arc: cursors for simple for loop variables (#15008)

* arc: cursors for simple for loop variables

* merged devel

compiler/injectdestructors.nim

@@ -1062,5 +1062,5 @@ proc injectDestructorCalls*(g: ModuleGraph; owner: PSym; n: PNode): PNode =
 
   if g.config.arcToExpand.hasKey(owner.name.s):
     echo "--expandArc: ", owner.name.s
-    echo renderTree(result, {renderIr})
+    echo renderTree(result, {renderIr, renderNoComments})
     echo "-- end of expandArc ------------------------"

compiler/transf.nim

@@ -350,7 +350,7 @@ proc transformYield(c: PTransf, n: PNode): PNode =
     # Choose the right assignment instruction according to the given ``lhs``
     # node since it may not be a nkSym (a stack-allocated skForVar) but a
     # nkDotExpr (a heap-allocated slot into the envP block)
-    case lhs.kind:
+    case lhs.kind
     of nkSym:
       internalAssert c.graph.config, lhs.sym.kind == skForVar
       result = newAsgnStmt(c, nkFastAsgn, lhs, rhs)
@@ -592,6 +592,22 @@ proc findWrongOwners(c: PTransf, n: PNode) =
   else:
     for i in 0..<n.safeLen: findWrongOwners(c, n[i])
 
+proc isSimpleIteratorVar(iter: PSym): bool =
+  proc rec(n: PNode; owner: PSym; dangerousYields: var int) =
+    case n.kind
+    of nkEmpty..nkNilLit: discard
+    of nkYieldStmt:
+      if n[0].kind == nkSym and n[0].sym.owner == owner:
+        discard "good: yield a single variable that we own"
+      else:
+        inc dangerousYields
+    else:
+      for c in n: rec(c, owner, dangerousYields)
+
+  var dangerousYields = 0
+  rec(iter.ast[bodyPos], iter, dangerousYields)
+  result = dangerousYields == 0
+
 proc transformFor(c: PTransf, n: PNode): PNode =
   # generate access statements for the parameters (unless they are constant)
   # put mapping from formal parameters to actual parameters
@@ -624,18 +640,22 @@ proc transformFor(c: PTransf, n: PNode): PNode =
 
   discard c.breakSyms.pop
 
+  let iter = call[0].sym
+
   var v = newNodeI(nkVarSection, n.info)
   for i in 0..<n.len - 2:
     if n[i].kind == nkVarTuple:
       for j in 0..<n[i].len-1:
         addVar(v, copyTree(n[i][j])) # declare new vars
     else:
+      if n[i].kind == nkSym and isSimpleIteratorVar(iter):
+        incl n[i].sym.flags, sfCursor
       addVar(v, copyTree(n[i])) # declare new vars
   stmtList.add(v)
 
+
   # Bugfix: inlined locals belong to the invoking routine, not to the invoked
   # iterator!
-  let iter = call[0].sym
   var newC = newTransCon(getCurrOwner(c))
   newC.forStmt = n
   newC.forLoopBody = loopBody

tests/arc/topt_cursor.nim

@@ -1,6 +1,6 @@
 discard """
   output: '''("string here", 80)'''
-  cmd: '''nim c --gc:arc --expandArc:main --hint:Performance:off $file'''
+  cmd: '''nim c --gc:arc --expandArc:main --expandArc:sio --hint:Performance:off $file'''
   nimout: '''--expandArc: main
 
 var
@@ -19,6 +19,24 @@ try:
     :tmpD_2]
 finally:
   `=destroy`(:tmpD_2)
+-- end of expandArc ------------------------
+--expandArc: sio
+
+block :tmp:
+  var x_cursor
+  var f = open("debug.txt", fmRead, 8000)
+  try:
+    var res
+    try:
+      res = TaintedString(newStringOfCap(80))
+      block :tmp_1:
+        while readLine(f, res):
+          x_cursor = res
+          echo [x_cursor]
+    finally:
+      `=destroy`(res)
+  finally:
+    close(f)
 -- end of expandArc ------------------------'''
 """
 
@@ -33,3 +51,10 @@ proc main(cond: bool) =
   echo x
 
 main(false)
+
+proc sio =
+  for x in lines("debug.txt"):
+    echo x
+
+if false:
+  sio()

tests/arc/topt_wasmoved_destroy_pairs.nim

@@ -28,13 +28,13 @@ var
 try:
   x = f()
   block :tmp:
-    var i
+    var i_cursor
     var i_1 = 0
     block :tmp_1:
       while i_1 < 4:
         var :tmpD
-        i = i_1
+        i_cursor = i_1
-        if i == 2:
+        if i_cursor == 2:
           return
         add(a):
           wasMoved(:tmpD)