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diff --git a/rcc-legacy/include/rcc/symtab.h b/rcc-legacy/include/rcc/symtab.h
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+++ b/rcc-legacy/include/rcc/symtab.h
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+/* Source code for RCC-Legacy.
+   Copyright (C) 2026 Richard Qin
+
+This file is part of RCC.
+
+RCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+RCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with RCC; see the file LICENSE.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#pragma once
+
+/// @file symtab.h
+/// @brief Scope chain symbol table.
+
+#include "rcc/sysy_type.h"
+
+#include <cassert>
+#include <string>
+#include <unordered_map>
+#include <variant>
+#include <vector>
+
+namespace rcc {
+
+/// Symbol information
+struct Symbol {
+    std::string name;
+    BType type = BType::Int;
+    bool is_const = false;
+    bool is_array = false;
+    bool is_param = false;
+    bool is_global = false;
+    std::vector<int> dims;  // Array dimensions
+
+    // Compile-time constant value (for constant folding and const array initialization)
+    std::variant<std::monostate, int32_t, float, std::vector<int32_t>, std::vector<float>>
+        const_val;
+
+    // IR phase: If variable needs an address (array, global), store its alloca/global address here
+    int alloca_temp_id = -1;  // Stack-allocated temp ID, -1 means unallocated
+
+    // Unique ID for Braun SSA: unique within a function, across scopes.
+    // Allocated by SymbolTable::allocate_uid() during Symbol construction.
+    int uid = -1;
+};
+
+/// Function signature
+struct FuncSig {
+    std::string name;
+    BType ret_type = BType::Void;
+    std::vector<std::pair<BType, bool>> params;  // (type, is_array)
+};
+
+/// Chained scope symbol table
+class SymbolTable {
+  public:
+    void enter_scope() { scopes_.emplace_back(); }
+
+    void leave_scope() {
+        assert(!scopes_.empty());
+        scopes_.pop_back();
+    }
+
+    /// Insert symbol in current scope. Returns false on duplicate definition.
+    bool insert(const std::string& name, Symbol sym) {
+        auto& cur = scopes_.back().symbols;
+        if (cur.count(name)) {
+            return false;
+        }
+        cur[name] = std::move(sym);
+        return true;
+    }
+
+    /// Lookup variable symbol from inner to outer scopes.
+    Symbol* lookup(const std::string& name) {
+        for (auto it = scopes_.rbegin(); it != scopes_.rend(); ++it) {
+            auto found = it->symbols.find(name);
+            if (found != it->symbols.end()) {
+                return &found->second;
+            }
+        }
+        return nullptr;
+    }
+
+    /// Register function signature.
+    void register_func(FuncSig sig) { func_table_[sig.name] = std::move(sig); }
+
+    /// Lookup function signature.
+    FuncSig* lookup_func(const std::string& name) {
+        auto it = func_table_.find(name);
+        return it != func_table_.end() ? &it->second : nullptr;
+    }
+
+    /// Register SysY runtime library functions.
+    void register_builtins();
+
+    /// Allocate a new Symbol uid.
+    /// Counter increments monotonically across enter/leave_scope without resetting.
+    int allocate_uid() { return next_uid_++; }
+
+  private:
+    struct Scope {
+        std::unordered_map<std::string, Symbol> symbols;
+    };
+    std::vector<Scope> scopes_;
+    std::unordered_map<std::string, FuncSig> func_table_;
+    int next_uid_ = 0;
+};
+
+}  // namespace rcc