項目的完整代碼在 C2j-Compiler

前言

在上一篇解釋完了一些基礎的Java字節碼指令后，就可以正式進入真正的代碼生成部分了。但是這部分先說的是代碼生成依靠的幾個類，也就是用來生成指令的操作。

這一篇用到的文件都在codegen下：

• Directive.java
• Instruction.java
• CodeGenerator.java
• ProgramGenerator.java

Directive.java

這個是枚舉類，用來生成一些比較特殊的指令

都生成像聲明一個類或者一個方法的范圍的指令，比較簡單。

public enum Directive {CLASS_PUBLIC(".class public"),END_CLASS(".end class"),SUPER(".super"),FIELD_PRIVATE_STATIC(".field private static"),METHOD_STATIC(".method static"),METHOD_PUBLIC(".method public"),FIELD_PUBLIC(".field public"),METHOD_PUBBLIC_STATIC(".method public static"),END_METHOD(".end method"),LIMIT_LOCALS(".limit locals"),LIMIT_STACK(".limit stack"),VAR(".var"),LINE(".line");private String text;Directive(String text) {this.text = text;}public String toString() {return text;} }

Instruction.java

這也是一個枚舉類，用來生成一些基本的指令

public enum Instruction {LDC("ldc"),GETSTATIC("getstatic"),SIPUSH("sipush"),IADD("iadd"),IMUL("imul"),ISUB("isub"),IDIV("idiv"),INVOKEVIRTUAL("invokevirtual"),INVOKESTATIC("invokestatic"),INVOKESPECIAL("invokespecial"),RETURN("return"),IRETURN("ireturn"),ILOAD("iload"),ISTORE("istore"),NEWARRAY("newarray"),NEW("new"),DUP("dup"),ASTORE("astore"),IASTORE("iastore"),ALOAD("aload"),PUTFIELD("putfield"),GETFIELD("getfield"),ANEWARRAY("anewarray"),AASTORE("aastore"),AALOAD("aaload"),IF_ICMPEG("if_icmpeq"), IF_ICMPNE("if_icmpne"),IF_ICMPLT("if_icmplt"),IF_ICMPGE("if_icmpge"),IF_ICMPGT("if_icmpgt"),IF_ICMPLE("if_icmple"),GOTO("goto"),IALOAD("iaload");private String text;Instruction(String s) {this.text = s;}public String toString() {return text;} }

CodeGenerator.java

重點來了，生成的邏輯主要都在CodeGenerator和ProgramGenerator里，CodeGenerator是ProgramGenerator的父類

CodeGenerator的構造函數new了一個輸出流，用來輸出字節碼到xxx.j里

public CodeGenerator() {String assemblyFileName = programName + ".j";try {bytecodeFile = new PrintWriter(new PrintStream(newFile(assemblyFileName)));} catch (FileNotFoundException e) {e.printStackTrace();}}

emit、emitString、emitDirective、emitBlankLine都屬于輸出基本指令的方法，都有多個重載方法來應對不一樣操作和操作數。需要注意的是，有的指令可能需要先緩存起來，在最后的時候一起提交，比如buffered、classDefine就是用來判斷是不是應該先緩存的布爾值

public void emitString(String s) {if (buffered) {bufferedContent += s + "\n";return;}if (classDefine) {classDefinition += s + "\n";return;}bytecodeFile.print(s);bytecodeFile.flush();}public void emit(Instruction opcode) {if (buffered) {bufferedContent += "\t" + opcode.toString() + "\n";return;}if (classDefine) {classDefinition += "\t" + opcode.toString() + "\n";return;}bytecodeFile.println("\t" + opcode.toString());bytecodeFile.flush();++instructionCount; }public void emitDirective(Directive directive, String operand1, String operand2, String operand3) {if (buffered) {bufferedContent += directive.toString() + " " + operand1 + " " + operand2 + " " + operand3 + "\n";return;}if (classDefine) {classDefinition += directive.toString() + " " + operand1 + " " + operand2 + " " + operand3 + "\n";return;}bytecodeFile.println(directive.toString() + " " + operand1 + " " + operand2 + " " + operand3);++instructionCount; }public void emitBlankLine() {if (buffered) {bufferedContent += "\n";return;}if (classDefine) {classDefinition += "\n";return;}bytecodeFile.println();bytecodeFile.flush(); }

ProgramGenerator.java

ProgramGenerator繼承了CodeGenerator，也就是繼承了一些基本的操作，在上一篇像結構體、數組的指令輸出都在這個類里

處理嵌套

先看四個屬性，這四個屬性主要是就來處理嵌套的分支和循環。

private int branch_count = 0; private int branch_out = 0; private String embedded = ""; private int loopCount = 0;

• 當沒嵌套一個ifelse語句時候 embedded屬性就會加上一個字符‘i’，而當退出一個分支的時候，就把這個‘i’切割掉

• branch_count和branch_out都用來標志相同作用域的分支跳轉

• 也就是說如果有嵌套就用embedded來處理，如果是用一個作用域的分支就用branch_count和branch_out來做標志

public void incraseIfElseEmbed() {embedded += "i"; }public void decraseIfElseEmbed() {embedded = embedded.substring(1); }public void emitBranchOut() {String s = "\n" + embedded + "branch_out" + branch_out + ":\n";this.emitString(s);branch_out++; }

loopCount則是對嵌套循環的處理

public void emitLoopBranch() {String s = "\n" + "loop" + loopCount + ":" + "\n";emitString(s); }public String getLoopBranch() {return "loop" + loopCount; }public void increaseLoopCount() {loopCount++; }

處理結構體

putStructToClassDeclaration是定義結構體的，也就是new一個類。declareStructAsClass則是處理結構體里的變量，也就是相當于處理類的屬性

• 結構體如果已經類的定義的話，就會加入structNameList，不要進行重復的定義
• symbol.getValueSetter()如果不是空的話就表明是一個結構體數組，這樣就直接從數組加載這個實例，不用在堆棧上創建
• declareStructAsClass則是依照上一篇說的Java字節碼有關類的指令來創建一個類

public void putStructToClassDeclaration(Symbol symbol) {Specifier sp = symbol.getSpecifierByType(Specifier.STRUCTURE);if (sp == null) {return;}StructDefine struct = sp.getStruct();if (structNameList.contains(struct.getTag())) {return;} else {structNameList.add(struct.getTag());}if (symbol.getValueSetter() == null) {this.emit(Instruction.NEW, struct.getTag());this.emit(Instruction.DUP);this.emit(Instruction.INVOKESPECIAL, struct.getTag() + "/" + "<init>()V");int idx = this.getLocalVariableIndex(symbol);this.emit(Instruction.ASTORE, "" + idx);}declareStructAsClass(struct); }private void declareStructAsClass(StructDefine struct) {this.setClassDefinition(true);this.emitDirective(Directive.CLASS_PUBLIC, struct.getTag());this.emitDirective(Directive.SUPER, "java/lang/Object");Symbol fields = struct.getFields();do {String fieldName = fields.getName() + " ";if (fields.getDeclarator(Declarator.ARRAY) != null) {fieldName += "[";}if (fields.hasType(Specifier.INT)) {fieldName += "I";} else if (fields.hasType(Specifier.CHAR)) {fieldName += "C";} else if (fields.hasType(Specifier.CHAR) && fields.getDeclarator(Declarator.POINTER) != null) {fieldName += "Ljava/lang/String;";}this.emitDirective(Directive.FIELD_PUBLIC, fieldName);fields = fields.getNextSymbol();} while (fields != null);this.emitDirective(Directive.METHOD_PUBLIC, "<init>()V");this.emit(Instruction.ALOAD, "0");String superInit = "java/lang/Object/<init>()V";this.emit(Instruction.INVOKESPECIAL, superInit);fields = struct.getFields();do {this.emit(Instruction.ALOAD, "0");String fieldName = struct.getTag() + "/" + fields.getName();String fieldType = "";if (fields.hasType(Specifier.INT)) {fieldType = "I";this.emit(Instruction.SIPUSH, "0");} else if (fields.hasType(Specifier.CHAR)) {fieldType = "C";this.emit(Instruction.SIPUSH, "0");} else if (fields.hasType(Specifier.CHAR) && fields.getDeclarator(Declarator.POINTER) != null) {fieldType = "Ljava/lang/String;";this.emit(Instruction.LDC, " ");}String classField = fieldName + " " + fieldType;this.emit(Instruction.PUTFIELD, classField);fields = fields.getNextSymbol();} while (fields != null);this.emit(Instruction.RETURN);this.emitDirective(Directive.END_METHOD);this.emitDirective(Directive.END_CLASS);this.setClassDefinition(false); }

獲取堆棧信息

其它有關Java字節碼其實都是根據上一篇來完成的，邏輯不復雜，現在來看一個方法：getLocalVariableIndex，這個方法是獲取變量當前在隊列里的位置的

• 先拿到當前執行的函數，然后拿到函數的對應參數，再反轉（這和參數壓棧的順序有關）
• 然后把當前符號對應作用域的符號都添加到列表里
• 之后遍歷這個列表就可以算出這個符號對應在隊列里的位置

public int getLocalVariableIndex(Symbol symbol) {TypeSystem typeSys = TypeSystem.getInstance();String funcName = nameStack.peek();Symbol funcSym = typeSys.getSymbolByText(funcName, 0, "main");ArrayList<Symbol> localVariables = new ArrayList<>();Symbol s = funcSym.getArgList();while (s != null) {localVariables.add(s);s = s.getNextSymbol();}Collections.reverse(localVariables);ArrayList<Symbol> list = typeSys.getSymbolsByScope(symbol.getScope());for (int i = 0; i < list.size(); i++) {if (!localVariables.contains(list.get(i))) {localVariables.add(list.get(i));}}for (int i = 0; i < localVariables.size(); i++) {if (localVariables.get(i) == symbol) {return i;}}return -1; }

小結

這一篇主要是根據上一篇的JVM字節碼來對不同的操作提供不同的方法來去輸出這些指令

歡迎Star!

轉載于:https://www.cnblogs.com/secoding/p/11388347.html

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