enables dfa for refc strings

compiler/injectdestructors.nim

@@ -165,11 +165,11 @@ proc isLastReadImpl(n: PNode; c: var Con; scope: var Scope): bool =
 
 template hasDestructorOrAsgn(c: var Con, typ: PType): bool =
   # bug #23354; an object type could have a non-trivial assignements when it is passed to a sink parameter
-  hasDestructor(c, typ) or (c.graph.config.selectedGC in {gcArc, gcOrc, gcAtomicArc} and
+  hasDestructor(c, typ) or (c.graph.config.selectedGC == gcRefc and typ.kind == tyString) or (c.graph.config.selectedGC in {gcArc, gcOrc, gcAtomicArc} and
         typ.kind == tyObject and not isTrivial(getAttachedOp(c.graph, typ, attachedAsgn)))
 
 proc isLastRead(n: PNode; c: var Con; s: var Scope): bool =
-  if not hasDestructorOrAsgn(c, n.typ): return true
+  if not hasDestructorOrAsgn(c, n.typ.skipTypes({tyGenericInst, tyAlias, tySink})): return true
 
   let m = skipConvDfa(n)
   result = isLastReadImpl(n, c, s)
@@ -286,7 +286,9 @@ proc deepAliases(dest, ri: PNode): bool =
     return aliases(dest, ri) != no
 
 proc genSink(c: var Con; s: var Scope; dest, ri: PNode; flags: set[MoveOrCopyFlag] = {}): PNode =
-  if (c.inLoopCond == 0 and (isFullyUnpackedTuple(dest) or IsDecl in flags or
+  if c.graph.config.selectedGC == gcRefc and dest.typ.skipTypes({tyGenericInst, tyAlias, tySink}).kind == tyString:
+    result = newFastAsgnStmt(dest, callCodegenProc(c.graph, "moveString", dest.info, ri))
+  elif (c.inLoopCond == 0 and (isFullyUnpackedTuple(dest) or IsDecl in flags or
       (isAnalysableFieldAccess(dest, c.owner) and isFirstWrite(dest, c)))) or
       isNoInit(dest) or IsReturn in flags:
     # optimize sink call into a bitwise memcopy

compiler/liftdestructors.nim

@@ -1036,6 +1036,8 @@ proc fillBody(c: var TLiftCtx; t: PType; body, x, y: PNode) =
   of tyString:
     if useNoGc(c, t):
       useSeqOrStrOp(c, t, body, x, y)
+    elif c.g.config.selectedGC == gcRefc:
+      defaultOp(c, t, body, x, y)
     elif tfHasAsgn in t.flags:
       discard considerUserDefinedOp(c, t, body, x, y)
     else:

compiler/semtypes.nim

@@ -2430,7 +2430,7 @@ proc processMagicType(c: PContext, m: PSym) =
   of mString:
     setMagicType(c.config, m, tyString, szUncomputedSize)
     rawAddSon(m.typ, getSysType(c.graph, m.info, tyChar))
-    if optSeqDestructors in c.config.globalOptions:
+    if optSeqDestructors in c.config.globalOptions or c.config.selectedGC == gcRefc:
       incl m.typ, tfHasAsgn
   of mCstring:
     setMagicIntegral(c.config, m, tyCstring, c.config.target.ptrSize)

lib/system/sysstr.nim

@@ -114,6 +114,12 @@ proc cstrToNimstr(str: cstring): NimString {.compilerRtl.} =
   if str == nil: NimString(nil)
   else: toNimStr(str, str.len)
 
+proc moveString(src: NimString): NimString {.compilerRtl.} =
+  if (src.reserved and strlitFlag) != 0:
+    result = toOwnedCopy(src)
+  else:
+    result = src
+
 proc copyString(src: NimString): NimString {.compilerRtl.} =
   ## Expects `src` to be initialized (len and terminating zero set)
   if src != nil: