diff --git a/src/codegen/regalloc.cpp b/src/codegen/regalloc.cpp
index c4bc3732a47e2ba1abda4e5a6578ead0ce759fc5..80e5f4492560f3855aacee4b721b9bfe5ce072f9 100644
--- a/src/codegen/regalloc.cpp
+++ b/src/codegen/regalloc.cpp
@@ -36,6 +36,8 @@ RegAllocator::no_reg_alloca(Value *v) {
         else if (instr->is_zext()) { // only alloca for true use
             bool alloc;
             ASSERT_CMPINST_USED_ONCE(instr);
+            if (instr->get_use_list().size() == 0)
+                return false;
             auto use_ins = dynamic_cast<Instruction *>(
                 instr->get_use_list().begin()->val_);
             // assert(use_ins != nullptr && "should only be instruction?");