codegen.java

這是一個javascript 的 interpreter是了解 web browser的好材料

            int N = directCallTargets.size();
            for (int j = 0; j != N; ++j) {
                cfw.addField(getDirectTargetFieldName(j),
                             mainClassSignature,
                             ClassFileWriter.ACC_PRIVATE);
            }
        }

        emitRegExpInit(cfw);
        emitConstantDudeInitializers(cfw);

        return cfw.toByteArray();
    }

    private void emitDirectConstructor(ClassFileWriter cfw,
                                       OptFunctionNode ofn)
    {
/*
    we generate ..
        Scriptable directConstruct(<directCallArgs>) {
            Scriptable newInstance = createObject(cx, scope);
            Object val = <body-name>(cx, scope, newInstance, <directCallArgs>);
            if (val instanceof Scriptable) {
                return (Scriptable) val;
            }
            return newInstance;
        }
*/
        cfw.startMethod(getDirectCtorName(ofn.fnode),
                        getBodyMethodSignature(ofn.fnode),
                        (short)(ClassFileWriter.ACC_STATIC
                                | ClassFileWriter.ACC_PRIVATE));

        int argCount = ofn.fnode.getParamCount();
        int firstLocal = (4 + argCount * 3) + 1;

        cfw.addALoad(0); // this
        cfw.addALoad(1); // cx
        cfw.addALoad(2); // scope
        cfw.addInvoke(ByteCode.INVOKEVIRTUAL,
                      "org/mozilla/javascript/BaseFunction",
                      "createObject",
                      "(Lorg/mozilla/javascript/Context;"
                      +"Lorg/mozilla/javascript/Scriptable;"
                      +")Lorg/mozilla/javascript/Scriptable;");
        cfw.addAStore(firstLocal);

        cfw.addALoad(0);
        cfw.addALoad(1);
        cfw.addALoad(2);
        cfw.addALoad(firstLocal);
        for (int i = 0; i < argCount; i++) {
            cfw.addALoad(4 + (i * 3));
            cfw.addDLoad(5 + (i * 3));
        }
        cfw.addALoad(4 + argCount * 3);
        cfw.addInvoke(ByteCode.INVOKESTATIC,
                      mainClassName,
                      getBodyMethodName(ofn.fnode),
                      getBodyMethodSignature(ofn.fnode));
        int exitLabel = cfw.acquireLabel();
        cfw.add(ByteCode.DUP); // make a copy of direct call result
        cfw.add(ByteCode.INSTANCEOF, "org/mozilla/javascript/Scriptable");
        cfw.add(ByteCode.IFEQ, exitLabel);
        // cast direct call result
        cfw.add(ByteCode.CHECKCAST, "org/mozilla/javascript/Scriptable");
        cfw.add(ByteCode.ARETURN);
        cfw.markLabel(exitLabel);

        cfw.addALoad(firstLocal);
        cfw.add(ByteCode.ARETURN);

        cfw.stopMethod((short)(firstLocal + 1));
    }

    static boolean isGenerator(ScriptOrFnNode node)
    {
        return (node.getType() == Token.FUNCTION ) &&
                ((FunctionNode)node).isGenerator();
    }

    // How dispatch to generators works:
    // Two methods are generated corresponding to a user-written generator.
    // One of these creates a generator object (NativeGenerator), which is
    // returned to the user. The other method contains all of the body code
    // of the generator.
    // When a user calls a generator, the call() method dispatches control to
    // to the method that creates the NativeGenerator object. Subsequently when
    // the user invokes .next(), .send() or any such method on the generator
    // object, the resumeGenerator() below dispatches the call to the
    // method corresponding to the generator body. As a matter of convention
    // the generator body is given the name of the generator activation function
    // appended by "_gen".
    private void generateResumeGenerator(ClassFileWriter cfw)
    {
        boolean hasGenerators = false;
        for (int i=0; i < scriptOrFnNodes.length; i++) {
            if (isGenerator(scriptOrFnNodes[i]))
            	hasGenerators = true;
        }

        // if there are no generators defined, we don't implement a
        // resumeGenerator(). The base class provides a default implementation. 
        if (!hasGenerators)
            return;

        cfw.startMethod("resumeGenerator",
                        "(Lorg/mozilla/javascript/Context;" +
                        "Lorg/mozilla/javascript/Scriptable;" +
                        "ILjava/lang/Object;" +
                        "Ljava/lang/Object;)Ljava/lang/Object;",
                        (short)(ClassFileWriter.ACC_PUBLIC
                                | ClassFileWriter.ACC_FINAL));

        // load arguments for dispatch to the corresponding *_gen method 
        cfw.addALoad(0);
        cfw.addALoad(1);
        cfw.addALoad(2);
        cfw.addALoad(4);
        cfw.addALoad(5);
        cfw.addILoad(3);

        cfw.addLoadThis();
        cfw.add(ByteCode.GETFIELD, cfw.getClassName(), ID_FIELD_NAME, "I");

        int startSwitch = cfw.addTableSwitch(0, scriptOrFnNodes.length - 1);
        cfw.markTableSwitchDefault(startSwitch);
        int endlabel = cfw.acquireLabel();

        for (int i = 0; i < scriptOrFnNodes.length; i++) {
            ScriptOrFnNode n = scriptOrFnNodes[i];
            cfw.markTableSwitchCase(startSwitch, i, (short)6);
            if (isGenerator(n)) {
                String type = "(" +
                              mainClassSignature +
                              "Lorg/mozilla/javascript/Context;" +
                              "Lorg/mozilla/javascript/Scriptable;" +
                              "Ljava/lang/Object;" +
                              "Ljava/lang/Object;I)Ljava/lang/Object;";
                cfw.addInvoke(ByteCode.INVOKESTATIC,
                              mainClassName,
                              getBodyMethodName(n) + "_gen",
                              type);
                cfw.add(ByteCode.ARETURN);
            } else {
                cfw.add(ByteCode.GOTO, endlabel);
            }
        }

        cfw.markLabel(endlabel);
        pushUndefined(cfw);
        cfw.add(ByteCode.ARETURN);


        // this method uses as many locals as there are arguments (hence 6)
        cfw.stopMethod((short)6);
    }

    private void generateCallMethod(ClassFileWriter cfw)
    {
        cfw.startMethod("call",
                        "(Lorg/mozilla/javascript/Context;" +
                        "Lorg/mozilla/javascript/Scriptable;" +
                        "Lorg/mozilla/javascript/Scriptable;" +
                        "[Ljava/lang/Object;)Ljava/lang/Object;",
                        (short)(ClassFileWriter.ACC_PUBLIC
                                | ClassFileWriter.ACC_FINAL));

        // Generate code for:
        // if (!ScriptRuntime.hasTopCall(cx)) {
        //     return ScriptRuntime.doTopCall(this, cx, scope, thisObj, args);
        // }

        int nonTopCallLabel = cfw.acquireLabel();
        cfw.addALoad(1); //cx
        cfw.addInvoke(ByteCode.INVOKESTATIC,
                      "org/mozilla/javascript/ScriptRuntime",
                      "hasTopCall",
                      "(Lorg/mozilla/javascript/Context;"
                      +")Z");
        cfw.add(ByteCode.IFNE, nonTopCallLabel);
        cfw.addALoad(0);
        cfw.addALoad(1);
        cfw.addALoad(2);
        cfw.addALoad(3);
        cfw.addALoad(4);
        cfw.addInvoke(ByteCode.INVOKESTATIC,
                      "org/mozilla/javascript/ScriptRuntime",
                      "doTopCall",
                      "(Lorg/mozilla/javascript/Callable;"
                      +"Lorg/mozilla/javascript/Context;"
                      +"Lorg/mozilla/javascript/Scriptable;"
                      +"Lorg/mozilla/javascript/Scriptable;"
                      +"[Ljava/lang/Object;"
                      +")Ljava/lang/Object;");
        cfw.add(ByteCode.ARETURN);
        cfw.markLabel(nonTopCallLabel);

        // Now generate switch to call the real methods
        cfw.addALoad(0);
        cfw.addALoad(1);
        cfw.addALoad(2);
        cfw.addALoad(3);
        cfw.addALoad(4);

        int end = scriptOrFnNodes.length;
        boolean generateSwitch = (2 <= end);

        int switchStart = 0;
        int switchStackTop = 0;
        if (generateSwitch) {
            cfw.addLoadThis();
            cfw.add(ByteCode.GETFIELD, cfw.getClassName(), ID_FIELD_NAME, "I");
            // do switch from (1,  end - 1) mapping 0 to
            // the default case
            switchStart = cfw.addTableSwitch(1, end - 1);
        }

        for (int i = 0; i != end; ++i) {
            ScriptOrFnNode n = scriptOrFnNodes[i];
            if (generateSwitch) {
                if (i == 0) {
                    cfw.markTableSwitchDefault(switchStart);
                    switchStackTop = cfw.getStackTop();
                } else {
                    cfw.markTableSwitchCase(switchStart, i - 1,
                                            switchStackTop);
                }
            }
            if (n.getType() == Token.FUNCTION) {
                OptFunctionNode ofn = OptFunctionNode.get(n);
                if (ofn.isTargetOfDirectCall()) {
                    int pcount = ofn.fnode.getParamCount();
                    if (pcount != 0) {
                        // loop invariant:
                        // stack top == arguments array from addALoad4()
                        for (int p = 0; p != pcount; ++p) {
                            cfw.add(ByteCode.ARRAYLENGTH);
                            cfw.addPush(p);
                            int undefArg = cfw.acquireLabel();
                            int beyond = cfw.acquireLabel();
                            cfw.add(ByteCode.IF_ICMPLE, undefArg);
                            // get array[p]
                            cfw.addALoad(4);
                            cfw.addPush(p);
                            cfw.add(ByteCode.AALOAD);
                            cfw.add(ByteCode.GOTO, beyond);
                            cfw.markLabel(undefArg);
                            pushUndefined(cfw);
                            cfw.markLabel(beyond);
                            // Only one push
                            cfw.adjustStackTop(-1);
                            cfw.addPush(0.0);
                            // restore invariant
                            cfw.addALoad(4);
                        }
                    }
                }
            }
            cfw.addInvoke(ByteCode.INVOKESTATIC,
                          mainClassName,
                          getBodyMethodName(n),
                          getBodyMethodSignature(n));
            cfw.add(ByteCode.ARETURN);
        }
        cfw.stopMethod((short)5);
        // 5: this, cx, scope, js this, args[]
    }

    private void generateMain(ClassFileWriter cfw)
    {
        cfw.startMethod("main", "([Ljava/lang/String;)V",
                        (short)(ClassFileWriter.ACC_PUBLIC
                                | ClassFileWriter.ACC_STATIC));

        // load new ScriptImpl()
        cfw.add(ByteCode.NEW, cfw.getClassName());
        cfw.add(ByteCode.DUP);
        cfw.addInvoke(ByteCode.INVOKESPECIAL, cfw.getClassName(),
                      "<init>", "()V");
         // load 'args'
        cfw.add(ByteCode.ALOAD_0);
        // Call mainMethodClass.main(Script script, String[] args)
        cfw.addInvoke(ByteCode.INVOKESTATIC,
                      mainMethodClass,
                      "main",
                      "(Lorg/mozilla/javascript/Script;[Ljava/lang/String;)V");
        cfw.add(ByteCode.RETURN);
        // 1 = String[] args
        cfw.stopMethod((short)1);
    }

    private void generateExecute(ClassFileWriter cfw)
    {
        cfw.startMethod("exec",
                        "(Lorg/mozilla/javascript/Context;"
                        +"Lorg/mozilla/javascript/Scriptable;"
                        +")Ljava/lang/Object;",
                        (short)(ClassFileWriter.ACC_PUBLIC
                                | ClassFileWriter.ACC_FINAL));

        final int CONTEXT_ARG = 1;
        final int SCOPE_ARG = 2;

        cfw.addLoadThis();
        cfw.addALoad(CONTEXT_ARG);
        cfw.addALoad(SCOPE_ARG);
        cfw.add(ByteCode.DUP);
        cfw.add(ByteCode.ACONST_NULL);
        cfw.addInvoke(ByteCode.INVOKEVIRTUAL,
                      cfw.getClassName(),
                      "call",
                      "(Lorg/mozilla/javascript/Context;"
                      +"Lorg/mozilla/javascript/Scriptable;"
                      +"Lorg/mozilla/javascript/Scriptable;"
                      +"[Ljava/lang/Object;"
                      +")Ljava/lang/Object;");

        cfw.add(ByteCode.ARETURN);
        // 3 = this + context + scope
        cfw.stopMethod((short)3);
    }

    private void generateScriptCtor(ClassFileWriter cfw)
    {
        cfw.startMethod("<init>", "()V", ClassFileWriter.ACC_PUBLIC);

        cfw.addLoadThis();
        cfw.addInvoke(ByteCode.INVOKESPECIAL, SUPER_CLASS_NAME,
                      "<init>", "()V");
        // set id to 0
        cfw.addLoadThis();
        cfw.addPush(0);
        cfw.add(ByteCode.PUTFIELD, cfw.getClassName(), ID_FIELD_NAME, "I");

        cfw.add(ByteCode.RETURN);
        // 1 parameter = this
        cfw.stopMethod((short)1);
    }

    private void generateFunctionConstructor(ClassFileWriter cfw)
    {