Simplify always true and always false bdd nodes

Author: josevalim

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

@@ -4448,6 +4448,10 @@ defmodule Module.Types.Descr do
           {:eq, _, _} ->
             bdd1
         end
+        |> case do
+          {_, :bdd_top, _, :bdd_top} -> :bdd_top
+          other -> other
+        end
     end
   end
 
@@ -4537,6 +4541,10 @@ defmodule Module.Types.Descr do
           {:eq, _, _} ->
             :bdd_bot
         end
+        |> case do
+          {_, :bdd_bot, u, :bdd_bot} -> u
+          other -> other
+        end
     end
   end
 
@@ -4601,6 +4609,10 @@ defmodule Module.Types.Descr do
           {:eq, bdd, _} ->
             bdd
         end
+        |> case do
+          {_, :bdd_bot, u, :bdd_bot} -> u
+          other -> other
+        end
     end
   end
 

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

@@ -2504,6 +2504,20 @@ defmodule Module.Types.DescrTest do
       assert subtype?(map2, map1)
     end
 
+    test "map intersection and then difference" do
+      actual = open_map(__struct__: atom(), __exception__: atom([true]))
+
+      expected =
+        for i <- 1..50 do
+          name = :"name_#{i}"
+          closed_map([__struct__: atom([name])] ++ [{name, binary()}])
+        end
+        |> Enum.reduce(&union/2)
+
+      common = intersection(actual, expected)
+      difference(actual, common)
+    end
+
     test "struct difference" do
       entries =
         [