C code gen: generate even better code for the GC

lib/system/gc.nim

@@ -230,7 +230,8 @@ proc decRef(c: PCell) {.inline.} =
   if --c.refcount:
     rtlAddZCT(c)
   elif canBeCycleRoot(c):
-    # XXX if 'incRef' does this check, it should be unnecessary in 'decRef'
+    # unfortunately this is necessary here too, because a cycle might just
+    # have been broken up and we could recycle it.
     rtlAddCycleRoot(c) 
 
 proc incRef(c: PCell) {.inline.} = 
@@ -241,6 +242,11 @@ proc incRef(c: PCell) {.inline.} =
 proc nimGCref(p: pointer) {.compilerProc, inline.} = incRef(usrToCell(p))
 proc nimGCunref(p: pointer) {.compilerProc, inline.} = decRef(usrToCell(p))
 
+proc nimGCunrefNoCycle(p: pointer) {.compilerProc, inline.} =
+  var c = usrToCell(p)
+  if --c.refcount:
+    rtlAddZCT(c)
+
 proc asgnRef(dest: ppointer, src: pointer) {.compilerProc, inline.} =
   # the code generator calls this proc!
   sysAssert(not isOnStack(dest), "asgnRef")
@@ -252,7 +258,7 @@ proc asgnRef(dest: ppointer, src: pointer) {.compilerProc, inline.} =
 proc asgnRefNoCycle(dest: ppointer, src: pointer) {.compilerProc, inline.} =
   # the code generator calls this proc if it is known at compile time that no 
   # cycle is possible.
-  if src != nil: 
+  if src != nil:
     var c = usrToCell(src)
     ++c.refcount
   if dest[] != nil: 
@@ -761,7 +767,7 @@ proc collectCT(gch: var TGcHeap) =
     inc(gch.stat.stackScans)
     collectZCT(gch)
     when cycleGC:
-      if getOccupiedMem() >= gch.cycleThreshold or stressGC:
+      if getOccupiedMem(gch.region) >= gch.cycleThreshold or stressGC:
         collectCycles(gch)
         collectZCT(gch)
         inc(gch.stat.cycleCollections)

lib/system/sysstr.nim

@@ -72,6 +72,20 @@ proc copyString(src: NimString): NimString {.compilerProc.} =
     result.len = src.len
     c_memcpy(result.data, src.data, (src.len + 1) * sizeof(Char))
 
+proc copyStringRC1(src: NimString): NimString {.compilerProc.} =
+  if src != nil:
+    var s = src.space
+    if s < 8: s = 7
+    when defined(newObjRC1):
+      result = cast[NimString](newObjRC1(addr(strDesc), sizeof(TGenericSeq) +
+                               (s+1) * sizeof(char)))
+    else:
+      result = cast[NimString](newObj(addr(strDesc), sizeof(TGenericSeq) +
+                               (s+1) * sizeof(char)))
+    result.space = s
+    result.len = src.len
+    c_memcpy(result.data, src.data, (src.len + 1) * sizeof(Char))
+
 proc hashString(s: string): int {.compilerproc.} =
   # the compiler needs exactly the same hash function!
   # this used to be used for efficient generation of string case statements