BytecodeUtil.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef vm_BytecodeUtil_h
#define vm_BytecodeUtil_h

/*
 * JS bytecode definitions.
 */

#include "mozilla/Attributes.h"
#include "mozilla/EndianUtils.h"

#include <algorithm>

#include "jstypes.h"
#include "NamespaceImports.h"

#include "frontend/SourceNotes.h"
#include "js/TypeDecls.h"
#include "js/UniquePtr.h"
#include "vm/Opcodes.h"
#include "vm/Printer.h"

/*
 * JS operation bytecodes.
 */
typedef enum JSOp {
#define ENUMERATE_OPCODE(op, val, ...) op = val,
  FOR_EACH_OPCODE(ENUMERATE_OPCODE)
#undef ENUMERATE_OPCODE

      JSOP_LIMIT
} JSOp;

/*
 * [SMDOC] Bytecode Format flags (JOF_*)
 */
enum {
  JOF_BYTE = 0,         /* single bytecode, no immediates */
  JOF_UINT8 = 1,        /* unspecified uint8_t argument */
  JOF_UINT16 = 2,       /* unspecified uint16_t argument */
  JOF_UINT24 = 3,       /* unspecified uint24_t argument */
  JOF_UINT32 = 4,       /* unspecified uint32_t argument */
  JOF_INT8 = 5,         /* int8_t literal */
  JOF_INT32 = 6,        /* int32_t literal */
  JOF_JUMP = 7,         /* int32_t jump offset */
  JOF_TABLESWITCH = 8,  /* table switch */
  JOF_ENVCOORD = 9,     /* embedded ScopeCoordinate immediate */
  JOF_ARGC = 10,        /* uint16_t argument count */
  JOF_QARG = 11,        /* function argument index */
  JOF_LOCAL = 12,       /* var or block-local variable */
  JOF_RESUMEINDEX = 13, /* yield, await, or gosub resume index */
  JOF_ATOM = 14,        /* uint32_t constant index */
  JOF_OBJECT = 15,      /* uint32_t object index */
  JOF_REGEXP = 16,      /* uint32_t regexp index */
  JOF_DOUBLE = 17,      /* uint32_t index for double value */
  JOF_SCOPE = 18,       /* uint32_t scope index */
  JOF_CODE_OFFSET = 19, /* int32_t bytecode offset */
  JOF_ICINDEX = 20,     /* uint32_t IC index */
  JOF_LOOPENTRY = 21,   /* JSOP_LOOPENTRY, combines JOF_ICINDEX and JOF_UINT8 */
  JOF_BIGINT = 22,      /* uint32_t index for BigInt value */
  JOF_TYPEMASK = 0x001f, /* mask for above immediate types */

  JOF_NAME = 1 << 5,     /* name operation */
  JOF_PROP = 2 << 5,     /* obj.prop operation */
  JOF_ELEM = 3 << 5,     /* obj[index] operation */
  JOF_MODEMASK = 3 << 5, /* mask for above addressing modes */

  JOF_PROPSET = 1 << 7,      /* property/element/name set operation */
  JOF_PROPINIT = 1 << 8,     /* property/element/name init operation */
  JOF_DETECTING = 1 << 9,    /* object detection for warning-quelling */
  JOF_CHECKSLOPPY = 1 << 10, /* Op can only be generated in sloppy mode */
  JOF_CHECKSTRICT = 1 << 11, /* Op can only be generated in strict mode */
  JOF_INVOKE = 1 << 12,      /* JSOP_CALL, JSOP_FUNCALL, JSOP_FUNAPPLY,
                                JSOP_NEW, JSOP_EVAL, JSOP_CALLITER */
  JOF_GNAME = 1 << 13,       /* predicted global name */
  JOF_TYPESET = 1 << 14,     /* has an entry in a script's type sets */
  JOF_IC = 1 << 15,          /* Baseline may use an IC for this op */
};

/* Shorthand for type from format. */

static inline uint32_t JOF_TYPE(uint32_t fmt) { return fmt & JOF_TYPEMASK; }

/* Shorthand for mode from format. */

static inline uint32_t JOF_MODE(uint32_t fmt) { return fmt & JOF_MODEMASK; }

/*
 * Immediate operand getters, setters, and bounds.
 */

static MOZ_ALWAYS_INLINE uint8_t GET_UINT8(jsbytecode* pc) {
  return uint8_t(pc[1]);
}

static MOZ_ALWAYS_INLINE void SET_UINT8(jsbytecode* pc, uint8_t u) {
  pc[1] = jsbytecode(u);
}

/* Common uint16_t immediate format helpers. */

static inline jsbytecode UINT16_HI(uint16_t i) { return jsbytecode(i >> 8); }

static inline jsbytecode UINT16_LO(uint16_t i) { return jsbytecode(i); }

static MOZ_ALWAYS_INLINE uint16_t GET_UINT16(const jsbytecode* pc) {
#if MOZ_LITTLE_ENDIAN
  uint16_t result;
  memcpy(&result, pc + 1, sizeof(result));
  return result;
#else
  return uint16_t((pc[2] << 8) | pc[1]);
#endif
}

static MOZ_ALWAYS_INLINE void SET_UINT16(jsbytecode* pc, uint16_t i) {
#if MOZ_LITTLE_ENDIAN
  memcpy(pc + 1, &i, sizeof(i));
#else
  pc[1] = UINT16_LO(i);
  pc[2] = UINT16_HI(i);
#endif
}

static const unsigned UINT16_LIMIT = 1 << 16;

/* Helpers for accessing the offsets of jump opcodes. */
static const unsigned JUMP_OFFSET_LEN = 4;
static const int32_t JUMP_OFFSET_MIN = INT32_MIN;
static const int32_t JUMP_OFFSET_MAX = INT32_MAX;

static MOZ_ALWAYS_INLINE uint32_t GET_UINT24(const jsbytecode* pc) {
#if MOZ_LITTLE_ENDIAN
  // Do a single 32-bit load (for opcode and operand), then shift off the
  // opcode.
  uint32_t result;
  memcpy(&result, pc, 4);
  return result >> 8;
#else
  return unsigned((pc[3] << 16) | (pc[2] << 8) | pc[1]);
#endif
}

static MOZ_ALWAYS_INLINE void SET_UINT24(jsbytecode* pc, uint32_t i) {
  MOZ_ASSERT(i < (1 << 24));

#if MOZ_LITTLE_ENDIAN
  memcpy(pc + 1, &i, 3);
#else
  pc[1] = jsbytecode(i);
  pc[2] = jsbytecode(i >> 8);
  pc[3] = jsbytecode(i >> 16);
#endif
}

static MOZ_ALWAYS_INLINE int8_t GET_INT8(const jsbytecode* pc) {
  return int8_t(pc[1]);
}

static MOZ_ALWAYS_INLINE uint32_t GET_UINT32(const jsbytecode* pc) {
#if MOZ_LITTLE_ENDIAN
  uint32_t result;
  memcpy(&result, pc + 1, sizeof(result));
  return result;
#else
  return (uint32_t(pc[4]) << 24) | (uint32_t(pc[3]) << 16) |
         (uint32_t(pc[2]) << 8) | uint32_t(pc[1]);
#endif
}

static MOZ_ALWAYS_INLINE void SET_UINT32(jsbytecode* pc, uint32_t u) {
#if MOZ_LITTLE_ENDIAN
  memcpy(pc + 1, &u, sizeof(u));
#else
  pc[1] = jsbytecode(u);
  pc[2] = jsbytecode(u >> 8);
  pc[3] = jsbytecode(u >> 16);
  pc[4] = jsbytecode(u >> 24);
#endif
}

static MOZ_ALWAYS_INLINE int32_t GET_INT32(const jsbytecode* pc) {
  return static_cast<int32_t>(GET_UINT32(pc));
}

static MOZ_ALWAYS_INLINE void SET_INT32(jsbytecode* pc, int32_t i) {
  SET_UINT32(pc, static_cast<uint32_t>(i));
}

static MOZ_ALWAYS_INLINE int32_t GET_JUMP_OFFSET(jsbytecode* pc) {
  return GET_INT32(pc);
}

static MOZ_ALWAYS_INLINE void SET_JUMP_OFFSET(jsbytecode* pc, int32_t off) {
  SET_INT32(pc, off);
}

static MOZ_ALWAYS_INLINE int32_t GET_CODE_OFFSET(jsbytecode* pc) {
  return GET_INT32(pc);
}

static MOZ_ALWAYS_INLINE void SET_CODE_OFFSET(jsbytecode* pc, int32_t off) {
  SET_INT32(pc, off);
}

static const unsigned UINT32_INDEX_LEN = 4;

static MOZ_ALWAYS_INLINE uint32_t GET_UINT32_INDEX(const jsbytecode* pc) {
  return GET_UINT32(pc);
}

static MOZ_ALWAYS_INLINE void SET_UINT32_INDEX(jsbytecode* pc, uint32_t index) {
  SET_UINT32(pc, index);
}

// Index limit is determined by SN_4BYTE_OFFSET_FLAG, see
// frontend/BytecodeEmitter.h.
static const unsigned INDEX_LIMIT_LOG2 = 31;
static const uint32_t INDEX_LIMIT = uint32_t(1) << INDEX_LIMIT_LOG2;

static inline jsbytecode ARGC_HI(uint16_t argc) { return UINT16_HI(argc); }

static inline jsbytecode ARGC_LO(uint16_t argc) { return UINT16_LO(argc); }

static inline uint16_t GET_ARGC(const jsbytecode* pc) { return GET_UINT16(pc); }

static const unsigned ARGC_LIMIT = UINT16_LIMIT;

static inline uint16_t GET_ARGNO(const jsbytecode* pc) {
  return GET_UINT16(pc);
}

static inline void SET_ARGNO(jsbytecode* pc, uint16_t argno) {
  SET_UINT16(pc, argno);
}

static const unsigned ARGNO_LEN = 2;
static const unsigned ARGNO_LIMIT = UINT16_LIMIT;

static inline uint32_t GET_LOCALNO(const jsbytecode* pc) {
  return GET_UINT24(pc);
}

static inline void SET_LOCALNO(jsbytecode* pc, uint32_t varno) {
  SET_UINT24(pc, varno);
}

static const unsigned LOCALNO_LEN = 3;
static const unsigned LOCALNO_BITS = 24;
static const uint32_t LOCALNO_LIMIT = 1 << LOCALNO_BITS;

static inline uint32_t GET_RESUMEINDEX(const jsbytecode* pc) {
  return GET_UINT24(pc);
}

static inline void SET_RESUMEINDEX(jsbytecode* pc, uint32_t resumeIndex) {
  SET_UINT24(pc, resumeIndex);
}

static inline uint32_t GET_ICINDEX(const jsbytecode* pc) {
  return GET_UINT32(pc);
}

static inline void SET_ICINDEX(jsbytecode* pc, uint32_t icIndex) {
  SET_UINT32(pc, icIndex);
}

static inline unsigned LoopEntryDepthHint(jsbytecode* pc) {
  MOZ_ASSERT(*pc == JSOP_LOOPENTRY);
  return GET_UINT8(pc + 4) & 0x7f;
}

static inline bool LoopEntryCanIonOsr(jsbytecode* pc) {
  MOZ_ASSERT(*pc == JSOP_LOOPENTRY);
  return GET_UINT8(pc + 4) & 0x80;
}

static inline void SetLoopEntryDepthHintAndFlags(jsbytecode* pc,
                                                 unsigned loopDepth,
                                                 bool canIonOsr) {
  MOZ_ASSERT(*pc == JSOP_LOOPENTRY);
  uint8_t data = std::min(loopDepth, unsigned(0x7f)) | (canIonOsr ? 0x80 : 0);
  SET_UINT8(pc + 4, data);
}

/*
 * Describes the 'hops' component of a JOF_ENVCOORD opcode.
 *
 * Note: this component is only 8 bits wide, limiting the maximum number of
 * scopes between a use and def to roughly 255. This is a pretty small limit but
 * note that SpiderMonkey's recursive descent parser can only parse about this
 * many functions before hitting the C-stack recursion limit so this shouldn't
 * be a significant limitation in practice.
 */

static inline uint8_t GET_ENVCOORD_HOPS(jsbytecode* pc) {
  return GET_UINT8(pc);
}

static inline void SET_ENVCOORD_HOPS(jsbytecode* pc, uint8_t hops) {
  SET_UINT8(pc, hops);
}

static const unsigned ENVCOORD_HOPS_LEN = 1;
static const unsigned ENVCOORD_HOPS_BITS = 8;
static const unsigned ENVCOORD_HOPS_LIMIT = 1 << ENVCOORD_HOPS_BITS;

/* Describes the 'slot' component of a JOF_ENVCOORD opcode. */
static inline uint32_t GET_ENVCOORD_SLOT(const jsbytecode* pc) {
  return GET_UINT24(pc);
}

static inline void SET_ENVCOORD_SLOT(jsbytecode* pc, uint32_t slot) {
  SET_UINT24(pc, slot);
}

static const unsigned ENVCOORD_SLOT_LEN = 3;
static const unsigned ENVCOORD_SLOT_BITS = 24;
static const uint32_t ENVCOORD_SLOT_LIMIT = 1 << ENVCOORD_SLOT_BITS;

struct JSCodeSpec {
  uint8_t length;  /* length including opcode byte */
  int8_t nuses;    /* arity, -1 if variadic */
  int8_t ndefs;    /* number of stack results */
  uint32_t format; /* immediate operand format */

  uint32_t type() const { return JOF_TYPE(format); }
};

namespace js {

extern const JSCodeSpec CodeSpec[];
extern const char* const CodeName[];

/* Shorthand for type from opcode. */

static inline uint32_t JOF_OPTYPE(JSOp op) {
  return JOF_TYPE(CodeSpec[op].format);
}

static inline bool IsJumpOpcode(JSOp op) { return JOF_OPTYPE(op) == JOF_JUMP; }

static inline bool BytecodeFallsThrough(JSOp op) {
  switch (op) {
    case JSOP_GOTO:
    case JSOP_DEFAULT:
    case JSOP_RETURN:
    case JSOP_RETRVAL:
    case JSOP_FINALYIELDRVAL:
    case JSOP_THROW:
    case JSOP_THROWMSG:
    case JSOP_TABLESWITCH:
      return false;
    case JSOP_GOSUB:
      /* These fall through indirectly, after executing a 'finally'. */
      return true;
    default:
      return true;
  }
}

static inline bool BytecodeIsJumpTarget(JSOp op) {
  switch (op) {
    case JSOP_JUMPTARGET:
    case JSOP_LOOPHEAD:
    case JSOP_LOOPENTRY:
      return true;
    default:
      return false;
  }
}

MOZ_ALWAYS_INLINE unsigned StackUses(jsbytecode* pc) {
  JSOp op = JSOp(*pc);
  int nuses = CodeSpec[op].nuses;
  if (nuses >= 0) {
    return nuses;
  }

  MOZ_ASSERT(nuses == -1);
  switch (op) {
    case JSOP_POPN:
      return GET_UINT16(pc);
    case JSOP_NEW:
    case JSOP_SUPERCALL:
      return 2 + GET_ARGC(pc) + 1;
    default:
      /* stack: fun, this, [argc arguments] */
      MOZ_ASSERT(op == JSOP_CALL || op == JSOP_CALL_IGNORES_RV ||
                 op == JSOP_EVAL || op == JSOP_CALLITER ||
                 op == JSOP_STRICTEVAL || op == JSOP_FUNCALL ||
                 op == JSOP_FUNAPPLY);
      return 2 + GET_ARGC(pc);
  }
}

MOZ_ALWAYS_INLINE unsigned StackDefs(jsbytecode* pc) {
  int ndefs = CodeSpec[*pc].ndefs;
  MOZ_ASSERT(ndefs >= 0);
  return ndefs;
}

#if defined(DEBUG) || defined(JS_JITSPEW)
/*
 * Given bytecode address pc in script's main program code, compute the operand
 * stack depth just before (JSOp) *pc executes.  If *pc is not reachable, return
 * false.
 */
extern bool ReconstructStackDepth(JSContext* cx, JSScript* script,
                                  jsbytecode* pc, uint32_t* depth,
                                  bool* reachablePC);
#endif

} /* namespace js */

#define JSDVG_IGNORE_STACK 0
#define JSDVG_SEARCH_STACK 1

namespace js {

/*
 * Find the source expression that resulted in v, and return a newly allocated
 * C-string containing it.  Fall back on v's string conversion (fallback) if we
 * can't find the bytecode that generated and pushed v on the operand stack.
 *
 * Search the current stack frame if spindex is JSDVG_SEARCH_STACK.  Don't
 * look for v on the stack if spindex is JSDVG_IGNORE_STACK.  Otherwise,
 * spindex is the negative index of v, measured from cx->fp->sp, or from a
 * lower frame's sp if cx->fp is native.
 *
 * The optional argument skipStackHits can be used to skip a hit in the stack
 * frame. This can be useful in self-hosted code that wants to report value
 * errors containing decompiled values that are useful for the user, instead of
 * values used internally by the self-hosted code.
 *
 * The caller must call JS_free on the result after a successful call.
 */
UniqueChars DecompileValueGenerator(JSContext* cx, int spindex, HandleValue v,
                                    HandleString fallback,
                                    int skipStackHits = 0);

/*
 * Decompile the formal argument at formalIndex in the nearest non-builtin
 * stack frame, falling back with converting v to source.
 */
JSString* DecompileArgument(JSContext* cx, int formalIndex, HandleValue v);

static inline unsigned GetBytecodeLength(jsbytecode* pc) {
  JSOp op = (JSOp)*pc;
  MOZ_ASSERT(op < JSOP_LIMIT);
  MOZ_ASSERT(CodeSpec[op].length > 0);
  return CodeSpec[op].length;
}

static inline bool BytecodeIsPopped(jsbytecode* pc) {
  jsbytecode* next = pc + GetBytecodeLength(pc);
  return JSOp(*next) == JSOP_POP;
}

static inline bool BytecodeFlowsToBitop(jsbytecode* pc) {
  // Look for simple bytecode for integer conversions like (x | 0) or (x & -1).
  jsbytecode* next = pc + GetBytecodeLength(pc);
  if (*next == JSOP_BITOR || *next == JSOP_BITAND) {
    return true;
  }
  if (*next == JSOP_INT8 && GET_INT8(next) == -1) {
    next += GetBytecodeLength(next);
    if (*next == JSOP_BITAND) {
      return true;
    }
    return false;
  }
  if (*next == JSOP_ONE) {
    next += GetBytecodeLength(next);
    if (*next == JSOP_NEG) {
      next += GetBytecodeLength(next);
      if (*next == JSOP_BITAND) {
        return true;
      }
    }
    return false;
  }
  if (*next == JSOP_ZERO) {
    next += GetBytecodeLength(next);
    if (*next == JSOP_BITOR) {
      return true;
    }
    return false;
  }
  return false;
}

extern bool IsValidBytecodeOffset(JSContext* cx, JSScript* script,
                                  size_t offset);

inline bool FlowsIntoNext(JSOp op) {
  // JSOP_YIELD/JSOP_AWAIT is considered to flow into the next instruction,
  // like JSOP_CALL.
  switch (op) {
    case JSOP_RETRVAL:
    case JSOP_RETURN:
    case JSOP_THROW:
    case JSOP_GOTO:
    case JSOP_RETSUB:
    case JSOP_FINALYIELDRVAL:
      return false;
    default:
      return true;
  }
}

inline bool IsArgOp(JSOp op) { return JOF_OPTYPE(op) == JOF_QARG; }

inline bool IsLocalOp(JSOp op) { return JOF_OPTYPE(op) == JOF_LOCAL; }

inline bool IsAliasedVarOp(JSOp op) { return JOF_OPTYPE(op) == JOF_ENVCOORD; }

inline bool IsGlobalOp(JSOp op) { return CodeSpec[op].format & JOF_GNAME; }

inline bool IsPropertySetOp(JSOp op) {
  return CodeSpec[op].format & JOF_PROPSET;
}

inline bool IsPropertyInitOp(JSOp op) {
  return CodeSpec[op].format & JOF_PROPINIT;
}

inline bool IsEqualityOp(JSOp op) {
  return op == JSOP_EQ || op == JSOP_NE || op == JSOP_STRICTEQ ||
         op == JSOP_STRICTNE;
}

inline bool IsCheckStrictOp(JSOp op) {
  return CodeSpec[op].format & JOF_CHECKSTRICT;
}

#ifdef DEBUG
inline bool IsCheckSloppyOp(JSOp op) {
  return CodeSpec[op].format & JOF_CHECKSLOPPY;
}
#endif

inline bool IsAtomOp(JSOp op) { return JOF_OPTYPE(op) == JOF_ATOM; }

inline bool IsGetPropPC(jsbytecode* pc) {
  JSOp op = JSOp(*pc);
  return op == JSOP_LENGTH || op == JSOP_GETPROP || op == JSOP_CALLPROP;
}

inline bool IsHiddenInitOp(JSOp op) {
  return op == JSOP_INITHIDDENPROP || op == JSOP_INITHIDDENELEM ||
         op == JSOP_INITHIDDENPROP_GETTER || op == JSOP_INITHIDDENELEM_GETTER ||
         op == JSOP_INITHIDDENPROP_SETTER || op == JSOP_INITHIDDENELEM_SETTER;
}

inline bool IsStrictSetPC(jsbytecode* pc) {
  JSOp op = JSOp(*pc);
  return op == JSOP_STRICTSETPROP || op == JSOP_STRICTSETNAME ||
         op == JSOP_STRICTSETGNAME || op == JSOP_STRICTSETELEM;
}

inline bool IsSetPropPC(jsbytecode* pc) {
  JSOp op = JSOp(*pc);
  return op == JSOP_SETPROP || op == JSOP_STRICTSETPROP || op == JSOP_SETNAME ||
         op == JSOP_STRICTSETNAME || op == JSOP_SETGNAME ||
         op == JSOP_STRICTSETGNAME;
}

inline bool IsGetElemPC(jsbytecode* pc) {
  JSOp op = JSOp(*pc);
  return op == JSOP_GETELEM || op == JSOP_CALLELEM;
}

inline bool IsSetElemPC(jsbytecode* pc) {
  JSOp op = JSOp(*pc);
  return op == JSOP_SETELEM || op == JSOP_STRICTSETELEM;
}

inline bool IsElemPC(jsbytecode* pc) { return CodeSpec[*pc].format & JOF_ELEM; }

inline bool IsCallOp(JSOp op) { return CodeSpec[op].format & JOF_INVOKE; }

inline bool IsCallPC(jsbytecode* pc) { return IsCallOp(JSOp(*pc)); }

inline bool IsStrictEvalPC(jsbytecode* pc) {
  JSOp op = JSOp(*pc);
  return op == JSOP_STRICTEVAL || op == JSOP_STRICTSPREADEVAL;
}

inline bool IsConstructorCallOp(JSOp op) {
  return op == JSOP_NEW || op == JSOP_SUPERCALL || op == JSOP_SPREADNEW ||
         op == JSOP_SPREADSUPERCALL;
}
inline bool IsConstructorCallPC(const jsbytecode* pc) {
  return IsConstructorCallOp(JSOp(*pc));
}

inline bool IsSpreadCallPC(jsbytecode* pc) {
  JSOp op = JSOp(*pc);
  return op == JSOP_SPREADCALL || op == JSOP_SPREADNEW ||
         op == JSOP_SPREADSUPERCALL || op == JSOP_SPREADEVAL ||
         op == JSOP_STRICTSPREADEVAL;
}

static inline int32_t GetBytecodeInteger(jsbytecode* pc) {
  switch (JSOp(*pc)) {
    case JSOP_ZERO:
      return 0;
    case JSOP_ONE:
      return 1;
    case JSOP_UINT16:
      return GET_UINT16(pc);
    case JSOP_UINT24:
      return GET_UINT24(pc);
    case JSOP_INT8:
      return GET_INT8(pc);
    case JSOP_INT32:
      return GET_INT32(pc);
    default:
      MOZ_CRASH("Bad op");
  }
}

inline bool BytecodeOpHasIC(JSOp op) { return CodeSpec[op].format & JOF_IC; }

/*
 * Counts accumulated for a single opcode in a script. The counts tracked vary
 * between opcodes, and this structure ensures that counts are accessed in a
 * coherent fashion.
 */
class PCCounts {
  /*
   * Offset of the pc inside the script. This fields is used to lookup opcode
   * which have annotations.
   */
  size_t pcOffset_;

  /*
   * Record the number of execution of one instruction, or the number of
   * throws executed.
   */
  uint64_t numExec_;

 public:
  explicit PCCounts(size_t off) : pcOffset_(off), numExec_(0) {}

  size_t pcOffset() const { return pcOffset_; }

  // Used for sorting and searching.
  bool operator<(const PCCounts& rhs) const {
    return pcOffset_ < rhs.pcOffset_;
  }

  uint64_t& numExec() { return numExec_; }
  uint64_t numExec() const { return numExec_; }

  static const char numExecName[];
};

static inline jsbytecode* GetNextPc(jsbytecode* pc) {
  return pc + GetBytecodeLength(pc);
}

typedef Vector<jsbytecode*, 4, SystemAllocPolicy> PcVector;

bool GetSuccessorBytecodes(JSScript* script, jsbytecode* pc,
                           PcVector& successors);
bool GetPredecessorBytecodes(JSScript* script, jsbytecode* pc,
                             PcVector& predecessors);

#if defined(DEBUG) || defined(JS_JITSPEW)
/*
 * Disassemblers, for debugging only.
 */
extern MOZ_MUST_USE bool Disassemble(JSContext* cx,
                                     JS::Handle<JSScript*> script, bool lines,
                                     Sprinter* sp);

unsigned Disassemble1(JSContext* cx, JS::Handle<JSScript*> script,
                      jsbytecode* pc, unsigned loc, bool lines, Sprinter* sp);

#endif

extern MOZ_MUST_USE bool DumpRealmPCCounts(JSContext* cx);

}  // namespace js

#endif /* vm_BytecodeUtil_h */