Optimize DNFs to avoid negations when possible

Author: josevalim

lib/elixir/lib/module/types/descr.ex

@@ -2756,7 +2756,7 @@ defmodule Module.Types.Descr do
   # Takes all the lines from the root to the leaves finishing with a 1,
   # and compile into tuples of positive and negative nodes. Positive nodes are
   # those followed by a left path, negative nodes are those followed by a right path.
-  def map_bdd_to_dnf(bdd) do
+  defp map_bdd_to_dnf(bdd) do
     bdd_to_dnf(bdd)
     |> Enum.reduce([], fn {pos, negs}, acc ->
       case non_empty_map_literals_intersection(pos) do
@@ -4591,6 +4591,9 @@ defmodule Module.Types.Descr do
       :bdd_top ->
         [{pos, neg} | acc]
 
+      {fun, :bdd_top, right} ->
+        bdd_to_dnf([{[fun | pos], neg} | acc], pos, neg, right)
+
       {fun, left, right} ->
         bdd_to_dnf(bdd_to_dnf(acc, [fun | pos], neg, left), pos, [fun | neg], right)
     end

lib/elixir/test/elixir/module/types/descr_test.exs

@@ -2352,7 +2352,7 @@ defmodule Module.Types.DescrTest do
              )
              |> union(difference(open_map(x: atom()), open_map(x: boolean())))
              |> to_quoted_string() ==
-               "%{..., x: atom() and not boolean()} or\n  (%{..., a: integer(), b: atom(), c: boolean()} and not %{..., x: atom() and not boolean()})"
+               "%{..., a: integer(), b: atom(), c: boolean()} or %{..., x: atom() and not boolean()}"
 
       assert closed_map(a: number(), b: atom(), c: pid())
              |> difference(closed_map(a: integer(), b: atom(), c: pid()))