add todo

Author: oscarddssmith

src/llvm-alloc-opt.cpp

@@ -753,6 +753,7 @@ void Optimizer::moveToStack(CallInst *orig_inst, size_t sz, bool has_ref, AllocF
                 return;
             }
             if (pass.gc_loaded_func == callee) {
+                // TODO: handle data pointer forwarding, length forwarding, and fence removal
                 user->replaceUsesOfWith(orig_i, Constant::getNullValue(orig_i->getType()));
                 return;
             }