more progress on destructor based strings

16 files changed, 288 insertions, 253 deletions

diff --git a/compiler/ccgcalls.nim b/compiler/ccgcalls.nim
index 9712d5dce..ab15b9f2f 100644
--- a/compiler/ccgcalls.nim
+++ b/compiler/ccgcalls.nim
@@ -124,15 +124,19 @@ proc openArrayLoc(p: BProc, n: PNode): Rope =
     of tyString, tySequence:
       if skipTypes(n.typ, abstractInst).kind == tyVar and
             not compileToCpp(p.module):
-        result = "(*$1)$3, (*$1 ? (*$1)->$2 : 0)" % [a.rdLoc, lenField(p), dataField(p)]
+        var t: TLoc
+        t.r = "(*$1)" % [a.rdLoc]
+        result = "(*$1)$3, $2" % [a.rdLoc, lenExpr(p, t), dataField(p)]
       else:
-        result = "$1$3, ($1 ? $1->$2 : 0)" % [a.rdLoc, lenField(p), dataField(p)]
+        result = "$1$3, $2" % [a.rdLoc, lenExpr(p, a), dataField(p)]
     of tyArray:
       result = "$1, $2" % [rdLoc(a), rope(lengthOrd(p.config, a.t))]
     of tyPtr, tyRef:
       case lastSon(a.t).kind
       of tyString, tySequence:
-        result = "(*$1)$3, (*$1 ? (*$1)->$2 : 0)" % [a.rdLoc, lenField(p), dataField(p)]
+        var t: TLoc
+        t.r = "(*$1)" % [a.rdLoc]
+        result = "(*$1)$3, (*$1 ? (*$1)->$2 : 0)" % [a.rdLoc, lenExpr(p, t), dataField(p)]
       of tyArray:
         result = "$1, $2" % [rdLoc(a), rope(lengthOrd(p.config, lastSon(a.t)))]
       else:
diff --git a/compiler/ccgexprs.nim b/compiler/ccgexprs.nim
index 736701780..689e2483e 100644
--- a/compiler/ccgexprs.nim
+++ b/compiler/ccgexprs.nim
@@ -254,7 +254,12 @@ proc genGenericAsgn(p: BProc, dest, src: TLoc, flags: TAssignmentFlags) =
   # tfShallow flag for the built-in string type too! So we check only
   # here for this flag, where it is reasonably safe to do so
   # (for objects, etc.):
-  if needToCopy notin flags or
+  if p.config.selectedGC == gcDestructors:
+    useStringh(p.module)
+    linefmt(p, cpsStmts,
+         "memcpy((void*)$1, (NIM_CONST void*)$2, sizeof($3));$n",
+         addrLoc(p.config, dest), addrLoc(p.config, src), rdLoc(dest))
+  elif needToCopy notin flags or
       tfShallow in skipTypes(dest.t, abstractVarRange).flags:
     if dest.storage == OnStack or not usesWriteBarrier(p.config):
       useStringh(p.module)
@@ -280,14 +285,18 @@ proc genAssignment(p: BProc, dest, src: TLoc, flags: TAssignmentFlags) =
   of tyRef:
     genRefAssign(p, dest, src, flags)
   of tySequence:
-    if (needToCopy notin flags and src.storage != OnStatic) or canMove(src.lode):
+    if p.config.selectedGC == gcDestructors:
+      genGenericAsgn(p, dest, src, flags)
+    elif (needToCopy notin flags and src.storage != OnStatic) or canMove(src.lode):
       genRefAssign(p, dest, src, flags)
     else:
       linefmt(p, cpsStmts, "#genericSeqAssign($1, $2, $3);$n",
               addrLoc(p.config, dest), rdLoc(src),
               genTypeInfo(p.module, dest.t, dest.lode.info))
   of tyString:
-    if (needToCopy notin flags and src.storage != OnStatic) or canMove(src.lode):
+    if p.config.selectedGC == gcDestructors:
+      genGenericAsgn(p, dest, src, flags)
+    elif (needToCopy notin flags and src.storage != OnStatic) or canMove(src.lode):
       genRefAssign(p, dest, src, flags)
     else:
       if dest.storage == OnStack or not usesWriteBarrier(p.config):
@@ -457,6 +466,13 @@ proc binaryStmt(p: BProc, e: PNode, d: var TLoc, frmt: string) =
   initLocExpr(p, e.sons[2], b)
   lineCg(p, cpsStmts, frmt, rdLoc(a), rdLoc(b))
 
+proc binaryStmtAddr(p: BProc, e: PNode, d: var TLoc, frmt: string) =
+  var a, b: TLoc
+  if d.k != locNone: internalError(p.config, e.info, "binaryStmtAddr")
+  initLocExpr(p, e.sons[1], a)
+  initLocExpr(p, e.sons[2], b)
+  lineCg(p, cpsStmts, frmt, addrLoc(p.config, a), rdLoc(b))
+
 proc unaryStmt(p: BProc, e: PNode, d: var TLoc, frmt: string) =
   var a: TLoc
   if d.k != locNone: internalError(p.config, e.info, "unaryStmt")
@@ -893,8 +909,8 @@ proc genBoundsCheck(p: BProc; arr, a, b: TLoc) =
   of tySequence, tyString:
     linefmt(p, cpsStmts,
       "if ($2-$1 != -1 && " &
-      "(!$3 || (NU)($1) >= (NU)($3->$4) || (NU)($2) >= (NU)($3->$4))) #raiseIndexError();$n",
-      rdLoc(a), rdLoc(b), rdLoc(arr), lenField(p))
+      "((NU)($1) >= (NU)$3 || (NU)($2) >= (NU)$3)) #raiseIndexError();$n",
+      rdLoc(a), rdLoc(b), lenExpr(p, arr))
   else: discard
 
 proc genOpenArrayElem(p: BProc, n, x, y: PNode, d: var TLoc) =
@@ -918,12 +934,12 @@ proc genSeqElem(p: BProc, n, x, y: PNode, d: var TLoc) =
   if optBoundsCheck in p.options:
     if ty.kind == tyString and (not defined(nimNoZeroTerminator) or optLaxStrings in p.options):
       linefmt(p, cpsStmts,
-              "if (!$2 || (NU)($1) > (NU)($2->$3)) #raiseIndexError();$n",
-              rdLoc(b), rdLoc(a), lenField(p))
+              "if ((NU)($1) > (NU)$2) #raiseIndexError();$n",
+              rdLoc(b), lenExpr(p, a))
     else:
       linefmt(p, cpsStmts,
-              "if (!$2 || (NU)($1) >= (NU)($2->$3)) #raiseIndexError();$n",
-              rdLoc(b), rdLoc(a), lenField(p))
+              "if ((NU)($1) >= (NU)$2) #raiseIndexError();$n",
+              rdLoc(b), lenExpr(p, a))
   if d.k == locNone: d.storage = OnHeap
   if skipTypes(a.t, abstractVar).kind in {tyRef, tyPtr}:
     a.r = ropecg(p.module, "(*$1)", a.r)
@@ -1013,6 +1029,12 @@ proc genEcho(p: BProc, n: PNode) =
 proc gcUsage(conf: ConfigRef; n: PNode) =
   if conf.selectedGC == gcNone: message(conf, n.info, warnGcMem, n.renderTree)
 
+proc strLoc(p: BProc; d: TLoc): Rope =
+  if p.config.selectedGc == gcDestructors:
+    result = addrLoc(p.config, d)
+  else:
+    result = rdLoc(d)
+
 proc genStrConcat(p: BProc, e: PNode, d: var TLoc) =
   #   <Nim code>
   #   s = 'Hello ' & name & ', how do you feel?' & 'z'
@@ -1040,13 +1062,14 @@ proc genStrConcat(p: BProc, e: PNode, d: var TLoc) =
     initLocExpr(p, e.sons[i + 1], a)
     if skipTypes(e.sons[i + 1].typ, abstractVarRange).kind == tyChar:
       inc(L)
-      add(appends, ropecg(p.module, "#appendChar($1, $2);$n", tmp.r, rdLoc(a)))
+      add(appends, ropecg(p.module, "#appendChar($1, $2);$n", strLoc(p, tmp), rdLoc(a)))
     else:
       if e.sons[i + 1].kind in {nkStrLit..nkTripleStrLit}:
         inc(L, len(e.sons[i + 1].strVal))
       else:
-        addf(lens, "($1 ? $1->$2 : 0) + ", [rdLoc(a), lenField(p)])
-      add(appends, ropecg(p.module, "#appendString($1, $2);$n", tmp.r, rdLoc(a)))
+        add(lens, lenExpr(p, a))
+        add(lens, " + ")
+      add(appends, ropecg(p.module, "#appendString($1, $2);$n", strLoc(p, tmp), rdLoc(a)))
   linefmt(p, cpsStmts, "$1 = #rawNewString($2$3);$n", tmp.r, lens, rope(L))
   add(p.s(cpsStmts), appends)
   if d.k == locNone:
@@ -1079,16 +1102,21 @@ proc genStrAppend(p: BProc, e: PNode, d: var TLoc) =
     if skipTypes(e.sons[i + 2].typ, abstractVarRange).kind == tyChar:
       inc(L)
       add(appends, ropecg(p.module, "#appendChar($1, $2);$n",
-                        rdLoc(dest), rdLoc(a)))
+                        strLoc(p, dest), rdLoc(a)))
     else:
       if e.sons[i + 2].kind in {nkStrLit..nkTripleStrLit}:
         inc(L, len(e.sons[i + 2].strVal))
       else:
-        addf(lens, "($1 ? $1->$2 : 0) + ", [rdLoc(a), lenField(p)])
+        add(lens, lenExpr(p, a))
+        add(lens, " + ")
       add(appends, ropecg(p.module, "#appendString($1, $2);$n",
-                        rdLoc(dest), rdLoc(a)))
-  linefmt(p, cpsStmts, "$1 = #resizeString($1, $2$3);$n",
-          rdLoc(dest), lens, rope(L))
+                        strLoc(p, dest), rdLoc(a)))
+  if p.config.selectedGC == gcDestructors:
+    linefmt(p, cpsStmts, "#prepareAdd($1, $2$3);$n",
+            addrLoc(p.config, dest), lens, rope(L))
+  else:
+    linefmt(p, cpsStmts, "$1 = #resizeString($1, $2$3);$n",
+            rdLoc(dest), lens, rope(L))
   add(p.s(cpsStmts), appends)
   gcUsage(p.config, e)
 
@@ -1440,7 +1468,7 @@ proc genRepr(p: BProc, e: PNode, d: var TLoc) =
       putIntoDest(p, b, e, "$1, $1Len_0" % [rdLoc(a)], a.storage)
     of tyString, tySequence:
       putIntoDest(p, b, e,
-                  "$1$3, ($1 ? $1->$2 : 0)" % [rdLoc(a), lenField(p), dataField(p)], a.storage)
+                  "$1$3, $2" % [rdLoc(a), lenExpr(p, a), dataField(p)], a.storage)
     of tyArray:
       putIntoDest(p, b, e,
                   "$1, $2" % [rdLoc(a), rope(lengthOrd(p.config, a.t))], a.storage)
@@ -1787,11 +1815,11 @@ proc genStrEquals(p: BProc, e: PNode, d: var TLoc) =
   if a.kind in {nkStrLit..nkTripleStrLit} and a.strVal == "":
     initLocExpr(p, e.sons[2], x)
     putIntoDest(p, d, e,
-      ropecg(p.module, "(!($1) || ($1)->$2 == 0)", rdLoc(x), lenField(p)))
+      ropecg(p.module, "($1 == 0)", lenExpr(p, x)))
   elif b.kind in {nkStrLit..nkTripleStrLit} and b.strVal == "":
     initLocExpr(p, e.sons[1], x)
     putIntoDest(p, d, e,
-      ropecg(p.module, "(!($1) || ($1)->$2 == 0)", rdLoc(x), lenField(p)))
+      ropecg(p.module, "($1 == 0)", lenExpr(p, x)))
   else:
     binaryExpr(p, e, d, "#eqStrings($1, $2)")
 
@@ -1851,7 +1879,11 @@ proc genMagicExpr(p: BProc, e: PNode, d: var TLoc, op: TMagic) =
         getTypeDesc(p.module, ranged), res])
 
   of mConStrStr: genStrConcat(p, e, d)
-  of mAppendStrCh: binaryStmt(p, e, d, "$1 = #addChar($1, $2);$n")
+  of mAppendStrCh:
+    if p.config.selectedGC == gcDestructors:
+      binaryStmtAddr(p, e, d, "#nimAddCharV1($1, $2);$n")
+    else:
+      binaryStmt(p, e, d, "$1 = #addChar($1, $2);$n")
   of mAppendStrStr: genStrAppend(p, e, d)
   of mAppendSeqElem: genSeqElemAppend(p, e, d)
   of mEqStr: genStrEquals(p, e, d)
diff --git a/compiler/ccgtrav.nim b/compiler/ccgtrav.nim
index e74d5a953..5a6dc8a6e 100644
--- a/compiler/ccgtrav.nim
+++ b/compiler/ccgtrav.nim
@@ -107,8 +107,11 @@ proc genTraverseProcSeq(c: TTraversalClosure, accessor: Rope, typ: PType) =
   var i: TLoc
   getTemp(p, getSysType(c.p.module.g.graph, unknownLineInfo(), tyInt), i)
   let oldCode = p.s(cpsStmts)
-  lineF(p, cpsStmts, "for ($1 = 0; $1 < $2->$3; $1++) {$n",
-      [i.r, accessor, lenField(c.p)])
+  var a: TLoc
+  a.r = accessor
+
+  lineF(p, cpsStmts, "for ($1 = 0; $1 < $2; $1++) {$n",
+      [i.r, lenExpr(c.p, a)])
   let oldLen = p.s(cpsStmts).len
   genTraverseProc(c, "$1$3[$2]" % [accessor, i.r, dataField(c.p)], typ.sons[0])
   if p.s(cpsStmts).len == oldLen:
diff --git a/compiler/ccgtypes.nim b/compiler/ccgtypes.nim
index 66ad34c32..756711642 100644
--- a/compiler/ccgtypes.nim
+++ b/compiler/ccgtypes.nim
@@ -282,7 +282,7 @@ proc getSimpleTypeDesc(m: BModule, typ: PType): Rope =
   of tyString:
     case detectStrVersion(m)
     of 2:
-      discard cgsym(m, "string")
+      discard cgsym(m, "NimStringV2")
       result = typeNameOrLiteral(m, typ, "NimStringV2")
     else:
       discard cgsym(m, "NimStringDesc")
diff --git a/compiler/cgen.nim b/compiler/cgen.nim
index 32891c62c..0ca7533d4 100644
--- a/compiler/cgen.nim
+++ b/compiler/cgen.nim
@@ -235,9 +235,20 @@ proc getTempName(m: BModule): Rope =
   result = m.tmpBase & rope(m.labels)
   inc m.labels
 
+proc rdLoc(a: TLoc): Rope =
+  # 'read' location (deref if indirect)
+  result = a.r
+  if lfIndirect in a.flags: result = "(*$1)" % [result]
+
 proc lenField(p: BProc): Rope =
   result = rope(if p.module.compileToCpp: "len" else: "Sup.len")
 
+proc lenExpr(p: BProc; a: TLoc): Rope =
+  if p.config.selectedGc == gcDestructors:
+    result = rdLoc(a) & ".len"
+  else:
+    result = "($1 ? $1->$2 : 0)" % [rdLoc(a), lenField(p)]
+
 proc dataField(p: BProc): Rope =
   result = rope"->data"
 
@@ -246,11 +257,6 @@ include ccgtypes
 
 # ------------------------------ Manager of temporaries ------------------
 
-proc rdLoc(a: TLoc): Rope =
-  # 'read' location (deref if indirect)
-  result = a.r
-  if lfIndirect in a.flags: result = "(*$1)" % [result]
-
 proc addrLoc(conf: ConfigRef; a: TLoc): Rope =
   result = a.r
   if lfIndirect notin a.flags and mapType(conf, a.t) != ctArray:
diff --git a/compiler/transf.nim b/compiler/transf.nim
index dae8d1ee6..acfccb5ff 100644
--- a/compiler/transf.nim
+++ b/compiler/transf.nim
@@ -1049,8 +1049,8 @@ proc transformStmt*(g: ModuleGraph; module: PSym, n: PNode): PNode =
     when useEffectSystem: trackTopLevelStmt(g, module, result)
     #if n.info ?? "temp.nim":
     #  echo renderTree(result, {renderIds})
-    if c.needsDestroyPass:
-      result = injectDestructorCalls(g, module, result)
+    #if c.needsDestroyPass:
+    #  result = injectDestructorCalls(g, module, result)
     incl(result.flags, nfTransf)
 
 proc transformExpr*(g: ModuleGraph; module: PSym, n: PNode): PNode =
@@ -1062,6 +1062,6 @@ proc transformExpr*(g: ModuleGraph; module: PSym, n: PNode): PNode =
     liftDefer(c, result)
     # expressions are not to be injected with destructor calls as that
     # the list of top level statements needs to be collected before.
-    if c.needsDestroyPass:
-      result = injectDestructorCalls(g, module, result)
+    #if c.needsDestroyPass:
+    #  result = injectDestructorCalls(g, module, result)
     incl(result.flags, nfTransf)
diff --git a/lib/core/strs.nim b/lib/core/strs.nim
index 1ef4f09de..c07c4605e 100644
--- a/lib/core/strs.nim
+++ b/lib/core/strs.nim
@@ -14,28 +14,15 @@ when false:
 
   #proc rawNewStringNoInit(space: int): NimString {.compilerProc.}
   # seems to be unused.
-  proc rawNewString(space: int): NimString {.compilerProc.}
-  proc mnewString(len: int): NimString {.compilerProc.}
-  proc copyStrLast(s: NimString, start, last: int): NimString {.compilerProc.}
-  proc nimToCStringConv(s: NimString): cstring {.compilerProc, inline.}
-  proc copyStr(s: NimString, start: int): NimString {.compilerProc.}
-  proc toNimStr(str: cstring, len: int): NimString {.compilerProc.}
-  proc cstrToNimstr(str: cstring): NimString {.compilerRtl.}
-  proc copyString(src: NimString): NimString {.compilerRtl.}
-  proc copyStringRC1(src: NimString): NimString {.compilerRtl.}
   proc copyDeepString(src: NimString): NimString {.inline.}
-  proc addChar(s: NimString, c: char): NimString
-  proc resizeString(dest: NimString, addlen: int): NimString {.compilerRtl.}
-  proc appendString(dest, src: NimString) {.compilerproc, inline.}
-  proc appendChar(dest: NimString, c: char) {.compilerproc, inline.}
   proc setLengthStr(s: NimString, newLen: int): NimString {.compilerRtl.}
   # ----------------- sequences ----------------------------------------------
 
-  proc incrSeqV3(s: PGenericSeq, typ: PNimType): PGenericSeq {.compilerProc.} =
+  proc incrSeqV3(s: PGenericSeq, typ: PNimType): PGenericSeq {.compilerProc.}
   proc setLengthSeqV2(s: PGenericSeq, typ: PNimType, newLen: int): PGenericSeq {.
       compilerRtl.}
-  proc newSeq(typ: PNimType, len: int): pointer {.compilerRtl.} =
-  proc newSeqRC1(typ: PNimType, len: int): pointer {.compilerRtl.} =
+  proc newSeq(typ: PNimType, len: int): pointer {.compilerRtl.}
+  proc newSeqRC1(typ: PNimType, len: int): pointer {.compilerRtl.}
 
 import allocators
 
@@ -45,35 +32,36 @@ type
     region: Allocator
     data: UncheckedArray[char]
 
-  NimString {.core.} = object
+  NimStringV2 {.core.} = object
     len: int
-    p: ptr StrContent ## invariant. Never nil
+    p: ptr StrContent ## can be nil if len == 0.
 
 const nimStrVersion {.core.} = 2
 
-template isLiteral(s): bool = s.len == 0 or s.p.region == nil
+template isLiteral(s): bool = s.p == nil or s.p.region == nil
 
 template contentSize(cap): int = cap + 1 + sizeof(int) + sizeof(Allocator)
 
 template frees(s) =
   if not isLiteral(s):
-    s.p.region.dealloc(s.p, contentSize(s.p.cap))
+    s.p.region.dealloc(s.p.region, s.p, contentSize(s.p.cap))
 
-proc `=destroy`(s: var NimString) =
+proc `=destroy`(s: var NimStringV2) =
   frees(s)
   s.len = 0
+  s.p = nil
 
 template lose(a) =
   frees(a)
 
-proc `=sink`(a: var NimString, b: NimString) =
+proc `=sink`(a: var NimStringV2, b: NimStringV2) =
   # we hope this is optimized away for not yet alive objects:
   if unlikely(a.p == b.p): return
   lose(a)
   a.len = b.len
   a.p = b.p
 
-proc `=`(a: var NimString; b: NimString) =
+proc `=`(a: var NimStringV2; b: NimStringV2) =
   if unlikely(a.p == b.p): return
   lose(a)
   a.len = b.len
@@ -85,7 +73,7 @@ proc `=`(a: var NimString; b: NimString) =
     # we have to allocate the 'cap' here, consider
     # 'let y = newStringOfCap(); var x = y'
     # on the other hand... These get turned into moves now.
-    a.p = cast[ptr StrContent](region.alloc(contentSize(b.len)))
+    a.p = cast[ptr StrContent](region.alloc(region, contentSize(b.len)))
     a.p.region = region
     a.p.cap = b.len
     copyMem(unsafeAddr a.p.data[0], unsafeAddr b.p.data[0], b.len+1)
@@ -95,12 +83,12 @@ proc resize(old: int): int {.inline.} =
   elif old < 65536: result = old * 2
   else: result = old * 3 div 2 # for large arrays * 3/2 is better
 
-proc prepareAdd(s: var NimString; addlen: int) =
+proc prepareAdd(s: var NimStringV2; addlen: int) {.compilerRtl.} =
   if isLiteral(s):
     let oldP = s.p
     # can't mutate a literal, so we need a fresh copy here:
     let region = getLocalAllocator()
-    s.p = cast[ptr StrContent](region.alloc(contentSize(s.len + addlen)))
+    s.p = cast[ptr StrContent](region.alloc(region, contentSize(s.len + addlen)))
     s.p.region = region
     s.p.cap = s.len + addlen
     if s.len > 0:
@@ -108,61 +96,65 @@ proc prepareAdd(s: var NimString; addlen: int) =
       copyMem(unsafeAddr s.p.data[0], unsafeAddr oldP.data[0], s.len)
   elif s.len + addlen > s.p.cap:
     let cap = max(s.len + addlen, resize(s.p.cap))
-    s.p = s.p.region.realloc(s.p, oldSize = contentSize(s.p.cap), newSize = contentSize(cap))
+    s.p = cast[ptr StrContent](s.p.region.realloc(s.p.region, s.p,
+      oldSize = contentSize(s.p.cap),
+      newSize = contentSize(cap)))
     s.p.cap = cap
 
-proc nimAddCharV1(s: var NimString; c: char) {.compilerRtl.} =
+proc nimAddCharV1(s: var NimStringV2; c: char) {.compilerRtl.} =
   prepareAdd(s, 1)
   s.p.data[s.len] = c
   s.p.data[s.len+1] = '\0'
   inc s.len
 
-proc ensure(s: var string; newLen: int) =
-  let old = s.cap
-  if newLen >= old:
-    s.cap = max((old * 3) shr 1, newLen)
-    if s.cap > 0:
-      s.data = cast[type(s.data)](realloc(s.data, old + 1, s.cap + 1))
-
-proc add*(s: var string; y: string) =
-  if y.len != 0:
-    let newLen = s.len + y.len
-    ensure(s, newLen)
-    copyMem(addr s.data[len], y.data, y.data.len + 1)
-    s.len = newLen
-
-proc newString*(len: int): string =
-  result.len = len
-  result.cap = len
-  if len > 0:
-    result.data = alloc0(len+1)
-
-converter toCString(x: string): cstring {.core, inline.} =
-  if x.len == 0: cstring"" else: cast[cstring](x.data)
-
-proc newStringOfCap*(cap: int): string =
-  result.len = 0
-  result.cap = cap
-  if cap > 0:
-    result.data = alloc(cap+1)
-
-proc `&`*(a, b: string): string =
-  let sum = a.len + b.len
-  result = newStringOfCap(sum)
-  result.len = sum
-  copyMem(addr result.data[0], a.data, a.len)
-  copyMem(addr result.data[a.len], b.data, b.len)
-  if sum > 0:
-    result.data[sum] = '\0'
-
-proc concat(x: openArray[string]): string {.core.} =
-  ## used be the code generator to optimize 'x & y & z ...'
-  var sum = 0
-  for i in 0 ..< x.len: inc(sum, x[i].len)
-  result = newStringOfCap(sum)
-  sum = 0
-  for i in 0 ..< x.len:
-    let L = x[i].len
-    copyMem(addr result.data[sum], x[i].data, L)
-    inc(sum, L)
-
+proc toNimStr(str: cstring, len: int): NimStringV2 {.compilerProc.} =
+  if len <= 0:
+    result = NimStringV2(len: 0, p: nil)
+  else:
+    let region = getLocalAllocator()
+    var p = cast[ptr StrContent](region.alloc(region, contentSize(len)))
+    p.region = region
+    p.cap = len
+    if len > 0:
+      # we are about to append, so there is no need to copy the \0 terminator:
+      copyMem(unsafeAddr p.data[0], str, len)
+    result = NimStringV2(len: 0, p: p)
+
+proc cstrToNimstr(str: cstring): NimStringV2 {.compilerRtl.} =
+  if str == nil: toNimStr(str, 0)
+  else: toNimStr(str, str.len)
+
+proc nimToCStringConv(s: NimStringV2): cstring {.compilerProc, inline.} =
+  if s.len == 0: result = cstring""
+  else: result = cstring(unsafeAddr s.p.data)
+
+proc appendString(dest: var NimStringV2; src: NimStringV2) {.compilerproc, inline.} =
+  if src.len > 0:
+    # also copy the \0 terminator:
+    copyMem(unsafeAddr dest.p.data[dest.len], unsafeAddr src.p.data[0], src.len+1)
+
+proc appendChar(dest: var NimStringV2; c: char) {.compilerproc, inline.} =
+  dest.p.data[dest.len] = c
+  dest.p.data[dest.len+1] = '\0'
+  inc dest.len
+
+proc rawNewString(space: int): NimStringV2 {.compilerProc.} =
+  # this is also 'system.newStringOfCap'.
+  if space <= 0:
+    result = NimStringV2(len: 0, p: nil)
+  else:
+    let region = getLocalAllocator()
+    var p = cast[ptr StrContent](region.alloc(region, contentSize(space)))
+    p.region = region
+    p.cap = space
+    result = NimStringV2(len: 0, p: p)
+
+proc mnewString(len: int): NimStringV2 {.compilerProc.} =
+  if len <= 0:
+    result = NimStringV2(len: 0, p: nil)
+  else:
+    let region = getLocalAllocator()
+    var p = cast[ptr StrContent](region.alloc(region, contentSize(len)))
+    p.region = region
+    p.cap = len
+    result = NimStringV2(len: len, p: p)
diff --git a/lib/system.nim b/lib/system.nim
index 620dff724..1defe20ee 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -211,6 +211,7 @@ proc new*(T: typedesc): auto =
   new(r)
   return r
 
+const ThisIsSystem = true
 
 proc internalNew*[T](a: var ref T) {.magic: "New", noSideEffect.}
   ## leaked implementation detail. Do not use.
@@ -426,8 +427,9 @@ when not defined(JS) and not defined(gcDestructors):
     NimString = ptr NimStringDesc
 
 when not defined(JS) and not defined(nimscript):
-  template space(s: PGenericSeq): int {.dirty.} =
-    s.reserved and not (seqShallowFlag or strlitFlag)
+  when not defined(gcDestructors):
+    template space(s: PGenericSeq): int {.dirty.} =
+      s.reserved and not (seqShallowFlag or strlitFlag)
   include "system/hti"
 
 type
@@ -730,7 +732,8 @@ proc newSeqOfCap*[T](cap: Natural): seq[T] {.
   ## ``cap``.
   discard
 
-when not defined(JS):
+when not defined(JS) and not defined(gcDestructors):
+  # XXX enable this for --gc:destructors
   proc newSeqUninitialized*[T: SomeNumber](len: Natural): seq[T] =
     ## creates a new sequence of type ``seq[T]`` with length ``len``.
     ##
@@ -1502,11 +1505,11 @@ const hasAlloc = (hostOS != "standalone" or not defined(nogc)) and not defined(n
 
 when not defined(JS) and not defined(nimscript) and hostOS != "standalone":
   include "system/cgprocs"
-when not defined(JS) and not defined(nimscript) and hasAlloc:
+when not defined(JS) and not defined(nimscript) and hasAlloc and not defined(gcDestructors):
   proc addChar(s: NimString, c: char): NimString {.compilerProc, benign.}
 
-proc add *[T](x: var seq[T], y: T) {.magic: "AppendSeqElem", noSideEffect.}
-proc add *[T](x: var seq[T], y: openArray[T]) {.noSideEffect.} =
+proc add*[T](x: var seq[T], y: T) {.magic: "AppendSeqElem", noSideEffect.}
+proc add*[T](x: var seq[T], y: openArray[T]) {.noSideEffect.} =
   ## Generic proc for adding a data item `y` to a container `x`.
   ## For containers that have an order, `add` means *append*. New generic
   ## containers should also call their adding proc `add` for consistency.
@@ -2829,6 +2832,58 @@ else:
     if x < 0: -x else: x
 {.pop.}
 
+when not defined(JS):
+  proc likely_proc(val: bool): bool {.importc: "likely", nodecl, nosideeffect.}
+  proc unlikely_proc(val: bool): bool {.importc: "unlikely", nodecl, nosideeffect.}
+
+template likely*(val: bool): bool =
+  ## Hints the optimizer that `val` is likely going to be true.
+  ##
+  ## You can use this template to decorate a branch condition. On certain
+  ## platforms this can help the processor predict better which branch is
+  ## going to be run. Example:
+  ##
+  ## .. code-block:: nim
+  ##   for value in inputValues:
+  ##     if likely(value <= 100):
+  ##       process(value)
+  ##     else:
+  ##       echo "Value too big!"
+  ##
+  ## On backends without branch prediction (JS and the nimscript VM), this
+  ## template will not affect code execution.
+  when nimvm:
+    val
+  else:
+    when defined(JS):
+      val
+    else:
+      likely_proc(val)
+
+template unlikely*(val: bool): bool =
+  ## Hints the optimizer that `val` is likely going to be false.
+  ##
+  ## You can use this proc to decorate a branch condition. On certain
+  ## platforms this can help the processor predict better which branch is
+  ## going to be run. Example:
+  ##
+  ## .. code-block:: nim
+  ##   for value in inputValues:
+  ##     if unlikely(value > 100):
+  ##       echo "Value too big!"
+  ##     else:
+  ##       process(value)
+  ##
+  ## On backends without branch prediction (JS and the nimscript VM), this
+  ## template will not affect code execution.
+  when nimvm:
+    val
+  else:
+    when defined(JS):
+      val
+    else:
+      unlikely_proc(val)
+
 type
   FileSeekPos* = enum ## Position relative to which seek should happen
                       # The values are ordered so that they match with stdio
@@ -2862,10 +2917,11 @@ when not defined(JS): #and not defined(nimscript):
       when declared(nimGC_setStackBottom):
         nimGC_setStackBottom(locals)
 
-    {.push profiler: off.}
-    var
-      strDesc = TNimType(size: sizeof(string), kind: tyString, flags: {ntfAcyclic})
-    {.pop.}
+    when not defined(gcDestructors):
+      {.push profiler: off.}
+      var
+        strDesc = TNimType(size: sizeof(string), kind: tyString, flags: {ntfAcyclic})
+      {.pop.}
 
 
   # ----------------- IO Part ------------------------------------------------
@@ -3302,8 +3358,9 @@ when not defined(JS): #and not defined(nimscript):
       while f.readLine(res): yield res
 
   when not defined(nimscript) and hasAlloc:
-    include "system/assign"
-    include "system/repr"
+    when not defined(gcDestructors):
+      include "system/assign"
+      include "system/repr"
 
   when hostOS != "standalone" and not defined(nimscript):
     proc getCurrentException*(): ref Exception {.compilerRtl, inl, benign.} =
@@ -3410,58 +3467,6 @@ proc quit*(errormsg: string, errorcode = QuitFailure) {.noReturn.} =
 {.pop.} # checks
 {.pop.} # hints
 
-when not defined(JS):
-  proc likely_proc(val: bool): bool {.importc: "likely", nodecl, nosideeffect.}
-  proc unlikely_proc(val: bool): bool {.importc: "unlikely", nodecl, nosideeffect.}
-
-template likely*(val: bool): bool =
-  ## Hints the optimizer that `val` is likely going to be true.
-  ##
-  ## You can use this template to decorate a branch condition. On certain
-  ## platforms this can help the processor predict better which branch is
-  ## going to be run. Example:
-  ##
-  ## .. code-block:: nim
-  ##   for value in inputValues:
-  ##     if likely(value <= 100):
-  ##       process(value)
-  ##     else:
-  ##       echo "Value too big!"
-  ##
-  ## On backends without branch prediction (JS and the nimscript VM), this
-  ## template will not affect code execution.
-  when nimvm:
-    val
-  else:
-    when defined(JS):
-      val
-    else:
-      likely_proc(val)
-
-template unlikely*(val: bool): bool =
-  ## Hints the optimizer that `val` is likely going to be false.
-  ##
-  ## You can use this proc to decorate a branch condition. On certain
-  ## platforms this can help the processor predict better which branch is
-  ## going to be run. Example:
-  ##
-  ## .. code-block:: nim
-  ##   for value in inputValues:
-  ##     if unlikely(value > 100):
-  ##       echo "Value too big!"
-  ##     else:
-  ##       process(value)
-  ##
-  ## On backends without branch prediction (JS and the nimscript VM), this
-  ## template will not affect code execution.
-  when nimvm:
-    val
-  else:
-    when defined(JS):
-      val
-    else:
-      unlikely_proc(val)
-
 proc `/`*(x, y: int): float {.inline, noSideEffect.} =
   ## integer division that results in a float.
   result = toFloat(x) / toFloat(y)
@@ -4090,6 +4095,21 @@ template once*(body: untyped): untyped =
 
 {.pop.} #{.push warning[GcMem]: off, warning[Uninit]: off.}
 
+proc substr*(s: string, first, last: int): string =
+  let L = max(min(last, high(s)) - first + 1, 0)
+  result = newString(L)
+  for i in 0 .. L-1:
+    result[i] = s[i+first]
+
+proc substr*(s: string, first = 0): string =
+  ## copies a slice of `s` into a new string and returns this new
+  ## string. The bounds `first` and `last` denote the indices of
+  ## the first and last characters that shall be copied. If ``last``
+  ## is omitted, it is treated as ``high(s)``. If ``last >= s.len``, ``s.len``
+  ## is used instead: This means ``substr`` can also be used to `cut`:idx:
+  ## or `limit`:idx: a string's length.
+  result = substr(s, first, high(s))
+
 when defined(nimconfig):
   include "system/nimscript"
 
@@ -4164,21 +4184,6 @@ when not defined(js):
   proc toOpenArrayByte*(x: string; first, last: int): openarray[byte] {.
     magic: "Slice".}
 
-proc substr*(s: string, first, last: int): string =
-  let L = max(min(last, high(s)) - first + 1, 0)
-  result = newString(L)
-  for i in 0 .. L-1:
-    result[i] = s[i+first]
-
-proc substr*(s: string, first = 0): string =
-  ## copies a slice of `s` into a new string and returns this new
-  ## string. The bounds `first` and `last` denote the indices of
-  ## the first and last characters that shall be copied. If ``last``
-  ## is omitted, it is treated as ``high(s)``. If ``last >= s.len``, ``s.len``
-  ## is used instead: This means ``substr`` can also be used to `cut`:idx:
-  ## or `limit`:idx: a string's length.
-  result = substr(s, first, high(s))
-
 type
   ForLoopStmt* {.compilerProc.} = object ## special type that marks a macro
                                          ## as a `for-loop macro`:idx:
diff --git a/lib/system/assign.nim b/lib/system/assign.nim
index 16b56aba7..2b74e6682 100644
--- a/lib/system/assign.nim
+++ b/lib/system/assign.nim
@@ -202,11 +202,6 @@ proc objectInit(dest: pointer, typ: PNimType) =
 
 # ---------------------- assign zero -----------------------------------------
 
-proc nimDestroyRange[T](r: T) {.compilerProc.} =
-  # internal proc used for destroying sequences and arrays
-  mixin `=destroy`
-  for i in countup(0, r.len - 1): `=destroy`(r[i])
-
 proc genericReset(dest: pointer, mt: PNimType) {.compilerProc, benign.}
 proc genericResetAux(dest: pointer, n: ptr TNimNode) =
   var d = cast[ByteAddress](dest)
diff --git a/lib/system/cgprocs.nim b/lib/system/cgprocs.nim
index 660c68116..72219c2b7 100644
--- a/lib/system/cgprocs.nim
+++ b/lib/system/cgprocs.nim
@@ -12,7 +12,6 @@
 type
   LibHandle = pointer       # private type
   ProcAddr = pointer        # library loading and loading of procs:
-{.deprecated: [TLibHandle: LibHandle, TProcAddr: ProcAddr].}
 
 proc nimLoadLibrary(path: string): LibHandle {.compilerproc.}
 proc nimUnloadLibrary(lib: LibHandle) {.compilerproc.}
diff --git a/lib/system/gc_ms.nim b/lib/system/gc_ms.nim
index 75f9c6749..96221b175 100644
--- a/lib/system/gc_ms.nim
+++ b/lib/system/gc_ms.nim
@@ -264,12 +264,13 @@ proc forAllChildren(cell: PCell, op: WalkOp) =
     of tyRef, tyOptAsRef: # common case
       forAllChildrenAux(cellToUsr(cell), cell.typ.base, op)
     of tySequence:
-      var d = cast[ByteAddress](cellToUsr(cell))
-      var s = cast[PGenericSeq](d)
-      if s != nil:
-        for i in 0..s.len-1:
-          forAllChildrenAux(cast[pointer](d +% i *% cell.typ.base.size +%
-            GenericSeqSize), cell.typ.base, op)
+      when not defined(gcDestructors):
+        var d = cast[ByteAddress](cellToUsr(cell))
+        var s = cast[PGenericSeq](d)
+        if s != nil:
+          for i in 0..s.len-1:
+            forAllChildrenAux(cast[pointer](d +% i *% cell.typ.base.size +%
+              GenericSeqSize), cell.typ.base, op)
     else: discard
 
 proc rawNewObj(typ: PNimType, size: int, gch: var GcHeap): pointer =
@@ -310,53 +311,54 @@ proc newObjNoInit(typ: PNimType, size: int): pointer {.compilerRtl.} =
   result = rawNewObj(typ, size, gch)
   when defined(memProfiler): nimProfile(size)
 
-proc newSeq(typ: PNimType, len: int): pointer {.compilerRtl.} =
-  # `newObj` already uses locks, so no need for them here.
-  let size = addInt(mulInt(len, typ.base.size), GenericSeqSize)
-  result = newObj(typ, size)
-  cast[PGenericSeq](result).len = len
-  cast[PGenericSeq](result).reserved = len
-  when defined(memProfiler): nimProfile(size)
-
 proc newObjRC1(typ: PNimType, size: int): pointer {.compilerRtl.} =
   result = rawNewObj(typ, size, gch)
   zeroMem(result, size)
   when defined(memProfiler): nimProfile(size)
 
-proc newSeqRC1(typ: PNimType, len: int): pointer {.compilerRtl.} =
-  let size = addInt(mulInt(len, typ.base.size), GenericSeqSize)
-  result = newObj(typ, size)
-  cast[PGenericSeq](result).len = len
-  cast[PGenericSeq](result).reserved = len
-  when defined(memProfiler): nimProfile(size)
-
-proc growObj(old: pointer, newsize: int, gch: var GcHeap): pointer =
-  acquire(gch)
-  collectCT(gch, newsize + sizeof(Cell))
-  var ol = usrToCell(old)
-  sysAssert(ol.typ != nil, "growObj: 1")
-  gcAssert(ol.typ.kind in {tyString, tySequence}, "growObj: 2")
-
-  var res = cast[PCell](rawAlloc(gch.region, newsize + sizeof(Cell)))
-  var elemSize = 1
-  if ol.typ.kind != tyString: elemSize = ol.typ.base.size
-  incTypeSize ol.typ, newsize
-
-  var oldsize = cast[PGenericSeq](old).len*elemSize + GenericSeqSize
-  copyMem(res, ol, oldsize + sizeof(Cell))
-  zeroMem(cast[pointer](cast[ByteAddress](res)+% oldsize +% sizeof(Cell)),
-          newsize-oldsize)
-  sysAssert((cast[ByteAddress](res) and (MemAlign-1)) == 0, "growObj: 3")
-  when withBitvectors: incl(gch.allocated, res)
-  when useCellIds:
-    inc gch.idGenerator
-    res.id = gch.idGenerator
-  release(gch)
-  result = cellToUsr(res)
-  when defined(memProfiler): nimProfile(newsize-oldsize)
+when not defined(gcDestructors):
+  proc newSeq(typ: PNimType, len: int): pointer {.compilerRtl.} =
+    # `newObj` already uses locks, so no need for them here.
+    let size = addInt(mulInt(len, typ.base.size), GenericSeqSize)
+    result = newObj(typ, size)
+    cast[PGenericSeq](result).len = len
+    cast[PGenericSeq](result).reserved = len
+    when defined(memProfiler): nimProfile(size)
+
+  proc newSeqRC1(typ: PNimType, len: int): pointer {.compilerRtl.} =
+    let size = addInt(mulInt(len, typ.base.size), GenericSeqSize)
+    result = newObj(typ, size)
+    cast[PGenericSeq](result).len = len
+    cast[PGenericSeq](result).reserved = len
+    when defined(memProfiler): nimProfile(size)
+
+  proc growObj(old: pointer, newsize: int, gch: var GcHeap): pointer =
+    acquire(gch)
+    collectCT(gch, newsize + sizeof(Cell))
+    var ol = usrToCell(old)
+    sysAssert(ol.typ != nil, "growObj: 1")
+    gcAssert(ol.typ.kind in {tyString, tySequence}, "growObj: 2")
+
+    var res = cast[PCell](rawAlloc(gch.region, newsize + sizeof(Cell)))
+    var elemSize = 1
+    if ol.typ.kind != tyString: elemSize = ol.typ.base.size
+    incTypeSize ol.typ, newsize
+
+    var oldsize = cast[PGenericSeq](old).len*elemSize + GenericSeqSize
+    copyMem(res, ol, oldsize + sizeof(Cell))
+    zeroMem(cast[pointer](cast[ByteAddress](res)+% oldsize +% sizeof(Cell)),
+            newsize-oldsize)
+    sysAssert((cast[ByteAddress](res) and (MemAlign-1)) == 0, "growObj: 3")
+    when withBitvectors: incl(gch.allocated, res)
+    when useCellIds:
+      inc gch.idGenerator
+      res.id = gch.idGenerator
+    release(gch)
+    result = cellToUsr(res)
+    when defined(memProfiler): nimProfile(newsize-oldsize)
 
-proc growObj(old: pointer, newsize: int): pointer {.rtl.} =
-  result = growObj(old, newsize, gch)
+  proc growObj(old: pointer, newsize: int): pointer {.rtl.} =
+    result = growObj(old, newsize, gch)
 
 {.push profiler:off.}
 
diff --git a/lib/system/hti.nim b/lib/system/hti.nim
index 45b1d1cd3..bb3769ac4 100644
--- a/lib/system/hti.nim
+++ b/lib/system/hti.nim
@@ -7,7 +7,7 @@
 #    distribution, for details about the copyright.
 #
 
-when declared(NimString):
+when declared(ThisIsSystem):
   # we are in system module:
   {.pragma: codegenType, compilerproc.}
 else:
diff --git a/lib/system/jssys.nim b/lib/system/jssys.nim
index e12bab184..5fff869f0 100644
--- a/lib/system/jssys.nim
+++ b/lib/system/jssys.nim
@@ -31,8 +31,6 @@ type
 
   JSRef = ref RootObj # Fake type.
 
-{.deprecated: [TSafePoint: SafePoint, TCallFrame: CallFrame].}
-
 var
   framePtr {.importc, nodecl, volatile.}: PCallFrame
   excHandler {.importc, nodecl, volatile.}: int = 0
@@ -506,7 +504,7 @@ proc chckNilDisp(p: pointer) {.compilerproc.} =
   if p == nil:
     sysFatal(NilAccessError, "cannot dispatch; dispatcher is nil")
 
-type NimString = string # hack for hti.nim
+const ThisIsSystem = true # for hti.nim
 include "system/hti"
 
 proc isFatPointer(ti: PNimType): bool =
diff --git a/lib/system/mmdisp.nim b/lib/system/mmdisp.nim
index ff2da7aba..e7e14b948 100644
--- a/lib/system/mmdisp.nim
+++ b/lib/system/mmdisp.nim
@@ -554,7 +554,7 @@ else:
   else:
     include "system/gc"
 
-when not declared(nimNewSeqOfCap):
+when not declared(nimNewSeqOfCap) and not defined(gcDestructors):
   proc nimNewSeqOfCap(typ: PNimType, cap: int): pointer {.compilerproc.} =
     when defined(gcRegions):
       let s = mulInt(cap, typ.base.size)  # newStr already adds GenericSeqSize
diff --git a/lib/system/sysio.nim b/lib/system/sysio.nim
index f3a576be0..f6e691c0d 100644
--- a/lib/system/sysio.nim
+++ b/lib/system/sysio.nim
@@ -148,7 +148,7 @@ proc readLine(f: File, line: var TaintedString): bool =
   if line.string.isNil:
     line = TaintedString(newStringOfCap(80))
   else:
-    when not defined(nimscript):
+    when not defined(nimscript) and not defined(gcDestructors):
       sp = cint(cast[PGenericSeq](line.string).space)
     line.string.setLen(sp)
   while true:
diff --git a/lib/system/widestrs.nim b/lib/system/widestrs.nim
index a8b28c279..85e5e1462 100644
--- a/lib/system/widestrs.nim
+++ b/lib/system/widestrs.nim
@@ -10,13 +10,12 @@
 # Nim support for C/C++'s `wide strings`:idx:. This is part of the system
 # module! Do not import it directly!
 
-when not declared(NimString):
+when not declared(ThisIsSystem):
   {.error: "You must not import this module explicitly".}
 
 type
   Utf16Char* = distinct int16
   WideCString* = ref UncheckedArray[Utf16Char]
-{.deprecated: [TUtf16Char: Utf16Char].}
 
 proc len*(w: WideCString): int =
   ## returns the length of a widestring. This traverses the whole string to