fixes #19977; rework inlining of 'var openarray' iterators for C++ (#23258)

fixes #19977

(cherry picked from commit f7c6e04)

Author: ringabout

compiler/transf.nim

@@ -472,7 +472,8 @@ proc transformYield(c: PTransf, n: PNode): PNode =
 
 proc transformAddrDeref(c: PTransf, n: PNode, kinds: TNodeKinds): PNode =
   result = transformSons(c, n)
-  if c.graph.config.backend == backendCpp or sfCompileToCpp in c.module.flags: return
+  # inlining of 'var openarray' iterators; bug #19977
+  if n.typ.kind != tyOpenArray and (c.graph.config.backend == backendCpp or sfCompileToCpp in c.module.flags): return
   var n = result
   case n[0].kind
   of nkObjUpConv, nkObjDownConv, nkChckRange, nkChckRangeF, nkChckRange64:

tests/iter/titervaropenarray.nim

@@ -1,6 +1,6 @@
 discard """
   output: "123"
-  targets: "c"
+  targets: "c cpp"
 """
 # Try to break the transformation pass:
 iterator iterAndZero(a: var openArray[int]): int =