Nim/compiler/ccgcalls.nim

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

proc canRaiseDisp(p: BProc; n: PNode): bool =
  # we assume things like sysFatal cannot raise themselves
  if n.kind == nkSym and {sfNeverRaises, sfImportc, sfCompilerProc} * n.sym.flags != {}:
    result = false
  elif optPanics in p.config.globalOptions or
      (n.kind == nkSym and sfSystemModule in getModule(n.sym).flags and
       sfSystemRaisesDefect notin n.sym.flags):
    # we know we can be strict:
    result = canRaise(n)
  else:
    # we have to be *very* conservative:
    result = canRaiseConservative(n)

proc preventNrvo(p: BProc; dest, le, ri: PNode): bool =
  proc locationEscapes(p: BProc; le: PNode; inTryStmt: bool): bool =
    var n = le
    while true:
      # do NOT follow nkHiddenDeref here!
      case n.kind
      of nkSym:
        # we don't own the location so it escapes:
        if n.sym.owner != p.prc:
          return true
        elif inTryStmt and sfUsedInFinallyOrExcept in n.sym.flags:
          # it is also an observable store if the location is used
          # in 'except' or 'finally'
          return true
        return false
      of nkDotExpr, nkBracketExpr, nkObjUpConv, nkObjDownConv,
          nkCheckedFieldExpr:
        n = n[0]
      of nkHiddenStdConv, nkHiddenSubConv, nkConv:
        n = n[1]
      else:
        # cannot analyse the location; assume the worst
        return true

  if le != nil:
    for i in 1..<ri.len:
      let r = ri[i]
      if isPartOf(le, r) != arNo: return true
    # we use the weaker 'canRaise' here in order to prevent too many
    # annoying warnings, see #14514
    if canRaise(ri[0]) and
        locationEscapes(p, le, p.nestedTryStmts.len > 0):
      message(p.config, le.info, warnObservableStores, $le)
  # bug #19613 prevent dangerous aliasing too:
  if dest != nil and dest != le:
    for i in 1..<ri.len:
      let r = ri[i]
      if isPartOf(dest, r) != arNo: return true

proc hasNoInit(call: PNode): bool {.inline.} =
  result = call[0].kind == nkSym and sfNoInit in call[0].sym.flags

proc isHarmlessStore(p: BProc; canRaise: bool; d: TLoc): bool =
  if d.k in {locTemp, locNone} or not canRaise:
    result = true
  elif d.k == locLocalVar and p.withinTryWithExcept == 0:
    # we cannot observe a store to a local variable if the current proc
    # has no error handler:
    result = true
  else:
    result = false

proc fixupCall(p: BProc, le, ri: PNode, d: var TLoc,
               callee, params: Rope) =
  let canRaise = p.config.exc == excGoto and canRaiseDisp(p, ri[0])
  genLineDir(p, ri)
  var pl = callee & "(" & params
  # getUniqueType() is too expensive here:
  var typ = skipTypes(ri[0].typ, abstractInst)
  if typ[0] != nil:
    if isInvalidReturnType(p.config, typ):
      if params.len != 0: pl.add(", ")
      # beware of 'result = p(result)'. We may need to allocate a temporary:
      if d.k in {locTemp, locNone} or not preventNrvo(p, d.lode, le, ri):
        # Great, we can use 'd':
        if d.k == locNone: getTemp(p, typ[0], d, needsInit=true)
        elif d.k notin {locTemp} and not hasNoInit(ri):
          # reset before pass as 'result' var:
          discard "resetLoc(p, d)"
        pl.add(addrLoc(p.config, d))
        pl.add(");\n")
        line(p, cpsStmts, pl)
      else:
        var tmp: TLoc
        getTemp(p, typ[0], tmp, needsInit=true)
        pl.add(addrLoc(p.config, tmp))
        pl.add(");\n")
        line(p, cpsStmts, pl)
        genAssignment(p, d, tmp, {}) # no need for deep copying
      if canRaise: raiseExit(p)
    else:
      pl.add(")")
      if p.module.compileToCpp:
        if lfSingleUse in d.flags:
          # do not generate spurious temporaries for C++! For C we're better off
          # with them to prevent undefined behaviour and because the codegen
          # is free to emit expressions multiple times!
          d.k = locCall
          d.r = pl
          excl d.flags, lfSingleUse
        else:
          if d.k == locNone and p.splitDecls == 0:
            getTempCpp(p, typ[0], d, pl)
          else:
            if d.k == locNone: getTemp(p, typ[0], d)
            var list: TLoc
            initLoc(list, locCall, d.lode, OnUnknown)
            list.r = pl
            genAssignment(p, d, list, {}) # no need for deep copying
            if canRaise: raiseExit(p)

      elif isHarmlessStore(p, canRaise, d):
        if d.k == locNone: getTemp(p, typ[0], d)
        assert(d.t != nil)        # generate an assignment to d:
        var list: TLoc
        initLoc(list, locCall, d.lode, OnUnknown)
        list.r = pl
        genAssignment(p, d, list, {}) # no need for deep copying
        if canRaise: raiseExit(p)
      else:
        var tmp: TLoc
        getTemp(p, typ[0], tmp, needsInit=true)
        var list: TLoc
        initLoc(list, locCall, d.lode, OnUnknown)
        list.r = pl
        genAssignment(p, tmp, list, {}) # no need for deep copying
        if canRaise: raiseExit(p)
        genAssignment(p, d, tmp, {})
  else:
    pl.add(");\n")
    line(p, cpsStmts, pl)
    if canRaise: raiseExit(p)

proc genBoundsCheck(p: BProc; arr, a, b: TLoc)

proc reifiedOpenArray(n: PNode): bool {.inline.} =
  var x = n
  while x.kind in {nkAddr, nkHiddenAddr, nkHiddenStdConv, nkHiddenDeref}:
    x = x[0]
  if x.kind == nkSym and x.sym.kind == skParam:
    result = false
  else:
    result = true

proc genOpenArraySlice(p: BProc; q: PNode; formalType, destType: PType; prepareForMutation = false): (Rope, Rope) =
  var a, b, c: TLoc
  initLocExpr(p, q[1], a)
  initLocExpr(p, q[2], b)
  initLocExpr(p, q[3], c)
  # but first produce the required index checks:
  if optBoundsCheck in p.options:
    genBoundsCheck(p, a, b, c)
  if prepareForMutation:
    linefmt(p, cpsStmts, "#nimPrepareStrMutationV2($1);$n", [byRefLoc(p, a)])
  let ty = skipTypes(a.t, abstractVar+{tyPtr})
  let dest = getTypeDesc(p.module, destType)
  let lengthExpr = "($1)-($2)+1" % [rdLoc(c), rdLoc(b)]
  case ty.kind
  of tyArray:
    let first = toInt64(firstOrd(p.config, ty))
    if first == 0:
      result = ("($3*)(($1)+($2))" % [rdLoc(a), rdLoc(b), dest],
                lengthExpr)
    else:
      var lit = newRopeAppender()
      intLiteral(first, lit)
      result = ("($4*)($1)+(($2)-($3))" %
        [rdLoc(a), rdLoc(b), lit, dest],
        lengthExpr)
  of tyOpenArray, tyVarargs:
    if reifiedOpenArray(q[1]):
      result = ("($3*)($1.Field0)+($2)" % [rdLoc(a), rdLoc(b), dest],
                lengthExpr)
    else:
      result = ("($3*)($1)+($2)" % [rdLoc(a), rdLoc(b), dest],
                lengthExpr)
  of tyUncheckedArray, tyCstring:
    result = ("($3*)($1)+($2)" % [rdLoc(a), rdLoc(b), dest],
              lengthExpr)
  of tyString, tySequence:
    let atyp = skipTypes(a.t, abstractInst)
    if formalType.skipTypes(abstractInst).kind in {tyVar} and atyp.kind == tyString and
        optSeqDestructors in p.config.globalOptions:
      linefmt(p, cpsStmts, "#nimPrepareStrMutationV2($1);$n", [byRefLoc(p, a)])
    if atyp.kind in {tyVar} and not compileToCpp(p.module):
      result = ("(($5) ? (($4*)(*$1)$3+($2)) : NIM_NIL)" %
                  [rdLoc(a), rdLoc(b), dataField(p), dest, dataFieldAccessor(p, "*" & rdLoc(a))],
                lengthExpr)
    else:
      result = ("(($5) ? (($4*)$1$3+($2)) : NIM_NIL)" %
                  [rdLoc(a), rdLoc(b), dataField(p), dest, dataFieldAccessor(p, rdLoc(a))],
                lengthExpr)
  else:
    internalError(p.config, "openArrayLoc: " & typeToString(a.t))

proc openArrayLoc(p: BProc, formalType: PType, n: PNode; result: var Rope) =
  var q = skipConv(n)
  var skipped = false
  while q.kind == nkStmtListExpr and q.len > 0:
    skipped = true
    q = q.lastSon
  if getMagic(q) == mSlice:
    # magic: pass slice to openArray:
    if skipped:
      q = skipConv(n)
      while q.kind == nkStmtListExpr and q.len > 0:
        for i in 0..<q.len-1:
          genStmts(p, q[i])
        q = q.lastSon
    let (x, y) = genOpenArraySlice(p, q, formalType, n.typ[0])
    result.add x & ", " & y
  else:
    var a: TLoc
    initLocExpr(p, if n.kind == nkHiddenStdConv: n[1] else: n, a)
    case skipTypes(a.t, abstractVar+{tyStatic}).kind
    of tyOpenArray, tyVarargs:
      if reifiedOpenArray(n):
        if a.t.kind in {tyVar, tyLent}:
          result.add "$1->Field0, $1->Field1" % [rdLoc(a)]
        else:
          result.add "$1.Field0, $1.Field1" % [rdLoc(a)]
      else:
        result.add "$1, $1Len_0" % [rdLoc(a)]
    of tyString, tySequence:
      let ntyp = skipTypes(n.typ, abstractInst)
      if formalType.skipTypes(abstractInst).kind in {tyVar} and ntyp.kind == tyString and
          optSeqDestructors in p.config.globalOptions:
        linefmt(p, cpsStmts, "#nimPrepareStrMutationV2($1);$n", [byRefLoc(p, a)])
      if ntyp.kind in {tyVar} and not compileToCpp(p.module):
        var t: TLoc
        t.r = "(*$1)" % [a.rdLoc]
        result.add "($4) ? ((*$1)$3) : NIM_NIL, $2" %
                     [a.rdLoc, lenExpr(p, t), dataField(p),
                      dataFieldAccessor(p, "*" & a.rdLoc)]
      else:
        result.add "($4) ? ($1$3) : NIM_NIL, $2" %
                     [a.rdLoc, lenExpr(p, a), dataField(p), dataFieldAccessor(p, a.rdLoc)]
    of tyArray:
      result.add "$1, $2" % [rdLoc(a), rope(lengthOrd(p.config, a.t))]
    of tyPtr, tyRef:
      case lastSon(a.t).kind
      of tyString, tySequence:
        var t: TLoc
        t.r = "(*$1)" % [a.rdLoc]
        result.add "($4) ? ((*$1)$3) : NIM_NIL, $2" %
                     [a.rdLoc, lenExpr(p, t), dataField(p),
                      dataFieldAccessor(p, "*" & a.rdLoc)]
      of tyArray:
        result.add "$1, $2" % [rdLoc(a), rope(lengthOrd(p.config, lastSon(a.t)))]
      else:
        internalError(p.config, "openArrayLoc: " & typeToString(a.t))
    else: internalError(p.config, "openArrayLoc: " & typeToString(a.t))

proc withTmpIfNeeded(p: BProc, a: TLoc, needsTmp: bool): TLoc =
  # Bug https://github.com/status-im/nimbus-eth2/issues/1549
  # Aliasing is preferred over stack overflows.
  # Also don't regress for non ARC-builds, too risky.
  if needsTmp and a.lode.typ != nil and p.config.selectedGC in {gcArc, gcAtomicArc, gcOrc} and
      getSize(p.config, a.lode.typ) < 1024:
    getTemp(p, a.lode.typ, result, needsInit=false)
    genAssignment(p, result, a, {})
  else:
    result = a

proc literalsNeedsTmp(p: BProc, a: TLoc): TLoc =
  getTemp(p, a.lode.typ, result, needsInit=false)
  genAssignment(p, result, a, {})

proc genArgStringToCString(p: BProc, n: PNode; result: var Rope; needsTmp: bool) {.inline.} =
  var a: TLoc
  initLocExpr(p, n[0], a)
  appcg(p.module, result, "#nimToCStringConv($1)", [withTmpIfNeeded(p, a, needsTmp).rdLoc])

proc genArg(p: BProc, n: PNode, param: PSym; call: PNode; result: var Rope; needsTmp = false) =
  var a: TLoc
  if n.kind == nkStringToCString:
    genArgStringToCString(p, n, result, needsTmp)
  elif skipTypes(param.typ, abstractVar).kind in {tyOpenArray, tyVarargs}:
    var n = if n.kind != nkHiddenAddr: n else: n[0]
    openArrayLoc(p, param.typ, n, result)
  elif ccgIntroducedPtr(p.config, param, call[0].typ[0]) and 
    (optByRef notin param.options or not p.module.compileToCpp):
    initLocExpr(p, n, a)
    if n.kind in {nkCharLit..nkNilLit}:
      addAddrLoc(p.config, literalsNeedsTmp(p, a), result)
    else:
      addAddrLoc(p.config, withTmpIfNeeded(p, a, needsTmp), result)
  elif p.module.compileToCpp and param.typ.kind in {tyVar} and
      n.kind == nkHiddenAddr:
    initLocExprSingleUse(p, n[0], a)
    # if the proc is 'importc'ed but not 'importcpp'ed then 'var T' still
    # means '*T'. See posix.nim for lots of examples that do that in the wild.
    let callee = call[0]
    if callee.kind == nkSym and
        {sfImportc, sfInfixCall, sfCompilerProc} * callee.sym.flags == {sfImportc} and
        {lfHeader, lfNoDecl} * callee.sym.loc.flags != {}:
      addAddrLoc(p.config, a, result)
    else:
      addRdLoc(a, result)
  else:
    initLocExprSingleUse(p, n, a)
    addRdLoc(withTmpIfNeeded(p, a, needsTmp), result)
  #assert result != nil

proc genArgNoParam(p: BProc, n: PNode; result: var Rope; needsTmp = false) =
  var a: TLoc
  if n.kind == nkStringToCString:
    genArgStringToCString(p, n, result, needsTmp)
  else:
    initLocExprSingleUse(p, n, a)
    addRdLoc(withTmpIfNeeded(p, a, needsTmp), result)

import aliasanalysis

proc potentialAlias(n: PNode, potentialWrites: seq[PNode]): bool =
  for p in potentialWrites:
    if p.aliases(n) != no or n.aliases(p) != no:
      return true

proc skipTrivialIndirections(n: PNode): PNode =
  result = n
  while true:
    case result.kind
    of nkDerefExpr, nkHiddenDeref, nkAddr, nkHiddenAddr, nkObjDownConv, nkObjUpConv:
      result = result[0]
    of nkHiddenStdConv, nkHiddenSubConv:
      result = result[1]
    else: break

proc getPotentialWrites(n: PNode; mutate: bool; result: var seq[PNode]) =
  case n.kind:
  of nkLiterals, nkIdent, nkFormalParams: discard
  of nkSym:
    if mutate: result.add n
  of nkAsgn, nkFastAsgn, nkSinkAsgn:
    getPotentialWrites(n[0], true, result)
    getPotentialWrites(n[1], mutate, result)
  of nkAddr, nkHiddenAddr:
    getPotentialWrites(n[0], true, result)
  of nkBracketExpr, nkDotExpr, nkCheckedFieldExpr:
    getPotentialWrites(n[0], mutate, result)
  of nkCallKinds:
    case n.getMagic:
    of mIncl, mExcl, mInc, mDec, mAppendStrCh, mAppendStrStr, mAppendSeqElem,
        mAddr, mNew, mNewFinalize, mWasMoved, mDestroy, mReset:
      getPotentialWrites(n[1], true, result)
      for i in 2..<n.len:
        getPotentialWrites(n[i], mutate, result)
    of mSwap:
      for i in 1..<n.len:
        getPotentialWrites(n[i], true, result)
    else:
      for i in 1..<n.len:
        getPotentialWrites(n[i], mutate, result)
  else:
    for s in n:
      getPotentialWrites(s, mutate, result)

proc getPotentialReads(n: PNode; result: var seq[PNode]) =
  case n.kind:
  of nkLiterals, nkIdent, nkFormalParams: discard
  of nkSym: result.add n
  else:
    for s in n:
      getPotentialReads(s, result)

proc genParams(p: BProc, ri: PNode, typ: PType; result: var Rope) =
  # We must generate temporaries in cases like #14396
  # to keep the strict Left-To-Right evaluation
  var needTmp = newSeq[bool](ri.len - 1)
  var potentialWrites: seq[PNode]
  for i in countdown(ri.len - 1, 1):
    if ri[i].skipTrivialIndirections.kind == nkSym:
      needTmp[i - 1] = potentialAlias(ri[i], potentialWrites)
    else:
      #if not ri[i].typ.isCompileTimeOnly:
      var potentialReads: seq[PNode]
      getPotentialReads(ri[i], potentialReads)
      for n in potentialReads:
        if not needTmp[i - 1]:
          needTmp[i - 1] = potentialAlias(n, potentialWrites)
      getPotentialWrites(ri[i], false, potentialWrites)
    if ri[i].kind in {nkHiddenAddr, nkAddr}:
      # Optimization: don't use a temp, if we would only take the address anyway
      needTmp[i - 1] = false

  var oldLen = result.len
  for i in 1..<ri.len:
    if i < typ.len:
      assert(typ.n[i].kind == nkSym)
      let paramType = typ.n[i]
      if not paramType.typ.isCompileTimeOnly:
        if oldLen != result.len:
          result.add(", ")
          oldLen = result.len
        genArg(p, ri[i], paramType.sym, ri, result, needTmp[i-1])
    else:
      if oldLen != result.len:
        result.add(", ")
        oldLen = result.len
      genArgNoParam(p, ri[i], result, needTmp[i-1])

proc addActualSuffixForHCR(res: var Rope, module: PSym, sym: PSym) =
  if sym.flags * {sfImportc, sfNonReloadable} == {} and sym.loc.k == locProc and
      (sym.typ.callConv == ccInline or sym.owner.id == module.id):
    res = res & "_actual".rope

proc genPrefixCall(p: BProc, le, ri: PNode, d: var TLoc) =
  var op: TLoc
  # this is a hotspot in the compiler
  initLocExpr(p, ri[0], op)
  # getUniqueType() is too expensive here:
  var typ = skipTypes(ri[0].typ, abstractInstOwned)
  assert(typ.kind == tyProc)
  assert(typ.len == typ.n.len)

  var params = newRopeAppender()
  genParams(p, ri, typ, params)

  var callee = rdLoc(op)
  if p.hcrOn and ri[0].kind == nkSym:
    callee.addActualSuffixForHCR(p.module.module, ri[0].sym)
  fixupCall(p, le, ri, d, callee, params)

proc genClosureCall(p: BProc, le, ri: PNode, d: var TLoc) =

  proc addComma(r: Rope): Rope =
    if r.len == 0: r else: r & ", "

  const PatProc = "$1.ClE_0? $1.ClP_0($3$1.ClE_0):(($4)($1.ClP_0))($2)"
  const PatIter = "$1.ClP_0($3$1.ClE_0)" # we know the env exists

  var op: TLoc
  initLocExpr(p, ri[0], op)

  # getUniqueType() is too expensive here:
  var typ = skipTypes(ri[0].typ, abstractInstOwned)
  assert(typ.kind == tyProc)
  assert(typ.len == typ.n.len)

  var pl = newRopeAppender()
  genParams(p, ri, typ, pl)

  template genCallPattern {.dirty.} =
    if tfIterator in typ.flags:
      lineF(p, cpsStmts, PatIter & ";$n", [rdLoc(op), pl, pl.addComma, rawProc])
    else:
      lineF(p, cpsStmts, PatProc & ";$n", [rdLoc(op), pl, pl.addComma, rawProc])

  let rawProc = getClosureType(p.module, typ, clHalf)
  let canRaise = p.config.exc == excGoto and canRaiseDisp(p, ri[0])
  if typ[0] != nil:
    if isInvalidReturnType(p.config, typ):
      if ri.len > 1: pl.add(", ")
      # beware of 'result = p(result)'. We may need to allocate a temporary:
      if d.k in {locTemp, locNone} or not preventNrvo(p, d.lode, le, ri):
        # Great, we can use 'd':
        if d.k == locNone:
          getTemp(p, typ[0], d, needsInit=true)
        elif d.k notin {locTemp} and not hasNoInit(ri):
          # reset before pass as 'result' var:
          discard "resetLoc(p, d)"
        pl.add(addrLoc(p.config, d))
        genCallPattern()
        if canRaise: raiseExit(p)
      else:
        var tmp: TLoc
        getTemp(p, typ[0], tmp, needsInit=true)
        pl.add(addrLoc(p.config, tmp))
        genCallPattern()
        if canRaise: raiseExit(p)
        genAssignment(p, d, tmp, {}) # no need for deep copying
    elif isHarmlessStore(p, canRaise, d):
      if d.k == locNone: getTemp(p, typ[0], d)
      assert(d.t != nil)        # generate an assignment to d:
      var list: TLoc
      initLoc(list, locCall, d.lode, OnUnknown)
      if tfIterator in typ.flags:
        list.r = PatIter % [rdLoc(op), pl, pl.addComma, rawProc]
      else:
        list.r = PatProc % [rdLoc(op), pl, pl.addComma, rawProc]
      genAssignment(p, d, list, {}) # no need for deep copying
      if canRaise: raiseExit(p)
    else:
      var tmp: TLoc
      getTemp(p, typ[0], tmp)
      assert(d.t != nil)        # generate an assignment to d:
      var list: TLoc
      initLoc(list, locCall, d.lode, OnUnknown)
      if tfIterator in typ.flags:
        list.r = PatIter % [rdLoc(op), pl, pl.addComma, rawProc]
      else:
        list.r = PatProc % [rdLoc(op), pl, pl.addComma, rawProc]
      genAssignment(p, tmp, list, {})
      if canRaise: raiseExit(p)
      genAssignment(p, d, tmp, {})
  else:
    genCallPattern()
    if canRaise: raiseExit(p)

proc genOtherArg(p: BProc; ri: PNode; i: int; typ: PType; result: var Rope;
                 argsCounter: var int) =
  if i < typ.len:
    # 'var T' is 'T&' in C++. This means we ignore the request of
    # any nkHiddenAddr when it's a 'var T'.
    let paramType = typ.n[i]
    assert(paramType.kind == nkSym)
    if paramType.typ.isCompileTimeOnly:
      discard
    elif typ[i].kind in {tyVar} and ri[i].kind == nkHiddenAddr:
      if argsCounter > 0: result.add ", "
      genArgNoParam(p, ri[i][0], result)
      inc argsCounter
    else:
      if argsCounter > 0: result.add ", "
      genArgNoParam(p, ri[i], result) #, typ.n[i].sym)
      inc argsCounter
  else:
    if tfVarargs notin typ.flags:
      localError(p.config, ri.info, "wrong argument count")
    else:
      if argsCounter > 0: result.add ", "
      genArgNoParam(p, ri[i], result)
      inc argsCounter

discard """
Dot call syntax in C++
======================

so c2nim translates 'this' sometimes to 'T' and sometimes to 'var T'
both of which are wrong, but often more convenient to use.
For manual wrappers it can also be 'ptr T'

Fortunately we know which parameter is the 'this' parameter and so can fix this
mess in the codegen.
now ... if the *argument* is a 'ptr' the codegen shall emit -> and otherwise .
but this only depends on the argument and not on how the 'this' was declared
however how the 'this' was declared affects whether we end up with
wrong 'addr' and '[]' ops...

Since I'm tired I'll enumerate all the cases here:

var
  x: ptr T
  y: T

proc t(x: T)
x[].t()  --> (*x).t()  is correct.
y.t()    --> y.t()  is correct

proc u(x: ptr T)
x.u()          --> needs to become  x->u()
(addr y).u()   --> needs to become  y.u()

proc v(x: var T)
--> first skip the implicit 'nkAddr' node
x[].v()        --> (*x).v()  is correct, but might have been eliminated due
                   to the nkAddr node! So for this case we need to generate '->'
y.v()          --> y.v() is correct

"""

proc skipAddrDeref(node: PNode): PNode =
  var n = node
  var isAddr = false
  case n.kind
  of nkAddr, nkHiddenAddr:
    n = n[0]
    isAddr = true
  of nkDerefExpr, nkHiddenDeref:
    n = n[0]
  else: return n
  if n.kind == nkObjDownConv: n = n[0]
  if isAddr and n.kind in {nkDerefExpr, nkHiddenDeref}:
    result = n[0]
  elif n.kind in {nkAddr, nkHiddenAddr}:
    result = n[0]
  else:
    result = node

proc genThisArg(p: BProc; ri: PNode; i: int; typ: PType; result: var Rope) =
  # for better or worse c2nim translates the 'this' argument to a 'var T'.
  # However manual wrappers may also use 'ptr T'. In any case we support both
  # for convenience.
  internalAssert p.config, i < typ.len
  assert(typ.n[i].kind == nkSym)
  # if the parameter is lying (tyVar) and thus we required an additional deref,
  # skip the deref:
  var ri = ri[i]
  while ri.kind == nkObjDownConv: ri = ri[0]
  let t = typ[i].skipTypes({tyGenericInst, tyAlias, tySink})
  if t.kind in {tyVar}:
    let x = if ri.kind == nkHiddenAddr: ri[0] else: ri
    if x.typ.kind == tyPtr:
      genArgNoParam(p, x, result)
      result.add("->")
    elif x.kind in {nkHiddenDeref, nkDerefExpr} and x[0].typ.kind == tyPtr:
      genArgNoParam(p, x[0], result)
      result.add("->")
    else:
      genArgNoParam(p, x, result)
      result.add(".")
  elif t.kind == tyPtr:
    if ri.kind in {nkAddr, nkHiddenAddr}:
      genArgNoParam(p, ri[0], result)
      result.add(".")
    else:
      genArgNoParam(p, ri, result)
      result.add("->")
  else:
    ri = skipAddrDeref(ri)
    if ri.kind in {nkAddr, nkHiddenAddr}: ri = ri[0]
    genArgNoParam(p, ri, result) #, typ.n[i].sym)
    result.add(".")

proc genPatternCall(p: BProc; ri: PNode; pat: string; typ: PType; result: var Rope) =
  var i = 0
  var j = 1
  while i < pat.len:
    case pat[i]
    of '@':
      var argsCounter = 0
      for k in j..<ri.len:
        genOtherArg(p, ri, k, typ, result, argsCounter)
      inc i
    of '#':
      if i+1 < pat.len and pat[i+1] in {'+', '@'}:
        let ri = ri[j]
        if ri.kind in nkCallKinds:
          let typ = skipTypes(ri[0].typ, abstractInst)
          if pat[i+1] == '+': genArgNoParam(p, ri[0], result)
          result.add("(")
          if 1 < ri.len:
            var argsCounterB = 0
            genOtherArg(p, ri, 1, typ, result, argsCounterB)
          for k in j+1..<ri.len:
            var argsCounterB = 0
            genOtherArg(p, ri, k, typ, result, argsCounterB)
          result.add(")")
        else:
          localError(p.config, ri.info, "call expression expected for C++ pattern")
        inc i
      elif i+1 < pat.len and pat[i+1] == '.':
        genThisArg(p, ri, j, typ, result)
        inc i
      elif i+1 < pat.len and pat[i+1] == '[':
        var arg = ri[j].skipAddrDeref
        while arg.kind in {nkAddr, nkHiddenAddr, nkObjDownConv}: arg = arg[0]
        genArgNoParam(p, arg, result)
        #result.add debugTree(arg, 0, 10)
      else:
        var argsCounter = 0
        genOtherArg(p, ri, j, typ, result, argsCounter)
      inc j
      inc i
    of '\'':
      var idx, stars: int
      if scanCppGenericSlot(pat, i, idx, stars):
        var t = resolveStarsInCppType(typ, idx, stars)
        if t == nil: result.add("void")
        else: result.add(getTypeDesc(p.module, t))
    else:
      let start = i
      while i < pat.len:
        if pat[i] notin {'@', '#', '\''}: inc(i)
        else: break
      if i - 1 >= start:
        result.add(substr(pat, start, i - 1))

proc genInfixCall(p: BProc, le, ri: PNode, d: var TLoc) =
  var op: TLoc
  initLocExpr(p, ri[0], op)
  # getUniqueType() is too expensive here:
  var typ = skipTypes(ri[0].typ, abstractInst)
  assert(typ.kind == tyProc)
  assert(typ.len == typ.n.len)
  # don't call '$' here for efficiency:
  let pat = $ri[0].sym.loc.r
  internalAssert p.config, pat.len > 0
  if pat.contains({'#', '(', '@', '\''}):
    var pl = newRopeAppender()
    genPatternCall(p, ri, pat, typ, pl)
    # simpler version of 'fixupCall' that works with the pl+params combination:
    var typ = skipTypes(ri[0].typ, abstractInst)
    if typ[0] != nil:
      if p.module.compileToCpp and lfSingleUse in d.flags:
        # do not generate spurious temporaries for C++! For C we're better off
        # with them to prevent undefined behaviour and because the codegen
        # is free to emit expressions multiple times!
        d.k = locCall
        d.r = pl
        excl d.flags, lfSingleUse
      else:
        if d.k == locNone: getTemp(p, typ[0], d)
        assert(d.t != nil)        # generate an assignment to d:
        var list: TLoc
        initLoc(list, locCall, d.lode, OnUnknown)
        list.r = pl
        genAssignment(p, d, list, {}) # no need for deep copying
    else:
      pl.add(";\n")
      line(p, cpsStmts, pl)
  else:
    var pl = newRopeAppender()
    var argsCounter = 0
    if 1 < ri.len:
      genThisArg(p, ri, 1, typ, pl)
    pl.add(op.r)
    var params = newRopeAppender()
    for i in 2..<ri.len:
      assert(typ.len == typ.n.len)
      genOtherArg(p, ri, i, typ, params, argsCounter)
    fixupCall(p, le, ri, d, pl, params)

proc genNamedParamCall(p: BProc, ri: PNode, d: var TLoc) =
  # generates a crappy ObjC call
  var op: TLoc
  initLocExpr(p, ri[0], op)
  var pl = "["
  # getUniqueType() is too expensive here:
  var typ = skipTypes(ri[0].typ, abstractInst)
  assert(typ.kind == tyProc)
  assert(typ.len == typ.n.len)

  # don't call '$' here for efficiency:
  let pat = $ri[0].sym.loc.r
  internalAssert p.config, pat.len > 0
  var start = 3
  if ' ' in pat:
    start = 1
    pl.add(op.r)
    if ri.len > 1:
      pl.add(": ")
      genArg(p, ri[1], typ.n[1].sym, ri, pl)
      start = 2
  else:
    if ri.len > 1:
      genArg(p, ri[1], typ.n[1].sym, ri, pl)
      pl.add(" ")
    pl.add(op.r)
    if ri.len > 2:
      pl.add(": ")
      genArg(p, ri[2], typ.n[2].sym, ri, pl)
  for i in start..<ri.len:
    assert(typ.len == typ.n.len)
    if i >= typ.len:
      internalError(p.config, ri.info, "varargs for objective C method?")
    assert(typ.n[i].kind == nkSym)
    var param = typ.n[i].sym
    pl.add(" ")
    pl.add(param.name.s)
    pl.add(": ")
    genArg(p, ri[i], param, ri, pl)
  if typ[0] != nil:
    if isInvalidReturnType(p.config, typ):
      if ri.len > 1: pl.add(" ")
      # beware of 'result = p(result)'. We always allocate a temporary:
      if d.k in {locTemp, locNone}:
        # We already got a temp. Great, special case it:
        if d.k == locNone: getTemp(p, typ[0], d, needsInit=true)
        pl.add("Result: ")
        pl.add(addrLoc(p.config, d))
        pl.add("];\n")
        line(p, cpsStmts, pl)
      else:
        var tmp: TLoc
        getTemp(p, typ[0], tmp, needsInit=true)
        pl.add(addrLoc(p.config, tmp))
        pl.add("];\n")
        line(p, cpsStmts, pl)
        genAssignment(p, d, tmp, {}) # no need for deep copying
    else:
      pl.add("]")
      if d.k == locNone: getTemp(p, typ[0], d)
      assert(d.t != nil)        # generate an assignment to d:
      var list: TLoc
      initLoc(list, locCall, ri, OnUnknown)
      list.r = pl
      genAssignment(p, d, list, {}) # no need for deep copying
  else:
    pl.add("];\n")
    line(p, cpsStmts, pl)

proc notYetAlive(n: PNode): bool {.inline.} =
  let r = getRoot(n)
  result = r != nil and r.loc.lode == nil

proc isInactiveDestructorCall(p: BProc, e: PNode): bool =
  #[ Consider this example.

    var :tmpD_3281815
    try:
      if true:
        return
      let args_3280013 =
        wasMoved_3281816(:tmpD_3281815)
        `=_3280036`(:tmpD_3281815, [1])
        :tmpD_3281815
    finally:
      `=destroy_3280027`(args_3280013)

  We want to return early but the 'finally' section is traversed before
  the 'let args = ...' statement. We exploit this to generate better
  code for 'return'. ]#
  result = e.len == 2 and e[0].kind == nkSym and
    e[0].sym.name.s == "=destroy" and notYetAlive(e[1].skipAddr)

proc genAsgnCall(p: BProc, le, ri: PNode, d: var TLoc) =
  if p.withinBlockLeaveActions > 0 and isInactiveDestructorCall(p, ri):
    return
  if ri[0].typ.skipTypes({tyGenericInst, tyAlias, tySink, tyOwned}).callConv == ccClosure:
    genClosureCall(p, le, ri, d)
  elif ri[0].kind == nkSym and sfInfixCall in ri[0].sym.flags:
    genInfixCall(p, le, ri, d)
  elif ri[0].kind == nkSym and sfNamedParamCall in ri[0].sym.flags:
    genNamedParamCall(p, ri, d)
  else:
    genPrefixCall(p, le, ri, d)

proc genCall(p: BProc, e: PNode, d: var TLoc) = genAsgnCall(p, nil, e, d)