Prevent the compiler from hanging

Closes erlang#6578
bjorng · Dec 19, 2022 · 539d17b · 539d17b
1 parent 48be617
commit 539d17b
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Showing 2 changed files with 19 additions and 3 deletions.
diff --git a/lib/compiler/src/beam_ssa_type.erl b/lib/compiler/src/beam_ssa_type.erl
@@ -222,10 +222,16 @@ sig_function_1(Id, StMap, State0, FuncDb) ->
     WlChanged = wl_changed(Wl0, State#sig_st.wl),
     #{ Id := #func_info{succ_types=SuccTypes0}=Entry0 } = FuncDb,
 
-    if
-        SuccTypes0 =:= SuccTypes ->
+    case SuccTypes of
+        [] ->
+            %% Can never succeed. (Handling this case explicitly is necessary
+            %% for correctness in rare circumstances to prevent osciallation.)
+            {false, WlChanged, State, FuncDb};
+        SuccTypes0 ->
+            %% No change from last time.
             {false, WlChanged, State, FuncDb};
-        SuccTypes0 =/= SuccTypes ->
+        _ ->
+            %% Success types were refined. Continue iterating.
             Entry = Entry0#func_info{succ_types=SuccTypes},
             {true, WlChanged, State, FuncDb#{ Id := Entry }}
     end.

diff --git a/lib/compiler/test/compilation_SUITE_data/infinite_loop.erl b/lib/compiler/test/compilation_SUITE_data/infinite_loop.erl
@@ -30,3 +30,13 @@ mutually_recursive(X) ->
     %% This LC will be implemented as mutually recursive functions.
     %% Analyzing them would cause an infinite loop.
     [0 || _ <- [], <<_>> <= X].
+
+%% GH-6578. The type optimization pass would oscillate between no success
+%% types and [any()] -> bitstring().
+
+gh_6578(X) ->
+    <<
+      0
+      || (+(is_alive())) <
+             [gh_6578(gh_6578(0))|| X] andalso ok
+    >>.