From 1f29da6177682c5f3679a08b0cdc06f73fd29d5c Mon Sep 17 00:00:00 2001
From: Hugo Heuzard <hugo.heuzard@gmail.com>
Date: Sun, 21 Jan 2024 14:00:43 +0100
Subject: [PATCH 1/2] Test: expose global DCE issue with the toplevel

---
 compiler/tests-toplevel/test_toplevel.ml        | 9 +++++----
 compiler/tests-toplevel/test_toplevel.reference | 4 ++--
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/compiler/tests-toplevel/test_toplevel.ml b/compiler/tests-toplevel/test_toplevel.ml
index 8ab784373e..db7a81eba6 100644
--- a/compiler/tests-toplevel/test_toplevel.ml
+++ b/compiler/tests-toplevel/test_toplevel.ml
@@ -1,6 +1,7 @@
 let () =
   let content = {|
 let () = print_endline "hello";;
+1+1;;
 1+;;
 Missing_module.f;;
 |} in
@@ -12,10 +13,10 @@ Missing_module.f;;
     try
       Location.reset ();
       let phr = !Toploop.parse_toplevel_phrase lexbuf in
-      if not (Toploop.execute_phrase true Format.std_formatter phr) then raise Exit
+      let res = Toploop.execute_phrase true Format.std_formatter phr in
+      flush_all ();
+      if not res then raise Exit
     with
-    | End_of_file ->
-        flush_all ();
-        exit 0
+    | End_of_file -> exit 0
     | x -> Location.report_exception Format.std_formatter x
   done
diff --git a/compiler/tests-toplevel/test_toplevel.reference b/compiler/tests-toplevel/test_toplevel.reference
index 3ab394a970..1695687c25 100644
--- a/compiler/tests-toplevel/test_toplevel.reference
+++ b/compiler/tests-toplevel/test_toplevel.reference
@@ -1,5 +1,5 @@
 hello
-Line 3, characters 2-4:
+Line 4, characters 2-4:
 Error: Syntax error
-Line 4, characters 0-16:
+Line 5, characters 0-16:
 Error: Unbound module Missing_module

From 0afbc3baf7774e5e49adbed9abff3478f621c130 Mon Sep 17 00:00:00 2001
From: Hugo Heuzard <hugo.heuzard@gmail.com>
Date: Sun, 21 Jan 2024 08:26:48 +0100
Subject: [PATCH 2/2] Compiler: fix toplevel with globaldeacode

---
 CHANGES.md                                      | 3 +++
 compiler/lib/global_deadcode.ml                 | 9 +++++++++
 compiler/tests-toplevel/test_toplevel.reference | 1 +
 3 files changed, 13 insertions(+)

diff --git a/CHANGES.md b/CHANGES.md
index 291479df2d..aff4441c57 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -5,6 +5,9 @@
 * Compiler: no longer rely on IIFE for scoping variable inside loops
 * Lib: add ellipse to canvasRenderingContext2D (@FayCarsons, #1555)
 
+## Bug fixes
+* Compiler: fix global dead code elimination in a toplevel context
+
 # 5.6.0 (2024-01-02) - Lille
 
 ## Features/Changes
diff --git a/compiler/lib/global_deadcode.ml b/compiler/lib/global_deadcode.ml
index bc8017d5d9..9af29d950e 100644
--- a/compiler/lib/global_deadcode.ml
+++ b/compiler/lib/global_deadcode.ml
@@ -246,6 +246,15 @@ let liveness prog pure_funs (global_info : Global_flow.info) =
     | Stop | Branch _ | Poptrap _ | Pushtrap _ -> ()
   in
   Addr.Map.iter (fun _ block -> live_block block) prog.blocks;
+  Code.traverse
+    { Code.fold = Code.fold_children }
+    (fun pc () ->
+      match Addr.Map.find pc prog.blocks with
+      | { branch = Return x, _; _ } -> add_top x
+      | _ -> ())
+    prog.start
+    prog.blocks
+    ();
   live_vars
 
 (* Returns the set of variables given a table of variables. *)
diff --git a/compiler/tests-toplevel/test_toplevel.reference b/compiler/tests-toplevel/test_toplevel.reference
index 1695687c25..58eb84ed85 100644
--- a/compiler/tests-toplevel/test_toplevel.reference
+++ b/compiler/tests-toplevel/test_toplevel.reference
@@ -1,4 +1,5 @@
 hello
+- : int = 2
 Line 4, characters 2-4:
 Error: Syntax error
 Line 5, characters 0-16: