diff --git a/taichi/ir/ir.cpp b/taichi/ir/ir.cpp
index c3ccdda92395e..175cba9dc2170 100644
--- a/taichi/ir/ir.cpp
+++ b/taichi/ir/ir.cpp
@@ -571,9 +571,11 @@ void DelayedIRModifier::replace_with(Stmt *stmt,
 }
 
 bool DelayedIRModifier::modify_ir() {
+  bool force_modified = modified_;
+  modified_ = false;
   if (to_insert_before.empty() && to_insert_after.empty() && to_erase.empty() &&
       to_replace_with.empty())
-    return false;
+    return force_modified;
   for (auto &i : to_insert_before) {
     i.first->parent->insert_before(i.first, std::move(i.second));
   }
@@ -593,6 +595,10 @@ bool DelayedIRModifier::modify_ir() {
   return true;
 }
 
+void DelayedIRModifier::mark_as_modified() {
+  modified_ = true;
+}
+
 LocalAddress::LocalAddress(Stmt *var, int offset) : var(var), offset(offset) {
   TI_ASSERT(var->is<AllocaStmt>());
 }
diff --git a/taichi/ir/ir.h b/taichi/ir/ir.h
index 89499a121f67c..1b0ee54a3f927 100644
--- a/taichi/ir/ir.h
+++ b/taichi/ir/ir.h
@@ -729,6 +729,7 @@ class DelayedIRModifier {
   std::vector<std::pair<Stmt *, VecStatement>> to_insert_after;
   std::vector<std::tuple<Stmt *, VecStatement, bool>> to_replace_with;
   std::vector<Stmt *> to_erase;
+  bool modified_{false};
 
  public:
   ~DelayedIRModifier();
@@ -741,6 +742,9 @@ class DelayedIRModifier {
                     VecStatement &&new_statements,
                     bool replace_usages = true);
   bool modify_ir();
+
+  // Force the next call of modify_ir() to return true.
+  void mark_as_modified();
 };
 
 struct LocalAddress {
diff --git a/taichi/transforms/alg_simp.cpp b/taichi/transforms/alg_simp.cpp
index f0d95e9f619f0..6aa925de3817e 100644
--- a/taichi/transforms/alg_simp.cpp
+++ b/taichi/transforms/alg_simp.cpp
@@ -48,9 +48,19 @@ class AlgSimp : public BasicStmtVisitor {
   }
 
   void visit(UnaryOpStmt *stmt) override {
-    if (stmt->is_cast() && stmt->cast_type == stmt->operand->ret_type) {
-      stmt->replace_with(stmt->operand);
-      modifier.erase(stmt);
+    if (stmt->is_cast()) {
+      if (stmt->cast_type == stmt->operand->ret_type) {
+        stmt->replace_with(stmt->operand);
+        modifier.erase(stmt);
+      } else if (stmt->operand->is<UnaryOpStmt>() &&
+                 stmt->operand->as<UnaryOpStmt>()->is_cast()) {
+        auto prev_cast = stmt->operand->as<UnaryOpStmt>();
+        if (stmt->op_type == UnaryOpType::cast_bits &&
+            prev_cast->op_type == UnaryOpType::cast_bits) {
+          stmt->operand = prev_cast->operand;
+          modifier.mark_as_modified();
+        }
+      }
     }
   }