WasmInterpreter::GetThread(int id) {
  CHECK_EQ(0, id);  // only one thread for now.
  return ToThread(&internals_->threads_[id]);
}

void WasmInterpreter::AddFunctionForTesting(const WasmFunction* function) {
  internals_->codemap_.AddFunction(function, nullptr, nullptr);
}

void WasmInterpreter::SetFunctionCodeForTesting(const WasmFunction* function,
                                                const byte* start,
                                                const byte* end) {
  internals_->codemap_.SetFunctionCode(function, start, end);
}

void WasmInterpreter::SetCallIndirectTestMode() {
  internals_->codemap_.set_call_indirect_through_module(true);
}

ControlTransferMap WasmInterpreter::ComputeControlTransfersForTesting(
    Zone* zone, const WasmModule* module, const byte* start, const byte* end) {
  // Create some dummy structures, to avoid special-casing the implementation
  // just for testing.
  FunctionSig sig(0, 0, nullptr);
  WasmFunction function{&sig, 0, 0, {0, 0}, false, false};
  InterpreterCode code{
      &function, BodyLocalDecls(zone), start, end, nullptr, nullptr, nullptr};

  // Now compute and return the control transfers.
  SideTable side_table(zone, module, &code);
  return side_table.map_;
}

//============================================================================
// Implementation of the frame inspection interface.
//============================================================================
const WasmFunction* InterpretedFrame::function() const {
  return ToImpl(this)->function();
}
int InterpretedFrame::pc() const { return ToImpl(this)->pc(); }
int InterpretedFrame::GetParameterCount() const {
  return ToImpl(this)->GetParameterCount();
}
int InterpretedFrame::GetLocalCount() const {
  return ToImpl(this)->GetLocalCount();
}
int InterpretedFrame::GetStackHeight() const {
  return ToImpl(this)->GetStackHeight();
}
WasmValue InterpretedFrame::GetLocalValue(int index) const {
  return ToImpl(this)->GetLocalValue(index);
}
WasmValue InterpretedFrame::GetStackValue(int index) const {
  return ToImpl(this)->GetStackValue(index);
}
void InterpretedFrameDeleter::operator()(InterpretedFrame* ptr) {
  delete ToImpl(ptr);
}

#undef TRACE
#undef FOREACH_INTERNAL_OPCODE
#undef WASM_CTYPES
#undef FOREACH_SIMPLE_BINOP
#undef FOREACH_OTHER_BINOP
#undef FOREACH_I32CONV_FLOATOP
#undef FOREACH_OTHER_UNOP

}  // namespace wasm
}  // namespace internal
}  // namespace v8