Nim/compiler/ccgreset.nim

#
#
#           The Nim Compiler
#        (c) Copyright 2020 Andreas Rumpf
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

# included from cgen.nim

## Code specialization instead of the old, incredibly slow 'genericReset'
## implementation.

proc specializeResetT(p: BProc, accessor: Rope, typ: PType)

proc specializeResetN(p: BProc, accessor: Rope, n: PNode;
                     typ: PType) =
  if n == nil: return
  case n.kind
  of nkRecList:
    for i in 0..<n.len:
      specializeResetN(p, accessor, n[i], typ)
  of nkRecCase:
    if (n[0].kind != nkSym): internalError(p.config, n.info, "specializeResetN")
    let disc = n[0].sym
    if disc.loc.snippet == "": fillObjectFields(p.module, typ)
    if disc.loc.t == nil:
      internalError(p.config, n.info, "specializeResetN()")
    lineF(p, cpsStmts, "switch ($1.$2) {$n", [accessor, disc.loc.snippet])
    for i in 1..<n.len:
      let branch = n[i]
      assert branch.kind in {nkOfBranch, nkElse}
      if branch.kind == nkOfBranch:
        genCaseRange(p, branch)
      else:
        lineF(p, cpsStmts, "default:$n", [])
      specializeResetN(p, accessor, lastSon(branch), typ)
      lineF(p, cpsStmts, "break;$n", [])
    lineF(p, cpsStmts, "} $n", [])
    specializeResetT(p, "$1.$2" % [accessor, disc.loc.snippet], disc.loc.t)
  of nkSym:
    let field = n.sym
    if field.typ.kind == tyVoid: return
    if field.loc.snippet == "": fillObjectFields(p.module, typ)
    if field.loc.t == nil:
      internalError(p.config, n.info, "specializeResetN()")
    specializeResetT(p, "$1.$2" % [accessor, field.loc.snippet], field.loc.t)
  else: internalError(p.config, n.info, "specializeResetN()")

proc specializeResetT(p: BProc, accessor: Rope, typ: PType) =
  if typ == nil: return

  case typ.kind
  of tyGenericInst, tyGenericBody, tyTypeDesc, tyAlias, tyDistinct, tyInferred,
     tySink, tyOwned:
    specializeResetT(p, accessor, skipModifier(typ))
  of tyArray:
    let arraySize = lengthOrd(p.config, typ.indexType)
    var i: TLoc = getTemp(p, getSysType(p.module.g.graph, unknownLineInfo, tyInt))
    linefmt(p, cpsStmts, "for ($1 = 0; $1 < $2; $1++) {$n",
            [i.snippet, arraySize])
    specializeResetT(p, ropecg(p.module, "$1[$2]", [accessor, i.snippet]), typ.elementType)
    lineF(p, cpsStmts, "}$n", [])
  of tyObject:
    var x = typ.baseClass
    if x != nil: x = x.skipTypes(skipPtrs)
    specializeResetT(p, accessor.parentObj(p.module), x)
    if typ.n != nil:
      if typ.sym != nil and sfImportc in typ.sym.flags:
        # imported C struct, nimZeroMem
        lineCg(p, cpsStmts, "#nimZeroMem((void**)&$1, sizeof($2));$n",
            [accessor, getTypeDesc(p.module, typ)])
      else:
        specializeResetN(p, accessor, typ.n, typ)
        if isCaseObj(typ.n):
          # The active branch was released above. Clear the complete object so
          # stale bytes from overlapping branches cannot be traced by the GC.
          # type
          #   Foo = object
          #     case kind: bool
          #     of true:
          #       a: ref Bar   # 8 bytes (pointer)
          #     of false:
          #       b: int       # 4 bytes
          # specializeResetT for b emits accessor.b = 0 — writes 4 bytes
          # But the union is 8 bytes wide (sized by the largest branch)
          # The remaining 4 bytes where a used to live are untouched
          # Those stale bytes could contain a heap pointer the GC traces → crash
          lineCg(p, cpsStmts, "#nimZeroMem((void**)&$1, sizeof($2));$n",
                 [accessor, getTypeDesc(p.module, typ)])
  of tyTuple:
    let typ = getUniqueType(typ)
    for i, a in typ.ikids:
      specializeResetT(p, ropecg(p.module, "$1.Field$2", [accessor, i]), a)

  of tyString, tyRef, tySequence:
    lineCg(p, cpsStmts, "#unsureAsgnRef((void**)&$1, NIM_NIL);$n", [accessor])

  of tyProc:
    if typ.callConv == ccClosure:
      lineCg(p, cpsStmts, "#unsureAsgnRef((void**)&$1.ClE_0, NIM_NIL);$n", [accessor])
      lineCg(p, cpsStmts, "$1.ClP_0 = NIM_NIL;$n", [accessor])
    else:
      lineCg(p, cpsStmts, "$1 = NIM_NIL;$n", [accessor])
  of tyChar, tyBool, tyEnum, tyRange, tyInt..tyUInt64:
    lineCg(p, cpsStmts, "$1 = 0;$n", [accessor])
  of tyCstring, tyPointer, tyPtr, tyVar, tyLent:
    lineCg(p, cpsStmts, "$1 = NIM_NIL;$n", [accessor])
  of tySet:
    case mapSetType(p.config, typ)
    of ctArray:
      lineCg(p, cpsStmts, "#nimZeroMem($1, sizeof($2));$n",
          [accessor, getTypeDesc(p.module, typ)])
    of ctInt8, ctInt16, ctInt32, ctInt64:
      lineCg(p, cpsStmts, "$1 = 0;$n", [accessor])
    else:
      raiseAssert "unexpected set type kind"
  of tyNone, tyEmpty, tyNil, tyUntyped, tyTyped, tyGenericInvocation,
      tyGenericParam, tyOrdinal, tyOpenArray, tyForward, tyVarargs,
      tyUncheckedArray, tyError, tyBuiltInTypeClass, tyUserTypeClass,
      tyUserTypeClassInst, tyCompositeTypeClass, tyAnd, tyOr, tyNot,
      tyAnything, tyStatic, tyFromExpr, tyConcept, tyVoid, tyIterable:
    discard

proc specializeReset(p: BProc, a: TLoc) =
  specializeResetT(p, rdLoc(a), a.t)