gc-ext: only sweep unmarked objects (#45035)

This prior conditional was a fixed constant branch, so this seems more like the intent.

(cherry picked from commit ac51add)

src/gc.c

@@ -548,20 +548,21 @@ JL_DLLEXPORT void jl_finalize_th(jl_ptls_t ptls, jl_value_t *o)
     arraylist_free(&copied_list);
 }
 
+// explicitly scheduled objects for the sweepfunc callback
 static void gc_sweep_foreign_objs_in_list(arraylist_t *objs)
 {
     size_t p = 0;
     for (size_t i = 0; i < objs->len; i++) {
-        jl_value_t *v = (jl_value_t *)(objs->items[i]);
-        jl_datatype_t *t = (jl_datatype_t *)(jl_typeof(v));
+        jl_value_t *v = (jl_value_t*)(objs->items[i]);
+        jl_datatype_t *t = (jl_datatype_t*)(jl_typeof(v));
         const jl_datatype_layout_t *layout = t->layout;
         jl_fielddescdyn_t *desc = (jl_fielddescdyn_t*)jl_dt_layout_fields(layout);
-        if (!gc_ptr_tag(v, 1)) {
+
+        int bits = jl_astaggedvalue(v)->bits.gc;
+        if (!gc_marked(bits))
             desc->sweepfunc(v);
-        }
-        else {
+        else
             objs->items[p++] = v;
-        }
     }
     objs->len = p;
 }

test/gcext/gcext.c

@@ -561,8 +561,10 @@ void sweep_stack_data(jl_value_t *p)
 {
     obj_sweeps++;
     dynstack_t *stk = (dynstack_t *)p;
-    if (stk->size > stk->capacity)
-        jl_error("internal error during sweeping");
+    if (stk->size > stk->capacity) {
+        assert(0 && "internal error during sweeping");
+        abort();
+    }
 }
 
 // Safely execute Julia code