write DCE

include/IR/IR_basic.h

@@ -64,7 +64,11 @@ class GlobalVarDefItem : public LLVMIRItemBase {
     }
   }
 };
-class ActionItem : public LLVMIRItemBase {};
+class ActionItem : public LLVMIRItemBase {
+ public:
+  bool marked_as_useless;
+  ActionItem() : marked_as_useless(false) {}
+};
 class JMPActionItem : public ActionItem {
  public:
   std::shared_ptr<class PhiItem> corresponding_phi;

include/opt/dce.h

@@ -0,0 +1,4 @@
+#pragma once
+#include "IR/IR_basic.h"
+
+std::shared_ptr<ModuleItem> DCE(std::shared_ptr<ModuleItem> src);

include/opt/opt.h

@@ -2,4 +2,5 @@
 #include "gen.h"
 #include "global_var_cache.h"
 #include "mem2reg.h"
-#include "regalloc.h"
+#include "regalloc.h"
+#include "dce.h"