some opt

midend/llvm/use/IrUser.java

@@ -18,11 +18,10 @@ public class IrUser extends IrValue {
     }
 
     public void addUse(IrValue value) {
-        if (value == null) {
-            return;
-        }
         uses.add(value);
-        value.addUser(this);
+        if (value != null) {
+            value.addUser(this);
+        }
     }
 
     public IrValue getUse(int index) {
@@ -32,6 +31,44 @@ public class IrUser extends IrValue {
         return uses.get(index);
     }
 
+    public void setUse(int index, IrValue value) {
+        if (index >= uses.size() || index < 0) {
+            return;
+        }
+        IrValue oldValue = uses.get(index);
+        if (oldValue != null) {
+            oldValue.deleteUser(this);
+        }
+        uses.set(index, value);
+        if (value != null) {
+            value.addUser(this);
+        }
+    }
+
+    public void deleteUse(IrValue value) {
+        uses.remove(value);
+        if (value != null) {
+            value.deleteUser(this);
+        }   
+    }
+
+    public void clearUses() {
+        for (IrValue value : uses) {
+            if (value != null) {
+                value.deleteUser(this);
+            }
+        }
+        uses.clear();
+    }
+
+    public void deleteUse(int index) {
+        if (index >= uses.size() || index < 0) {
+            return;
+        }
+        IrValue value = uses.get(index);
+        deleteUse(value);
+    }
+
     public int getNumUses() {
         return uses.size();
     }