codegen.java

Javassist是一个开源的分析、编辑和创建Java字节码的类库。是由东京技术学院的数学和计算机科学系的 Shigeru Chiba 所创建的。它已加入了开放源代码JBoss 应用服务器项目,通过使

/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999-2006 Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */

package javassist.compiler;

import java.util.ArrayList;
import java.util.Arrays;
import javassist.compiler.ast.*;
import javassist.bytecode.*;

/* The code generator is implemeted by three files:
 * CodeGen.java, MemberCodeGen.java, and JvstCodeGen.
 * I just wanted to split a big file into three smaller ones.
 */

public abstract class CodeGen extends Visitor implements Opcode, TokenId {
    static final String javaLangObject = "java.lang.Object";
    static final String jvmJavaLangObject = "java/lang/Object";

    static final String javaLangString = "java.lang.String";
    static final String jvmJavaLangString = "java/lang/String";

    protected Bytecode bytecode;
    private int tempVar;
    TypeChecker typeChecker;

    /**
     * true if the last visited node is a return statement.
     */
    protected boolean hasReturned;

    /**
     * Must be true if compilation is for a static method.
     */
    public boolean inStaticMethod;

    protected ArrayList breakList, continueList;

    /**
     * doit() in ReturnHook is called from atReturn().
     */
    protected static abstract class ReturnHook {
        ReturnHook next;
        protected abstract void doit(Bytecode b, int opcode);
        protected ReturnHook(CodeGen gen) {
            next = gen.returnHooks;
            gen.returnHooks = this;
        }

        protected void remove(CodeGen gen) {
            gen.returnHooks = next;
        }
    }

    protected ReturnHook returnHooks;

    /* The following fields are used by atXXX() methods
     * for returning the type of the compiled expression.
     */
    protected int exprType;     // VOID, NULL, CLASS, BOOLEAN, INT, ...
    protected int arrayDim;
    protected String className; // JVM-internal representation

    public CodeGen(Bytecode b) {
        bytecode = b;
        tempVar = -1;
        typeChecker = null;
        hasReturned = false;
        inStaticMethod = false;
        breakList = null;
        continueList = null;
        returnHooks = null;
    }

    public void setTypeChecker(TypeChecker checker) {
        typeChecker = checker;
    }

    protected static void fatal() throws CompileError {
        throw new CompileError("fatal");
    }

    public static boolean is2word(int type, int dim) {
        return dim == 0 && (type == DOUBLE || type == LONG); 
    }

    public int getMaxLocals() { return bytecode.getMaxLocals(); }

    public void setMaxLocals(int n) {
        bytecode.setMaxLocals(n);
    }

    protected void incMaxLocals(int size) {
        bytecode.incMaxLocals(size);
    }

    /**
     * Returns a local variable that single or double words can be
     * stored in.
     */
    protected int getTempVar() {
        if (tempVar < 0) {
            tempVar = getMaxLocals();
            incMaxLocals(2);
        }

        return tempVar;
    }

    protected int getLocalVar(Declarator d) {
        int v = d.getLocalVar();
        if (v < 0) {
            v = getMaxLocals(); // delayed variable allocation.
            d.setLocalVar(v);
            incMaxLocals(1);
        }

        return v;
    }

    /**
     * Returns the JVM-internal representation of this class name.
     */
    protected abstract String getThisName();

    /**
     * Returns the JVM-internal representation of this super class name.
     */
    protected abstract String getSuperName() throws CompileError;

    /* Converts a class name into a JVM-internal representation.
     *
     * It may also expand a simple class name to java.lang.*.
     * For example, this converts Object into java/lang/Object.
     */
    protected abstract String resolveClassName(ASTList name)
        throws CompileError;

    /* Expands a simple class name to java.lang.*.
     * For example, this converts Object into java/lang/Object.
     */
    protected abstract String resolveClassName(String jvmClassName)
        throws CompileError;

    /**
     * @param name      the JVM-internal representation.
     *                  name is not exapnded to java.lang.*.
     */
    protected static String toJvmArrayName(String name, int dim) {
        if (name == null)
            return null;

        if (dim == 0)
            return name;
        else {
            StringBuffer sbuf = new StringBuffer();
            int d = dim;
            while (d-- > 0)
                sbuf.append('[');

            sbuf.append('L');
            sbuf.append(name);
            sbuf.append(';');

            return sbuf.toString();
        }
    }

    protected static String toJvmTypeName(int type, int dim) {
        char c = 'I';
        switch(type) {
        case BOOLEAN :
            c = 'Z';
            break;
        case BYTE :
            c = 'B';
            break;
        case CHAR :
            c = 'C';
            break;
        case SHORT :
            c = 'S';
            break;
        case INT :
            c = 'I';
            break;
        case LONG :
            c = 'J';
            break;
        case FLOAT :
            c = 'F';
            break;
        case DOUBLE :
            c = 'D';
            break;
        case VOID :
            c = 'V';
            break;
        }

        StringBuffer sbuf = new StringBuffer();
        while (dim-- > 0)
                sbuf.append('[');

        sbuf.append(c);
        return sbuf.toString();
    }

    public void compileExpr(ASTree expr) throws CompileError {
        doTypeCheck(expr);
        expr.accept(this);
    }

    public boolean compileBooleanExpr(boolean branchIf, ASTree expr)
        throws CompileError
    {
        doTypeCheck(expr);
        return booleanExpr(branchIf, expr);
    }

    public void doTypeCheck(ASTree expr) throws CompileError {
        if (typeChecker != null)
            expr.accept(typeChecker);
    }

    public void atASTList(ASTList n) throws CompileError { fatal(); }
    
    public void atPair(Pair n) throws CompileError { fatal(); }

    public void atSymbol(Symbol n) throws CompileError { fatal(); }

    public void atFieldDecl(FieldDecl field) throws CompileError {
        field.getInit().accept(this);
    }

    public void atMethodDecl(MethodDecl method) throws CompileError {
        ASTList mods = method.getModifiers();
        setMaxLocals(1);
        while (mods != null) {
            Keyword k = (Keyword)mods.head();
            mods = mods.tail();
            if (k.get() == STATIC) {
                setMaxLocals(0);
                inStaticMethod = true;
            }
        }
            
        ASTList params = method.getParams();
        while (params != null) {
            atDeclarator((Declarator)params.head());
            params = params.tail();
        }

        Stmnt s = method.getBody();
        atMethodBody(s, method.isConstructor(),
                     method.getReturn().getType() == VOID);
    }

    /**
     * @param isCons	true if super() must be called.
     *			false if the method is a class initializer.
     */
    public void atMethodBody(Stmnt s, boolean isCons, boolean isVoid)
        throws CompileError
    {
        if (s == null)
            return;

        if (isCons && needsSuperCall(s))
            insertDefaultSuperCall();

        hasReturned = false;
        s.accept(this);
        if (!hasReturned)
            if (isVoid) {
                bytecode.addOpcode(Opcode.RETURN);
                hasReturned = true;
            }
            else
                throw new CompileError("no return statement");
    }

    private boolean needsSuperCall(Stmnt body) throws CompileError {
        if (body.getOperator() == BLOCK)
            body = (Stmnt)body.head();

        if (body != null && body.getOperator() == EXPR) {
            ASTree expr = body.head();
            if (expr != null && expr instanceof Expr
                && ((Expr)expr).getOperator() == CALL) {
                ASTree target = ((Expr)expr).head();
                if (target instanceof Keyword) {
                    int token = ((Keyword)target).get();
                    return token != THIS && token != SUPER;
                }
            }
        }

        return true;
    }

    protected abstract void insertDefaultSuperCall() throws CompileError;

    public void atStmnt(Stmnt st) throws CompileError {
        if (st == null)
            return;     // empty

        int op = st.getOperator();
        if (op == EXPR) {
            ASTree expr = st.getLeft();
            doTypeCheck(expr);
            if (expr instanceof AssignExpr)
                atAssignExpr((AssignExpr)expr, false);
            else if (isPlusPlusExpr(expr)) {
                Expr e = (Expr)expr;
                atPlusPlus(e.getOperator(), e.oprand1(), e, false);
            }
            else {
                expr.accept(this);
                if (is2word(exprType, arrayDim))
                    bytecode.addOpcode(POP2);
                else if (exprType != VOID)
                    bytecode.addOpcode(POP);
            }
        }
        else if (op == DECL || op == BLOCK) {
            ASTList list = st;
            while (list != null) {
                ASTree h = list.head();
                list = list.tail();
                if (h != null)
                    h.accept(this);
            }
        }
        else if (op == IF)
            atIfStmnt(st);
        else if (op == WHILE || op == DO)
            atWhileStmnt(st, op == WHILE);
        else if (op == FOR)
            atForStmnt(st);
        else if (op == BREAK || op == CONTINUE)
            atBreakStmnt(st, op == BREAK);
        else if (op == TokenId.RETURN)
            atReturnStmnt(st);
        else if (op == THROW)
            atThrowStmnt(st);
        else if (op == TRY)
            atTryStmnt(st);
        else if (op == SWITCH)
            atSwitchStmnt(st);
        else if (op == SYNCHRONIZED)
            atSyncStmnt(st);
        else {
            // LABEL, SWITCH label stament might be null?.
            hasReturned = false;
            throw new CompileError(
                "sorry, not supported statement: TokenId " + op);
        }
    }

    private void atIfStmnt(Stmnt st) throws CompileError {
        ASTree expr = st.head();
        Stmnt thenp = (Stmnt)st.tail().head();
        Stmnt elsep = (Stmnt)st.tail().tail().head();
        compileBooleanExpr(false, expr);
        int pc = bytecode.currentPc();
        int pc2 = 0;
        bytecode.addIndex(0);   // correct later

        hasReturned = false;
        if (thenp != null)
            thenp.accept(this);

        boolean thenHasReturned = hasReturned;
        hasReturned = false;

        if (elsep != null && !thenHasReturned) {
            bytecode.addOpcode(Opcode.GOTO);
            pc2 = bytecode.currentPc();
            bytecode.addIndex(0);
        }

        bytecode.write16bit(pc, bytecode.currentPc() - pc + 1);

        if (elsep != null) {
            elsep.accept(this);
            if (!thenHasReturned)
                bytecode.write16bit(pc2, bytecode.currentPc() - pc2 + 1);

            hasReturned = thenHasReturned && hasReturned;
        }
    }

    private void atWhileStmnt(Stmnt st, boolean notDo) throws CompileError {
        ArrayList prevBreakList = breakList;
        ArrayList prevContList = continueList;
        breakList = new ArrayList();
        continueList = new ArrayList();

        ASTree expr = st.head();
        Stmnt body = (Stmnt)st.tail();

        int pc = 0;
        if (notDo) {
            bytecode.addOpcode(Opcode.GOTO);
            pc = bytecode.currentPc();
            bytecode.addIndex(0);
        }

        int pc2 = bytecode.currentPc();
        if (body != null)
            body.accept(this);

        int pc3 = bytecode.currentPc();
        if (notDo)
            bytecode.write16bit(pc, pc3 - pc + 1);

        boolean alwaysBranch = compileBooleanExpr(true, expr);
        bytecode.addIndex(pc2 - bytecode.currentPc() + 1);

        patchGoto(breakList, bytecode.currentPc());
        patchGoto(continueList, pc3);
        continueList = prevContList;
        breakList = prevBreakList;
        hasReturned = alwaysBranch;
    }

    protected void patchGoto(ArrayList list, int targetPc) {
        int n = list.size();
        for (int i = 0; i < n; ++i) {
            int pc = ((Integer)list.get(i)).intValue();
            bytecode.write16bit(pc, targetPc - pc + 1);
        }
    }

    private void atForStmnt(Stmnt st) throws CompileError {
        ArrayList prevBreakList = breakList;
        ArrayList prevContList = continueList;
        breakList = new ArrayList();
        continueList = new ArrayList();

        Stmnt init = (Stmnt)st.head();
        ASTList p = st.tail();
        ASTree expr = p.head();
        p = p.tail();
        Stmnt update = (Stmnt)p.head();
        Stmnt body = (Stmnt)p.tail();

        if (init != null)
            init.accept(this);

        int pc = bytecode.currentPc();
        int pc2 = 0;
        if (expr != null) {
            compileBooleanExpr(false, expr);
            pc2 = bytecode.currentPc();
            bytecode.addIndex(0);
        }

        if (body != null)
            body.accept(this);