Nim/compiler/vm.nim

#
#
#           The Nim Compiler
#        (c) Copyright 2015 Andreas Rumpf
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

## This file implements the new evaluation engine for Nim code.
## An instruction is 1-3 int32s in memory, it is a register based VM.

import ast except getstr

import
  strutils, msgs, vmdef, vmgen, nimsets, types, passes,
  parser, vmdeps, idents, trees, renderer, options, transf, parseutils,
  vmmarshal, gorgeimpl, lineinfos, tables, btrees, macrocacheimpl,
  modulegraphs, sighashes, int128

from semfold import leValueConv, ordinalValToString
from evaltempl import evalTemplate

const
  traceCode = defined(nimVMDebug)

when hasFFI:
  import evalffi

type
  PStackFrame* = ref TStackFrame
  TStackFrame* = object
    prc: PSym                 # current prc; proc that is evaluated
    slots: seq[TFullReg]      # parameters passed to the proc + locals;
                              # parameters come first
    next: PStackFrame         # for stacking
    comesFrom: int
    safePoints: seq[int]      # used for exception handling
                              # XXX 'break' should perform cleanup actions
                              # What does the C backend do for it?

proc stackTraceAux(c: PCtx; x: PStackFrame; pc: int; recursionLimit=100) =
  if x != nil:
    if recursionLimit == 0:
      var calls = 0
      var x = x
      while x != nil:
        inc calls
        x = x.next
      msgWriteln(c.config, $calls & " calls omitted\n")
      return
    stackTraceAux(c, x.next, x.comesFrom, recursionLimit-1)
    var info = c.debug[pc]
    # we now use a format similar to the one in lib/system/excpt.nim
    var s = ""
    # todo: factor with quotedFilename
    if optExcessiveStackTrace in c.config.globalOptions:
      s = toFullPath(c.config, info)
    else:
      s = toFilename(c.config, info)
    var line = toLinenumber(info)
    var col = toColumn(info)
    if line > 0:
      s.add('(')
      s.add($line)
      s.add(", ")
      s.add($(col + ColOffset))
      s.add(')')
    if x.prc != nil:
      for k in 1..max(1, 25-s.len): s.add(' ')
      s.add(x.prc.name.s)
    msgWriteln(c.config, s)

proc stackTraceImpl(c: PCtx, tos: PStackFrame, pc: int,
  msg: string, lineInfo: TLineInfo, infoOrigin: InstantiationInfo) {.noinline.} =
  # noinline to avoid code bloat
  msgWriteln(c.config, "stack trace: (most recent call last)")
  stackTraceAux(c, tos, pc)
  let action = if c.mode == emRepl: doRaise else: doNothing
    # XXX test if we want 'globalError' for every mode
  let lineInfo = if lineInfo == TLineInfo.default: c.debug[pc] else: lineInfo
  liMessage(c.config, lineInfo, errGenerated, msg, action, infoOrigin)

template stackTrace(c: PCtx, tos: PStackFrame, pc: int,
                    msg: string, lineInfo: TLineInfo = TLineInfo.default) =
  stackTraceImpl(c, tos, pc, msg, lineInfo, instantiationInfo(-2, fullPaths = true))
  return

proc bailOut(c: PCtx; tos: PStackFrame) =
  stackTrace(c, tos, c.exceptionInstr, "unhandled exception: " &
             c.currentExceptionA[3].skipColon.strVal &
             " [" & c.currentExceptionA[2].skipColon.strVal & "]")

when not defined(nimComputedGoto):
  {.pragma: computedGoto.}

proc ensureKind(n: var TFullReg, kind: TRegisterKind) =
  if n.kind != kind:
    n = TFullReg(kind: kind)

template ensureKind(k: untyped) {.dirty.} =
  ensureKind(regs[ra], k)

template decodeB(k: untyped) {.dirty.} =
  let rb = instr.regB
  ensureKind(k)

template decodeBC(k: untyped) {.dirty.} =
  let rb = instr.regB
  let rc = instr.regC
  ensureKind(k)

template declBC() {.dirty.} =
  let rb = instr.regB
  let rc = instr.regC

template decodeBImm(k: untyped) {.dirty.} =
  let rb = instr.regB
  let imm = instr.regC - byteExcess
  ensureKind(k)

template decodeBx(k: untyped) {.dirty.} =
  let rbx = instr.regBx - wordExcess
  ensureKind(k)

template move(a, b: untyped) {.dirty.} = system.shallowCopy(a, b)
# XXX fix minor 'shallowCopy' overloading bug in compiler

proc derefPtrToReg(address: BiggestInt, typ: PType, r: var TFullReg, isAssign: bool): bool =
  # nim bug: `isAssign: static bool` doesn't work, giving odd compiler error
  template fun(field, T, rkind) =
    if isAssign:
      cast[ptr T](address)[] = T(r.field)
    else:
      r.ensureKind(rkind)
      let val = cast[ptr T](address)[]
      when T is SomeInteger:
        r.field = BiggestInt(val)
      else:
        r.field = val
    return true

  ## see also typeinfo.getBiggestInt
  case typ.kind
  of tyInt: fun(intVal, int, rkInt)
  of tyInt8: fun(intVal, int8, rkInt)
  of tyInt16: fun(intVal, int16, rkInt)
  of tyInt32: fun(intVal, int32, rkInt)
  of tyInt64: fun(intVal, int64, rkInt)
  of tyUInt: fun(intVal, uint, rkInt)
  of tyUInt8: fun(intVal, uint8, rkInt)
  of tyUInt16: fun(intVal, uint16, rkInt)
  of tyUInt32: fun(intVal, uint32, rkInt)
  of tyUInt64: fun(intVal, uint64, rkInt) # note: differs from typeinfo.getBiggestInt
  of tyFloat: fun(floatVal, float, rkFloat)
  of tyFloat32: fun(floatVal, float32, rkFloat)
  of tyFloat64: fun(floatVal, float64, rkFloat)
  else: return false

proc createStrKeepNode(x: var TFullReg; keepNode=true) =
  if x.node.isNil or not keepNode:
    x.node = newNode(nkStrLit)
  elif x.node.kind == nkNilLit and keepNode:
    when defined(useNodeIds):
      let id = x.node.id
    x.node[] = TNode(kind: nkStrLit)
    when defined(useNodeIds):
      x.node.id = id
  elif x.node.kind notin {nkStrLit..nkTripleStrLit} or
      nfAllConst in x.node.flags:
    # XXX this is hacky; tests/txmlgen triggers it:
    x.node = newNode(nkStrLit)
    # It not only hackey, it is also wrong for tgentemplate. The primary
    # cause of bugs like these is that the VM does not properly distinguish
    # between variable definitions (var foo = e) and variable updates (foo = e).

include vmhooks

template createStr(x) =
  x.node = newNode(nkStrLit)

template createSet(x) =
  x.node = newNode(nkCurly)

proc moveConst(x: var TFullReg, y: TFullReg) =
  x.ensureKind(y.kind)
  case x.kind
  of rkNone: discard
  of rkInt: x.intVal = y.intVal
  of rkFloat: x.floatVal = y.floatVal
  of rkNode: x.node = y.node
  of rkRegisterAddr: x.regAddr = y.regAddr
  of rkNodeAddr: x.nodeAddr = y.nodeAddr

# this seems to be the best way to model the reference semantics
# of system.NimNode:
template asgnRef(x, y: untyped) = moveConst(x, y)

proc copyValue(src: PNode): PNode =
  if src == nil or nfIsRef in src.flags:
    return src
  result = newNode(src.kind)
  result.info = src.info
  result.typ = src.typ
  result.flags = src.flags * PersistentNodeFlags
  result.comment = src.comment
  when defined(useNodeIds):
    if result.id == nodeIdToDebug:
      echo "COMES FROM ", src.id
  case src.kind
  of nkCharLit..nkUInt64Lit: result.intVal = src.intVal
  of nkFloatLit..nkFloat128Lit: result.floatVal = src.floatVal
  of nkSym: result.sym = src.sym
  of nkIdent: result.ident = src.ident
  of nkStrLit..nkTripleStrLit: result.strVal = src.strVal
  else:
    newSeq(result.sons, src.len)
    for i in 0..<src.len:
      result[i] = copyValue(src[i])

proc asgnComplex(x: var TFullReg, y: TFullReg) =
  x.ensureKind(y.kind)
  case x.kind
  of rkNone: discard
  of rkInt: x.intVal = y.intVal
  of rkFloat: x.floatVal = y.floatVal
  of rkNode: x.node = copyValue(y.node)
  of rkRegisterAddr: x.regAddr = y.regAddr
  of rkNodeAddr: x.nodeAddr = y.nodeAddr

proc fastAsgnComplex(x: var TFullReg, y: TFullReg) =
  x.ensureKind(y.kind)
  case x.kind
  of rkNone: discard
  of rkInt: x.intVal = y.intVal
  of rkFloat: x.floatVal = y.floatVal
  of rkNode: x.node = y.node
  of rkRegisterAddr: x.regAddr = y.regAddr
  of rkNodeAddr: x.nodeAddr = y.nodeAddr

proc writeField(n: var PNode, x: TFullReg) =
  case x.kind
  of rkNone: discard
  of rkInt:
    if n.kind == nkNilLit:
      n[] = TNode(kind: nkIntLit) # ideally, `nkPtrLit`
    n.intVal = x.intVal
  of rkFloat: n.floatVal = x.floatVal
  of rkNode: n = copyValue(x.node)
  of rkRegisterAddr: writeField(n, x.regAddr[])
  of rkNodeAddr: n = x.nodeAddr[]

proc putIntoReg(dest: var TFullReg; n: PNode) =
  case n.kind
  of nkStrLit..nkTripleStrLit:
    dest = TFullReg(kind: rkNode, node: newStrNode(nkStrLit, n.strVal))
  of nkIntLit: # use `nkPtrLit` once this is added
    if dest.kind == rkNode: dest.node = n
    elif n.typ != nil and n.typ.kind in PtrLikeKinds:
      dest = TFullReg(kind: rkNode, node: n)
    else:
      dest = TFullReg(kind: rkInt, intVal: n.intVal)
  of {nkCharLit..nkUInt64Lit} - {nkIntLit}:
    dest = TFullReg(kind: rkInt, intVal: n.intVal)
  of nkFloatLit..nkFloat128Lit:
    dest = TFullReg(kind: rkFloat, floatVal: n.floatVal)
  else:
    dest = TFullReg(kind: rkNode, node: n)

proc regToNode(x: TFullReg): PNode =
  case x.kind
  of rkNone: result = newNode(nkEmpty)
  of rkInt: result = newNode(nkIntLit); result.intVal = x.intVal
  of rkFloat: result = newNode(nkFloatLit); result.floatVal = x.floatVal
  of rkNode: result = x.node
  of rkRegisterAddr: result = regToNode(x.regAddr[])
  of rkNodeAddr: result = x.nodeAddr[]

template getstr(a: untyped): untyped =
  (if a.kind == rkNode: a.node.strVal else: $chr(int(a.intVal)))

proc pushSafePoint(f: PStackFrame; pc: int) =
  when not defined(nimNoNilSeqs):
    if f.safePoints.isNil: f.safePoints = @[]
  f.safePoints.add(pc)

proc popSafePoint(f: PStackFrame) =
  discard f.safePoints.pop()

type
  ExceptionGoto = enum
    ExceptionGotoHandler,
    ExceptionGotoFinally,
    ExceptionGotoUnhandled

proc findExceptionHandler(c: PCtx, f: PStackFrame, exc: PNode):
    tuple[why: ExceptionGoto, where: int] =
  let raisedType = exc.typ.skipTypes(abstractPtrs)

  while f.safePoints.len > 0:
    var pc = f.safePoints.pop()

    var matched = false
    var pcEndExcept = pc

    # Scan the chain of exceptions starting at pc.
    # The structure is the following:
    # pc - opcExcept, <end of this block>
    #      - opcExcept, <pattern1>
    #      - opcExcept, <pattern2>
    #        ...
    #      - opcExcept, <patternN>
    #      - Exception handler body
    #    - ... more opcExcept blocks may follow
    #    - ... an optional opcFinally block may follow
    #
    # Note that the exception handler body already contains a jump to the
    # finally block or, if that's not present, to the point where the execution
    # should continue.
    # Also note that opcFinally blocks are the last in the chain.
    while c.code[pc].opcode == opcExcept:
      # Where this Except block ends
      pcEndExcept = pc + c.code[pc].regBx - wordExcess
      inc pc

      # A series of opcExcept follows for each exception type matched
      while c.code[pc].opcode == opcExcept:
        let excIndex = c.code[pc].regBx - wordExcess
        let exceptType =
          if excIndex > 0: c.types[excIndex].skipTypes(abstractPtrs)
          else: nil

        # echo typeToString(exceptType), " ", typeToString(raisedType)

        # Determine if the exception type matches the pattern
        if exceptType.isNil or inheritanceDiff(raisedType, exceptType) <= 0:
          matched = true
          break

        inc pc

      # Skip any further ``except`` pattern and find the first instruction of
      # the handler body
      while c.code[pc].opcode == opcExcept:
        inc pc

      if matched:
        break

      # If no handler in this chain is able to catch this exception we check if
      # the "parent" chains are able to. If this chain ends with a `finally`
      # block we must execute it before continuing.
      pc = pcEndExcept

    # Where the handler body starts
    let pcBody = pc

    if matched:
      return (ExceptionGotoHandler, pcBody)
    elif c.code[pc].opcode == opcFinally:
      # The +1 here is here because we don't want to execute it since we've
      # already pop'd this statepoint from the stack.
      return (ExceptionGotoFinally, pc + 1)

  return (ExceptionGotoUnhandled, 0)

proc cleanUpOnReturn(c: PCtx; f: PStackFrame): int =
  # Walk up the chain of safepoints and return the PC of the first `finally`
  # block we find or -1 if no such block is found.
  # Note that the safepoint is removed once the function returns!
  result = -1

  # Traverse the stack starting from the end in order to execute the blocks in
  # the intended order
  for i in 1..f.safePoints.len:
    var pc = f.safePoints[^i]
    # Skip the `except` blocks
    while c.code[pc].opcode == opcExcept:
      pc += c.code[pc].regBx - wordExcess
    if c.code[pc].opcode == opcFinally:
      discard f.safePoints.pop
      return pc + 1

proc opConv(c: PCtx; dest: var TFullReg, src: TFullReg, desttyp, srctyp: PType): bool =
  if desttyp.kind == tyString:
    dest.ensureKind(rkNode)
    dest.node = newNode(nkStrLit)
    let styp = srctyp.skipTypes(abstractRange)
    case styp.kind
    of tyEnum:
      let n = styp.n
      let x = src.intVal.int
      if x <% n.len and (let f = n[x].sym; f.position == x):
        dest.node.strVal = if f.ast.isNil: f.name.s else: f.ast.strVal
      else:
        for i in 0..<n.len:
          if n[i].kind != nkSym: internalError(c.config, "opConv for enum")
          let f = n[i].sym
          if f.position == x:
            dest.node.strVal = if f.ast.isNil: f.name.s else: f.ast.strVal
            return
        dest.node.strVal = styp.sym.name.s & " " & $x
    of tyInt..tyInt64:
      dest.node.strVal = $src.intVal
    of tyUInt..tyUInt64:
      dest.node.strVal = $uint64(src.intVal)
    of tyBool:
      dest.node.strVal = if src.intVal == 0: "false" else: "true"
    of tyFloat..tyFloat128:
      dest.node.strVal = $src.floatVal
    of tyString:
      dest.node.strVal = src.node.strVal
    of tyCString:
      if src.node.kind == nkBracket:
        # Array of chars
        var strVal = ""
        for son in src.node.sons:
          let c = char(son.intVal)
          if c == '\0': break
          strVal.add(c)
        dest.node.strVal = strVal
      else:
        dest.node.strVal = src.node.strVal
    of tyChar:
      dest.node.strVal = $chr(src.intVal)
    else:
      internalError(c.config, "cannot convert to string " & desttyp.typeToString)
  else:
    case skipTypes(desttyp, abstractVarRange).kind
    of tyInt..tyInt64:
      dest.ensureKind(rkInt)
      case skipTypes(srctyp, abstractRange).kind
      of tyFloat..tyFloat64:
        dest.intVal = int(src.floatVal)
      else:
        dest.intVal = src.intVal
      if toInt128(dest.intVal) < firstOrd(c.config, desttyp) or toInt128(dest.intVal) > lastOrd(c.config, desttyp):
        return true
    of tyUInt..tyUInt64:
      dest.ensureKind(rkInt)
      case skipTypes(srctyp, abstractRange).kind
      of tyFloat..tyFloat64:
        dest.intVal = int(src.floatVal)
      else:
        let srcDist = (sizeof(src.intVal) - srctyp.size) * 8
        let destDist = (sizeof(dest.intVal) - desttyp.size) * 8

        var value = cast[BiggestUInt](src.intVal)
        value = (value shl srcDist) shr srcDist
        value = (value shl destDist) shr destDist
        dest.intVal = cast[BiggestInt](value)
    of tyBool:
      dest.ensureKind(rkInt)
      dest.intVal =
        case skipTypes(srctyp, abstractRange).kind
          of tyFloat..tyFloat64: int(src.floatVal != 0.0)
          else: int(src.intVal != 0)
    of tyFloat..tyFloat64:
      dest.ensureKind(rkFloat)
      case skipTypes(srctyp, abstractRange).kind
      of tyInt..tyInt64, tyUInt..tyUInt64, tyEnum, tyBool, tyChar:
        dest.floatVal = toBiggestFloat(src.intVal)
      else:
        dest.floatVal = src.floatVal
    of tyObject:
      if srctyp.skipTypes(abstractVarRange).kind != tyObject:
        internalError(c.config, "invalid object-to-object conversion")
      # A object-to-object conversion is essentially a no-op
      moveConst(dest, src)
    else:
      asgnComplex(dest, src)

proc compile(c: PCtx, s: PSym): int =
  result = vmgen.genProc(c, s)
  when debugEchoCode: c.echoCode result
  #c.echoCode

template handleJmpBack() {.dirty.} =
  if c.loopIterations <= 0:
    if allowInfiniteLoops in c.features:
      c.loopIterations = c.config.maxLoopIterationsVM
    else:
      msgWriteln(c.config, "stack trace: (most recent call last)")
      stackTraceAux(c, tos, pc)
      globalError(c.config, c.debug[pc], errTooManyIterations % $c.config.maxLoopIterationsVM)
  dec(c.loopIterations)

proc recSetFlagIsRef(arg: PNode) =
  if arg.kind notin {nkStrLit..nkTripleStrLit}:
    arg.flags.incl(nfIsRef)
  for i in 0..<arg.safeLen:
    arg[i].recSetFlagIsRef

proc setLenSeq(c: PCtx; node: PNode; newLen: int; info: TLineInfo) =
  let typ = node.typ.skipTypes(abstractInst+{tyRange}-{tyTypeDesc})
  let oldLen = node.len
  setLen(node.sons, newLen)
  if oldLen < newLen:
    for i in oldLen..<newLen:
      node[i] = getNullValue(typ[0], info, c.config)

const
  errNilAccess = "attempt to access a nil address"
  errOverOrUnderflow = "over- or underflow"
  errConstantDivisionByZero = "division by zero"
  errIllegalConvFromXtoY = "illegal conversion from '$1' to '$2'"
  errTooManyIterations = "interpretation requires too many iterations; " &
    "if you are sure this is not a bug in your code, compile with `--maxLoopIterationsVM:number` (current value: $1)"
  errFieldXNotFound = "node lacks field: "


template maybeHandlePtr(node2: PNode, reg: TFullReg, isAssign2: bool): bool =
  let node = node2 # prevent double evaluation
  if node.kind == nkNilLit:
    stackTrace(c, tos, pc, errNilAccess)
  let typ = node.typ
  if nfIsPtr in node.flags or (typ != nil and typ.kind == tyPtr):
    assert node.kind == nkIntLit, $(node.kind)
    assert typ != nil
    let typ2 = if typ.kind == tyPtr: typ[0] else: typ
    if not derefPtrToReg(node.intVal, typ2, reg, isAssign = isAssign2):
      # tyObject not supported in this context
      stackTrace(c, tos, pc, "deref unsupported ptr type: " & $(typeToString(typ), typ.kind))
    true
  else:
    false

when not defined(nimHasSinkInference):
  {.pragma: nosinks.}

proc rawExecute(c: PCtx, start: int, tos: PStackFrame): TFullReg =
  var pc = start
  var tos = tos
  # Used to keep track of where the execution is resumed.
  var savedPC = -1
  var savedFrame: PStackFrame
  var regs: seq[TFullReg] # alias to tos.slots for performance
  move(regs, tos.slots)
  #echo "NEW RUN ------------------------"
  while true:
    #{.computedGoto.}
    let instr = c.code[pc]
    let ra = instr.regA

    when traceCode:
      template regDescr(name, r): string =
        let kind = if r < regs.len: $regs[r].kind else: ""
        let ret = name & ": " & $r & " " & $kind
        alignLeft(ret, 15)
      echo "PC:$pc $opcode $ra $rb $rc" % [
        "pc", $pc, "opcode", alignLeft($c.code[pc].opcode, 15),
        "ra", regDescr("ra", ra), "rb", regDescr("rb", instr.regB),
        "rc", regDescr("rc", instr.regC)]

    case instr.opcode
    of opcEof: return regs[ra]
    of opcRet:
      let newPc = c.cleanUpOnReturn(tos)
      # Perform any cleanup action before returning
      if newPc < 0:
        pc = tos.comesFrom
        tos = tos.next
        let retVal = regs[0]
        if tos.isNil:
          return retVal

        move(regs, tos.slots)
        assert c.code[pc].opcode in {opcIndCall, opcIndCallAsgn}
        if c.code[pc].opcode == opcIndCallAsgn:
          regs[c.code[pc].regA] = retVal
      else:
        savedPC = pc
        savedFrame = tos
        # The -1 is needed because at the end of the loop we increment `pc`
        pc = newPc - 1
    of opcYldYoid: assert false
    of opcYldVal: assert false
    of opcAsgnInt:
      decodeB(rkInt)
      regs[ra].intVal = regs[rb].intVal
    of opcAsgnFloat:
      decodeB(rkFloat)
      regs[ra].floatVal = regs[rb].floatVal
    of opcCastFloatToInt32:
      let rb = instr.regB
      ensureKind(rkInt)
      regs[ra].intVal = cast[int32](float32(regs[rb].floatVal))
    of opcCastFloatToInt64:
      let rb = instr.regB
      ensureKind(rkInt)
      regs[ra].intVal = cast[int64](regs[rb].floatVal)
    of opcCastIntToFloat32:
      let rb = instr.regB
      ensureKind(rkFloat)
      regs[ra].floatVal = cast[float32](regs[rb].intVal)
    of opcCastIntToFloat64:
      let rb = instr.regB
      ensureKind(rkFloat)
      regs[ra].floatVal = cast[float64](regs[rb].intVal)

    of opcCastPtrToInt: # RENAME opcCastPtrOrRefToInt
      decodeBImm(rkInt)
      case imm
      of 1: # PtrLikeKinds
        case regs[rb].kind
        of rkNode:
          regs[ra].intVal = cast[int](regs[rb].node.intVal)
        of rkNodeAddr:
          regs[ra].intVal = cast[int](regs[rb].nodeAddr)
        else:
          stackTrace(c, tos, pc, "opcCastPtrToInt: got " & $regs[rb].kind)
      of 2: # tyRef
        regs[ra].intVal = cast[int](regs[rb].node)
      else: assert false, $imm
    of opcCastIntToPtr:
      let rb = instr.regB
      let typ = regs[ra].node.typ
      let node2 = newNodeIT(nkIntLit, c.debug[pc], typ)
      case regs[rb].kind
      of rkInt: node2.intVal = regs[rb].intVal
      of rkNode:
        if regs[rb].node.typ.kind notin PtrLikeKinds:
          stackTrace(c, tos, pc, "opcCastIntToPtr: regs[rb].node.typ: " & $regs[rb].node.typ.kind)
        node2.intVal = regs[rb].node.intVal
      else: stackTrace(c, tos, pc, "opcCastIntToPtr: regs[rb].kind: " & $regs[rb].kind)
      regs[ra].node = node2
    of opcAsgnComplex:
      asgnComplex(regs[ra], regs[instr.regB])
    of opcFastAsgnComplex:
      fastAsgnComplex(regs[ra], regs[instr.regB])
    of opcAsgnRef:
      asgnRef(regs[ra], regs[instr.regB])
    of opcNodeToReg:
      let ra = instr.regA
      let rb = instr.regB
      # opcDeref might already have loaded it into a register. XXX Let's hope
      # this is still correct this way:
      if regs[rb].kind != rkNode:
        regs[ra] = regs[rb]
      else:
        assert regs[rb].kind == rkNode
        let nb = regs[rb].node
        case nb.kind
        of nkCharLit..nkUInt64Lit:
          ensureKind(rkInt)
          regs[ra].intVal = nb.intVal
        of nkFloatLit..nkFloat64Lit:
          ensureKind(rkFloat)
          regs[ra].floatVal = nb.floatVal
        else:
          ensureKind(rkNode)
          regs[ra].node = nb
    of opcLdArr:
      # a = b[c]
      decodeBC(rkNode)
      if regs[rc].intVal > high(int):
        stackTrace(c, tos, pc, formatErrorIndexBound(regs[rc].intVal, high(int)))
      let idx = regs[rc].intVal.int
      let src = regs[rb].node
      if src.kind in {nkStrLit..nkTripleStrLit}:
        if idx <% src.strVal.len:
          regs[ra].node = newNodeI(nkCharLit, c.debug[pc])
          regs[ra].node.intVal = src.strVal[idx].ord
        else:
          stackTrace(c, tos, pc, formatErrorIndexBound(idx, src.strVal.len-1))
      elif src.kind notin {nkEmpty..nkFloat128Lit} and idx <% src.len:
        regs[ra].node = src[idx]
      else:
        stackTrace(c, tos, pc, formatErrorIndexBound(idx, src.safeLen-1))
    of opcLdArrAddr:
      # a = addr(b[c])
      decodeBC(rkNodeAddr)
      if regs[rc].intVal > high(int):
        stackTrace(c, tos, pc, formatErrorIndexBound(regs[rc].intVal, high(int)))
      let idx = regs[rc].intVal.int
      let src = if regs[rb].kind == rkNode: regs[rb].node else: regs[rb].nodeAddr[]
      if src.kind notin {nkEmpty..nkTripleStrLit} and idx <% src.len:
        regs[ra].nodeAddr = addr src.sons[idx]
      else:
        stackTrace(c, tos, pc, formatErrorIndexBound(idx, src.safeLen-1))
    of opcLdStrIdx:
      decodeBC(rkInt)
      let idx = regs[rc].intVal.int
      let s = regs[rb].node.strVal
      if idx <% s.len:
        regs[ra].intVal = s[idx].ord
      else:
        stackTrace(c, tos, pc, formatErrorIndexBound(idx, s.len-1))
    of opcWrArr:
      # a[b] = c
      decodeBC(rkNode)
      let idx = regs[rb].intVal.int
      let arr = regs[ra].node
      if arr.kind in {nkStrLit..nkTripleStrLit}:
        if idx <% arr.strVal.len:
          arr.strVal[idx] = chr(regs[rc].intVal)
        else:
          stackTrace(c, tos, pc, formatErrorIndexBound(idx, arr.strVal.len-1))
      elif idx <% arr.len:
        writeField(arr[idx], regs[rc])
      else:
        stackTrace(c, tos, pc, formatErrorIndexBound(idx, arr.safeLen-1))
    of opcLdObj:
      # a = b.c
      decodeBC(rkNode)
      let src = regs[rb].node
      case src.kind
      of nkEmpty..nkNilLit:
        # for nkPtrLit, this could be supported in the future, use something like:
        # derefPtrToReg(src.intVal + offsetof(src.typ, rc), typ_field, regs[ra], isAssign = false)
        # where we compute the offset in bytes for field rc
        stackTrace(c, tos, pc, errNilAccess & " " & $("kind", src.kind, "typ", typeToString(src.typ), "rc", rc))
      of nkObjConstr:
        let n = src[rc + 1].skipColon
        regs[ra].node = n
      else:
        let n = src[rc]
        regs[ra].node = n
    of opcLdObjAddr:
      # a = addr(b.c)
      decodeBC(rkNodeAddr)
      let src = if regs[rb].kind == rkNode: regs[rb].node else: regs[rb].nodeAddr[]
      case src.kind
      of nkEmpty..nkNilLit:
        stackTrace(c, tos, pc, errNilAccess)
      of nkObjConstr:
        let n = src.sons[rc + 1]
        if n.kind == nkExprColonExpr:
          regs[ra].nodeAddr = addr n.sons[1]
        else:
          regs[ra].nodeAddr = addr src.sons[rc + 1]
      else:
        regs[ra].nodeAddr = addr src.sons[rc]
    of opcWrObj:
      # a.b = c
      decodeBC(rkNode)
      assert regs[ra].node != nil
      let shiftedRb = rb + ord(regs[ra].node.kind == nkObjConstr)
      let dest = regs[ra].node
      if dest.kind == nkNilLit:
        stackTrace(c, tos, pc, errNilAccess)
      elif dest[shiftedRb].kind == nkExprColonExpr:
        writeField(dest[shiftedRb][1], regs[rc])
      else:
        writeField(dest[shiftedRb], regs[rc])
    of opcWrStrIdx:
      decodeBC(rkNode)
      let idx = regs[rb].intVal.int
      if idx <% regs[ra].node.strVal.len:
        regs[ra].node.strVal[idx] = chr(regs[rc].intVal)
      else:
        stackTrace(c, tos, pc, formatErrorIndexBound(idx, regs[ra].node.strVal.len-1))
    of opcAddrReg:
      decodeB(rkRegisterAddr)
      regs[ra].regAddr = addr(regs[rb])
    of opcAddrNode:
      decodeB(rkNodeAddr)
      if regs[rb].kind == rkNode:
        regs[ra].nodeAddr = addr(regs[rb].node)
      else:
        stackTrace(c, tos, pc, "limited VM support for 'addr'")
    of opcLdDeref:
      # a = b[]
      let ra = instr.regA
      let rb = instr.regB
      case regs[rb].kind
      of rkNodeAddr:
        ensureKind(rkNode)
        regs[ra].node = regs[rb].nodeAddr[]
      of rkRegisterAddr:
        ensureKind(regs[rb].regAddr.kind)
        regs[ra] = regs[rb].regAddr[]
      of rkNode:
        if regs[rb].node.kind == nkRefTy:
          regs[ra].node = regs[rb].node[0]
        elif not maybeHandlePtr(regs[rb].node, regs[ra], false):
          ## eg: typ.kind = tyObject
          ensureKind(rkNode)
          regs[ra].node = regs[rb].node
      else:
        stackTrace(c, tos, pc, errNilAccess & " kind: " & $regs[rb].kind)
    of opcWrDeref:
      # a[] = c; b unused
      let ra = instr.regA
      let rc = instr.regC
      case regs[ra].kind
      of rkNodeAddr:
        let n = regs[rc].regToNode
        # `var object` parameters are sent as rkNodeAddr. When they are mutated
        # vmgen generates opcWrDeref, which means that we must dereference
        # twice.
        # TODO: This should likely be handled differently in vmgen.
        if (nfIsRef notin regs[ra].nodeAddr[].flags and
            nfIsRef notin n.flags):
          regs[ra].nodeAddr[][] = n[]
        else:
          regs[ra].nodeAddr[] = n
      of rkRegisterAddr: regs[ra].regAddr[] = regs[rc]
      of rkNode:
         # xxx: also check for nkRefTy as in opcLdDeref?
        if not maybeHandlePtr(regs[ra].node, regs[rc], true):
          regs[ra].node[] = regs[rc].regToNode[]
          regs[ra].node.flags.incl nfIsRef
      else: stackTrace(c, tos, pc, errNilAccess)
    of opcAddInt:
      decodeBC(rkInt)
      let
        bVal = regs[rb].intVal
        cVal = regs[rc].intVal
        sum = bVal +% cVal
      if (sum xor bVal) >= 0 or (sum xor cVal) >= 0:
        regs[ra].intVal = sum
      else:
        stackTrace(c, tos, pc, errOverOrUnderflow)
    of opcAddImmInt:
      decodeBImm(rkInt)
      #message(c.config, c.debug[pc], warnUser, "came here")
      #debug regs[rb].node
      let
        bVal = regs[rb].intVal
        cVal = imm
        sum = bVal +% cVal
      if (sum xor bVal) >= 0 or (sum xor cVal) >= 0:
        regs[ra].intVal = sum
      else:
        stackTrace(c, tos, pc, errOverOrUnderflow)
    of opcSubInt:
      decodeBC(rkInt)
      let
        bVal = regs[rb].intVal
        cVal = regs[rc].intVal
        diff = bVal -% cVal
      if (diff xor bVal) >= 0 or (diff xor not cVal) >= 0:
        regs[ra].intVal = diff
      else:
        stackTrace(c, tos, pc, errOverOrUnderflow)
    of opcSubImmInt:
      decodeBImm(rkInt)
      let
        bVal = regs[rb].intVal
        cVal = imm
        diff = bVal -% cVal
      if (diff xor bVal) >= 0 or (diff xor not cVal) >= 0:
        regs[ra].intVal = diff
      else:
        stackTrace(c, tos, pc, errOverOrUnderflow)
    of opcLenSeq:
      decodeBImm(rkInt)
      #assert regs[rb].kind == nkBracket
      let high = (imm and 1) # discard flags
      if (imm and nimNodeFlag) != 0:
        # used by mNLen (NimNode.len)
        regs[ra].intVal = regs[rb].node.safeLen - high
      else:
        # safeArrLen also return string node len
        # used when string is passed as openArray in VM
        regs[ra].intVal = regs[rb].node.safeArrLen - high
    of opcLenStr:
      decodeBImm(rkInt)
      assert regs[rb].kind == rkNode
      regs[ra].intVal = regs[rb].node.strVal.len - imm
    of opcIncl:
      decodeB(rkNode)
      let b = regs[rb].regToNode
      if not inSet(regs[ra].node, b):
        regs[ra].node.add copyTree(b)
    of opcInclRange:
      decodeBC(rkNode)
      var r = newNode(nkRange)
      r.add regs[rb].regToNode
      r.add regs[rc].regToNode
      regs[ra].node.add r.copyTree
    of opcExcl:
      decodeB(rkNode)
      var b = newNodeIT(nkCurly, regs[ra].node.info, regs[ra].node.typ)
      b.add regs[rb].regToNode
      var r = diffSets(c.config, regs[ra].node, b)
      discardSons(regs[ra].node)
      for i in 0..<r.len: regs[ra].node.add r[i]
    of opcCard:
      decodeB(rkInt)
      regs[ra].intVal = nimsets.cardSet(c.config, regs[rb].node)
    of opcMulInt:
      decodeBC(rkInt)
      let
        bVal = regs[rb].intVal
        cVal = regs[rc].intVal
        product = bVal *% cVal
        floatProd = toBiggestFloat(bVal) * toBiggestFloat(cVal)
        resAsFloat = toBiggestFloat(product)
      if resAsFloat == floatProd:
        regs[ra].intVal = product
      elif 32.0 * abs(resAsFloat - floatProd) <= abs(floatProd):
        regs[ra].intVal = product
      else:
        stackTrace(c, tos, pc, errOverOrUnderflow)
    of opcDivInt:
      decodeBC(rkInt)
      if regs[rc].intVal == 0: stackTrace(c, tos, pc, errConstantDivisionByZero)
      else: regs[ra].intVal = regs[rb].intVal div regs[rc].intVal
    of opcModInt:
      decodeBC(rkInt)
      if regs[rc].intVal == 0: stackTrace(c, tos, pc, errConstantDivisionByZero)
      else: regs[ra].intVal = regs[rb].intVal mod regs[rc].intVal
    of opcAddFloat:
      decodeBC(rkFloat)
      regs[ra].floatVal = regs[rb].floatVal + regs[rc].floatVal
    of opcSubFloat:
      decodeBC(rkFloat)
      regs[ra].floatVal = regs[rb].floatVal - regs[rc].floatVal
    of opcMulFloat:
      decodeBC(rkFloat)
      regs[ra].floatVal = regs[rb].floatVal * regs[rc].floatVal
    of opcDivFloat:
      decodeBC(rkFloat)
      regs[ra].floatVal = regs[rb].floatVal / regs[rc].floatVal
    of opcShrInt:
      decodeBC(rkInt)
      let b = cast[uint64](regs[rb].intVal)
      let c = cast[uint64](regs[rc].intVal)
      let a = cast[int64](b shr c)
      regs[ra].intVal = a
    of opcShlInt:
      decodeBC(rkInt)
      regs[ra].intVal = regs[rb].intVal shl regs[rc].intVal
    of opcAshrInt:
      decodeBC(rkInt)
      regs[ra].intVal = ashr(regs[rb].intVal, regs[rc].intVal)
    of opcBitandInt:
      decodeBC(rkInt)
      regs[ra].intVal = regs[rb].intVal and regs[rc].intVal
    of opcBitorInt:
      decodeBC(rkInt)
      regs[ra].intVal = regs[rb].intVal or regs[rc].intVal
    of opcBitxorInt:
      decodeBC(rkInt)
      regs[ra].intVal = regs[rb].intVal xor regs[rc].intVal
    of opcAddu:
      decodeBC(rkInt)
      regs[ra].intVal = regs[rb].intVal +% regs[rc].intVal
    of opcSubu:
      decodeBC(rkInt)
      regs[ra].intVal = regs[rb].intVal -% regs[rc].intVal
    of opcMulu:
      decodeBC(rkInt)
      regs[ra].intVal = regs[rb].intVal *% regs[rc].intVal
    of opcDivu:
      decodeBC(rkInt)
      regs[ra].intVal = regs[rb].intVal /% regs[rc].intVal
    of opcModu:
      decodeBC(rkInt)
      regs[ra].intVal = regs[rb].intVal %% regs[rc].intVal
    of opcEqInt:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].intVal == regs[rc].intVal)
    of opcLeInt:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].intVal <= regs[rc].intVal)
    of opcLtInt:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].intVal < regs[rc].intVal)
    of opcEqFloat:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].floatVal == regs[rc].floatVal)
    of opcLeFloat:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].floatVal <= regs[rc].floatVal)
    of opcLtFloat:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].floatVal < regs[rc].floatVal)
    of opcLeu:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].intVal <=% regs[rc].intVal)
    of opcLtu:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].intVal <% regs[rc].intVal)
    of opcEqRef:
      var ret = false
      decodeBC(rkInt)
      template getTyp(n): untyped =
        n.typ.skipTypes(abstractInst)
      proc ptrEquality(n1: ptr PNode, n2: PNode): bool =
        ## true if n2.intVal represents a ptr equal to n1
        let p1 = cast[int](n1)
        case n2.kind
        of nkNilLit: return p1 == 0
        of nkIntLit: # TODO: nkPtrLit
          # for example, n1.kind == nkFloatLit (ptr float)
          # the problem is that n1.typ == nil so we can't compare n1.typ and n2.typ
          # this is the best we can do (pending making sure we assign a valid n1.typ to nodeAddr's)
          let t2 = n2.getTyp
          return t2.kind in PtrLikeKinds and n2.intVal == p1
        else: return false

      if regs[rb].kind == rkNodeAddr:
        if regs[rc].kind == rkNodeAddr:
          ret = regs[rb].nodeAddr == regs[rc].nodeAddr
        else:
          ret = ptrEquality(regs[rb].nodeAddr, regs[rc].node)
      elif regs[rc].kind == rkNodeAddr:
        ret = ptrEquality(regs[rc].nodeAddr, regs[rb].node)
      else:
        let nb = regs[rb].node
        let nc = regs[rc].node
        if nb.kind != nc.kind: discard
        elif (nb == nc) or (nb.kind == nkNilLit): ret = true
        elif nb.kind == nkIntLit and nb.intVal == nc.intVal: # TODO: nkPtrLit
          let tb = nb.getTyp
          let tc = nc.getTyp
          ret = tb.kind in PtrLikeKinds and tc.kind == tb.kind
      regs[ra].intVal = ord(ret)
    of opcEqNimNode:
      decodeBC(rkInt)
      regs[ra].intVal =
        ord(exprStructuralEquivalent(regs[rb].node, regs[rc].node,
                                     strictSymEquality=true))
    of opcSameNodeType:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].node.typ.sameTypeOrNil regs[rc].node.typ)
    of opcXor:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].intVal != regs[rc].intVal)
    of opcNot:
      decodeB(rkInt)
      assert regs[rb].kind == rkInt
      regs[ra].intVal = 1 - regs[rb].intVal
    of opcUnaryMinusInt:
      decodeB(rkInt)
      assert regs[rb].kind == rkInt
      let val = regs[rb].intVal
      if val != int64.low:
        regs[ra].intVal = -val
      else:
        stackTrace(c, tos, pc, errOverOrUnderflow)
    of opcUnaryMinusFloat:
      decodeB(rkFloat)
      assert regs[rb].kind == rkFloat
      regs[ra].floatVal = -regs[rb].floatVal
    of opcBitnotInt:
      decodeB(rkInt)
      assert regs[rb].kind == rkInt
      regs[ra].intVal = not regs[rb].intVal
    of opcEqStr:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].node.strVal == regs[rc].node.strVal)
    of opcLeStr:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].node.strVal <= regs[rc].node.strVal)
    of opcLtStr:
      decodeBC(rkInt)
      regs[ra].intVal = ord(regs[rb].node.strVal < regs[rc].node.strVal)
    of opcLeSet:
      decodeBC(rkInt)
      regs[ra].intVal = ord(containsSets(c.config, regs[rb].node, regs[rc].node))
    of opcEqSet:
      decodeBC(rkInt)
      regs[ra].intVal = ord(equalSets(c.config, regs[rb].node, regs[rc].node))
    of opcLtSet:
      decodeBC(rkInt)
      let a = regs[rb].node
      let b = regs[rc].node
      regs[ra].intVal = ord(containsSets(c.config, a, b) and not equalSets(c.config, a, b))
    of opcMulSet:
      decodeBC(rkNode)
      createSet(regs[ra])
      move(regs[ra].node.sons,
            nimsets.intersectSets(c.config, regs[rb].node, regs[rc].node).sons)
    of opcPlusSet:
      decodeBC(rkNode)
      createSet(regs[ra])
      move(regs[ra].node.sons,
           nimsets.unionSets(c.config, regs[rb].node, regs[rc].node).sons)
    of opcMinusSet:
      decodeBC(rkNode)
      createSet(regs[ra])
      move(regs[ra].node.sons,
           nimsets.diffSets(c.config, regs[rb].node, regs[rc].node).sons)
    of opcConcatStr:
      decodeBC(rkNode)
      createStr regs[ra]
      regs[ra].node.strVal = getstr(regs[rb])
      for i in rb+1..rb+rc-1:
        regs[ra].node.strVal.add getstr(regs[i])
    of opcAddStrCh:
      decodeB(rkNode)
      regs[ra].node.strVal.add(regs[rb].intVal.chr)
    of opcAddStrStr:
      decodeB(rkNode)
      regs[ra].node.strVal.add(regs[rb].node.strVal)
    of opcAddSeqElem:
      decodeB(rkNode)
      if regs[ra].node.kind == nkBracket:
        regs[ra].node.add(copyValue(regs[rb].regToNode))
      else:
        stackTrace(c, tos, pc, errNilAccess)
    of opcGetImpl:
      decodeB(rkNode)
      var a = regs[rb].node
      if a.kind == nkVarTy: a = a[0]
      if a.kind == nkSym:
        regs[ra].node = if a.sym.ast.isNil: newNode(nkNilLit)
                        else: copyTree(a.sym.ast)
        regs[ra].node.flags.incl nfIsRef
      else:
        stackTrace(c, tos, pc, "node is not a symbol")
    of opcGetImplTransf:
      decodeB(rkNode)
      let a = regs[rb].node
      if a.kind == nkSym:
        regs[ra].node =
          if a.sym.ast.isNil:
            newNode(nkNilLit)
          else:
            let ast = a.sym.ast.shallowCopy
            for i in 0..<a.sym.ast.len:
              ast[i] = a.sym.ast[i]
            ast[bodyPos] = transformBody(c.graph, a.sym, cache=true)
            ast.copyTree()
    of opcSymOwner:
      decodeB(rkNode)
      let a = regs[rb].node
      if a.kind == nkSym:
        regs[ra].node = if a.sym.owner.isNil: newNode(nkNilLit)
                        else: newSymNode(a.sym.skipGenericOwner)
        regs[ra].node.flags.incl nfIsRef
      else:
        stackTrace(c, tos, pc, "node is not a symbol")
    of opcSymIsInstantiationOf:
      decodeBC(rkInt)
      let a = regs[rb].node
      let b = regs[rc].node
      if a.kind == nkSym and a.sym.kind in skProcKinds and
         b.kind == nkSym and b.sym.kind in skProcKinds:
        regs[ra].intVal =
          if sfFromGeneric in a.sym.flags and a.sym.owner == b.sym: 1
          else: 0
      else:
        stackTrace(c, tos, pc, "node is not a proc symbol")
    of opcEcho:
      let rb = instr.regB
      if rb == 1:
        msgWriteln(c.config, regs[ra].node.strVal, {msgStdout})
      else:
        var outp = ""
        for i in ra..ra+rb-1:
          #if regs[i].kind != rkNode: debug regs[i]
          outp.add(regs[i].node.strVal)
        msgWriteln(c.config, outp, {msgStdout})
    of opcContainsSet:
      decodeBC(rkInt)
      regs[ra].intVal = ord(inSet(regs[rb].node, regs[rc].regToNode))
    of opcSubStr:
      decodeBC(rkNode)
      inc pc
      assert c.code[pc].opcode == opcSubStr
      let rd = c.code[pc].regA
      createStr regs[ra]
      regs[ra].node.strVal = substr(regs[rb].node.strVal,
                                    regs[rc].intVal.int, regs[rd].intVal.int)
    of opcParseFloat:
      decodeBC(rkInt)
      inc pc
      assert c.code[pc].opcode == opcParseFloat
      let rd = c.code[pc].regA
      var rcAddr = addr(regs[rc])
      if rcAddr.kind == rkRegisterAddr: rcAddr = rcAddr.regAddr
      elif regs[rc].kind != rkFloat:
        regs[rc] = TFullReg(kind: rkFloat)
      regs[ra].intVal = parseBiggestFloat(regs[rb].node.strVal,
                                          rcAddr.floatVal, regs[rd].intVal.int)
    of opcRangeChck:
      let rb = instr.regB
      let rc = instr.regC
      if not (leValueConv(regs[rb].regToNode, regs[ra].regToNode) and
              leValueConv(regs[ra].regToNode, regs[rc].regToNode)):
        stackTrace(c, tos, pc,
          errIllegalConvFromXtoY % [
             $regs[ra].regToNode, "[" & $regs[rb].regToNode & ".." & $regs[rc].regToNode & "]"])
    of opcIndCall, opcIndCallAsgn:
      # dest = call regStart, n; where regStart = fn, arg1, ...
      let rb = instr.regB
      let rc = instr.regC
      let bb = regs[rb].node
      let isClosure = bb.kind == nkTupleConstr
      let prc = if not isClosure: bb.sym else: bb[0].sym
      if prc.offset < -1:
        # it's a callback:
        c.callbacks[-prc.offset-2].value(
          VmArgs(ra: ra, rb: rb, rc: rc, slots: cast[ptr UncheckedArray[TFullReg]](addr regs[0]),
                 currentException: c.currentExceptionA,
                 currentLineInfo: c.debug[pc]))
      elif importcCond(prc):
        if compiletimeFFI notin c.config.features:
          globalError(c.config, c.debug[pc], "VM not allowed to do FFI, see `compiletimeFFI`")
        # we pass 'tos.slots' instead of 'regs' so that the compiler can keep
        # 'regs' in a register:
        when hasFFI:
          if prc.position - 1 < 0:
            globalError(c.config, c.debug[pc],
              "VM call invalid: prc.position: " & $prc.position)
          let prcValue = c.globals[prc.position-1]
          if prcValue.kind == nkEmpty:
            globalError(c.config, c.debug[pc], "cannot run " & prc.name.s)
          var slots2: TNodeSeq
          slots2.setLen(tos.slots.len)
          for i in 0..<tos.slots.len:
            slots2[i] = regToNode(tos.slots[i])
          let newValue = callForeignFunction(c.config, prcValue, prc.typ, slots2,
                                             rb+1, rc-1, c.debug[pc])
          if newValue.kind != nkEmpty:
            assert instr.opcode == opcIndCallAsgn
            putIntoReg(regs[ra], newValue)
        else:
          globalError(c.config, c.debug[pc], "VM not built with FFI support")
      elif prc.kind != skTemplate:
        let newPc = compile(c, prc)
        # tricky: a recursion is also a jump back, so we use the same
        # logic as for loops:
        if newPc < pc: handleJmpBack()
        #echo "new pc ", newPc, " calling: ", prc.name.s
        var newFrame = PStackFrame(prc: prc, comesFrom: pc, next: tos)
        newSeq(newFrame.slots, prc.offset+ord(isClosure))
        if not isEmptyType(prc.typ[0]):
          putIntoReg(newFrame.slots[0], getNullValue(prc.typ[0], prc.info, c.config))
        for i in 1..rc-1:
          newFrame.slots[i] = regs[rb+i]
        if isClosure:
          newFrame.slots[rc] = TFullReg(kind: rkNode, node: regs[rb].node[1])
        tos = newFrame
        move(regs, newFrame.slots)
        # -1 for the following 'inc pc'
        pc = newPc-1
      else:
        # for 'getAst' support we need to support template expansion here:
        let genSymOwner = if tos.next != nil and tos.next.prc != nil:
                            tos.next.prc
                          else:
                            c.module
        var macroCall = newNodeI(nkCall, c.debug[pc])
        macroCall.add(newSymNode(prc))
        for i in 1..rc-1:
          let node = regs[rb+i].regToNode
          node.info = c.debug[pc]
          macroCall.add(node)
        var a = evalTemplate(macroCall, prc, genSymOwner, c.config, c.cache)
        if a.kind == nkStmtList and a.len == 1: a = a[0]
        a.recSetFlagIsRef
        ensureKind(rkNode)
        regs[ra].node = a
    of opcTJmp:
      # jump Bx if A != 0
      let rbx = instr.regBx - wordExcess - 1 # -1 for the following 'inc pc'
      if regs[ra].intVal != 0:
        inc pc, rbx
    of opcFJmp:
      # jump Bx if A == 0
      let rbx = instr.regBx - wordExcess - 1 # -1 for the following 'inc pc'
      if regs[ra].intVal == 0:
        inc pc, rbx
    of opcJmp:
      # jump Bx
      let rbx = instr.regBx - wordExcess - 1 # -1 for the following 'inc pc'
      inc pc, rbx
    of opcJmpBack:
      let rbx = instr.regBx - wordExcess - 1 # -1 for the following 'inc pc'
      inc pc, rbx
      handleJmpBack()
    of opcBranch:
      # we know the next instruction is a 'fjmp':
      let branch = c.constants[instr.regBx-wordExcess]
      var cond = false
      for j in 0..<branch.len - 1:
        if overlap(regs[ra].regToNode, branch[j]):
          cond = true
          break
      assert c.code[pc+1].opcode == opcFJmp
      inc pc
      # we skip this instruction so that the final 'inc(pc)' skips
      # the following jump
      if not cond:
        let instr2 = c.code[pc]
        let rbx = instr2.regBx - wordExcess - 1 # -1 for the following 'inc pc'
        inc pc, rbx
    of opcTry:
      let rbx = instr.regBx - wordExcess
      tos.pushSafePoint(pc + rbx)
      assert c.code[pc+rbx].opcode in {opcExcept, opcFinally}
    of opcExcept:
      # This opcode is never executed, it only holds information for the
      # exception handling routines.
      doAssert(false)
    of opcFinally:
      # Pop the last safepoint introduced by a opcTry. This opcode is only
      # executed _iff_ no exception was raised in the body of the `try`
      # statement hence the need to pop the safepoint here.
      doAssert(savedPC < 0)
      tos.popSafePoint()
    of opcFinallyEnd:
      # The control flow may not resume at the next instruction since we may be
      # raising an exception or performing a cleanup.
      if savedPC >= 0:
        pc = savedPC - 1
        savedPC = -1
        if tos != savedFrame:
          tos = savedFrame
          move(regs, tos.slots)
    of opcRaise:
      let raised =
        # Empty `raise` statement - reraise current exception
        if regs[ra].kind == rkNone:
          c.currentExceptionA
        else:
          regs[ra].node
      c.currentExceptionA = raised
      # Set the `name` field of the exception
      c.currentExceptionA[2].skipColon.strVal = c.currentExceptionA.typ.sym.name.s
      c.exceptionInstr = pc

      var frame = tos
      var jumpTo = findExceptionHandler(c, frame, raised)
      while jumpTo.why == ExceptionGotoUnhandled and not frame.next.isNil:
        frame = frame.next
        jumpTo = findExceptionHandler(c, frame, raised)

      case jumpTo.why:
      of ExceptionGotoHandler:
        # Jump to the handler, do nothing when the `finally` block ends.
        savedPC = -1
        pc = jumpTo.where - 1
        if tos != frame:
          tos = frame
          move(regs, tos.slots)
      of ExceptionGotoFinally:
        # Jump to the `finally` block first then re-jump here to continue the
        # traversal of the exception chain
        savedPC = pc
        savedFrame = tos
        pc = jumpTo.where - 1
        if tos != frame:
          tos = frame
          move(regs, tos.slots)
      of ExceptionGotoUnhandled:
        # Nobody handled this exception, error out.
        bailOut(c, tos)
    of opcNew:
      ensureKind(rkNode)
      let typ = c.types[instr.regBx - wordExcess]
      regs[ra].node = getNullValue(typ, c.debug[pc], c.config)
      regs[ra].node.flags.incl nfIsRef
    of opcNewSeq:
      let typ = c.types[instr.regBx - wordExcess]
      inc pc
      ensureKind(rkNode)
      let instr2 = c.code[pc]
      let count = regs[instr2.regA].intVal.int
      regs[ra].node = newNodeI(nkBracket, c.debug[pc])
      regs[ra].node.typ = typ
      newSeq(regs[ra].node.sons, count)
      for i in 0..<count:
        regs[ra].node[i] = getNullValue(typ[0], c.debug[pc], c.config)
    of opcNewStr:
      decodeB(rkNode)
      regs[ra].node = newNodeI(nkStrLit, c.debug[pc])
      regs[ra].node.strVal = newString(regs[rb].intVal.int)
    of opcLdImmInt:
      # dest = immediate value
      decodeBx(rkInt)
      regs[ra].intVal = rbx
    of opcLdNull:
      ensureKind(rkNode)
      let typ = c.types[instr.regBx - wordExcess]
      regs[ra].node = getNullValue(typ, c.debug[pc], c.config)
      # opcLdNull really is the gist of the VM's problems: should it load
      # a fresh null to  regs[ra].node  or to regs[ra].node[]? This really
      # depends on whether regs[ra] represents the variable itself or whether
      # it holds the indirection! Due to the way registers are re-used we cannot
      # say for sure here! --> The codegen has to deal with it
      # via 'genAsgnPatch'.
    of opcLdNullReg:
      let typ = c.types[instr.regBx - wordExcess]
      if typ.skipTypes(abstractInst+{tyRange}-{tyTypeDesc}).kind in {
          tyFloat..tyFloat128}:
        ensureKind(rkFloat)
        regs[ra].floatVal = 0.0
      else:
        ensureKind(rkInt)
        regs[ra].intVal = 0
    of opcLdConst:
      let rb = instr.regBx - wordExcess
      let cnst = c.constants[rb]
      if fitsRegister(cnst.typ):
        reset(regs[ra])
        putIntoReg(regs[ra], cnst)
      else:
        ensureKind(rkNode)
        regs[ra].node = cnst
    of opcAsgnConst:
      let rb = instr.regBx - wordExcess
      let cnst = c.constants[rb]
      if fitsRegister(cnst.typ):
        putIntoReg(regs[ra], cnst)
      else:
        ensureKind(rkNode)
        regs[ra].node = cnst.copyTree
    of opcLdGlobal:
      let rb = instr.regBx - wordExcess - 1
      ensureKind(rkNode)
      regs[ra].node = c.globals[rb]
    of opcLdGlobalDerefFFI:
      let rb = instr.regBx - wordExcess - 1
      let node = c.globals[rb]
      let typ = node.typ
      doAssert node.kind == nkIntLit, $(node.kind)
      if typ.kind == tyPtr:
        ensureKind(rkNode)
        # use nkPtrLit once this is added
        let node2 = newNodeIT(nkIntLit, c.debug[pc], typ)
        node2.intVal = cast[ptr int](node.intVal)[]
        node2.flags.incl nfIsPtr
        regs[ra].node = node2
      elif not derefPtrToReg(node.intVal, typ, regs[ra], isAssign = false):
        stackTrace(c, tos, pc, "opcLdDeref unsupported type: " & $(typeToString(typ), typ[0].kind))
    of opcLdGlobalAddrDerefFFI:
      let rb = instr.regBx - wordExcess - 1
      let node = c.globals[rb]
      let typ = node.typ
      var node2 = newNodeIT(nkIntLit, node.info, typ)
      node2.intVal = node.intVal
      node2.flags.incl nfIsPtr
      ensureKind(rkNode)
      regs[ra].node = node2
    of opcLdGlobalAddr:
      let rb = instr.regBx - wordExcess - 1
      ensureKind(rkNodeAddr)
      regs[ra].nodeAddr = addr(c.globals[rb])
    of opcRepr:
      decodeB(rkNode)
      createStr regs[ra]
      regs[ra].node.strVal = renderTree(regs[rb].regToNode, {renderNoComments, renderDocComments})
    of opcQuit:
      if c.mode in {emRepl, emStaticExpr, emStaticStmt}:
        message(c.config, c.debug[pc], hintQuitCalled)
        msgQuit(int8(toInt(getOrdValue(regs[ra].regToNode, onError = toInt128(1)))))
      else:
        return TFullReg(kind: rkNone)
    of opcInvalidField:
      stackTrace(c, tos, pc, errFieldXNotFound & regs[ra].node.strVal)
    of opcSetLenStr:
      decodeB(rkNode)
      #createStrKeepNode regs[ra]
      regs[ra].node.strVal.setLen(regs[rb].intVal.int)
    of opcOf:
      decodeBC(rkInt)
      let typ = c.types[regs[rc].intVal.int]
      regs[ra].intVal = ord(inheritanceDiff(regs[rb].node.typ, typ) <= 0)
    of opcIs:
      decodeBC(rkInt)
      let t1 = regs[rb].node.typ.skipTypes({tyTypeDesc})
      let t2 = c.types[regs[rc].intVal.int]
      # XXX: This should use the standard isOpImpl
      let match = if t2.kind == tyUserTypeClass: true
                  else: sameType(t1, t2)
      regs[ra].intVal = ord(match)
    of opcSetLenSeq:
      decodeB(rkNode)
      let newLen = regs[rb].intVal.int
      if regs[ra].node.isNil: stackTrace(c, tos, pc, errNilAccess)
      else: c.setLenSeq(regs[ra].node, newLen, c.debug[pc])
    of opcNarrowS:
      decodeB(rkInt)
      let min = -(1.BiggestInt shl (rb-1))
      let max = (1.BiggestInt shl (rb-1))-1
      if regs[ra].intVal < min or regs[ra].intVal > max:
        stackTrace(c, tos, pc, "unhandled exception: value out of range")
    of opcNarrowU:
      decodeB(rkInt)
      regs[ra].intVal = regs[ra].intVal and ((1'i64 shl rb)-1)
    of opcSignExtend:
      # like opcNarrowS, but no out of range possible
      decodeB(rkInt)
      let imm = 64 - rb
      regs[ra].intVal = ashr(regs[ra].intVal shl imm, imm)
    of opcIsNil:
      decodeB(rkInt)
      let node = regs[rb].node
      regs[ra].intVal = ord(
        # Note that `nfIsRef` + `nkNilLit` represents an allocated
        # reference with the value `nil`, so `isNil` should be false!
        (node.kind == nkNilLit and nfIsRef notin node.flags) or
        (not node.typ.isNil and node.typ.kind == tyProc and
          node.typ.callConv == ccClosure and node[0].kind == nkNilLit and
          node[1].kind == nkNilLit))
    of opcNBindSym:
      # cannot use this simple check
      # if dynamicBindSym notin c.config.features:

      # bindSym with static input
      decodeBx(rkNode)
      regs[ra].node = copyTree(c.constants[rbx])
      regs[ra].node.flags.incl nfIsRef
    of opcNDynBindSym:
      # experimental bindSym
      let
        rb = instr.regB
        rc = instr.regC
        idx = int(regs[rb+rc-1].intVal)
        callback = c.callbacks[idx].value
        args = VmArgs(ra: ra, rb: rb, rc: rc, slots: cast[ptr UncheckedArray[TFullReg]](addr regs[0]),
                currentException: c.currentExceptionA,
                currentLineInfo: c.debug[pc])
      callback(args)
      regs[ra].node.flags.incl nfIsRef
    of opcNChild:
      decodeBC(rkNode)
      let idx = regs[rc].intVal.int
      let src = regs[rb].node
      if src.kind in {nkEmpty..nkNilLit}:
        stackTrace(c, tos, pc, "cannot get child of node kind: n" & $src.kind)
      elif idx >=% src.len:
        stackTrace(c, tos, pc, formatErrorIndexBound(idx, src.len-1))
      else:
        regs[ra].node = src[idx]
    of opcNSetChild:
      decodeBC(rkNode)
      let idx = regs[rb].intVal.int
      var dest = regs[ra].node
      if nfSem in dest.flags and allowSemcheckedAstModification notin c.config.legacyFeatures:
        stackTrace(c, tos, pc, "typechecked nodes may not be modified")
      elif dest.kind in {nkEmpty..nkNilLit}:
        stackTrace(c, tos, pc, "cannot set child of node kind: n" & $dest.kind)
      elif idx >=% dest.len:
        stackTrace(c, tos, pc, formatErrorIndexBound(idx, dest.len-1))
      else:
        dest[idx] = regs[rc].node
    of opcNAdd:
      decodeBC(rkNode)
      var u = regs[rb].node
      if nfSem in u.flags and allowSemcheckedAstModification notin c.config.legacyFeatures:
        stackTrace(c, tos, pc, "typechecked nodes may not be modified")
      elif u.kind in {nkEmpty..nkNilLit}:
        stackTrace(c, tos, pc, "cannot add to node kind: n" & $u.kind)
      else:
        u.add(regs[rc].node)
      regs[ra].node = u
    of opcNAddMultiple:
      decodeBC(rkNode)
      let x = regs[rc].node
      var u = regs[rb].node
      if nfSem in u.flags and allowSemcheckedAstModification notin c.config.legacyFeatures:
        stackTrace(c, tos, pc, "typechecked nodes may not be modified")
      elif u.kind in {nkEmpty..nkNilLit}:
        stackTrace(c, tos, pc, "cannot add to node kind: n" & $u.kind)
      else:
        for i in 0..<x.len: u.add(x[i])
      regs[ra].node = u
    of opcNKind:
      decodeB(rkInt)
      regs[ra].intVal = ord(regs[rb].node.kind)
      c.comesFromHeuristic = regs[rb].node.info
    of opcNSymKind:
      decodeB(rkInt)
      let a = regs[rb].node
      if a.kind == nkSym:
        regs[ra].intVal = ord(a.sym.kind)
      else:
        stackTrace(c, tos, pc, "node is not a symbol")
      c.comesFromHeuristic = regs[rb].node.info
    of opcNIntVal:
      decodeB(rkInt)
      let a = regs[rb].node
      if a.kind in {nkCharLit..nkUInt64Lit}:
        regs[ra].intVal = a.intVal
      elif a.kind == nkSym and a.sym.kind == skEnumField:
        regs[ra].intVal = a.sym.position
      else:
        stackTrace(c, tos, pc, errFieldXNotFound & "intVal")
    of opcNFloatVal:
      decodeB(rkFloat)
      let a = regs[rb].node
      case a.kind
      of nkFloatLit..nkFloat64Lit: regs[ra].floatVal = a.floatVal
      else: stackTrace(c, tos, pc, errFieldXNotFound & "floatVal")
    of opcNSymbol:
      decodeB(rkNode)
      let a = regs[rb].node
      if a.kind == nkSym:
        regs[ra].node = copyNode(a)
      else:
        stackTrace(c, tos, pc, errFieldXNotFound & "symbol")
    of opcNIdent:
      decodeB(rkNode)
      let a = regs[rb].node
      if a.kind == nkIdent:
        regs[ra].node = copyNode(a)
      else:
        stackTrace(c, tos, pc, errFieldXNotFound & "ident")
    of opcNodeId:
      decodeB(rkInt)
      when defined(useNodeIds):
        regs[ra].intVal = regs[rb].node.id
      else:
        regs[ra].intVal = -1
    of opcNGetType:
      let rb = instr.regB
      let rc = instr.regC
      case rc
      of 0:
        # getType opcode:
        ensureKind(rkNode)
        if regs[rb].kind == rkNode and regs[rb].node.typ != nil:
          regs[ra].node = opMapTypeToAst(c.cache, regs[rb].node.typ, c.debug[pc])
        elif regs[rb].kind == rkNode and regs[rb].node.kind == nkSym and regs[rb].node.sym.typ != nil:
          regs[ra].node = opMapTypeToAst(c.cache, regs[rb].node.sym.typ, c.debug[pc])
        else:
          stackTrace(c, tos, pc, "node has no type")
      of 1:
        # typeKind opcode:
        ensureKind(rkInt)
        if regs[rb].kind == rkNode and regs[rb].node.typ != nil:
          regs[ra].intVal = ord(regs[rb].node.typ.kind)
        elif regs[rb].kind == rkNode and regs[rb].node.kind == nkSym and regs[rb].node.sym.typ != nil:
          regs[ra].intVal = ord(regs[rb].node.sym.typ.kind)
        #else:
        #  stackTrace(c, tos, pc, "node has no type")
      of 2:
        # getTypeInst opcode:
        ensureKind(rkNode)
        if regs[rb].kind == rkNode and regs[rb].node.typ != nil:
          regs[ra].node = opMapTypeInstToAst(c.cache, regs[rb].node.typ, c.debug[pc])
        elif regs[rb].kind == rkNode and regs[rb].node.kind == nkSym and regs[rb].node.sym.typ != nil:
          regs[ra].node = opMapTypeInstToAst(c.cache, regs[rb].node.sym.typ, c.debug[pc])
        else:
          stackTrace(c, tos, pc, "node has no type")
      else:
        # getTypeImpl opcode:
        ensureKind(rkNode)
        if regs[rb].kind == rkNode and regs[rb].node.typ != nil:
          regs[ra].node = opMapTypeImplToAst(c.cache, regs[rb].node.typ, c.debug[pc])
        elif regs[rb].kind == rkNode and regs[rb].node.kind == nkSym and regs[rb].node.sym.typ != nil:
          regs[ra].node = opMapTypeImplToAst(c.cache, regs[rb].node.sym.typ, c.debug[pc])
        else:
          stackTrace(c, tos, pc, "node has no type")
    of opcNGetSize:
      decodeBImm(rkInt)
      let n = regs[rb].node
      case imm
      of 0: # size
        if n.typ == nil:
          stackTrace(c, tos, pc, "node has no type")
        else:
          regs[ra].intVal = getSize(c.config, n.typ)
      of 1: # align
        if n.typ == nil:
          stackTrace(c, tos, pc, "node has no type")
        else:
          regs[ra].intVal = getAlign(c.config, n.typ)
      else: # offset
        if n.kind != nkSym:
          stackTrace(c, tos, pc, "node is not a symbol")
        elif n.sym.kind != skField:
          stackTrace(c, tos, pc, "symbol is not a field (nskField)")
        else:
          regs[ra].intVal = n.sym.offset
    of opcNStrVal:
      decodeB(rkNode)
      createStr regs[ra]
      let a = regs[rb].node
      case a.kind
      of nkStrLit..nkTripleStrLit:
        regs[ra].node.strVal = a.strVal
      of nkCommentStmt:
        regs[ra].node.strVal = a.comment
      of nkIdent:
        regs[ra].node.strVal = a.ident.s
      of nkSym:
        regs[ra].node.strVal = a.sym.name.s
      else:
        stackTrace(c, tos, pc, errFieldXNotFound & "strVal")
    of opcNSigHash:
      decodeB(rkNode)
      createStr regs[ra]
      if regs[rb].node.kind != nkSym:
        stackTrace(c, tos, pc, "node is not a symbol")
      else:
        regs[ra].node.strVal = $sigHash(regs[rb].node.sym)
    of opcSlurp:
      decodeB(rkNode)
      createStr regs[ra]
      regs[ra].node.strVal = opSlurp(regs[rb].node.strVal, c.debug[pc],
                                     c.module, c.config)
    of opcGorge:
      decodeBC(rkNode)
      inc pc
      let rd = c.code[pc].regA
      createStr regs[ra]
      if defined(nimsuggest) or c.config.cmd == cmdCheck:
        discard "don't run staticExec for 'nim suggest'"
        regs[ra].node.strVal = ""
      else:
        when defined(nimcore):
          regs[ra].node.strVal = opGorge(regs[rb].node.strVal,
                                        regs[rc].node.strVal, regs[rd].node.strVal,
                                        c.debug[pc], c.config)[0]
        else:
          regs[ra].node.strVal = ""
          globalError(c.config, c.debug[pc], "VM is not built with 'gorge' support")
    of opcNError, opcNWarning, opcNHint:
      decodeB(rkNode)
      let a = regs[ra].node
      let b = regs[rb].node
      let info = if b.kind == nkNilLit: c.debug[pc] else: b.info
      if instr.opcode == opcNError:
        stackTrace(c, tos, pc, a.strVal, info)
      elif instr.opcode == opcNWarning:
        message(c.config, info, warnUser, a.strVal)
      elif instr.opcode == opcNHint:
        message(c.config, info, hintUser, a.strVal)
    of opcParseExprToAst:
      decodeB(rkNode)
      # c.debug[pc].line.int - countLines(regs[rb].strVal) ?
      var error: string
      let ast = parseString(regs[rb].node.strVal, c.cache, c.config,
                            toFullPath(c.config, c.debug[pc]), c.debug[pc].line.int,
                            proc (conf: ConfigRef; info: TLineInfo; msg: TMsgKind; arg: string) {.nosinks.} =
                              if error.len == 0 and msg <= errMax:
                                error = formatMsg(conf, info, msg, arg))
      if error.len > 0:
        c.errorFlag = error
      elif ast.len != 1:
        c.errorFlag = formatMsg(c.config, c.debug[pc], errGenerated,
          "expected expression, but got multiple statements")
      else:
        regs[ra].node = ast[0]
    of opcParseStmtToAst:
      decodeB(rkNode)
      var error: string
      let ast = parseString(regs[rb].node.strVal, c.cache, c.config,
                            toFullPath(c.config, c.debug[pc]), c.debug[pc].line.int,
                            proc (conf: ConfigRef; info: TLineInfo; msg: TMsgKind; arg: string) {.nosinks.} =
                              if error.len == 0 and msg <= errMax:
                                error = formatMsg(conf, info, msg, arg))
      if error.len > 0:
        c.errorFlag = error
      else:
        regs[ra].node = ast
    of opcQueryErrorFlag:
      createStr regs[ra]
      regs[ra].node.strVal = c.errorFlag
      c.errorFlag.setLen 0
    of opcCallSite:
      ensureKind(rkNode)
      if c.callsite != nil: regs[ra].node = c.callsite
      else: stackTrace(c, tos, pc, errFieldXNotFound & "callsite")
    of opcNGetLineInfo:
      decodeBImm(rkNode)
      let n = regs[rb].node
      case imm
      of 0: # getFile
        regs[ra].node = newStrNode(nkStrLit, toFullPath(c.config, n.info))
      of 1: # getLine
        regs[ra].node = newIntNode(nkIntLit, n.info.line.int)
      of 2: # getColumn
        regs[ra].node = newIntNode(nkIntLit, n.info.col)
      else:
        internalAssert c.config, false
      regs[ra].node.info = n.info
      regs[ra].node.typ = n.typ
    of opcNSetLineInfo:
      decodeB(rkNode)
      regs[ra].node.info = regs[rb].node.info
    of opcEqIdent:
      decodeBC(rkInt)
      # aliases for shorter and easier to understand code below
      var aNode = regs[rb].node
      var bNode = regs[rc].node
      # Skipping both, `nkPostfix` and `nkAccQuoted` for both
      # arguments.  `nkPostfix` exists only to tag exported symbols
      # and therefor it can be safely skipped. Nim has no postfix
      # operator. `nkAccQuoted` is used to quote an identifier that
      # wouldn't be allowed to use in an unquoted context.
      if aNode.kind == nkPostfix:
        aNode = aNode[1]
      if aNode.kind == nkAccQuoted:
        aNode = aNode[0]
      if bNode.kind == nkPostfix:
        bNode = bNode[1]
      if bNode.kind == nkAccQuoted:
        bNode = bNode[0]
      # These vars are of type `cstring` to prevent unnecessary string copy.
      var aStrVal: cstring = nil
      var bStrVal: cstring = nil
      # extract strVal from argument ``a``
      case aNode.kind
      of nkStrLit..nkTripleStrLit:
        aStrVal = aNode.strVal.cstring
      of nkIdent:
        aStrVal = aNode.ident.s.cstring
      of nkSym:
        aStrVal = aNode.sym.name.s.cstring
      of nkOpenSymChoice, nkClosedSymChoice:
        aStrVal = aNode[0].sym.name.s.cstring
      else:
        discard
      # extract strVal from argument ``b``
      case bNode.kind
      of nkStrLit..nkTripleStrLit:
        bStrVal = bNode.strVal.cstring
      of nkIdent:
        bStrVal = bNode.ident.s.cstring
      of nkSym:
        bStrVal = bNode.sym.name.s.cstring
      of nkOpenSymChoice, nkClosedSymChoice:
        bStrVal = bNode[0].sym.name.s.cstring
      else:
        discard
      regs[ra].intVal =
        if aStrVal != nil and bStrVal != nil:
          ord(idents.cmpIgnoreStyle(aStrVal, bStrVal, high(int)) == 0)
        else:
          0

    of opcStrToIdent:
      decodeB(rkNode)
      if regs[rb].node.kind notin {nkStrLit..nkTripleStrLit}:
        stackTrace(c, tos, pc, errFieldXNotFound & "strVal")
      else:
        regs[ra].node = newNodeI(nkIdent, c.debug[pc])
        regs[ra].node.ident = getIdent(c.cache, regs[rb].node.strVal)
        regs[ra].node.flags.incl nfIsRef
    of opcSetType:
      let typ = c.types[instr.regBx - wordExcess]
      if regs[ra].kind != rkNode:
        let temp = regToNode(regs[ra])
        ensureKind(rkNode)
        regs[ra].node = temp
        regs[ra].node.info = c.debug[pc]
      regs[ra].node.typ = typ
    of opcConv:
      let rb = instr.regB
      inc pc
      let desttyp = c.types[c.code[pc].regBx - wordExcess]
      inc pc
      let srctyp = c.types[c.code[pc].regBx - wordExcess]

      if opConv(c, regs[ra], regs[rb], desttyp, srctyp):
        stackTrace(c, tos, pc,
          errIllegalConvFromXtoY % [
          typeToString(srctyp), typeToString(desttyp)])
    of opcCast:
      let rb = instr.regB
      inc pc
      let desttyp = c.types[c.code[pc].regBx - wordExcess]
      inc pc
      let srctyp = c.types[c.code[pc].regBx - wordExcess]

      when hasFFI:
        let dest = fficast(c.config, regs[rb].node, desttyp)
        # todo: check whether this is correct
        # asgnRef(regs[ra], dest)
        putIntoReg(regs[ra], dest)
      else:
        globalError(c.config, c.debug[pc], "cannot evaluate cast")
    of opcNSetIntVal:
      decodeB(rkNode)
      var dest = regs[ra].node
      if dest.kind in {nkCharLit..nkUInt64Lit} and
         regs[rb].kind in {rkInt}:
        dest.intVal = regs[rb].intVal
      elif dest.kind == nkSym and dest.sym.kind == skEnumField:
        stackTrace(c, tos, pc, "`intVal` cannot be changed for an enum symbol.")
      else:
        stackTrace(c, tos, pc, errFieldXNotFound & "intVal")
    of opcNSetFloatVal:
      decodeB(rkNode)
      var dest = regs[ra].node
      if dest.kind in {nkFloatLit..nkFloat64Lit} and
         regs[rb].kind in {rkFloat}:
        dest.floatVal = regs[rb].floatVal
      else:
        stackTrace(c, tos, pc, errFieldXNotFound & "floatVal")
    of opcNSetSymbol:
      decodeB(rkNode)
      var dest = regs[ra].node
      if dest.kind == nkSym and regs[rb].node.kind == nkSym:
        dest.sym = regs[rb].node.sym
      else:
        stackTrace(c, tos, pc, errFieldXNotFound & "symbol")
    of opcNSetIdent:
      decodeB(rkNode)
      var dest = regs[ra].node
      if dest.kind == nkIdent and regs[rb].node.kind == nkIdent:
        dest.ident = regs[rb].node.ident
      else:
        stackTrace(c, tos, pc, errFieldXNotFound & "ident")
    of opcNSetType:
      decodeB(rkNode)
      let b = regs[rb].node
      internalAssert c.config, b.kind == nkSym and b.sym.kind == skType
      internalAssert c.config, regs[ra].node != nil
      regs[ra].node.typ = b.sym.typ
    of opcNSetStrVal:
      decodeB(rkNode)
      var dest = regs[ra].node
      if dest.kind in {nkStrLit..nkTripleStrLit} and
         regs[rb].kind in {rkNode}:
        dest.strVal = regs[rb].node.strVal
      elif dest.kind == nkCommentStmt and regs[rb].kind in {rkNode}:
        dest.comment = regs[rb].node.strVal
      else:
        stackTrace(c, tos, pc, errFieldXNotFound & "strVal")
    of opcNNewNimNode:
      decodeBC(rkNode)
      var k = regs[rb].intVal
      if k < 0 or k > ord(high(TNodeKind)):
        internalError(c.config, c.debug[pc],
          "request to create a NimNode of invalid kind")
      let cc = regs[rc].node

      let x = newNodeI(TNodeKind(int(k)),
        if cc.kind != nkNilLit:
          cc.info
        elif c.comesFromHeuristic.line != 0'u16:
          c.comesFromHeuristic
        elif c.callsite != nil and c.callsite.safeLen > 1:
          c.callsite[1].info
        else:
          c.debug[pc])
      x.flags.incl nfIsRef
      # prevent crashes in the compiler resulting from wrong macros:
      if x.kind == nkIdent: x.ident = c.cache.emptyIdent
      regs[ra].node = x
    of opcNCopyNimNode:
      decodeB(rkNode)
      regs[ra].node = copyNode(regs[rb].node)
    of opcNCopyNimTree:
      decodeB(rkNode)
      regs[ra].node = copyTree(regs[rb].node)
    of opcNDel:
      decodeBC(rkNode)
      let bb = regs[rb].intVal.int
      for i in 0..<regs[rc].intVal.int:
        delSon(regs[ra].node, bb)
    of opcGenSym:
      decodeBC(rkNode)
      let k = regs[rb].intVal
      let name = if regs[rc].node.strVal.len == 0: ":tmp"
                 else: regs[rc].node.strVal
      if k < 0 or k > ord(high(TSymKind)):
        internalError(c.config, c.debug[pc], "request to create symbol of invalid kind")
      var sym = newSym(k.TSymKind, getIdent(c.cache, name), c.module.owner, c.debug[pc])
      incl(sym.flags, sfGenSym)
      regs[ra].node = newSymNode(sym)
      regs[ra].node.flags.incl nfIsRef
    of opcNccValue:
      decodeB(rkInt)
      let destKey = regs[rb].node.strVal
      regs[ra].intVal = getOrDefault(c.graph.cacheCounters, destKey)
    of opcNccInc:
      let g = c.graph
      declBC()
      let destKey = regs[rb].node.strVal
      let by = regs[rc].intVal
      let v = getOrDefault(g.cacheCounters, destKey)
      g.cacheCounters[destKey] = v+by
      recordInc(c, c.debug[pc], destKey, by)
    of opcNcsAdd:
      let g = c.graph
      declBC()
      let destKey = regs[rb].node.strVal
      let val = regs[rc].node
      if not contains(g.cacheSeqs, destKey):
        g.cacheSeqs[destKey] = newTree(nkStmtList, val)
      else:
        g.cacheSeqs[destKey].add val
      recordAdd(c, c.debug[pc], destKey, val)
    of opcNcsIncl:
      let g = c.graph
      declBC()
      let destKey = regs[rb].node.strVal
      let val = regs[rc].node
      if not contains(g.cacheSeqs, destKey):
        g.cacheSeqs[destKey] = newTree(nkStmtList, val)
      else:
        block search:
          for existing in g.cacheSeqs[destKey]:
            if exprStructuralEquivalent(existing, val, strictSymEquality=true):
              break search
          g.cacheSeqs[destKey].add val
      recordIncl(c, c.debug[pc], destKey, val)
    of opcNcsLen:
      let g = c.graph
      decodeB(rkInt)
      let destKey = regs[rb].node.strVal
      regs[ra].intVal =
        if contains(g.cacheSeqs, destKey): g.cacheSeqs[destKey].len else: 0
    of opcNcsAt:
      let g = c.graph
      decodeBC(rkNode)
      let idx = regs[rc].intVal
      let destKey = regs[rb].node.strVal
      if contains(g.cacheSeqs, destKey) and idx <% g.cacheSeqs[destKey].len:
        regs[ra].node = g.cacheSeqs[destKey][idx.int]
      else:
        stackTrace(c, tos, pc, formatErrorIndexBound(idx, g.cacheSeqs[destKey].len-1))
    of opcNctPut:
      let g = c.graph
      let destKey = regs[ra].node.strVal
      let key = regs[instr.regB].node.strVal
      let val = regs[instr.regC].node
      if not contains(g.cacheTables, destKey):
        g.cacheTables[destKey] = initBTree[string, PNode]()
      if not contains(g.cacheTables[destKey], key):
        g.cacheTables[destKey].add(key, val)
        recordPut(c, c.debug[pc], destKey, key, val)
      else:
        stackTrace(c, tos, pc, "key already exists: " & key)
    of opcNctLen:
      let g = c.graph
      decodeB(rkInt)
      let destKey = regs[rb].node.strVal
      regs[ra].intVal =
        if contains(g.cacheTables, destKey): g.cacheTables[destKey].len else: 0
    of opcNctGet:
      let g = c.graph
      decodeBC(rkNode)
      let destKey = regs[rb].node.strVal
      let key = regs[rc].node.strVal
      if contains(g.cacheTables, destKey):
        if contains(g.cacheTables[destKey], key):
          regs[ra].node = getOrDefault(g.cacheTables[destKey], key)
        else:
          stackTrace(c, tos, pc, "key does not exist: " & key)
      else:
        stackTrace(c, tos, pc, "key does not exist: " & destKey)
    of opcNctHasNext:
      let g = c.graph
      decodeBC(rkInt)
      let destKey = regs[rb].node.strVal
      regs[ra].intVal =
        if g.cacheTables.contains(destKey):
          ord(btrees.hasNext(g.cacheTables[destKey], regs[rc].intVal.int))
        else:
          0
    of opcNctNext:
      let g = c.graph
      decodeBC(rkNode)
      let destKey = regs[rb].node.strVal
      let index = regs[rc].intVal
      if contains(g.cacheTables, destKey):
        let (k, v, nextIndex) = btrees.next(g.cacheTables[destKey], index.int)
        regs[ra].node = newTree(nkTupleConstr, newStrNode(k, c.debug[pc]), v,
                                newIntNode(nkIntLit, nextIndex))
      else:
        stackTrace(c, tos, pc, "key does not exist: " & destKey)

    of opcTypeTrait:
      # XXX only supports 'name' for now; we can use regC to encode the
      # type trait operation
      decodeB(rkNode)
      var typ = regs[rb].node.typ
      internalAssert c.config, typ != nil
      while typ.kind == tyTypeDesc and typ.len > 0: typ = typ[0]
      createStr regs[ra]
      regs[ra].node.strVal = typ.typeToString(preferExported)
    of opcMarshalLoad:
      let ra = instr.regA
      let rb = instr.regB
      inc pc
      let typ = c.types[c.code[pc].regBx - wordExcess]
      putIntoReg(regs[ra], loadAny(regs[rb].node.strVal, typ, c.cache, c.config))
    of opcMarshalStore:
      decodeB(rkNode)
      inc pc
      let typ = c.types[c.code[pc].regBx - wordExcess]
      createStrKeepNode(regs[ra])
      when not defined(nimNoNilSeqs):
        if regs[ra].node.strVal.isNil: regs[ra].node.strVal = newStringOfCap(1000)
      storeAny(regs[ra].node.strVal, typ, regs[rb].regToNode, c.config)

    inc pc

proc execute(c: PCtx, start: int): PNode =
  var tos = PStackFrame(prc: nil, comesFrom: 0, next: nil)
  newSeq(tos.slots, c.prc.maxSlots)
  result = rawExecute(c, start, tos).regToNode

proc execProc*(c: PCtx; sym: PSym; args: openArray[PNode]): PNode =
  if sym.kind in routineKinds:
    if sym.typ.len-1 != args.len:
      localError(c.config, sym.info,
        "NimScript: expected $# arguments, but got $#" % [
        $(sym.typ.len-1), $args.len])
    else:
      let start = genProc(c, sym)

      var tos = PStackFrame(prc: sym, comesFrom: 0, next: nil)
      let maxSlots = sym.offset
      newSeq(tos.slots, maxSlots)

      # setup parameters:
      if not isEmptyType(sym.typ[0]) or sym.kind == skMacro:
        putIntoReg(tos.slots[0], getNullValue(sym.typ[0], sym.info, c.config))
      # XXX We could perform some type checking here.
      for i in 1..<sym.typ.len:
        putIntoReg(tos.slots[i], args[i-1])

      result = rawExecute(c, start, tos).regToNode
  else:
    localError(c.config, sym.info,
      "NimScript: attempt to call non-routine: " & sym.name.s)

proc evalStmt*(c: PCtx, n: PNode) =
  let n = transformExpr(c.graph, c.module, n)
  let start = genStmt(c, n)
  # execute new instructions; this redundant opcEof check saves us lots
  # of allocations in 'execute':
  if c.code[start].opcode != opcEof:
    discard execute(c, start)

proc evalExpr*(c: PCtx, n: PNode): PNode =
  let n = transformExpr(c.graph, c.module, n)
  let start = genExpr(c, n)
  assert c.code[start].opcode != opcEof
  result = execute(c, start)

proc getGlobalValue*(c: PCtx; s: PSym): PNode =
  internalAssert c.config, s.kind in {skLet, skVar} and sfGlobal in s.flags
  result = c.globals[s.position-1]

include vmops

proc setupGlobalCtx*(module: PSym; graph: ModuleGraph) =
  if graph.vm.isNil:
    graph.vm = newCtx(module, graph.cache, graph)
    registerAdditionalOps(PCtx graph.vm)
  else:
    refresh(PCtx graph.vm, module)

proc myOpen(graph: ModuleGraph; module: PSym): PPassContext {.nosinks.} =
  #var c = newEvalContext(module, emRepl)
  #c.features = {allowCast, allowInfiniteLoops}
  #pushStackFrame(c, newStackFrame())

  # XXX produce a new 'globals' environment here:
  setupGlobalCtx(module, graph)
  result = PCtx graph.vm

proc myProcess(c: PPassContext, n: PNode): PNode =
  let c = PCtx(c)
  # don't eval errornous code:
  if c.oldErrorCount == c.config.errorCounter:
    evalStmt(c, n)
    result = newNodeI(nkEmpty, n.info)
  else:
    result = n
  c.oldErrorCount = c.config.errorCounter

proc myClose(graph: ModuleGraph; c: PPassContext, n: PNode): PNode =
  myProcess(c, n)

const evalPass* = makePass(myOpen, myProcess, myClose)

proc evalConstExprAux(module: PSym;
                      g: ModuleGraph; prc: PSym, n: PNode,
                      mode: TEvalMode): PNode =
  if g.config.errorCounter > 0: return n
  let n = transformExpr(g, module, n)
  setupGlobalCtx(module, g)
  var c = PCtx g.vm
  let oldMode = c.mode
  c.mode = mode
  let start = genExpr(c, n, requiresValue = mode!=emStaticStmt)
  if c.code[start].opcode == opcEof: return newNodeI(nkEmpty, n.info)
  assert c.code[start].opcode != opcEof
  when debugEchoCode: c.echoCode start
  var tos = PStackFrame(prc: prc, comesFrom: 0, next: nil)
  newSeq(tos.slots, c.prc.maxSlots)
  #for i in 0..<c.prc.maxSlots: tos.slots[i] = newNode(nkEmpty)
  result = rawExecute(c, start, tos).regToNode
  if result.info.col < 0: result.info = n.info
  c.mode = oldMode

proc evalConstExpr*(module: PSym; g: ModuleGraph; e: PNode): PNode =
  result = evalConstExprAux(module, g, nil, e, emConst)

proc evalStaticExpr*(module: PSym; g: ModuleGraph; e: PNode, prc: PSym): PNode =
  result = evalConstExprAux(module, g, prc, e, emStaticExpr)

proc evalStaticStmt*(module: PSym; g: ModuleGraph; e: PNode, prc: PSym) =
  discard evalConstExprAux(module, g, prc, e, emStaticStmt)

proc setupCompileTimeVar*(module: PSym; g: ModuleGraph; n: PNode) =
  discard evalConstExprAux(module, g, nil, n, emStaticStmt)

proc prepareVMValue(arg: PNode): PNode =
  ## strip nkExprColonExpr from tuple values recurively. That is how
  ## they are expected to be stored in the VM.

  # Early abort without copy. No transformation takes place.
  if arg.kind in nkLiterals:
    return arg

  result = copyNode(arg)
  if arg.kind == nkTupleConstr:
    for child in arg:
      if child.kind == nkExprColonExpr:
        result.add prepareVMValue(child[1])
      else:
        result.add prepareVMValue(child)
  else:
    for child in arg:
      result.add prepareVMValue(child)

proc setupMacroParam(x: PNode, typ: PType): TFullReg =
  case typ.kind
  of tyStatic:
    putIntoReg(result, prepareVMValue(x))
  else:
    var n = x
    if n.kind in {nkHiddenSubConv, nkHiddenStdConv}: n = n[1]
    n = n.canonValue
    n.flags.incl nfIsRef
    n.typ = x.typ
    result = TFullReg(kind: rkNode, node: n)

iterator genericParamsInMacroCall*(macroSym: PSym, call: PNode): (PSym, PNode) =
  let gp = macroSym.ast[genericParamsPos]
  for i in 0..<gp.len:
    let genericParam = gp[i].sym
    let posInCall = macroSym.typ.len + i
    if posInCall < call.len:
      yield (genericParam, call[posInCall])

# to prevent endless recursion in macro instantiation
const evalMacroLimit = 1000

proc errorNode(owner: PSym, n: PNode): PNode =
  result = newNodeI(nkEmpty, n.info)
  result.typ = newType(tyError, owner)
  result.typ.flags.incl tfCheckedForDestructor

proc evalMacroCall*(module: PSym; g: ModuleGraph;
                    n, nOrig: PNode, sym: PSym): PNode =
  if g.config.errorCounter > 0: return errorNode(module, n)

  # XXX globalError() is ugly here, but I don't know a better solution for now
  inc(g.config.evalMacroCounter)
  if g.config.evalMacroCounter > evalMacroLimit:
    globalError(g.config, n.info, "macro instantiation too nested")

  # immediate macros can bypass any type and arity checking so we check the
  # arity here too:
  if sym.typ.len > n.safeLen and sym.typ.len > 1:
    globalError(g.config, n.info, "in call '$#' got $#, but expected $# argument(s)" % [
        n.renderTree, $(n.safeLen-1), $(sym.typ.len-1)])

  setupGlobalCtx(module, g)
  var c = PCtx g.vm
  let oldMode = c.mode
  c.mode = emStaticStmt
  c.comesFromHeuristic.line = 0'u16
  c.callsite = nOrig
  let start = genProc(c, sym)

  var tos = PStackFrame(prc: sym, comesFrom: 0, next: nil)
  let maxSlots = sym.offset
  newSeq(tos.slots, maxSlots)
  # setup arguments:
  var L = n.safeLen
  if L == 0: L = 1
  # This is wrong for tests/reject/tind1.nim where the passed 'else' part
  # doesn't end up in the parameter:
  #InternalAssert tos.slots.len >= L

  # return value:
  tos.slots[0] = TFullReg(kind: rkNode, node: newNodeI(nkEmpty, n.info))

  # setup parameters:
  for i in 1..<sym.typ.len:
    tos.slots[i] = setupMacroParam(n[i], sym.typ[i])

  let gp = sym.ast[genericParamsPos]
  for i in 0..<gp.len:
    let idx = sym.typ.len + i
    if idx < n.len:
      tos.slots[idx] = setupMacroParam(n[idx], gp[i].sym.typ)
    else:
      dec(g.config.evalMacroCounter)
      c.callsite = nil
      localError(c.config, n.info, "expected " & $gp.len &
                 " generic parameter(s)")
  # temporary storage:
  #for i in L..<maxSlots: tos.slots[i] = newNode(nkEmpty)
  result = rawExecute(c, start, tos).regToNode
  if result.info.line < 0: result.info = n.info
  if cyclicTree(result): globalError(c.config, n.info, "macro produced a cyclic tree")
  dec(g.config.evalMacroCounter)
  c.callsite = nil
  c.mode = oldMode