WIP: SSO based strings for ARC/ORC, opt-in via -d:nimsso

compiler/ccgcalls.nim

@@ -344,7 +344,8 @@ proc expressionsNeedsTmp(p: BProc, a: TLoc): TLoc =
 
 proc genArgStringToCString(p: BProc, n: PNode; result: var Builder; needsTmp: bool) {.inline.} =
   var a = initLocExpr(p, n[0])
-  let ra = withTmpIfNeeded(p, a, needsTmp).rdLoc
+  let tmp = withTmpIfNeeded(p, a, needsTmp)
+  let ra = if p.config.isDefined("nimsso"): addrLoc(p.config, tmp) else: tmp.rdLoc
   result.addCall(cgsymValue(p.module, "nimToCStringConv"), ra)
 
 proc genArg(p: BProc, n: PNode, param: PSym; call: PNode; result: var Builder; needsTmp = false) =

compiler/ccgexprs.nim

@@ -320,12 +320,16 @@ proc genOpenArrayConv(p: BProc; d: TLoc; a: TLoc; flags: TAssignmentFlags) =
       p.s(cpsStmts).addCallStmt(
         cgsymValue(p.module, "nimPrepareStrMutationV2"),
         bra)
-
     let rd = d.rdLoc
-    let ra = a.rdLoc
-    p.s(cpsStmts).addFieldAssignment(rd, "Field0",
-      cIfExpr(dataFieldAccessor(p, ra), dataField(p, ra), NimNil))
     let la = lenExpr(p, a)
+    if p.config.isDefined("nimsso"):
+      let bra = byRefLoc(p, a)
+      p.s(cpsStmts).addFieldAssignment(rd, "Field0",
+        cCall(cgsymValue(p.module, "nimStrData"), bra))
+    else:
+      let ra = a.rdLoc
+      p.s(cpsStmts).addFieldAssignment(rd, "Field0",
+        cIfExpr(dataFieldAccessor(p, ra), dataField(p, ra), NimNil))
     p.s(cpsStmts).addFieldAssignment(rd, "Field1", la)
   else:
     internalError(p.config, a.lode.info, "cannot handle " & $a.t.kind)
@@ -1316,8 +1320,13 @@ proc genSeqElem(p: BProc, n, x, y: PNode, d: var TLoc) =
     let bra = byRefLoc(p, a)
     p.s(cpsStmts).addCallStmt(cgsymValue(p.module, "nimPrepareStrMutationV2"),
       bra)
-  let ra = rdLoc(a)
-  putIntoDest(p, d, n, subscript(dataField(p, ra), rcb), a.storage)
+  if p.config.isDefined("nimsso") and ty.kind == tyString:
+    let bra = byRefLoc(p, a)
+    putIntoDest(p, d, n,
+      subscript(cCall(cgsymValue(p.module, "nimStrData"), bra), rcb), a.storage)
+  else:
+    let ra = rdLoc(a)
+    putIntoDest(p, d, n, subscript(dataField(p, ra), rcb), a.storage)
 
 proc genBracketExpr(p: BProc; n: PNode; d: var TLoc) =
   var ty = skipTypes(n[0].typ, abstractVarRange + tyUserTypeClasses)
@@ -2124,12 +2133,20 @@ proc genRepr(p: BProc, e: PNode, d: var TLoc) =
       let ra = rdLoc(a)
       putIntoDest(p, b, e, ra & cArgumentSeparator & ra & "Len_0", a.storage)
     of tyString, tySequence:
-      let ra = rdLoc(a)
       let la = lenExpr(p, a)
-      putIntoDest(p, b, e,
-        cIfExpr(dataFieldAccessor(p, ra), dataField(p, ra), NimNil) &
-          cArgumentSeparator & la,
-        a.storage)
+      if p.config.isDefined("nimsso") and
+          skipTypes(a.t, abstractVarRange).kind == tyString:
+        let bra = byRefLoc(p, a)
+        putIntoDest(p, b, e,
+          cCall(cgsymValue(p.module, "nimStrData"), bra) &
+            cArgumentSeparator & la,
+          a.storage)
+      else:
+        let ra = rdLoc(a)
+        putIntoDest(p, b, e,
+          cIfExpr(dataFieldAccessor(p, ra), dataField(p, ra), NimNil) &
+            cArgumentSeparator & la,
+          a.storage)
     of tyArray:
       let ra = rdLoc(a)
       let la = cIntValue(lengthOrd(p.config, a.t))
@@ -2710,9 +2727,9 @@ proc genConv(p: BProc, e: PNode, d: var TLoc) =
 
 proc convStrToCStr(p: BProc, n: PNode, d: var TLoc) =
   var a: TLoc = initLocExpr(p, n[0])
+  let arg = if p.config.isDefined("nimsso"): addrLoc(p.config, a) else: rdLoc(a)
   putIntoDest(p, d, n,
-    cgCall(p, "nimToCStringConv", rdLoc(a)),
-#   "($1 ? $1->data : (NCSTRING)\"\")" % [a.rdLoc],
+    cgCall(p, "nimToCStringConv", arg),
     a.storage)
 
 proc convCStrToStr(p: BProc, n: PNode, d: var TLoc) =
@@ -2789,13 +2806,19 @@ proc genMove(p: BProc; n: PNode; d: var TLoc) =
     var src: TLoc = initLocExpr(p, n[2])
     let destVal = rdLoc(a)
     let srcVal = rdLoc(src)
-    p.s(cpsStmts).addSingleIfStmt(
-      cOp(NotEqual,
-        dotField(destVal, "p"),
-        dotField(srcVal, "p"))):
+    if p.config.isDefined("nimsso") and
+        n[1].typ.skipTypes(abstractVar).kind == tyString:
+      # SmallString: destroy dst then struct-copy src; no .p field aliasing needed
       genStmts(p, n[3])
-    p.s(cpsStmts).addFieldAssignment(destVal, "len", dotField(srcVal, "len"))
-    p.s(cpsStmts).addFieldAssignment(destVal, "p", dotField(srcVal, "p"))
+      genAssignment(p, a, src, {})
+    else:
+      p.s(cpsStmts).addSingleIfStmt(
+        cOp(NotEqual,
+          dotField(destVal, "p"),
+          dotField(srcVal, "p"))):
+        genStmts(p, n[3])
+      p.s(cpsStmts).addFieldAssignment(destVal, "len", dotField(srcVal, "len"))
+      p.s(cpsStmts).addFieldAssignment(destVal, "p", dotField(srcVal, "p"))
   else:
     if d.k == locNone: d = getTemp(p, n.typ)
     if p.config.selectedGC in {gcArc, gcAtomicArc, gcOrc, gcYrc}:
@@ -2832,15 +2855,19 @@ proc genDestroy(p: BProc; n: PNode) =
     case t.kind
     of tyString:
       var a: TLoc = initLocExpr(p, arg)
-      let ra = rdLoc(a)
-      let rp = dotField(ra, "p")
-      p.s(cpsStmts).addSingleIfStmt(
-        cOp(And, rp,
-          cOp(Not, cOp(BitAnd, NimInt,
-            derefField(rp, "cap"),
-            NimStrlitFlag)))):
-        let fn = if optThreads in p.config.globalOptions: "deallocShared" else: "dealloc"
-        p.s(cpsStmts).addCallStmt(cgsymValue(p.module, fn), rp)
+      if p.config.isDefined("nimsso"):
+        # SmallString: delegate to nimDestroyStrV1 (rc-based, handles static strings)
+        p.s(cpsStmts).addCallStmt(cgsymValue(p.module, "nimDestroyStrV1"), rdLoc(a))
+      else:
+        let ra = rdLoc(a)
+        let rp = dotField(ra, "p")
+        p.s(cpsStmts).addSingleIfStmt(
+          cOp(And, rp,
+            cOp(Not, cOp(BitAnd, NimInt,
+              derefField(rp, "cap"),
+              NimStrlitFlag)))):
+          let fn = if optThreads in p.config.globalOptions: "deallocShared" else: "dealloc"
+          p.s(cpsStmts).addCallStmt(cgsymValue(p.module, fn), rp)
     of tySequence:
       var a: TLoc = initLocExpr(p, arg)
       let ra = rdLoc(a)
@@ -4200,7 +4227,10 @@ proc genBracedInit(p: BProc, n: PNode; isConst: bool; optionalType: PType; resul
       genConstObjConstr(p, n, isConst, result)
     of tyString, tyCstring:
       if optSeqDestructors in p.config.globalOptions and n.kind != nkNilLit and ty == tyString:
-        genStringLiteralV2Const(p.module, n, isConst, result)
+        if p.config.isDefined("nimsso"):
+          genStringLiteralV3Const(p.module, n, isConst, result)
+        else:
+          genStringLiteralV2Const(p.module, n, isConst, result)
       else:
         var d: TLoc = initLocExpr(p, n)
         result.add rdLoc(d)

compiler/ccgliterals.nim

@@ -22,7 +22,11 @@ template detectVersion(field, corename) =
     result = 1
 
 proc detectStrVersion(m: BModule): int =
-  detectVersion(strVersion, "nimStrVersion")
+  if m.g.config.isDefined("nimsso") and
+      m.g.config.selectedGC in {gcArc, gcOrc, gcYrc, gcAtomicArc, gcHooks}:
+    result = 3
+  else:
+    detectVersion(strVersion, "nimStrVersion")
 
 proc detectSeqVersion(m: BModule): int =
   detectVersion(seqVersion, "nimSeqVersion")
@@ -128,6 +132,155 @@ proc genStringLiteralV2Const(m: BModule; n: PNode; isConst: bool; result: var Bu
     result.addField(strInit, name = "p"):
       result.add(cCast(ptrType("NimStrPayload"), cAddr(pureLit)))
 
+proc ssoCharLit(ch: char): string =
+  ## Return a C char literal for ch, with proper escaping.
+  const hexDigits = "0123456789abcdef"
+  result = "'"
+  case ch
+  of '\'': result.add("\\'")
+  of '\\': result.add("\\\\")
+  of '\0': result.add("\\0")
+  of '\n': result.add("\\n")
+  of '\r': result.add("\\r")
+  of '\t': result.add("\\t")
+  elif ch.ord < 32 or ch.ord == 127:
+    result.add("\\x")
+    result.add(hexDigits[ch.ord shr 4])
+    result.add(hexDigits[ch.ord and 0xf])
+  else:
+    result.add(ch)
+  result.add('\'')
+
+proc ssoPayloadLit(src: string; maxLen: int): string =
+  const AlwaysAvail = 7
+  result = "{"
+  for i in 0..<AlwaysAvail:
+    if i > 0: result.add(',')
+    let ch = if i < maxLen: src[i] else: '\0'
+    result.add(ssoCharLit(ch))
+  result.add('}')
+
+proc genStringLiteralV3Const(m: BModule; n: PNode; isConst: bool; result: var Builder) =
+  # Inline SmallString struct initializer for use inside const aggregate types.
+  # Short strings (<=7 chars) embed all chars directly. Long strings reference
+  # a static LongString block emitted separately into cfsStrData.
+  const AlwaysAvail = 7
+  let s = n.strVal
+
+  cgsym(m, "SmallString")
+  cgsym(m, "LongString")
+
+  var si: StructInitializer
+  result.addStructInitializer(si, kind = siOrderedStruct):
+    if s.len <= AlwaysAvail:
+      result.addField(si, name = "slen"):
+        result.addIntValue(s.len)
+      result.addField(si, name = "payload"):
+        result.add(ssoPayloadLit(s, s.len))
+      result.addField(si, name = "more"):
+        result.add(NimNil)
+    else:
+      # Emit the LongString block into cfsStrData and reference it inline.
+      let dataName = getTempName(m)
+      var res = newBuilder("")
+      res.addVarWithTypeAndInitializer(
+          if isConst: AlwaysConst else: Global,
+          name = dataName):
+        res.addSimpleStruct(m, name = "", baseType = ""):
+          res.addField(name = "rc", typ = NimInt)
+          res.addField(name = "fullLen", typ = NimInt)
+          res.addField(name = "capImpl", typ = NimInt)
+          res.addArrayField(name = "data", elementType = NimChar, len = s.len + 1)
+      do:
+        var di: StructInitializer
+        res.addStructInitializer(di, kind = siOrderedStruct):
+          res.addField(di, name = "rc"):
+            res.addIntValue(1)
+          res.addField(di, name = "fullLen"):
+            res.addIntValue(s.len)
+          res.addField(di, name = "capImpl"):
+            res.addIntValue(0)  # static, never freed
+          res.addField(di, name = "data"):
+            res.add(makeCString(s))
+      m.s[cfsStrData].add(extract(res))
+      result.addField(si, name = "slen"):
+        result.addIntValue(255)
+      result.addField(si, name = "payload"):
+        result.add(ssoPayloadLit(s, AlwaysAvail))
+      result.addField(si, name = "more"):
+        result.add(cCast(ptrType("LongString"), cAddr(dataName)))
+
+# ------ Version 3: SmallString (SSO) strings --------------------------------
+
+proc genStringLiteralV3(m: BModule; n: PNode; isConst: bool; result: var Builder) =
+  # SmallString literal. Always generate a fresh SmallString variable (like v2
+  # always generates a fresh outer NimStringV2). For long strings, cache the
+  # LongString payload to avoid duplicates within a module.
+  const AlwaysAvail = 7  # must match strs_v3.nim
+  let s = n.strVal
+  let tmp = getTempName(m)
+  result.add tmp
+
+  cgsym(m, "SmallString")
+  cgsym(m, "LongString")
+
+  var res = newBuilder("")
+  if s.len <= AlwaysAvail:
+    # Short: all chars fit in payload, more = NULL.
+    res.addVarWithInitializer(
+        if isConst: AlwaysConst else: Global,
+        name = tmp, typ = "SmallString"):
+      var si: StructInitializer
+      res.addStructInitializer(si, kind = siOrderedStruct):
+        res.addField(si, name = "slen"):
+          res.addIntValue(s.len)
+        res.addField(si, name = "payload"):
+          res.add(ssoPayloadLit(s, s.len))
+        res.addField(si, name = "more"):
+          res.add(NimNil)
+  else:
+    # Long: cache the LongString block to emit it only once per module per string.
+    # Always generate a fresh SmallString pointing at the (possibly cached) block.
+    let id = nodeTableTestOrSet(m.dataCache, n, m.labels)
+    var dataName: string
+    if id == m.labels:
+      dataName = getTempName(m)
+      res.addVarWithTypeAndInitializer(
+          if isConst: AlwaysConst else: Global,
+          name = dataName):
+        res.addSimpleStruct(m, name = "", baseType = ""):
+          res.addField(name = "rc", typ = NimInt)
+          res.addField(name = "fullLen", typ = NimInt)
+          res.addField(name = "capImpl", typ = NimInt)
+          res.addArrayField(name = "data", elementType = NimChar, len = s.len + 1)
+      do:
+        var di: StructInitializer
+        res.addStructInitializer(di, kind = siOrderedStruct):
+          res.addField(di, name = "rc"):
+            res.addIntValue(1)
+          res.addField(di, name = "fullLen"):
+            res.addIntValue(s.len)
+          res.addField(di, name = "capImpl"):
+            res.addIntValue(0)  # bit 0 = 0: static, never freed
+          res.addField(di, name = "data"):
+            res.add(makeCString(s))
+    else:
+      dataName = m.tmpBase & $id
+    # PayloadSize = AlwaysAvail + sizeof(pointer) - 1; sentinel slen = PayloadSize+1
+    # We just use a large value (255) that is guaranteed > PayloadSize on all platforms.
+    res.addVarWithInitializer(
+        if isConst: AlwaysConst else: Global,
+        name = tmp, typ = "SmallString"):
+      var si: StructInitializer
+      res.addStructInitializer(si, kind = siOrderedStruct):
+        res.addField(si, name = "slen"):
+          res.addIntValue(255)  # > PayloadSize on all platforms => long sentinel
+        res.addField(si, name = "payload"):
+          res.add(ssoPayloadLit(s, AlwaysAvail))
+        res.addField(si, name = "more"):
+          res.add(cCast(ptrType("LongString"), cAddr(dataName)))
+  m.s[cfsStrData].add(extract(res))
+
 # ------ Version selector ---------------------------------------------------
 
 proc genStringLiteralDataOnly(m: BModule; s: string; info: TLineInfo;
@@ -138,6 +291,8 @@ proc genStringLiteralDataOnly(m: BModule; s: string; info: TLineInfo;
     let tmp = getTempName(m)
     genStringLiteralDataOnlyV2(m, s, tmp, isConst)
     result.add tmp
+  of 3:
+    localError(m.config, info, "genStringLiteralDataOnly not supported for SmallString (nimsso)")
   else:
     localError(m.config, info, "cannot determine how to produce code for string literal")
 
@@ -148,5 +303,6 @@ proc genStringLiteral(m: BModule; n: PNode; result: var Builder) =
   case detectStrVersion(m)
   of 0, 1: genStringLiteralV1(m, n, result)
   of 2: genStringLiteralV2(m, n, isConst = true, result)
+  of 3: genStringLiteralV3(m, n, isConst = true, result)
   else:
     localError(m.config, n.info, "cannot determine how to produce code for string literal")

compiler/ccgtypes.nim

@@ -339,6 +339,10 @@ proc getSimpleTypeDesc(m: BModule; typ: PType): Rope =
       cgsym(m, "NimStrPayload")
       cgsym(m, "NimStringV2")
       result = typeNameOrLiteral(m, typ, "NimStringV2")
+    of 3:
+      cgsym(m, "LongString")
+      cgsym(m, "SmallString")
+      result = typeNameOrLiteral(m, typ, "SmallString")
     else:
       cgsym(m, "NimStringDesc")
       result = typeNameOrLiteral(m, typ, "NimStringDesc*")

compiler/cgen.nim

@@ -389,7 +389,11 @@ proc lenField(p: BProc, val: Rope): Rope {.inline.} =
 
 proc lenExpr(p: BProc; a: TLoc): Rope =
   if optSeqDestructors in p.config.globalOptions:
-    result = dotField(rdLoc(a), "len")
+    if p.config.isDefined("nimsso") and a.t != nil and
+        a.t.skipTypes(abstractInst).kind == tyString:
+      result = cCall(cgsymValue(p.module, "nimStrLen"), rdLoc(a))
+    else:
+      result = dotField(rdLoc(a), "len")
   else:
     let ra = rdLoc(a)
     result = cIfExpr(ra, lenField(p, ra), cIntValue(0))
@@ -530,7 +534,15 @@ proc resetLoc(p: BProc, loc: var TLoc) =
 
     let atyp = skipTypes(loc.t, abstractInst)
     let rl = rdLoc(loc)
-    if atyp.kind in {tyVar, tyLent}:
+    if typ.kind == tyString and p.config.isDefined("nimsso"):
+      # SmallString zero state: slen=0 suffices (slen<=AlwaysAvail => inline, no heap)
+      if atyp.kind in {tyVar, tyLent}:
+        p.s(cpsStmts).addAssignment(derefField(rl, "slen"), cIntValue(0))
+        p.s(cpsStmts).addAssignment(derefField(rl, "more"), NimNil)
+      else:
+        p.s(cpsStmts).addAssignment(dotField(rl, "slen"), cIntValue(0))
+        p.s(cpsStmts).addAssignment(dotField(rl, "more"), NimNil)
+    elif atyp.kind in {tyVar, tyLent}:
       p.s(cpsStmts).addAssignment(derefField(rl, "len"), cIntValue(0))
       p.s(cpsStmts).addAssignment(derefField(rl, "p"), NimNil)
     else:
@@ -580,8 +592,13 @@ proc constructLoc(p: BProc, loc: var TLoc, isTemp = false) =
   let typ = loc.t
   if optSeqDestructors in p.config.globalOptions and skipTypes(typ, abstractInst + {tyStatic}).kind in {tyString, tySequence}:
     let rl = rdLoc(loc)
-    p.s(cpsStmts).addFieldAssignment(rl, "len", cIntValue(0))
-    p.s(cpsStmts).addFieldAssignment(rl, "p", NimNil)
+    if skipTypes(typ, abstractInst + {tyStatic}).kind == tyString and p.config.isDefined("nimsso"):
+      # SmallString zero state: slen=0 suffices
+      p.s(cpsStmts).addFieldAssignment(rl, "slen", cIntValue(0))
+      p.s(cpsStmts).addFieldAssignment(rl, "more", NimNil)
+    else:
+      p.s(cpsStmts).addFieldAssignment(rl, "len", cIntValue(0))
+      p.s(cpsStmts).addFieldAssignment(rl, "p", NimNil)
   elif not isComplexValueType(typ):
     if containsGarbageCollectedRef(loc.t):
       var nilLoc: TLoc = initLoc(locTemp, loc.lode, OnStack)

compiler/liftdestructors.nim

@@ -701,11 +701,18 @@ proc fillStrOp(c: var TLiftCtx; t: PType; body, x, y: PNode) =
   of attachedAsgn, attachedDeepCopy, attachedDup:
     body.add callCodegenProc(c.g, "nimAsgnStrV2", c.info, genAddr(c, x), y)
   of attachedSink:
-    let moveCall = genBuiltin(c, mMove, "move", x)
-    moveCall.add y
-    doAssert t.destructor != nil
-    moveCall.add destructorCall(c, t.destructor, x)
-    body.add moveCall
+    if c.g.config.isDefined("nimsso"):
+      # SmallString: destroy old dst, then bit-copy src (no rc increment — this is a move).
+      # No .p aliasing check needed; rc-based destroy handles COW sharing correctly.
+      doAssert t.destructor != nil
+      body.add destructorCall(c, t.destructor, x)
+      body.add newAsgnStmt(x, y)
+    else:
+      let moveCall = genBuiltin(c, mMove, "move", x)
+      moveCall.add y
+      doAssert t.destructor != nil
+      moveCall.add destructorCall(c, t.destructor, x)
+      body.add moveCall
   of attachedDestructor:
     body.add genBuiltin(c, mDestroy, "destroy", x)
   of attachedTrace: