adds an experimental `mm:atomicArc` switch (#21798)

19 files changed, 71 insertions, 53 deletions

diff --git a/compiler/btrees.nim b/compiler/btrees.nim
index c79442249..92f07f6b0 100644
--- a/compiler/btrees.nim
+++ b/compiler/btrees.nim
@@ -68,7 +68,7 @@ proc copyHalf[Key, Val](h, result: Node[Key, Val]) =
       result.links[j] = h.links[Mhalf + j]
   else:
     for j in 0..<Mhalf:
-      when defined(gcArc) or defined(gcOrc):
+      when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
         result.vals[j] = move h.vals[Mhalf + j]
       else:
         shallowCopy(result.vals[j], h.vals[Mhalf + j])
@@ -91,7 +91,7 @@ proc insert[Key, Val](h: Node[Key, Val], key: Key, val: Val): Node[Key, Val] =
       if less(key, h.keys[j]): break
       inc j
     for i in countdown(h.entries, j+1):
-      when defined(gcArc) or defined(gcOrc):
+      when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
         h.vals[i] = move h.vals[i-1]
       else:
         shallowCopy(h.vals[i], h.vals[i-1])
diff --git a/compiler/ccgcalls.nim b/compiler/ccgcalls.nim
index 65c814fb9..b55c89c1d 100644
--- a/compiler/ccgcalls.nim
+++ b/compiler/ccgcalls.nim
@@ -269,7 +269,7 @@ 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, gcOrc} and
+  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, {})
diff --git a/compiler/ccgexprs.nim b/compiler/ccgexprs.nim
index e351e95b0..66f92f12e 100644
--- a/compiler/ccgexprs.nim
+++ b/compiler/ccgexprs.nim
@@ -382,7 +382,7 @@ proc genAssignment(p: BProc, dest, src: TLoc, flags: TAssignmentFlags) =
     else:
       linefmt(p, cpsStmts, "$1 = $2;$n", [rdLoc(dest), rdLoc(src)])
   of tyArray:
-    if containsGarbageCollectedRef(dest.t) and p.config.selectedGC notin {gcArc, gcOrc, gcHooks}:
+    if containsGarbageCollectedRef(dest.t) and p.config.selectedGC notin {gcArc, gcAtomicArc, gcOrc, gcHooks}:
       genGenericAsgn(p, dest, src, flags)
     else:
       linefmt(p, cpsStmts,
@@ -2403,7 +2403,7 @@ proc genSlice(p: BProc; e: PNode; d: var TLoc) =
   let (x, y) = genOpenArraySlice(p, e, e.typ, e.typ.lastSon,
     prepareForMutation = e[1].kind == nkHiddenDeref and
                          e[1].typ.skipTypes(abstractInst).kind == tyString and
-                         p.config.selectedGC in {gcArc, gcOrc})
+                         p.config.selectedGC in {gcArc, gcAtomicArc, gcOrc})
   if d.k == locNone: getTemp(p, e.typ, d)
   linefmt(p, cpsStmts, "$1.Field0 = $2; $1.Field1 = $3;$n", [rdLoc(d), x, y])
   when false:
@@ -2585,7 +2585,7 @@ proc genMagicExpr(p: BProc, e: PNode, d: var TLoc, op: TMagic) =
       let n = semparallel.liftParallel(p.module.g.graph, p.module.idgen, p.module.module, e)
       expr(p, n, d)
   of mDeepCopy:
-    if p.config.selectedGC in {gcArc, gcOrc} and optEnableDeepCopy notin p.config.globalOptions:
+    if p.config.selectedGC in {gcArc, gcAtomicArc, gcOrc} and optEnableDeepCopy notin p.config.globalOptions:
       localError(p.config, e.info,
         "for --gc:arc|orc 'deepcopy' support has to be enabled with --deepcopy:on")
 
diff --git a/compiler/cgen.nim b/compiler/cgen.nim
index a57654239..65f8040f5 100644
--- a/compiler/cgen.nim
+++ b/compiler/cgen.nim
@@ -1581,11 +1581,11 @@ proc genMainProc(m: BModule) =
     m.includeHeader("<libc/component.h>")
 
   let initStackBottomCall =
-    if m.config.target.targetOS == osStandalone or m.config.selectedGC in {gcNone, gcArc, gcOrc}: "".rope
+    if m.config.target.targetOS == osStandalone or m.config.selectedGC in {gcNone, gcArc, gcAtomicArc, gcOrc}: "".rope
     else: ropecg(m, "\t#initStackBottomWith((void *)&inner);$N", [])
   inc(m.labels)
 
-  let isVolatile = if m.config.selectedGC notin {gcNone, gcArc, gcOrc}: "1" else: "0"
+  let isVolatile = if m.config.selectedGC notin {gcNone, gcArc, gcAtomicArc, gcOrc}: "1" else: "0"
   appcg(m, m.s[cfsProcs], PreMainBody, [m.g.mainDatInit, m.g.otherModsInit, m.config.nimMainPrefix, posixCmdLine, isVolatile])
 
   if m.config.target.targetOS == osWindows and
@@ -1725,7 +1725,7 @@ proc registerModuleToMain(g: BModuleList; m: BModule) =
   if sfSystemModule in m.module.flags:
     if emulatedThreadVars(m.config) and m.config.target.targetOS != osStandalone:
       g.mainDatInit.add(ropecg(m, "\t#initThreadVarsEmulation();$N", []))
-    if m.config.target.targetOS != osStandalone and m.config.selectedGC notin {gcNone, gcArc, gcOrc}:
+    if m.config.target.targetOS != osStandalone and m.config.selectedGC notin {gcNone, gcArc, gcAtomicArc, gcOrc}:
       g.mainDatInit.add(ropecg(m, "\t#initStackBottomWith((void *)&inner);$N", []))
 
   if m.s[cfsInitProc].len > 0:
@@ -2177,7 +2177,7 @@ proc finalCodegenActions*(graph: ModuleGraph; m: BModule; n: PNode): PNode =
         cgsym(m, "rawWrite")
 
       # raise dependencies on behalf of genMainProc
-      if m.config.target.targetOS != osStandalone and m.config.selectedGC notin {gcNone, gcArc, gcOrc}:
+      if m.config.target.targetOS != osStandalone and m.config.selectedGC notin {gcNone, gcArc, gcAtomicArc, gcOrc}:
         cgsym(m, "initStackBottomWith")
       if emulatedThreadVars(m.config) and m.config.target.targetOS != osStandalone:
         cgsym(m, "initThreadVarsEmulation")
diff --git a/compiler/commands.nim b/compiler/commands.nim
index c31476b45..93a36e714 100644
--- a/compiler/commands.nim
+++ b/compiler/commands.nim
@@ -238,7 +238,7 @@ proc processCompile(conf: ConfigRef; filename: string) =
   extccomp.addExternalFileToCompile(conf, found)
 
 const
-  errNoneBoehmRefcExpectedButXFound = "'arc', 'orc', 'markAndSweep', 'boehm', 'go', 'none', 'regions', or 'refc' expected, but '$1' found"
+  errNoneBoehmRefcExpectedButXFound = "'arc', 'orc', 'atomicArc', 'markAndSweep', 'boehm', 'go', 'none', 'regions', or 'refc' expected, but '$1' found"
   errNoneSpeedOrSizeExpectedButXFound = "'none', 'speed' or 'size' expected, but '$1' found"
   errGuiConsoleOrLibExpectedButXFound = "'gui', 'console' or 'lib' expected, but '$1' found"
   errInvalidExceptionSystem = "'goto', 'setjmp', 'cpp' or 'quirky' expected, but '$1' found"
@@ -262,6 +262,7 @@ proc testCompileOptionArg*(conf: ConfigRef; switch, arg: string, info: TLineInfo
     of "go": result = conf.selectedGC == gcGo
     of "none": result = conf.selectedGC == gcNone
     of "stack", "regions": result = conf.selectedGC == gcRegions
+    of "atomicarc": result = conf.selectedGC == gcAtomicArc
     else: localError(conf, info, errNoneBoehmRefcExpectedButXFound % arg)
   of "opt":
     case arg.normalize
@@ -516,14 +517,7 @@ proc initOrcDefines*(conf: ConfigRef) =
   if conf.exc == excNone and conf.backend != backendCpp:
     conf.exc = excGoto
 
-proc registerArcOrc(pass: TCmdLinePass, conf: ConfigRef, isOrc: bool) =
-  if isOrc:
-    conf.selectedGC = gcOrc
-    defineSymbol(conf.symbols, "gcorc")
-  else:
-    conf.selectedGC = gcArc
-    defineSymbol(conf.symbols, "gcarc")
-
+proc registerArcOrc(pass: TCmdLinePass, conf: ConfigRef) =
   defineSymbol(conf.symbols, "gcdestructors")
   incl conf.globalOptions, optSeqDestructors
   incl conf.globalOptions, optTinyRtti
@@ -562,9 +556,17 @@ proc processMemoryManagementOption(switch, arg: string, pass: TCmdLinePass,
       conf.selectedGC = gcMarkAndSweep
       defineSymbol(conf.symbols, "gcmarkandsweep")
     of "destructors", "arc":
-      registerArcOrc(pass, conf, false)
+      conf.selectedGC = gcArc
+      defineSymbol(conf.symbols, "gcarc")
+      registerArcOrc(pass, conf)
     of "orc":
-      registerArcOrc(pass, conf, true)
+      conf.selectedGC = gcOrc
+      defineSymbol(conf.symbols, "gcorc")
+      registerArcOrc(pass, conf)
+    of "atomicarc":
+      conf.selectedGC = gcAtomicArc
+      defineSymbol(conf.symbols, "gcatomicarc")
+      registerArcOrc(pass, conf)
     of "hooks":
       conf.selectedGC = gcHooks
       defineSymbol(conf.symbols, "gchooks")
diff --git a/compiler/dfa.nim b/compiler/dfa.nim
index 61a921ba0..d145e31c3 100644
--- a/compiler/dfa.nim
+++ b/compiler/dfa.nim
@@ -493,7 +493,7 @@ proc constructCfg*(s: PSym; body: PNode; root: PSym): ControlFlowGraph =
     gen(c, body)
     if root.kind == skResult:
       genImplicitReturn(c)
-  when defined(gcArc) or defined(gcOrc):
+  when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
     result = c.code # will move
   else:
     shallowCopy(result, c.code)
diff --git a/compiler/injectdestructors.nim b/compiler/injectdestructors.nim
index d9a2da5a0..ab0fa02d9 100644
--- a/compiler/injectdestructors.nim
+++ b/compiler/injectdestructors.nim
@@ -66,7 +66,7 @@ proc hasDestructor(c: Con; t: PType): bool {.inline.} =
   result = ast.hasDestructor(t)
   when toDebug.len > 0:
     # for more effective debugging
-    if not result and c.graph.config.selectedGC in {gcArc, gcOrc}:
+    if not result and c.graph.config.selectedGC in {gcArc, gcOrc, gcAtomicArc}:
       assert(not containsGarbageCollectedRef(t))
 
 proc getTemp(c: var Con; s: var Scope; typ: PType; info: TLineInfo): PNode =
@@ -452,7 +452,7 @@ proc passCopyToSink(n: PNode; c: var Con; s: var Scope): PNode =
         ("passing '$1' to a sink parameter introduces an implicit copy; " &
         "if possible, rearrange your program's control flow to prevent it") % $n)
   else:
-    if c.graph.config.selectedGC in {gcArc, gcOrc}:
+    if c.graph.config.selectedGC in {gcArc, gcOrc, gcAtomicArc}:
       assert(not containsManagedMemory(n.typ))
     if n.typ.skipTypes(abstractInst).kind in {tyOpenArray, tyVarargs}:
       localError(c.graph.config, n.info, "cannot create an implicit openArray copy to be passed to a sink parameter")
@@ -495,7 +495,7 @@ proc ensureDestruction(arg, orig: PNode; c: var Con; s: var Scope): PNode =
     result = arg
 
 proc cycleCheck(n: PNode; c: var Con) =
-  if c.graph.config.selectedGC != gcArc: return
+  if c.graph.config.selectedGC notin {gcArc, gcAtomicArc}: return
   var value = n[1]
   if value.kind == nkClosure:
     value = value[1]
@@ -838,7 +838,7 @@ proc p(n: PNode; c: var Con; s: var Scope; mode: ProcessMode; tmpFlags = {sfSing
 
       if n[0].kind == nkSym and n[0].sym.magic in {mNew, mNewFinalize}:
         result[0] = copyTree(n[0])
-        if c.graph.config.selectedGC in {gcHooks, gcArc, gcOrc}:
+        if c.graph.config.selectedGC in {gcHooks, gcArc, gcAtomicArc, gcOrc}:
           let destroyOld = c.genDestroy(result[1])
           result = newTree(nkStmtList, destroyOld, result)
       else:
diff --git a/compiler/liftdestructors.nim b/compiler/liftdestructors.nim
index 3a997af82..34ab3cc8e 100644
--- a/compiler/liftdestructors.nim
+++ b/compiler/liftdestructors.nim
@@ -159,7 +159,7 @@ proc fillBodyObj(c: var TLiftCtx; n, body, x, y: PNode; enforceDefaultOp: bool)
     let f = n.sym
     let b = if c.kind == attachedTrace: y else: y.dotField(f)
     if (sfCursor in f.flags and f.typ.skipTypes(abstractInst).kind in {tyRef, tyProc} and
-        c.g.config.selectedGC in {gcArc, gcOrc, gcHooks}) or
+        c.g.config.selectedGC in {gcArc, gcAtomicArc, gcOrc, gcHooks}) or
         enforceDefaultOp:
       defaultOp(c, f.typ, body, x.dotField(f), b)
     else:
@@ -827,7 +827,7 @@ proc closureOp(c: var TLiftCtx; t: PType; body, x, y: PNode) =
     call[1] = y
     body.add newAsgnStmt(x, call)
   elif (optOwnedRefs in c.g.config.globalOptions and
-      optRefCheck in c.g.config.options) or c.g.config.selectedGC in {gcArc, gcOrc}:
+      optRefCheck in c.g.config.options) or c.g.config.selectedGC in {gcArc, gcAtomicArc, gcOrc}:
     let xx = genBuiltin(c, mAccessEnv, "accessEnv", x)
     xx.typ = getSysType(c.g, c.info, tyPointer)
     case c.kind
@@ -879,7 +879,7 @@ proc fillBody(c: var TLiftCtx; t: PType; body, x, y: PNode) =
       tyPtr, tyUncheckedArray, tyVar, tyLent:
     defaultOp(c, t, body, x, y)
   of tyRef:
-    if c.g.config.selectedGC in {gcArc, gcOrc}:
+    if c.g.config.selectedGC in {gcArc, gcOrc, gcAtomicArc}:
       atomicRefOp(c, t, body, x, y)
     elif (optOwnedRefs in c.g.config.globalOptions and
         optRefCheck in c.g.config.options):
@@ -888,7 +888,7 @@ proc fillBody(c: var TLiftCtx; t: PType; body, x, y: PNode) =
       defaultOp(c, t, body, x, y)
   of tyProc:
     if t.callConv == ccClosure:
-      if c.g.config.selectedGC in {gcArc, gcOrc}:
+      if c.g.config.selectedGC in {gcArc, gcOrc, gcAtomicArc}:
         atomicClosureOp(c, t, body, x, y)
       else:
         closureOp(c, t, body, x, y)
@@ -1039,7 +1039,7 @@ proc produceSym(g: ModuleGraph; c: PContext; typ: PType; kind: TTypeAttachedOp;
     result.ast[bodyPos].add newAsgnStmt(d, src)
   else:
     var tk: TTypeKind
-    if g.config.selectedGC in {gcArc, gcOrc, gcHooks}:
+    if g.config.selectedGC in {gcArc, gcOrc, gcHooks, gcAtomicArc}:
       tk = skipTypes(typ, {tyOrdinal, tyRange, tyInferred, tyGenericInst, tyStatic, tyAlias, tySink}).kind
     else:
       tk = tyNone # no special casing for strings and seqs
diff --git a/compiler/msgs.nim b/compiler/msgs.nim
index 8e391f2fb..05ace315e 100644
--- a/compiler/msgs.nim
+++ b/compiler/msgs.nim
@@ -226,7 +226,7 @@ proc setDirtyFile*(conf: ConfigRef; fileIdx: FileIndex; filename: AbsoluteFile)
 
 proc setHash*(conf: ConfigRef; fileIdx: FileIndex; hash: string) =
   assert fileIdx.int32 >= 0
-  when defined(gcArc) or defined(gcOrc):
+  when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
     conf.m.fileInfos[fileIdx.int32].hash = hash
   else:
     shallowCopy(conf.m.fileInfos[fileIdx.int32].hash, hash)
@@ -234,7 +234,7 @@ proc setHash*(conf: ConfigRef; fileIdx: FileIndex; hash: string) =
 
 proc getHash*(conf: ConfigRef; fileIdx: FileIndex): string =
   assert fileIdx.int32 >= 0
-  when defined(gcArc) or defined(gcOrc):
+  when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
     result = conf.m.fileInfos[fileIdx.int32].hash
   else:
     shallowCopy(result, conf.m.fileInfos[fileIdx.int32].hash)
diff --git a/compiler/nimfix/prettybase.nim b/compiler/nimfix/prettybase.nim
index 78c24bae3..b5a7ba42b 100644
--- a/compiler/nimfix/prettybase.nim
+++ b/compiler/nimfix/prettybase.nim
@@ -22,7 +22,7 @@ proc replaceDeprecated*(conf: ConfigRef; info: TLineInfo; oldSym, newSym: PIdent
   let last = first+identLen(line, first)-1
   if cmpIgnoreStyle(line[first..last], oldSym.s) == 0:
     var x = line.substr(0, first-1) & newSym.s & line.substr(last+1)
-    when defined(gcArc) or defined(gcOrc):
+    when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
       conf.m.fileInfos[info.fileIndex.int32].lines[info.line.int-1] = move x
     else:
       system.shallowCopy(conf.m.fileInfos[info.fileIndex.int32].lines[info.line.int-1], x)
@@ -38,7 +38,7 @@ proc replaceComment*(conf: ConfigRef; info: TLineInfo) =
   if line[first] != '#': inc first
 
   var x = line.substr(0, first-1) & "discard " & line.substr(first+1).escape
-  when defined(gcArc) or defined(gcOrc):
+  when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
     conf.m.fileInfos[info.fileIndex.int32].lines[info.line.int-1] = move x
   else:
     system.shallowCopy(conf.m.fileInfos[info.fileIndex.int32].lines[info.line.int-1], x)
diff --git a/compiler/options.nim b/compiler/options.nim
index da9c9cbbb..a9f1e7542 100644
--- a/compiler/options.nim
+++ b/compiler/options.nim
@@ -184,6 +184,7 @@ type
     gcRegions = "regions"
     gcArc = "arc"
     gcOrc = "orc"
+    gcAtomicArc = "atomicArc"
     gcMarkAndSweep = "markAndSweep"
     gcHooks = "hooks"
     gcRefc = "refc"
diff --git a/compiler/pragmas.nim b/compiler/pragmas.nim
index 10d77a17e..31414063a 100644
--- a/compiler/pragmas.nim
+++ b/compiler/pragmas.nim
@@ -535,7 +535,7 @@ proc processCompile(c: PContext, n: PNode) =
     n[i] = c.semConstExpr(c, n[i])
     case n[i].kind
     of nkStrLit, nkRStrLit, nkTripleStrLit:
-      when defined(gcArc) or defined(gcOrc):
+      when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
         result = n[i].strVal
       else:
         shallowCopy(result, n[i].strVal)
diff --git a/compiler/scriptconfig.nim b/compiler/scriptconfig.nim
index 27ea94aae..21b0eb195 100644
--- a/compiler/scriptconfig.nim
+++ b/compiler/scriptconfig.nim
@@ -227,7 +227,7 @@ proc runNimScript*(cache: IdentCache; scriptName: AbsoluteFile;
   if optOwnedRefs in oldGlobalOptions:
     conf.globalOptions.incl {optTinyRtti, optOwnedRefs, optSeqDestructors}
     defineSymbol(conf.symbols, "nimv2")
-  if conf.selectedGC in {gcArc, gcOrc}:
+  if conf.selectedGC in {gcArc, gcOrc, gcAtomicArc}:
     conf.globalOptions.incl {optTinyRtti, optSeqDestructors}
     defineSymbol(conf.symbols, "nimv2")
 
diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index a01466868..4dd7840f1 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -249,7 +249,7 @@ proc isCastable(c: PContext; dst, src: PType, info: TLineInfo): bool =
   if skipTypes(dst, abstractInst).kind == tyBuiltInTypeClass:
     return false
   let conf = c.config
-  if conf.selectedGC in {gcArc, gcOrc}:
+  if conf.selectedGC in {gcArc, gcOrc, gcAtomicArc}:
     let d = skipTypes(dst, abstractInst)
     let s = skipTypes(src, abstractInst)
     if d.kind == tyRef and s.kind == tyRef and s[0].isFinal != d[0].isFinal:
diff --git a/compiler/sempass2.nim b/compiler/sempass2.nim
index baa37a45f..7024c99fe 100644
--- a/compiler/sempass2.nim
+++ b/compiler/sempass2.nim
@@ -1480,7 +1480,7 @@ proc trackProc*(c: PContext; s: PSym, body: PNode) =
       let param = params[i].sym
       let typ = param.typ
       if isSinkTypeForParam(typ) or
-          (t.config.selectedGC in {gcArc, gcOrc} and
+          (t.config.selectedGC in {gcArc, gcOrc, gcAtomicArc} and
             (isClosure(typ.skipTypes(abstractInst)) or param.id in t.escapingParams)):
         createTypeBoundOps(t, typ, param.info)
       if isOutParam(typ) and param.id notin t.init:
diff --git a/compiler/semtypes.nim b/compiler/semtypes.nim
index 750ab2216..f4b284f7e 100644
--- a/compiler/semtypes.nim
+++ b/compiler/semtypes.nim
@@ -968,7 +968,7 @@ proc semAnyRef(c: PContext; n: PNode; kind: TTypeKind; prev: PType): PType =
       t.rawAddSonNoPropagationOfTypeFlags result
       result = t
     else: discard
-    if result.kind == tyRef and c.config.selectedGC in {gcArc, gcOrc}:
+    if result.kind == tyRef and c.config.selectedGC in {gcArc, gcOrc, gcAtomicArc}:
       result.flags.incl tfHasAsgn
 
 proc findEnforcedStaticType(t: PType): PType =
diff --git a/compiler/spawn.nim b/compiler/spawn.nim
index add36759d..7423fdfaa 100644
--- a/compiler/spawn.nim
+++ b/compiler/spawn.nim
@@ -37,7 +37,7 @@ proc spawnResult*(t: PType; inParallel: bool): TSpawnResult =
   else: srFlowVar
 
 proc flowVarKind(c: ConfigRef, t: PType): TFlowVarKind =
-  if c.selectedGC in {gcArc, gcOrc}: fvBlob
+  if c.selectedGC in {gcArc, gcOrc, gcAtomicArc}: fvBlob
   elif t.skipTypes(abstractInst).kind in {tyRef, tyString, tySequence}: fvGC
   elif containsGarbageCollectedRef(t): fvInvalid
   else: fvBlob
@@ -66,7 +66,7 @@ proc addLocalVar(g: ModuleGraph; varSection, varInit: PNode; idgen: IdGenerator;
   vpart[2] = if varInit.isNil: v else: vpart[1]
   varSection.add vpart
   if varInit != nil:
-    if g.config.selectedGC in {gcArc, gcOrc}:
+    if g.config.selectedGC in {gcArc, gcOrc, gcAtomicArc}:
       # inject destructors pass will do its own analysis
       varInit.add newFastMoveStmt(g, newSymNode(result), v)
     else:
diff --git a/compiler/vm.nim b/compiler/vm.nim
index dbb02cffa..ba3677cf1 100644
--- a/compiler/vm.nim
+++ b/compiler/vm.nim
@@ -121,7 +121,7 @@ template decodeBx(k: untyped) {.dirty.} =
   ensureKind(k)
 
 template move(a, b: untyped) {.dirty.} =
-  when defined(gcArc) or defined(gcOrc):
+  when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
     a = move b
   else:
     system.shallowCopy(a, b)
@@ -550,7 +550,7 @@ proc rawExecute(c: PCtx, start: int, tos: PStackFrame): TFullReg =
   # Used to keep track of where the execution is resumed.
   var savedPC = -1
   var savedFrame: PStackFrame
-  when defined(gcArc) or defined(gcOrc):
+  when defined(gcArc) or defined(gcOrc) or defined(gcAtomicArc):
     template updateRegsAlias = discard
     template regs: untyped = tos.slots
   else:
diff --git a/lib/system/arc.nim b/lib/system/arc.nim
index 55c4c412a..acb07174b 100644
--- a/lib/system/arc.nim
+++ b/lib/system/arc.nim
@@ -57,6 +57,21 @@ elif defined(nimArcIds):
 
   const traceId = -1
 
+when defined(gcAtomicArc) and hasThreadSupport:
+  template decrement(cell: Cell): untyped =
+    discard atomicDec(cell.rc, rcIncrement)
+  template increment(cell: Cell): untyped =
+    discard atomicInc(cell.rc, rcIncrement)
+  template count(x: Cell): untyped =
+    atomicLoadN(x.rc.addr, ATOMIC_ACQUIRE) shr rcShift
+else:
+  template decrement(cell: Cell): untyped =
+    dec(cell.rc, rcIncrement)
+  template increment(cell: Cell): untyped =
+    inc(cell.rc, rcIncrement)
+  template count(x: Cell): untyped =
+    x.rc shr rcShift
+
 proc nimNewObj(size, alignment: int): pointer {.compilerRtl.} =
   let hdrSize = align(sizeof(RefHeader), alignment)
   let s = size + hdrSize
@@ -69,7 +84,7 @@ proc nimNewObj(size, alignment: int): pointer {.compilerRtl.} =
     atomicInc gRefId
     if head(result).refId == traceId:
       writeStackTrace()
-      cfprintf(cstderr, "[nimNewObj] %p %ld\n", result, head(result).rc shr rcShift)
+      cfprintf(cstderr, "[nimNewObj] %p %ld\n", result, head(result).count)
   when traceCollector:
     cprintf("[Allocated] %p result: %p\n", result -! sizeof(RefHeader), result)
 
@@ -90,21 +105,21 @@ proc nimNewObjUninit(size, alignment: int): pointer {.compilerRtl.} =
     atomicInc gRefId
     if head(result).refId == traceId:
       writeStackTrace()
-      cfprintf(cstderr, "[nimNewObjUninit] %p %ld\n", result, head(result).rc shr rcShift)
+      cfprintf(cstderr, "[nimNewObjUninit] %p %ld\n", result, head(result).count)
 
   when traceCollector:
     cprintf("[Allocated] %p result: %p\n", result -! sizeof(RefHeader), result)
 
 proc nimDecWeakRef(p: pointer) {.compilerRtl, inl.} =
-  dec head(p).rc, rcIncrement
+  decrement head(p)
 
 proc nimIncRef(p: pointer) {.compilerRtl, inl.} =
   when defined(nimArcDebug):
     if head(p).refId == traceId:
       writeStackTrace()
-      cfprintf(cstderr, "[IncRef] %p %ld\n", p, head(p).rc shr rcShift)
+      cfprintf(cstderr, "[IncRef] %p %ld\n", p, head(p).count)
 
-  inc head(p).rc, rcIncrement
+  increment head(p)
   when traceCollector:
     cprintf("[INCREF] %p\n", head(p))
 
@@ -173,17 +188,17 @@ proc nimDecRefIsLast(p: pointer): bool {.compilerRtl, inl.} =
     when defined(nimArcDebug):
       if cell.refId == traceId:
         writeStackTrace()
-        cfprintf(cstderr, "[DecRef] %p %ld\n", p, cell.rc shr rcShift)
+        cfprintf(cstderr, "[DecRef] %p %ld\n", p, cell.count)
 
-    if (cell.rc and not rcMask) == 0:
+    if cell.count == 0:
       result = true
       when traceCollector:
         cprintf("[ABOUT TO DESTROY] %p\n", cell)
     else:
-      dec cell.rc, rcIncrement
+      decrement cell
       # According to Lins it's correct to do nothing else here.
       when traceCollector:
-        cprintf("[DeCREF] %p\n", cell)
+        cprintf("[DECREF] %p\n", cell)
 
 proc nimDupRef(dest: ptr pointer, src: pointer) {.compilerRtl, inl.} =
   dest[] = src