scoped memory management (#14790)

* fixes the regressions
* closes #13936
* scope based memory management implemented
* enabled tcontrolflow.nim test case
* final cleanups

compiler/ccgcalls.nim

@@ -644,7 +644,33 @@ proc genNamedParamCall(p: BProc, ri: PNode, d: var TLoc) =
     pl.add(~"];$n")
     line(p, cpsStmts, pl)
 
+proc notYetAlive(n: PNode): bool {.inline.} =
+  let r = getRoot(n)
+  result = r != nil and r.loc.lode == nil
+
+proc isInactiveDestructorCall(p: BProc, e: PNode): bool =
+  #[ Consider this example.
+
+    var :tmpD_3281815
+    try:
+      if true:
+        return
+      let args_3280013 =
+        wasMoved_3281816(:tmpD_3281815)
+        `=_3280036`(:tmpD_3281815, [1])
+        :tmpD_3281815
+    finally:
+      `=destroy_3280027`(args_3280013)
+
+  We want to return early but the 'finally' section is traversed before
+  the 'let args = ...' statement. We exploit this to generate better
+  code for 'return'. ]#
+  result = e.len == 2 and e[0].kind == nkSym and
+    e[0].sym.name.s == "=destroy" and notYetAlive(e[1].skipAddr)
+
 proc genCall(p: BProc, e: PNode, d: var TLoc) =
+  if p.withinBlockLeaveActions > 0 and isInactiveDestructorCall(p, e):
+    return
   if e[0].typ.skipTypes({tyGenericInst, tyAlias, tySink, tyOwned}).callConv == ccClosure:
     genClosureCall(p, nil, e, d)
   elif e[0].kind == nkSym and sfInfixCall in e[0].sym.flags:

compiler/ccgexprs.nim

@@ -2066,10 +2066,14 @@ proc skipAddr(n: PNode): PNode =
 
 proc genWasMoved(p: BProc; n: PNode) =
   var a: TLoc
-  initLocExpr(p, n[1].skipAddr, a)
-  resetLoc(p, a)
-  #linefmt(p, cpsStmts, "#nimZeroMem((void*)$1, sizeof($2));$n",
-  #  [addrLoc(p.config, a), getTypeDesc(p.module, a.t)])
+  let n1 = n[1].skipAddr
+  if p.withinBlockLeaveActions > 0 and notYetAlive(n1):
+    discard
+  else:
+    initLocExpr(p, n1, a)
+    resetLoc(p, a)
+    #linefmt(p, cpsStmts, "#nimZeroMem((void*)$1, sizeof($2));$n",
+    #  [addrLoc(p.config, a), getTypeDesc(p.module, a.t)])
 
 proc genMove(p: BProc; n: PNode; d: var TLoc) =
   var a: TLoc
@@ -2593,10 +2597,12 @@ proc expr(p: BProc, n: PNode, d: var TLoc) =
       else:
         putLocIntoDest(p, d, sym.loc)
     of skTemp:
-      if sym.loc.r == nil:
-        # we now support undeclared 'skTemp' variables for easier
-        # transformations in other parts of the compiler:
-        assignLocalVar(p, n)
+      when false:
+        # this is more harmful than helpful.
+        if sym.loc.r == nil:
+          # we now support undeclared 'skTemp' variables for easier
+          # transformations in other parts of the compiler:
+          assignLocalVar(p, n)
       if sym.loc.r == nil or sym.loc.t == nil:
         #echo "FAILED FOR PRCO ", p.prc.name.s
         #echo renderTree(p.prc.ast, {renderIds})

compiler/ccgstmts.nim

@@ -200,6 +200,7 @@ proc blockLeaveActions(p: BProc, howManyTrys, howManyExcepts: int) =
 
   var stack = newSeq[tuple[fin: PNode, inExcept: bool, label: Natural]](0)
 
+  inc p.withinBlockLeaveActions
   for i in 1..howManyTrys:
     let tryStmt = p.nestedTryStmts.pop
     if p.config.exc == excSetjmp:
@@ -217,6 +218,8 @@ proc blockLeaveActions(p: BProc, howManyTrys, howManyExcepts: int) =
     if finallyStmt != nil:
       genStmts(p, finallyStmt[0])
 
+  dec p.withinBlockLeaveActions
+
   # push old elements again:
   for i in countdown(howManyTrys-1, 0):
     p.nestedTryStmts.add(stack[i])
@@ -861,10 +864,10 @@ proc genStringCase(p: BProc, t: PNode, d: var TLoc) =
     genCaseGeneric(p, t, d, "", "if (#eqStrings($1, $2)) goto $3;$n")
 
 proc branchHasTooBigRange(b: PNode): bool =
-  for i in 0..<b.len-1:
+  for it in b:
     # last son is block
-    if (b[i].kind == nkRange) and
-        b[i][1].intVal - b[i][0].intVal > RangeExpandLimit:
+    if (it.kind == nkRange) and
+        it[1].intVal - it[0].intVal > RangeExpandLimit:
       return true
 
 proc ifSwitchSplitPoint(p: BProc, n: PNode): int =
@@ -988,9 +991,14 @@ proc genTryCpp(p: BProc, t: PNode, d: var TLoc) =
   let fin = if t[^1].kind == nkFinally: t[^1] else: nil
   p.nestedTryStmts.add((fin, false, 0.Natural))
 
-  startBlock(p, "try {$n")
-  expr(p, t[0], d)
-  endBlock(p)
+  if t.kind == nkHiddenTryStmt:
+    lineCg(p, cpsStmts, "try {$n", [])
+    expr(p, t[0], d)
+    lineCg(p, cpsStmts, "}$n", [])
+  else:
+    startBlock(p, "try {$n")
+    expr(p, t[0], d)
+    endBlock(p)
 
   # First pass: handle Nim based exceptions:
   lineCg(p, cpsStmts, "catch (#Exception* T$1_) {$n", [etmp+1])
@@ -1335,13 +1343,13 @@ proc genTrySetjmp(p: BProc, t: PNode, d: var TLoc) =
       linefmt(p, cpsStmts, "$1.status = _setjmp($1.context);$n", [safePoint])
     else:
       linefmt(p, cpsStmts, "$1.status = setjmp($1.context);$n", [safePoint])
-    startBlock(p, "if ($1.status == 0) {$n", [safePoint])
+    lineCg(p, cpsStmts, "if ($1.status == 0) {$n", [safePoint])
   let fin = if t[^1].kind == nkFinally: t[^1] else: nil
   p.nestedTryStmts.add((fin, quirkyExceptions, 0.Natural))
   expr(p, t[0], d)
   if not quirkyExceptions:
     linefmt(p, cpsStmts, "#popSafePoint();$n", [])
-    endBlock(p)
+    lineCg(p, cpsStmts, "}$n", [])
     startBlock(p, "else {$n")
     linefmt(p, cpsStmts, "#popSafePoint();$n", [])
     genRestoreFrameAfterException(p)

compiler/cgen.nim

@@ -1561,7 +1561,7 @@ 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();$N", []))
-    if m.config.target.targetOS != osStandalone and m.config.selectedGC != gcNone:
+    if m.config.target.targetOS != osStandalone and m.config.selectedGC notin {gcNone, gcArc, gcOrc}:
       g.mainDatInit.add(ropecg(m, "\t#initStackBottomWith((void *)&inner);$N", []))
 
   if m.s[cfsInitProc].len > 0:
@@ -1666,6 +1666,10 @@ proc genInitCode(m: BModule) =
     writeSection(preInitProc, cpsInit, m.hcrOn)
     writeSection(preInitProc, cpsStmts)
     prc.addf("}$N", [])
+    when false:
+      m.initProc.blocks[0].sections[cpsLocals].add m.preInitProc.s(cpsLocals)
+      m.initProc.blocks[0].sections[cpsInit].prepend m.preInitProc.s(cpsInit)
+      m.initProc.blocks[0].sections[cpsStmts].prepend m.preInitProc.s(cpsStmts)
 
   # add new scope for following code, because old vcc compiler need variable
   # be defined at the top of the block

compiler/cgendata.nim

@@ -97,6 +97,7 @@ type
                               # requires 'T x = T()' to become 'T x; x = T()'
                               # (yes, C++ is weird like that)
     withinTryWithExcept*: int # required for goto based exception handling
+    withinBlockLeaveActions*: int # complex to explain
     sigConflicts*: CountTable[string]
 
   TTypeSeq* = seq[PType]

compiler/semstmts.nim

@@ -229,8 +229,8 @@ proc semTry(c: PContext, n: PNode; flags: TExprFlags): PNode =
         a[0][2] = newSymNode(symbol, a[0][2].info)
 
       elif a.len == 1:
-          # count number of ``except: body`` blocks
-          inc catchAllExcepts
+        # count number of ``except: body`` blocks
+        inc catchAllExcepts
 
       else:
         # support ``except KeyError, ValueError, ... : body``

compiler/spawn.nim

@@ -10,7 +10,7 @@
 ## This module implements threadpool's ``spawn``.
 
 import ast, types, idents, magicsys, msgs, options, modulegraphs,
-  lowerings, liftdestructors
+  lowerings, liftdestructors, renderer
 from trees import getMagic, getRoot
 
 proc callProc(a: PNode): PNode =
@@ -321,7 +321,7 @@ proc wrapProcForSpawn*(g: ModuleGraph; owner: PSym; spawnExpr: PNode; retType: P
     result = newNodeI(nkStmtList, n.info)
 
   if n.kind notin nkCallKinds:
-    localError(g.config, n.info, "'spawn' takes a call expression")
+    localError(g.config, n.info, "'spawn' takes a call expression; got " & $n)
     return
   if optThreadAnalysis in g.config.globalOptions:
     if {tfThread, tfNoSideEffect} * n[0].typ.flags == {}: