diff --git a/compiler/include/compiler/backend/optree/optimizer/opt_builder.hpp b/compiler/include/compiler/backend/optree/optimizer/opt_builder.hpp
index b8edfd7e..fdf2f678 100644
--- a/compiler/include/compiler/backend/optree/optimizer/opt_builder.hpp
+++ b/compiler/include/compiler/backend/optree/optimizer/opt_builder.hpp
@@ -16,6 +16,14 @@ class OptBuilder : public Builder {
         Callback onInsert;
         Callback onUpdate;
         Callback onErase;
+
+        Notifier() = default;
+        Notifier(const Notifier &) = default;
+        Notifier(Notifier &&) = default;
+        ~Notifier() = default;
+
+        Notifier(const Callback &onInsert, const Callback &onUpdate, const Callback &onErase)
+            : onInsert(onInsert), onUpdate(onUpdate), onErase(onErase){};
     };
 
     OptBuilder(const Notifier &notifier) : Builder(), notifier(notifier){};
@@ -23,10 +31,13 @@ class OptBuilder : public Builder {
     OptBuilder(OptBuilder &&) = default;
     ~OptBuilder() override = default;
 
+    using Builder::insert;
+
     void insert(const Operation::Ptr &op) override;
     Operation::Ptr clone(const Operation::Ptr &op);
     void erase(const Operation::Ptr &op);
     void update(const Operation::Ptr &op, const std::function<void()> &actor);
+    void replace(const Operation::Ptr &op, const Operation::Ptr &newOp);
 
   private:
     const Notifier &notifier;
diff --git a/compiler/include/compiler/backend/optree/optimizer/transform_factories.hpp b/compiler/include/compiler/backend/optree/optimizer/transform_factories.hpp
index 66cdceeb..5cc1730a 100644
--- a/compiler/include/compiler/backend/optree/optimizer/transform_factories.hpp
+++ b/compiler/include/compiler/backend/optree/optimizer/transform_factories.hpp
@@ -6,6 +6,7 @@ namespace optree {
 namespace optimizer {
 
 BaseTransform::Ptr createEraseUnusedOps();
+BaseTransform::Ptr createFoldConstants();
 
 } // namespace optimizer
 } // namespace optree
diff --git a/compiler/include/compiler/optree/base_adaptor.hpp b/compiler/include/compiler/optree/base_adaptor.hpp
index 77315e6b..549ba0b1 100644
--- a/compiler/include/compiler/optree/base_adaptor.hpp
+++ b/compiler/include/compiler/optree/base_adaptor.hpp
@@ -74,6 +74,18 @@ struct Adaptor {
         return op.operator bool();
     }
 
+    operator const Operation::Ptr &() const {
+        return op;
+    }
+
+    operator Operation::Ptr() const {
+        return op;
+    }
+
+    Operation *const operator->() const {
+        return op.get();
+    }
+
     const utils::SourceRef &ref() const {
         return op->ref;
     }
diff --git a/compiler/include/compiler/optree/helpers.hpp b/compiler/include/compiler/optree/helpers.hpp
index 5a6a840c..14525973 100644
--- a/compiler/include/compiler/optree/helpers.hpp
+++ b/compiler/include/compiler/optree/helpers.hpp
@@ -14,4 +14,11 @@ Type::Ptr deduceTargetCastType(const Type::Ptr &outType, const Type::Ptr &inType
 ArithCastOp insertNumericCastOp(const Type::Ptr &resultType, const Value::Ptr &value, Builder &builder,
                                 utils::SourceRef &ref);
 
+template <typename AdaptorType>
+AdaptorType getValueOwnerAs(const Value::Ptr &value) {
+    if (value->owner.expired())
+        return {};
+    return value->owner.lock()->as<AdaptorType>();
+}
+
 } // namespace optree
diff --git a/compiler/lib/backend/optree/optimizer/opt_builder.cpp b/compiler/lib/backend/optree/optimizer/opt_builder.cpp
index ff884f6d..cfe64a85 100644
--- a/compiler/lib/backend/optree/optimizer/opt_builder.cpp
+++ b/compiler/lib/backend/optree/optimizer/opt_builder.cpp
@@ -8,22 +8,34 @@
 using namespace optree;
 using namespace optree::optimizer;
 
+namespace {
+
+void notifyInsertRecursively(const Operation::Ptr &op, const OptBuilder::Notifier &notifier) {
+    for (const auto &nestedOp : op->body) {
+        notifyInsertRecursively(nestedOp, notifier);
+        notifier.onInsert(nestedOp);
+    }
+}
+
+} // namespace
+
 void OptBuilder::insert(const Operation::Ptr &op) {
     Builder::insert(op);
     notifier.onInsert(op);
 }
 
 Operation::Ptr OptBuilder::clone(const Operation::Ptr &op) {
-    // TODO
-    notifier.onInsert(op);
+    auto newOp = op->clone();
+    notifyInsertRecursively(op, notifier);
+    insert(op);
     return op;
 }
 
 void OptBuilder::erase(const Operation::Ptr &op) {
     if (op->parent)
         setInsertPointAfter(op);
-    for (const auto &nestedOp : op->body)
-        erase(nestedOp);
+    for (auto it = op->body.rbegin(); it != op->body.rend(); ++it)
+        erase(*it);
     op->erase();
     notifier.onErase(op);
 }
@@ -32,3 +44,17 @@ void OptBuilder::update(const Operation::Ptr &op, const std::function<void()> &a
     actor();
     notifier.onUpdate(op);
 }
+
+void OptBuilder::replace(const Operation::Ptr &op, const Operation::Ptr &newOp) {
+    for (auto oldResultIt = op->results.begin(), newResultIt = newOp->results.begin();
+         oldResultIt != op->results.end() && newResultIt != newOp->results.end(); ++oldResultIt, ++newResultIt) {
+        const Value::Ptr &oldResult = *oldResultIt;
+        const Value::Ptr &newResult = *newResultIt;
+        for (const auto &use : oldResult->uses) {
+            auto user = use.lock();
+            update(user, [&] { user->operand(use.operandNumber) = newResult; });
+        }
+        newResult->uses.splice_after(newResult->uses.before_begin(), oldResult->uses);
+    }
+    erase(op);
+}
diff --git a/compiler/lib/backend/optree/optimizer/optimizer.cpp b/compiler/lib/backend/optree/optimizer/optimizer.cpp
index b8068155..a403f97c 100644
--- a/compiler/lib/backend/optree/optimizer/optimizer.cpp
+++ b/compiler/lib/backend/optree/optimizer/optimizer.cpp
@@ -13,6 +13,8 @@
 using namespace optree;
 using namespace optree::optimizer;
 
+namespace {
+
 class OperationSet {
     std::vector<Operation::Ptr> data;
     std::unordered_map<const Operation *, size_t> positions;
@@ -63,7 +65,35 @@ class OperationSet {
     }
 };
 
-namespace {
+class MutationTracker {
+    Operation *const trackedOp;
+    bool updatedTag;
+    bool erasedTag;
+
+  public:
+    MutationTracker(const MutationTracker &) = delete;
+    MutationTracker(MutationTracker &&) = delete;
+    ~MutationTracker() = default;
+
+    explicit MutationTracker(const Operation::Ptr &trackedOp)
+        : trackedOp(trackedOp.get()), updatedTag(false), erasedTag(false){};
+
+    bool updated() const {
+        return updatedTag;
+    }
+    bool erased() const {
+        return erasedTag;
+    }
+
+    void raiseUpdated(const Operation::Ptr &op) {
+        if (op.get() == trackedOp)
+            updatedTag = true;
+    }
+    void raiseErased(const Operation::Ptr &op) {
+        if (op.get() == trackedOp)
+            erasedTag = true;
+    }
+};
 
 void pushToSet(const Operation::Ptr &root, OperationSet &ops) {
     for (const auto &op : root->body)
@@ -71,28 +101,35 @@ void pushToSet(const Operation::Ptr &root, OperationSet &ops) {
     ops.push(root);
 }
 
-} // namespace
-
-Optimizer::Optimizer() : iterLimit(100U) {
-    transforms.emplace_back(createEraseUnusedOps());
-}
-
-void Optimizer::process(Program &program) const {
-    OperationSet ops;
-    bool mutated = false;
+OptBuilder::Notifier makeNotifier(OperationSet &ops, bool &mutated, MutationTracker &tracker) {
     OptBuilder::Notifier notifier;
     notifier.onInsert = [&ops, &mutated](const Operation::Ptr &op) {
         ops.push(op);
         mutated = true;
     };
-    notifier.onUpdate = [&ops, &mutated](const Operation::Ptr &op) {
+    notifier.onUpdate = [&ops, &mutated, &tracker](const Operation::Ptr &op) {
         ops.push(op);
         mutated = true;
+        tracker.raiseUpdated(op);
     };
-    notifier.onErase = [&ops, &mutated](const Operation::Ptr &op) {
+    notifier.onErase = [&ops, &mutated, &tracker](const Operation::Ptr &op) {
         ops.erase(op);
         mutated = true;
+        tracker.raiseErased(op);
     };
+    return notifier;
+}
+
+} // namespace
+
+Optimizer::Optimizer() : iterLimit(100U) {
+    transforms.emplace_back(createEraseUnusedOps());
+    transforms.emplace_back(createFoldConstants());
+}
+
+void Optimizer::process(Program &program) const {
+    OperationSet ops;
+    bool mutated = false;
     size_t iter = 0;
     do {
         mutated = false;
@@ -100,7 +137,11 @@ void Optimizer::process(Program &program) const {
         pushToSet(program.root, ops);
         while (!ops.empty()) {
             Operation::Ptr op = ops.pop();
+            MutationTracker tracker(op);
+            auto notifier = makeNotifier(ops, mutated, tracker);
             for (const auto &transform : transforms) {
+                if (tracker.erased())
+                    break;
                 if (!transform->canRun(op))
                     continue;
                 OptBuilder builder(notifier);
diff --git a/compiler/lib/backend/optree/optimizer/transforms/fold_constants.cpp b/compiler/lib/backend/optree/optimizer/transforms/fold_constants.cpp
new file mode 100644
index 00000000..88349930
--- /dev/null
+++ b/compiler/lib/backend/optree/optimizer/transforms/fold_constants.cpp
@@ -0,0 +1,65 @@
+#include "optimizer/transform.hpp"
+
+#include <cstdint>
+#include <memory>
+
+#include "compiler/optree/adaptors.hpp"
+#include "compiler/optree/definitions.hpp"
+#include "compiler/optree/helpers.hpp"
+#include "compiler/optree/operation.hpp"
+#include "compiler/optree/types.hpp"
+
+#include "optimizer/opt_builder.hpp"
+
+using namespace optree;
+using namespace optree::optimizer;
+
+namespace {
+
+struct FoldConstants : public Transform<ArithBinaryOp, ArithCastOp, LogicBinaryOp, LogicUnaryOp> {
+    using Transform::Transform;
+
+    static void foldArithBinaryOp(const ArithBinaryOp &op, OptBuilder &builder) {
+        auto lhsOp = getValueOwnerAs<ConstantOp>(op.lhs());
+        auto rhsOp = getValueOwnerAs<ConstantOp>(op.rhs());
+        if (!lhsOp || !rhsOp)
+            return;
+        auto type = op.result()->type;
+        if (type->is<IntegerType>()) {
+            int64_t folded = 0;
+            int64_t lhs = lhsOp.value().as<int64_t>();
+            int64_t rhs = rhsOp.value().as<int64_t>();
+            switch (op.kind()) {
+            case ArithBinOpKind::AddI:
+                folded = lhs + rhs;
+                break;
+            case ArithBinOpKind::MulI:
+                folded = lhs * rhs;
+                break;
+            default:
+                folded = -1; // TODO: extend
+            }
+            auto newOp = builder.insert<ConstantOp>(op.ref(), type, folded);
+            builder.replace(op, newOp);
+            return;
+        }
+        // TODO: support other types
+    }
+
+    void run(const Operation::Ptr &op, OptBuilder &builder) const override {
+        if (op->is<ArithBinaryOp>())
+            foldArithBinaryOp(op->as<ArithBinaryOp>(), builder);
+    }
+};
+
+} // namespace
+
+namespace optree {
+namespace optimizer {
+
+BaseTransform::Ptr createFoldConstants() {
+    return std::make_shared<FoldConstants>();
+}
+
+} // namespace optimizer
+} // namespace optree
diff --git a/compiler/lib/optree/operation.cpp b/compiler/lib/optree/operation.cpp
index b204bcdb..3d396520 100644
--- a/compiler/lib/optree/operation.cpp
+++ b/compiler/lib/optree/operation.cpp
@@ -75,8 +75,8 @@ Operation::SpecId Operation::getUnknownSpecId() {
 }
 
 void Operation::addOperand(const Value::Ptr &value) {
-    operands.emplace_back(value);
     addUse(value, operands.size());
+    operands.emplace_back(value);
 }
 
 void Operation::insertOperand(size_t operandNumber, const Value::Ptr &value) {