Created attachment 345135 [details]
reproducer

When Vala generates the _co() function finishing the async operation and giving the GAsyncResult the result, it somehow generates repeated code, for the example attachment:

static gboolean foo_bar_co (FooBarData* _data_) {
        ...

        if (_data_->_state_ == 0) {
                g_simple_async_result_complete_in_idle (_data_->_async_result);
        } else {
                g_simple_async_result_complete (_data_->_async_result);
        }
        g_object_unref (_data_->_async_result);
        return FALSE;
        if (_data_->_state_ == 0) {
                g_simple_async_result_complete_in_idle (_data_->_async_result);
        } else {
                g_simple_async_result_complete (_data_->_async_result);
        }
        g_object_unref (_data_->_async_result);
        return FALSE;
}

(FWIW, it's the same with --target-glib=2.36 and GTask). The repeated code is unneeded and unreachable. This happens to trigger numerous "Structurally dead code" warnings for Tracker in Coverity. The CIDs are:

1388725, 1388720, 1388503, 1388498, 1388496, 1388495, 1388494, 1388493, 1388724, 1388513, 1388507, 1388506, 1388505, 1388502, 1388501, 1388499, 1388497, 1388491, 1388490, 1388489, 1388488, 1388487, 1388486, 1388485.