JSSpecCompiler: Prepare for building SSA

This commit introduces NamedVariableDeclaration and
SSAVariableDeclaration and allows storing both of them in Variable node.
Also, it adds additional structures in FunctionDefinition and
BasicBlock, which will be used to store SSA form related information.

Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/AST/AST.h

@@ -33,16 +33,26 @@ public:
     {
     }
 
+    NodeSubtreePointer(VariableRef* tree_ptr)
+        : m_tree_ptr(tree_ptr)
+    {
+    }
+
     Tree get(Badge<RecursiveASTVisitor>);
     void replace_subtree(Badge<RecursiveASTVisitor>, NullableTree replacement);
 
 private:
-    Variant<Tree*, NullableTree*> m_tree_ptr;
+    Variant<Tree*, NullableTree*, VariableRef*> m_tree_ptr;
 };
 
 class VariableDeclaration : public RefCounted<VariableDeclaration> {
 public:
-    VariableDeclaration(StringView name)
+    virtual ~VariableDeclaration() = default;
+};
+
+class NamedVariableDeclaration : public VariableDeclaration {
+public:
+    NamedVariableDeclaration(StringView name)
         : m_name(name)
     {
     }
@@ -50,6 +60,17 @@ public:
     StringView m_name;
 };
 
+class SSAVariableDeclaration : public VariableDeclaration {
+public:
+    SSAVariableDeclaration(u64 version)
+        : m_version(version)
+    {
+    }
+
+    size_t m_index = 0;
+    u64 m_version;
+};
+
 class Node : public RefCounted<Node> {
 public:
     virtual ~Node() = default;
@@ -60,6 +81,7 @@ public:
     virtual Vector<NodeSubtreePointer> subtrees() { return {}; }
 
     virtual bool is_list() const { return false; }
+    virtual bool is_statement() { VERIFY_NOT_REACHED(); }
 
 protected:
     template<typename... Parameters>
@@ -78,11 +100,20 @@ protected:
 //   auto tmp3 = d;
 //   a = tmp1 + tmp2;
 // ```.
-class Statement : public Node { };
-class Expression : public Node { };
+class Statement : public Node {
+public:
+    bool is_statement() override { return true; }
+};
+
+class Expression : public Node {
+public:
+    bool is_statement() override { return false; }
+};
 
 class ControlFlowOperator : public Statement {
 public:
+    bool is_statement() override { return false; }
+
     virtual Vector<BasicBlockRef*> references() = 0;
 };
 
@@ -110,6 +141,7 @@ public:
 
     VariableRef m_return_value;
 
+    Vector<NodeSubtreePointer> subtrees() override { return { { &m_return_value } }; }
     Vector<BasicBlockRef*> references() override { return {}; }
 
 protected:
@@ -143,6 +175,7 @@ public:
     {
     }
 
+    Vector<NodeSubtreePointer> subtrees() override { return { { &m_condition } }; }
     Vector<BasicBlockRef*> references() override;
 
     Tree m_condition;
@@ -448,12 +481,15 @@ protected:
 
 class Variable : public Expression {
 public:
-    Variable(VariableDeclarationRef variable_declaration)
-        : m_variable_declaration(move(variable_declaration))
+    Variable(NamedVariableDeclarationRef name)
+        : m_name(move(name))
     {
     }
 
-    VariableDeclarationRef m_variable_declaration;
+    NamedVariableDeclarationRef m_name;
+    SSAVariableDeclarationRef m_ssa;
+
+    String name() const;
 
 protected:
     void dump_tree(StringBuilder& builder) override;