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.

const
  debugEchoCode = false
  traceCode = debugEchoCode

import ast except getstr

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

from semfold import leValueConv, ordinalValToString
from evaltempl import evalTemplate

from modulegraphs import ModuleGraph, PPassContext

when hasFFI:
  import evalffi

type
  TRegisterKind = enum
    rkNone, rkNode, rkInt, rkFloat, rkRegisterAddr, rkNodeAddr
  TFullReg = object   # with a custom mark proc, we could use the same
                      # data representation as LuaJit (tagged NaNs).
    case kind: TRegisterKind
    of rkNone: nil
    of rkInt: intVal: BiggestInt
    of rkFloat: floatVal: BiggestFloat
    of rkNode: node: PNode
    of rkRegisterAddr: regAddr: ptr TFullReg
    of rkNodeAddr: nodeAddr: ptr PNode

  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 the same format as in system/except.nim
    var s = substr(toFilename(c.config, info), 0)
    # this 'substr' prevents a strange corruption. XXX This needs to be
    # investigated eventually but first attempts to fix it broke everything
    # see the araq-wip-fixed-writebarrier branch.
    var line = toLinenumber(info)
    if line > 0:
      add(s, '(')
      add(s, $line)
      add(s, ')')
    if x.prc != nil:
      for k in 1..max(1, 25-s.len): add(s, ' ')
      add(s, x.prc.name.s)
    msgWriteln(c.config, s)

proc stackTrace(c: PCtx, tos: PStackFrame, pc: int,
                msg: string, lineInfo: TLineInfo) =
  msgWriteln(c.config, "stack trace: (most recent call last)")
  stackTraceAux(c, tos, pc)
  # XXX test if we want 'globalError' for every mode
  if c.mode == emRepl: globalError(c.config, lineInfo, msg)
  else: localError(c.config, lineInfo, msg)

proc stackTrace(c: PCtx, tos: PStackFrame, pc: int, msg: string) =
  stackTrace(c, tos, pc, msg, c.debug[pc])

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

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

proc myreset(n: var TFullReg) = reset(n)

template ensureKind(k: untyped) {.dirty.} =
  if regs[ra].kind != k:
    myreset(regs[ra])
    regs[ra].kind = 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 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
    system.reset(x.node[])
    x.node.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 defintions (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) =
  if x.kind != y.kind:
    myreset(x)
    x.kind = 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, sonsLen(src))
    for i in countup(0, sonsLen(src) - 1):
      result.sons[i] = copyValue(src.sons[i])

proc asgnComplex(x: var TFullReg, y: TFullReg) =
  if x.kind != y.kind:
    myreset(x)
    x.kind = 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 writeField(n: var PNode, x: TFullReg) =
  case x.kind
  of rkNone: discard
  of rkInt: 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.kind = rkNode
    createStr(dest)
    dest.node.strVal = n.strVal
  of nkCharLit..nkUInt64Lit:
    dest.kind = rkInt
    dest.intVal = n.intVal
  of nkFloatLit..nkFloat128Lit:
    dest.kind = rkFloat
    dest.floatVal = n.floatVal
  else:
    dest.kind = rkNode
    dest.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) =
  # XXX this needs a proper fix!
  if f.safePoints.len > 0:
    discard f.safePoints.pop()

proc cleanUpOnException(c: PCtx; tos: PStackFrame):
                                              tuple[pc: int, f: PStackFrame] =
  let raisedType = c.currentExceptionA.typ.skipTypes(abstractPtrs)
  var f = tos
  while true:
    while f.safePoints.len == 0:
      f = f.next
      if f.isNil: return (-1, nil)
    var pc2 = f.safePoints[f.safePoints.high]

    var nextExceptOrFinally = -1
    if c.code[pc2].opcode == opcExcept:
      nextExceptOrFinally = pc2 + c.code[pc2].regBx - wordExcess
      inc pc2
    while c.code[pc2].opcode == opcExcept:
      let excIndex = c.code[pc2].regBx-wordExcess
      let exceptType = if excIndex > 0: c.types[excIndex].skipTypes(
                          abstractPtrs)
                       else: nil
      #echo typeToString(exceptType), " ", typeToString(raisedType)
      if exceptType.isNil or inheritanceDiff(raisedType, exceptType) <= 0:
        # mark exception as handled but keep it in B for
        # the getCurrentException() builtin:
        c.currentExceptionB = c.currentExceptionA
        c.currentExceptionA = nil
        # execute the corresponding handler:
        while c.code[pc2].opcode == opcExcept: inc pc2
        discard f.safePoints.pop
        return (pc2, f)
      inc pc2
      if c.code[pc2].opcode != opcExcept and nextExceptOrFinally >= 0:
        # we're at the end of the *except list*, but maybe there is another
        # *except branch*?
        pc2 = nextExceptOrFinally+1
        if c.code[pc2].opcode == opcExcept:
          nextExceptOrFinally = pc2 + c.code[pc2].regBx - wordExcess

    if nextExceptOrFinally >= 0:
      pc2 = nextExceptOrFinally
    if c.code[pc2].opcode == opcFinally:
      # execute the corresponding handler, but don't quit walking the stack:
      discard f.safePoints.pop
      return (pc2+1, f)
    # not the right one:
    discard f.safePoints.pop

proc cleanUpOnReturn(c: PCtx; f: PStackFrame): int =
  for s in f.safePoints:
    var pc = s
    while c.code[pc].opcode == opcExcept:
      pc = pc + c.code[pc].regBx - wordExcess
    if c.code[pc].opcode == opcFinally:
      return pc
  return -1

proc opConv(c: PCtx; dest: var TFullReg, src: TFullReg, desttyp, srctyp: PType): bool =
  if desttyp.kind == tyString:
    if dest.kind != rkNode:
      myreset(dest)
      dest.kind = 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.sons[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.sons[i].kind != nkSym: internalError(c.config, "opConv for enum")
          let f = n.sons[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, abstractRange).kind
    of tyInt..tyInt64:
      if dest.kind != rkInt:
        myreset(dest); dest.kind = rkInt
      case skipTypes(srctyp, abstractRange).kind
      of tyFloat..tyFloat64:
        dest.intVal = int(src.floatVal)
      else:
        dest.intVal = src.intVal
      if dest.intVal < firstOrd(c.config, desttyp) or dest.intVal > lastOrd(c.config, desttyp):
        return true
    of tyUInt..tyUInt64:
      if dest.kind != rkInt:
        myreset(dest); dest.kind = 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
        when system.cpuEndian == bigEndian:
          dest.intVal = (src.intVal shr srcDist) shl srcDist
          dest.intVal = (dest.intVal shr destDist) shl destDist
        else:
          dest.intVal = (src.intVal shl srcDist) shr srcDist
          dest.intVal = (dest.intVal shl destDist) shr destDist
    of tyFloat..tyFloat64:
      if dest.kind != rkFloat:
        myreset(dest); dest.kind = rkFloat
      case skipTypes(srctyp, abstractRange).kind
      of tyInt..tyInt64, tyUInt..tyUInt64, tyEnum, tyBool, tyChar:
        dest.floatVal = toBiggestFloat(src.intVal)
      else:
        dest.floatVal = src.floatVal
    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 = MaxLoopIterations
    else:
      msgWriteln(c.config, "stack trace: (most recent call last)")
      stackTraceAux(c, tos, pc)
      globalError(c.config, c.debug[pc], errTooManyIterations)
  dec(c.loopIterations)

proc recSetFlagIsRef(arg: PNode) =
  arg.flags.incl(nfIsRef)
  for i in 0 ..< arg.safeLen:
    arg.sons[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.sons[i] = getNullValue(typ.sons[0], info, c.config)

const
  errIndexOutOfBounds = "index out of bounds"
  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 edit " &
    "compiler/vmdef.MaxLoopIterations and rebuild the compiler"
  errFieldXNotFound = "node lacks field: "

proc rawExecute(c: PCtx, start: int, tos: PStackFrame): TFullReg =
  var pc = start
  var tos = tos
  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
    #if c.traceActive:
    when traceCode:
      echo "PC ", pc, " ", c.code[pc].opcode, " ra ", ra, " rb ", instr.regB, " rc ", instr.regC
      # message(c.config, c.debug[pc], warnUser, "Trace")

    case instr.opcode
    of opcEof: return regs[ra]
    of opcRet:
      # XXX perform any cleanup actions
      pc = tos.comesFrom
      tos = tos.next
      let retVal = regs[0]
      if tos.isNil:
        #echo "RET ", retVal.rendertree
        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
        #echo "RET2 ", retVal.rendertree, " ", c.code[pc].regA
    of opcYldYoid: assert false
    of opcYldVal: assert false
    of opcAsgnInt:
      decodeB(rkInt)
      regs[ra].intVal = regs[rb].intVal
    of opcAsgnStr:
      decodeBC(rkNode)
      createStrKeepNode regs[ra], rc != 0
      regs[ra].node.strVal = regs[rb].node.strVal
    of opcAsgnFloat:
      decodeB(rkFloat)
      regs[ra].floatVal = regs[rb].floatVal
    of opcAsgnIntFromFloat32:
      let rb = instr.regB
      ensureKind(rkInt)
      regs[ra].intVal = cast[int32](float32(regs[rb].floatVal))
    of opcAsgnIntFromFloat64:
      let rb = instr.regB
      ensureKind(rkInt)
      regs[ra].intVal = cast[int64](regs[rb].floatVal)
    of opcAsgnFloat32FromInt:
      let rb = instr.regB
      ensureKind(rkFloat)
      regs[ra].floatVal = cast[float32](int32(regs[rb].intVal))
    of opcAsgnFloat64FromInt:
      let rb = instr.regB
      ensureKind(rkFloat)
      regs[ra].floatVal = cast[float64](int64(regs[rb].intVal))
    of opcAsgnComplex:
      asgnComplex(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, errIndexOutOfBounds)
      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, errIndexOutOfBounds)
      elif src.kind notin {nkEmpty..nkFloat128Lit} and idx <% src.len:
        regs[ra].node = src.sons[idx]
      else:
        stackTrace(c, tos, pc, errIndexOutOfBounds)
    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
      elif idx == s.len and optLaxStrings in c.config.options:
        regs[ra].intVal = 0
      else:
        stackTrace(c, tos, pc, errIndexOutOfBounds)
    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, errIndexOutOfBounds)
      elif idx <% arr.len:
        writeField(arr.sons[idx], regs[rc])
      else:
        stackTrace(c, tos, pc, errIndexOutOfBounds)
    of opcLdObj:
      # a = b.c
      decodeBC(rkNode)
      let src = regs[rb].node
      case src.kind
      of nkEmpty..nkNilLit:
        stackTrace(c, tos, pc, errNilAccess)
      of nkObjConstr:
        let n = src.sons[rc + 1].skipColon
        regs[ra].node = n
      else:
        let n = src.sons[rc]
        regs[ra].node = n
    of opcWrObj:
      # a.b = c
      decodeBC(rkNode)
      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.sons[shiftedRb].kind == nkExprColonExpr:
        writeField(dest.sons[shiftedRb].sons[1], regs[rc])
      else:
        writeField(dest.sons[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, errIndexOutOfBounds)
    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 == nkNilLit:
          stackTrace(c, tos, pc, errNilAccess)
        if regs[rb].node.kind == nkRefTy:
          regs[ra].node = regs[rb].node.sons[0]
        else:
          ensureKind(rkNode)
          regs[ra].node = regs[rb].node
      else:
        stackTrace(c, tos, pc, errNilAccess)
    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:
        if regs[ra].node.kind == nkNilLit:
          stackTrace(c, tos, pc, errNilAccess)
        assert nfIsRef in regs[ra].node.flags
        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):
        addSon(regs[ra].node, copyTree(b))
    of opcInclRange:
      decodeBC(rkNode)
      var r = newNode(nkRange)
      r.add regs[rb].regToNode
      r.add regs[rc].regToNode
      addSon(regs[ra].node, r.copyTree)
    of opcExcl:
      decodeB(rkNode)
      var b = newNodeIT(nkCurly, regs[ra].node.info, regs[ra].node.typ)
      addSon(b, regs[rb].regToNode)
      var r = diffSets(c.config, regs[ra].node, b)
      discardSons(regs[ra].node)
      for i in countup(0, sonsLen(r) - 1): addSon(regs[ra].node, r.sons[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)
      regs[ra].intVal = regs[rb].intVal shr regs[rc].intVal
    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:
      decodeBC(rkInt)
      if regs[rb].kind == rkNodeAddr:
        if regs[rc].kind == rkNodeAddr:
          regs[ra].intVal = ord(regs[rb].nodeAddr == regs[rc].nodeAddr)
        else:
          assert regs[rc].kind == rkNode
          # we know these cannot be equal
          regs[ra].intVal = ord(false)
      elif regs[rc].kind == rkNodeAddr:
        assert regs[rb].kind == rkNode
        # we know these cannot be equal
        regs[ra].intVal = ord(false)
      else:
        regs[ra].intVal = ord((regs[rb].node.kind == nkNilLit and
                              regs[rc].node.kind == nkNilLit) or
                              regs[rb].node == regs[rc].node)
    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 opcSymdiffSet:
      decodeBC(rkNode)
      createSet(regs[ra])
      move(regs[ra].node.sons,
           nimsets.symdiffSets(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)
      #createStrKeepNode regs[ra]
      regs[ra].node.strVal.add(regs[rb].intVal.chr)
    of opcAddStrStr:
      decodeB(rkNode)
      #createStrKeepNode regs[ra]
      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)
      let a = regs[rb].node
      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)
                          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:
        myreset(regs[rc])
        regs[rc].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.sons[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[pointer](regs),
                 currentException: c.currentExceptionB,
                 currentLineInfo: c.debug[pc]))
      elif sfImportc in prc.flags:
        if allowFFI notin c.features:
          globalError(c.config, c.debug[pc], "VM not allowed to do FFI")
        # we pass 'tos.slots' instead of 'regs' so that the compiler can keep
        # 'regs' in a register:
        when hasFFI:
          let prcValue = c.globals.sons[prc.position-1]
          if prcValue.kind == nkEmpty:
            globalError(c.config, c.debug[pc], "cannot run " & prc.name.s)
          let newValue = callForeignFunction(prcValue, prc.typ, tos.slots,
                                             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.sons[0]) or prc.kind == skMacro:
          putIntoReg(newFrame.slots[0], getNullValue(prc.typ.sons[0], prc.info, c.config))
        for i in 1 .. rc-1:
          newFrame.slots[i] = regs[rb+i]
        if isClosure:
          newFrame.slots[rc].kind = rkNode
          newFrame.slots[rc].node = regs[rb].node.sons[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)
        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 countup(0, sonsLen(branch) - 2):
        if overlap(regs[ra].regToNode, branch.sons[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:
      # just skip it; it's followed by a jump;
      # we'll execute in the 'raise' handler
      let rbx = instr.regBx - wordExcess - 1 # -1 for the following 'inc pc'
      inc pc, rbx
      while c.code[pc+1].opcode == opcExcept:
        let rbx = c.code[pc+1].regBx - wordExcess - 1
        inc pc, rbx
      #assert c.code[pc+1].opcode in {opcExcept, opcFinally}
      if c.code[pc+1].opcode != opcFinally:
        # in an except handler there is no active safe point for the 'try':
        tos.popSafePoint()
    of opcFinally:
      # just skip it; it's followed by the code we need to execute anyway
      tos.popSafePoint()
    of opcFinallyEnd:
      if c.currentExceptionA != nil:
        # we are in a cleanup run:
        let (newPc, newTos) = cleanUpOnException(c, tos)
        if newPc-1 < 0:
          bailOut(c, tos)
          return
        pc = newPc-1
        if tos != newTos:
          tos = newTos
          move(regs, tos.slots)
    of opcRaise:
      let raised = regs[ra].node
      c.currentExceptionA = raised
      c.exceptionInstr = pc
      let (newPc, newTos) = cleanUpOnException(c, tos)
      # -1 because of the following 'inc'
      if newPc-1 < 0:
        bailOut(c, tos)
        return
      pc = newPc-1
      if tos != newTos:
        tos = newTos
        move(regs, tos.slots)
    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.sons[i] = getNullValue(typ.sons[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 wether
      # 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.sons[rb]
      if fitsRegister(cnst.typ):
        myreset(regs[ra])
        putIntoReg(regs[ra], cnst)
      else:
        ensureKind(rkNode)
        regs[ra].node = cnst
    of opcAsgnConst:
      let rb = instr.regBx - wordExcess
      let cnst = c.constants.sons[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.sons[rb]
    of opcLdGlobalAddr:
      let rb = instr.regBx - wordExcess - 1
      ensureKind(rkNodeAddr)
      regs[ra].nodeAddr = addr(c.globals.sons[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(getOrdValue(regs[ra].regToNode)))
      else:
        return TFullReg(kind: rkNone)
    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 opcReset:
      internalError(c.config, c.debug[pc], "too implement")
    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 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.sons[0].kind == nkNilLit and
          node.sons[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.sons[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[pointer](regs),
                currentException: c.currentExceptionB,
                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 notin {nkEmpty..nkNilLit} and idx <% src.len:
        regs[ra].node = src.sons[idx]
      else:
        stackTrace(c, tos, pc, errIndexOutOfBounds)
    of opcNSetChild:
      decodeBC(rkNode)
      let idx = regs[rb].intVal.int
      var dest = regs[ra].node
      if dest.kind notin {nkEmpty..nkNilLit} and idx <% dest.len:
        dest.sons[idx] = regs[rc].node
      else:
        stackTrace(c, tos, pc, errIndexOutOfBounds)
    of opcNAdd:
      decodeBC(rkNode)
      var u = regs[rb].node
      if u.kind notin {nkEmpty..nkNilLit}:
        u.add(regs[rc].node)
      else:
        stackTrace(c, tos, pc, "cannot add to node kind: " & $u.kind)
      regs[ra].node = u
    of opcNAddMultiple:
      decodeBC(rkNode)
      let x = regs[rc].node
      var u = regs[rb].node
      if u.kind notin {nkEmpty..nkNilLit}:
        # XXX can be optimized:
        for i in 0..<x.len: u.add(x.sons[i])
      else:
        stackTrace(c, tos, pc, "cannot add to node kind: " & $u.kind)
      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
      case a.kind
      of nkCharLit..nkUInt64Lit: regs[ra].intVal = a.intVal
      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 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 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 opcSlurp:
      decodeB(rkNode)
      createStr regs[ra]
      regs[ra].node.strVal = opSlurp(regs[rb].node.strVal, c.debug[pc],
                                     c.module, c.config)
    of opcGorge:
      when defined(nimcore):
        decodeBC(rkNode)
        inc pc
        let rd = c.code[pc].regA

        createStr regs[ra]
        regs[ra].node.strVal = opGorge(regs[rb].node.strVal,
                                      regs[rc].node.strVal, regs[rd].node.strVal,
                                      c.debug[pc], c.config)[0]
      else:
        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) =
                              if error.len == 0 and msg <= errMax:
                                error = formatMsg(conf, info, msg, arg))
      if error.len > 0:
        c.errorFlag = error
      elif sonsLen(ast) != 1:
        c.errorFlag = formatMsg(c.config, c.debug[pc], errGenerated,
          "expected expression, but got multiple statements")
      else:
        regs[ra].node = ast.sons[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) =
                              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
      let aNode = regs[rb].node
      let bNode = regs[rc].node
      # these are cstring to prevent string copy, and cmpIgnoreStyle from
      # takes cstring arguments
      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
      # set result
      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:
      if regs[ra].kind != rkNode:
        internalError(c.config, c.debug[pc], "cannot set type")
      regs[ra].node.typ = c.types[instr.regBx - wordExcess]
    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(regs[rb], desttyp)
        asgnRef(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
      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 countup(0, regs[rc].intVal.int-1):
        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
      let destKey = regs[ra].node.strVal
      let by = regs[instr.regB].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
      let destKey = regs[ra].node.strVal
      let val = regs[instr.regB].node
      if not contains(g.cacheSeqs, destKey):
        g.cacheSeqs[destKey] = newTree(nkStmtList, val)
        # newNodeI(nkStmtList, c.debug[pc])
      else:
        g.cacheSeqs[destKey].add val
      recordAdd(c, c.debug[pc], destKey, val)
    of opcNcsIncl:
      let g = c.graph
      let destKey = regs[ra].node.strVal
      let val = regs[instr.regB].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, errIndexOutOfBounds)
    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.sons[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)
    of opcToNarrowInt:
      decodeBC(rkInt)
      let mask = (1'i64 shl rc) - 1 # 0xFF
      let signbit = 1'i64 shl (rc - 1) # 0x80
      let toggle = mask - signbit # 0x7F
      # algorithm: -((i8 and 0xFF) xor 0x7F) + 0x7F
      # mask off higher bits.
      # uses two's complement to sign-extend integer.
      # reajust integer into desired range.
      regs[ra].intVal = -((regs[rb].intVal and mask) xor toggle) + toggle

    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.sons[0]) or sym.kind == skMacro:
        putIntoReg(tos.slots[0], getNullValue(sym.typ.sons[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, noDestructors = true)
  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, noDestructors = true)
  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.sons[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 =
  #var c = newEvalContext(module, emRepl)
  #c.features = {allowCast, allowFFI, allowInfiniteLoops}
  #pushStackFrame(c, newStackFrame())

  # XXX produce a new 'globals' environment here:
  setupGlobalCtx(module, graph)
  result = PCtx graph.vm
  when hasFFI:
    PCtx(graph.vm).features = {allowFFI, allowCast}

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 =
  let n = transformExpr(g, module, n, noDestructors = true)
  setupGlobalCtx(module, g)
  var c = PCtx g.vm
  let oldMode = c.mode
  defer: c.mode = oldMode
  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

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 setupMacroParam(x: PNode, typ: PType): TFullReg =
  case typ.kind
  of tyStatic:
    putIntoReg(result, x)
  of tyTypeDesc:
    putIntoReg(result, x)
  else:
    result.kind = rkNode
    var n = x
    if n.kind in {nkHiddenSubConv, nkHiddenStdConv}: n = n.sons[1]
    n = n.canonValue
    n.flags.incl nfIsRef
    n.typ = x.typ
    result.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
    yield (genericParam, call[posInCall])

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

proc evalMacroCall*(module: PSym; g: ModuleGraph;
                    n, nOrig: PNode, sym: PSym): PNode =
  # 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
  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].kind = rkNode
  tos.slots[0].node = newNodeI(nkEmpty, n.info)

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

  let gp = sym.ast[genericParamsPos]
  for i in 0 ..< gp.len:
    if sfImmediate notin sym.flags:
      let idx = sym.typ.len + i
      if idx < n.len:
        tos.slots[idx] = setupMacroParam(n.sons[idx], gp[i].sym.typ)
      else:
        dec(g.config.evalMacroCounter)
        c.callsite = nil
        localError(c.config, n.info, "expected " & $gp.len &
                   " generic parameter(s)")
    elif gp[i].sym.typ.kind in {tyStatic, tyTypeDesc}:
      dec(g.config.evalMacroCounter)
      c.callsite = nil
      globalError(c.config, n.info, "static[T] or typedesc nor supported for .immediate macros")
  # 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