Fix #15909 (#15914)

compiler/varpartitions.nim

@@ -399,6 +399,7 @@ proc allRoots(n: PNode; result: var seq[PSym]; followDotExpr = true) =
 proc destMightOwn(c: var Partitions; dest: var VarIndex; n: PNode) =
   ## Analyse if 'n' is an expression that owns the data, if so mark 'dest'
   ## with 'ownsData'.
+  if n.typ == nil: return
   case n.kind
   of nkEmpty, nkCharLit..nkNilLit:
     # primitive literals including the empty are harmless:

tests/arc/t15909.nim

@@ -0,0 +1,16 @@
+discard """
+  action: run
+  cmd: "nim c --gc:arc $file"
+"""
+
+proc f1() {.noreturn.} = raise newException(CatchableError, "")
+
+proc f2(y: int): int =
+  if y != 0:
+    y
+  else:
+    f1()
+
+doAssert f2(5) == 5
+doAssertRaises(CatchableError):
+  discard f2(0)