項目的完整代碼在 C2j-Compiler

前言

在上一篇完成了符號表的構建，下一步就是輸出抽象語法樹(Abstract Syntax Tree，AST)

抽象語法樹（abstract syntax tree 或者縮寫為 AST），是源代碼的抽象語法結構的樹狀表現形式，這里特指編程語言的源代碼。樹上的每個節(jié)點都表示源代碼中的一種結構。

AST對于編譯器是至關重要的，現在的編譯型語言一般通過AST來生成IR，解釋型語言也可以不用虛擬機而直接遍歷AST來解釋執(zhí)行，之后要寫解釋器和編譯器都依賴這個AST

這一篇主要文件有：

• AstBuilder.java
• AstNode.java
• AstNodeImpl.java
• NodeKey.java
• NodeFactory.java

主要數據結構

AST節(jié)點的表示

public interface AstNode {AstNode addChild(AstNode node);AstNode getParent();ArrayList<AstNode> getChildren();void setAttribute(NodeKey key, Object value);Object getAttribute(NodeKey key);boolean isChildrenReverse();void reverseChildren();AstNode copy();}

這是對AstNode接口的實現，并且繼承HashMap，這里的NodeKey是

TokenType, VALUE, SYMBOL, PRODUCTION, TEXT

對應的value，

TokenType就是非終結符的類型

Text用來存儲解析對象的文本信息

Symbol對應的就是變量的符號對象

Value是對應對象解析的值，比如int a = 1，那么value的值就為1

public class AstNodeImpl extends HashMap<NodeKey, Object> implements AstNode {private Token type;private AstNodeImpl parent;private ArrayList<AstNode> children;String name;private boolean isChildrenReverse = false;public AstNodeImpl(Token type) {this.type = type;this.parent = null;this.children = new ArrayList<>();setAttribute(NodeKey.TokenType, type);}@Overridepublic AstNode addChild(AstNode node) {if (node != null) {children.add(node);((AstNodeImpl) node).parent = this;}return node;}@Overridepublic AstNode getParent() {return parent;}@Overridepublic void reverseChildren() {if (isChildrenReverse) {return;}Collections.reverse(children);isChildrenReverse = true;}@Overridepublic boolean isChildrenReverse() {return isChildrenReverse;}@Overridepublic ArrayList<AstNode> getChildren() {reverseChildren();return children;}@Overridepublic void setAttribute(NodeKey key, Object value) {if (key == NodeKey.TEXT) {name = (String) value;}put(key, value);}@Overridepublic Object getAttribute(NodeKey key) {return get(key);}@Overridepublic String toString() {String info = "";if (get(NodeKey.VALUE) != null) {info += "Node Value is " + get(NodeKey.VALUE).toString();}if (get(NodeKey.TEXT) != null) {info += "\nNode Text is " + get(NodeKey.TEXT).toString();}if (get(NodeKey.SYMBOL) != null) {info += "\nNode Symbol is " + get(NodeKey.SYMBOL).toString();}return info + "\n Node Type is " + type.toString();}@Overridepublic AstNode copy() {AstNodeImpl copy = (AstNodeImpl) NodeFactory.createICodeNode(type);Set<Entry<NodeKey, Object>> attributes = entrySet();Iterator<Map.Entry<NodeKey, Object>> it = attributes.iterator();while (it.hasNext()) {Map.Entry<NodeKey, Object> attribute = it.next();copy.put(attribute.getKey(), attribute.getValue());}return copy;} }

NodeFactory

NodeFactory就是簡單的返回一個節(jié)點的實現

public class NodeFactory {public static AstNode createICodeNode(Token type) {return new AstNodeImpl(type);} }

構造AST

AST的創(chuàng)建也是需要在語法分析過程中根據reduce操作進行操作的。也就是在takeActionForReduce方法中調用AstBuilder的buildSyntaxTree方法

在AstBuilder里面還是需要兩個堆棧來輔助操作

private Stack<AstNode> nodeStack = new Stack<>();private LRStateTableParser parser = null; private TypeSystem typeSystem = null; private Stack<Object> valueStack = null; private String functionName; private HashMap<String, AstNode> funcMap = new HashMap<>();private static AstBuilder instance;

構造AST的主要邏輯在buildSyntaxTree方法里，需要注意的是有一些節(jié)點在解釋執(zhí)行和代碼生成的時候是不一樣的，有時代碼生成需要的節(jié)點解釋執(zhí)行的話并不需要

在這里提一下UNARY這個非終結符，這個非終結符和NAME很像，但是它一般是代表進行運算和一些操作的時候，比如數組，++，--或者函數調用的時候

其實構建AST的過程和符號表的構建過程有點兒類似，都是根據reduce操作來創(chuàng)建信息和組合信息，符號表是組合修飾符說明符等，而AST則是組合節(jié)點間的關系變成一棵樹

我們只看幾個操作

• Specifiers_DeclList_Semi_TO_Def

  這個節(jié)點需要注意的是，從堆棧的什么地方拿到Symbol，這個需要從reduce次數和推導式中得出

* DEF -> SPECIFIERS DECL_LIST SEMI * DECL -> VAR_DECL * VAR_DECL -> NEW_NAME * | VAR_DECL LP RP * | VAR_DECL LP VAR_LIST RP * | LP VAR_DECL RP * | START VAR_DECL

從推導式可以看出，DEF節(jié)點的符號應該在valueStack.size() - 3，但是DECL和VAR_DECL沒有做reduce操作，所以符號應該在valueStack.size() - 2。這其實和前面的符號表構建算出之前符號的位置是一樣的。

• TO_UNARY

這里則是變量、數字或者字符串的節(jié)點，如果是個變量的號，這個節(jié)點就需要一個Symbol的value了

case SyntaxProductionInit.Number_TO_Unary: case SyntaxProductionInit.Name_TO_Unary: case SyntaxProductionInit.String_TO_Unary:node = NodeFactory.createICodeNode(Token.UNARY);if (production == SyntaxProductionInit.Name_TO_Unary) {assignSymbolToNode(node, text);}node.setAttribute(NodeKey.TEXT, text);break;

其余的節(jié)點無非是把一些語句拆分它的邏輯然后組成節(jié)點，真正的求值部分像Name_TO_Unary比較少，更多是比如把一個if else塊分成if節(jié)點、判斷節(jié)點、else節(jié)點，之后再按照這棵樹進行解釋執(zhí)行或者代碼生成

public AstNode buildSyntaxTree(int production, String text) {AstNode node = null;Symbol symbol = null;AstNode child = null;if (Start.STARTTYPE == Start.INTERPRETER) {int p1 = SyntaxProductionInit.Specifiers_DeclList_Semi_TO_Def;int p2 = SyntaxProductionInit.Def_To_DefList;int p3 = SyntaxProductionInit.DefList_Def_TO_DefList;boolean isReturn = production == p1 || production == p2 || production == p3;if (isReturn) {return null;}}switch (production) {case SyntaxProductionInit.Specifiers_DeclList_Semi_TO_Def:node = NodeFactory.createICodeNode(Token.DEF);symbol = (Symbol) valueStack.get(valueStack.size() - 2);node.setAttribute(NodeKey.SYMBOL, symbol);break;case SyntaxProductionInit.Def_To_DefList:node = NodeFactory.createICodeNode(Token.DEF_LIST);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.DefList_Def_TO_DefList:node = NodeFactory.createICodeNode(Token.DEF_LIST);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Number_TO_Unary:case SyntaxProductionInit.Name_TO_Unary:case SyntaxProductionInit.String_TO_Unary:node = NodeFactory.createICodeNode(Token.UNARY);if (production == SyntaxProductionInit.Name_TO_Unary) {assignSymbolToNode(node, text);}node.setAttribute(NodeKey.TEXT, text);break;case SyntaxProductionInit.Unary_LP_RP_TO_Unary:node = NodeFactory.createICodeNode(Token.UNARY);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Unary_LP_ARGS_RP_TO_Unary:node = NodeFactory.createICodeNode(Token.UNARY);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Unary_Incop_TO_Unary:case SyntaxProductionInit.Unary_DecOp_TO_Unary:case SyntaxProductionInit.LP_Expr_RP_TO_Unary:case SyntaxProductionInit.Start_Unary_TO_Unary:node = NodeFactory.createICodeNode(Token.UNARY);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Unary_LB_Expr_RB_TO_Unary:node = NodeFactory.createICodeNode(Token.UNARY);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Uanry_TO_Binary:node = NodeFactory.createICodeNode(Token.BINARY);child = nodeStack.pop();node.setAttribute(NodeKey.TEXT, child.getAttribute(NodeKey.TEXT));node.addChild(child);break;case SyntaxProductionInit.Binary_TO_NoCommaExpr:case SyntaxProductionInit.NoCommaExpr_Equal_NoCommaExpr_TO_NoCommaExpr:node = NodeFactory.createICodeNode(Token.NO_COMMA_EXPR);child = nodeStack.pop();String t = (String) child.getAttribute(NodeKey.TEXT);node.addChild(child);if (production == SyntaxProductionInit.NoCommaExpr_Equal_NoCommaExpr_TO_NoCommaExpr) {child = nodeStack.pop();t = (String) child.getAttribute(NodeKey.TEXT);node.addChild(child);}break;case SyntaxProductionInit.Binary_Plus_Binary_TO_Binary:case SyntaxProductionInit.Binary_DivOp_Binary_TO_Binary:case SyntaxProductionInit.Binary_Minus_Binary_TO_Binary:case SyntaxProductionInit.Binary_Start_Binary_TO_Binary:node = NodeFactory.createICodeNode(Token.BINARY);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Binary_RelOP_Binary_TO_Binray:node = NodeFactory.createICodeNode(Token.BINARY);node.addChild(nodeStack.pop());AstNode operator = NodeFactory.createICodeNode(Token.RELOP);operator.setAttribute(NodeKey.TEXT, parser.getRelOperatorText());node.addChild(operator);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.NoCommaExpr_TO_Expr:node = NodeFactory.createICodeNode(Token.EXPR);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Expr_Semi_TO_Statement:case SyntaxProductionInit.CompountStmt_TO_Statement:node = NodeFactory.createICodeNode(Token.STATEMENT);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.LocalDefs_TO_Statement:node = NodeFactory.createICodeNode(Token.STATEMENT);if (Start.STARTTYPE == Start.CODEGEN) {node.addChild(nodeStack.pop());}break;case SyntaxProductionInit.Statement_TO_StmtList:node = NodeFactory.createICodeNode(Token.STMT_LIST);if (nodeStack.size() > 0) {node.addChild(nodeStack.pop());}break;case SyntaxProductionInit.FOR_OptExpr_Test_EndOptExpr_Statement_TO_Statement:node = NodeFactory.createICodeNode(Token.STATEMENT);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.StmtList_Statement_TO_StmtList:node = NodeFactory.createICodeNode(Token.STMT_LIST);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Expr_TO_Test:node = NodeFactory.createICodeNode(Token.TEST);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.If_Test_Statement_TO_IFStatement:node = NodeFactory.createICodeNode(Token.IF_STATEMENT);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.IfElseStatemnt_Else_Statemenet_TO_IfElseStatement:node = NodeFactory.createICodeNode(Token.IF_ELSE_STATEMENT);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.While_LP_Test_Rp_TO_Statement:case SyntaxProductionInit.Do_Statement_While_Test_To_Statement:node = NodeFactory.createICodeNode(Token.STATEMENT);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Expr_Semi_TO_OptExpr:case SyntaxProductionInit.Semi_TO_OptExpr:node = NodeFactory.createICodeNode(Token.OPT_EXPR);if (production == SyntaxProductionInit.Expr_Semi_TO_OptExpr) {node.addChild(nodeStack.pop());}break;case SyntaxProductionInit.Expr_TO_EndOpt:node = NodeFactory.createICodeNode(Token.END_OPT_EXPR);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.LocalDefs_StmtList_TO_CompoundStmt:node = NodeFactory.createICodeNode(Token.COMPOUND_STMT);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.NewName_LP_RP_TO_FunctDecl:case SyntaxProductionInit.NewName_LP_VarList_RP_TO_FunctDecl:node = NodeFactory.createICodeNode(Token.FUNCT_DECL);node.addChild(nodeStack.pop());child = node.getChildren().get(0);functionName = (String) child.getAttribute(NodeKey.TEXT);symbol = assignSymbolToNode(node, functionName);break;case SyntaxProductionInit.NewName_TO_VarDecl:nodeStack.pop();break;case SyntaxProductionInit.NAME_TO_NewName:node = NodeFactory.createICodeNode(Token.NEW_NAME);node.setAttribute(NodeKey.TEXT, text);break;case SyntaxProductionInit.OptSpecifiers_FunctDecl_CompoundStmt_TO_ExtDef:node = NodeFactory.createICodeNode(Token.EXT_DEF);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());funcMap.put(functionName, node);break;case SyntaxProductionInit.NoCommaExpr_TO_Args:node = NodeFactory.createICodeNode(Token.ARGS);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.NoCommaExpr_Comma_Args_TO_Args:node = NodeFactory.createICodeNode(Token.ARGS);node.addChild(nodeStack.pop());node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Return_Semi_TO_Statement:node = NodeFactory.createICodeNode(Token.STATEMENT);break;case SyntaxProductionInit.Return_Expr_Semi_TO_Statement:node = NodeFactory.createICodeNode(Token.STATEMENT);node.addChild(nodeStack.pop());break;case SyntaxProductionInit.Unary_StructOP_Name_TO_Unary:node = NodeFactory.createICodeNode(Token.UNARY);node.addChild(nodeStack.pop());node.setAttribute(NodeKey.TEXT, text);break;default:break;}if (node != null) {node.setAttribute(NodeKey.PRODUCTION, production);nodeStack.push(node);}return node; }

小結

其實構造AST和創(chuàng)建符號表上非常相似，都是依據reduce操作的信息來完成。在AST的構建中的主要任務就是對源代碼語句里的邏輯進行分塊，比如對于一個ifelse語句：

上面的圖是我依據這個意思話的，和上面構造出來的AST不完全一致

另外我的github博客：https://dejavudwh.cn/

轉載于:https://www.cnblogs.com/secoding/p/11379216.html

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