diff --git a/taichi/ir/ir.cpp b/taichi/ir/ir.cpp
index 9c980bb06c2e8..d8d58b1557fcb 100644
--- a/taichi/ir/ir.cpp
+++ b/taichi/ir/ir.cpp
@@ -352,7 +352,7 @@ void Stmt::replace_operand_with(Stmt *old_stmt, Stmt *new_stmt) {
 
 Block *current_block = nullptr;
 
-Expr Var(Expr x) {
+Expr Var(const Expr &x) {
   auto var = Expr(std::make_shared<IdExpression>());
   current_ast_builder().insert(std::make_unique<FrontendAllocaStmt>(
       std::static_pointer_cast<IdExpression>(var.expr)->id, DataType::unknown));
diff --git a/taichi/ir/ir.h b/taichi/ir/ir.h
index 922e5ce3a282e..b85d43cbb7654 100644
--- a/taichi/ir/ir.h
+++ b/taichi/ir/ir.h
@@ -419,15 +419,17 @@ struct LaneAttribute {
   LaneAttribute(const std::vector<T> &data) : data(data) {
   }
 
-  LaneAttribute(const T &t) {
-    data.resize(1);
-    data[0] = t;
+  LaneAttribute(const T &t): data(1, t) {
   }
 
   void resize(int s) {
     data.resize(s);
   }
 
+  void reserve(int s) {
+    data.reserve(s);
+  }
+
   void push_back(const T &t) {
     data.push_back(t);
   }
@@ -1682,10 +1684,8 @@ struct LocalAddress {
   Stmt *var;
   int offset;
 
-  LocalAddress() : LocalAddress(nullptr, 0) {
-  }
-
   LocalAddress(Stmt *var, int offset) : var(var), offset(offset) {
+    TI_ASSERT(var->is<AllocaStmt>());
   }
 };
 
@@ -1745,6 +1745,7 @@ class LocalStoreStmt : public Stmt {
   // LaneAttribute<Stmt *> data;
 
   LocalStoreStmt(Stmt *ptr, Stmt *data) : ptr(ptr), data(data) {
+    TI_ASSERT(ptr->is<AllocaStmt>());
     TI_STMT_REG_FIELDS;
   }
 
@@ -2076,7 +2077,7 @@ class FrontendWhileStmt : public Stmt {
   Expr cond;
   std::unique_ptr<Block> body;
 
-  FrontendWhileStmt(Expr cond) : cond(load_if_ptr(cond)) {
+  FrontendWhileStmt(const Expr &cond) : cond(load_if_ptr(cond)) {
   }
 
   bool is_container_statement() const override {
@@ -2139,9 +2140,9 @@ extern Block *current_block;
 class IdExpression : public Expression {
  public:
   Identifier id;
-  IdExpression(std::string name = "") : id(name) {
+  IdExpression(const std::string &name = "") : id(name) {
   }
-  IdExpression(Identifier id) : id(id) {
+  IdExpression(const Identifier &id) : id(id) {
   }
 
   std::string serialize() override {
@@ -2168,7 +2169,7 @@ class AtomicOpExpression : public Expression {
   AtomicOpType op_type;
   Expr dest, val;
 
-  AtomicOpExpression(AtomicOpType op_type, Expr dest, Expr val)
+  AtomicOpExpression(AtomicOpType op_type, const Expr &dest, const Expr &val)
       : op_type(op_type), dest(dest), val(val) {
   }
 
@@ -2276,7 +2277,7 @@ class SNodeOpExpression : public Expression {
 class GlobalLoadExpression : public Expression {
  public:
   Expr ptr;
-  GlobalLoadExpression(Expr ptr) : ptr(ptr) {
+  GlobalLoadExpression(const Expr &ptr) : ptr(ptr) {
   }
 
   std::string serialize() override {
@@ -2372,7 +2373,8 @@ inline void SLP(int v) {
 
 class For {
  public:
-  For(Expr i, Expr s, Expr e, const std::function<void()> &func) {
+  For(const Expr &i, const Expr &s, const Expr &e,
+      const std::function<void()> &func) {
     auto stmt_unique = std::make_unique<FrontendForStmt>(i, s, e);
     auto stmt = stmt_unique.get();
     current_ast_builder().insert(std::move(stmt_unique));
@@ -2380,7 +2382,8 @@ class For {
     func();
   }
 
-  For(ExprGroup i, Expr global, const std::function<void()> &func) {
+  For(const ExprGroup &i, const Expr &global,
+      const std::function<void()> &func) {
     auto stmt_unique = std::make_unique<FrontendForStmt>(i, global);
     auto stmt = stmt_unique.get();
     current_ast_builder().insert(std::move(stmt_unique));
@@ -2393,7 +2396,7 @@ class For {
 
 class While {
  public:
-  While(Expr cond, const std::function<void()> &func) {
+  While(const Expr &cond, const std::function<void()> &func) {
     auto while_stmt = std::make_unique<FrontendWhileStmt>(cond);
     FrontendWhileStmt *ptr = while_stmt.get();
     current_ast_builder().insert(std::move(while_stmt));
@@ -2402,7 +2405,7 @@ class While {
   }
 };
 
-Expr Var(Expr x);
+Expr Var(const Expr &x);
 
 class VectorElement {
  public:
diff --git a/taichi/transforms/vector_split.cpp b/taichi/transforms/vector_split.cpp
index f1c38e52764d0..5caa0761b5635 100644
--- a/taichi/transforms/vector_split.cpp
+++ b/taichi/transforms/vector_split.cpp
@@ -172,14 +172,14 @@ class BasicBlockVectorSplit : public IRVisitor {
     for (int i = 0; i < current_split_factor; i++) {
       LaneAttribute<LocalAddress> ptr;
       int new_width = need_split ? max_width : stmt->width();
-      ptr.resize(new_width);
+      ptr.reserve(new_width);
       for (int j = 0; j < new_width; j++) {
         LocalAddress addr(stmt->ptr[lane_start(i) + j]);
         if (origin2split.find(addr.var) == origin2split.end()) {
-          ptr[j] = addr;
+          ptr.push_back(addr);
         } else {
-          ptr[j].var = lookup(addr.var, addr.offset / max_width);
-          ptr[j].offset = addr.offset % max_width;
+          ptr.push_back(LocalAddress(lookup(addr.var, addr.offset / max_width),
+                                     addr.offset % max_width));
         }
       }
       current_split[i] = Stmt::make<LocalLoadStmt>(ptr);