From d7117298f51000668cc99d1c81684e5d357230a7 Mon Sep 17 00:00:00 2001
From: Cody Tapscott <topolarity@tapscott.me>
Date: Thu, 6 Jun 2024 15:38:43 -0400
Subject: [PATCH] codegen: fix unsoundness in `globalop` NULL check

This code had not considered "mutation tearing", so the emitted
operations could be incorrect if any mutations were dropped.
---
 src/codegen.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/codegen.cpp b/src/codegen.cpp
index 3f1c714f9b30a..1f2ab7cccd2c9 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -3228,7 +3228,7 @@ static jl_cgval_t emit_globalop(jl_codectx_t &ctx, jl_module_t *mod, jl_sym_t *s
                     return jl_cgval_t();
             }
             bool isboxed = true;
-            bool maybe_null = jl_atomic_load_relaxed(&bnd->value) == NULL;
+            bool maybe_null = (!bnd->isdefined && !bnd->constp) || (jl_atomic_load_relaxed(&bnd->value) == NULL);
             return typed_store(ctx,
                                julia_binding_pvalue(ctx, bp),
                                rval, cmp, ty,