codegen.java

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

        final int SCOPE_ARG = 1;
        final int CONTEXT_ARG = 2;
        final int ID_ARG = 3;

        cfw.startMethod("<init>", FUNCTION_CONSTRUCTOR_SIGNATURE,
                        ClassFileWriter.ACC_PUBLIC);
        cfw.addALoad(0);
        cfw.addInvoke(ByteCode.INVOKESPECIAL, SUPER_CLASS_NAME,
                      "<init>", "()V");

        cfw.addLoadThis();
        cfw.addILoad(ID_ARG);
        cfw.add(ByteCode.PUTFIELD, cfw.getClassName(), ID_FIELD_NAME, "I");

        cfw.addLoadThis();
        cfw.addALoad(CONTEXT_ARG);
        cfw.addALoad(SCOPE_ARG);

        int start = (scriptOrFnNodes[0].getType() == Token.SCRIPT) ? 1 : 0;
        int end = scriptOrFnNodes.length;
        if (start == end) throw badTree();
        boolean generateSwitch = (2 <= end - start);

        int switchStart = 0;
        int switchStackTop = 0;
        if (generateSwitch) {
            cfw.addILoad(ID_ARG);
            // do switch from (start + 1,  end - 1) mapping start to
            // the default case
            switchStart = cfw.addTableSwitch(start + 1, end - 1);
        }

        for (int i = start; i != end; ++i) {
            if (generateSwitch) {
                if (i == start) {
                    cfw.markTableSwitchDefault(switchStart);
                    switchStackTop = cfw.getStackTop();
                } else {
                    cfw.markTableSwitchCase(switchStart, i - 1 - start,
                                            switchStackTop);
                }
            }
            OptFunctionNode ofn = OptFunctionNode.get(scriptOrFnNodes[i]);
            cfw.addInvoke(ByteCode.INVOKEVIRTUAL,
                          mainClassName,
                          getFunctionInitMethodName(ofn),
                          FUNCTION_INIT_SIGNATURE);
            cfw.add(ByteCode.RETURN);
        }

        // 4 = this + scope + context + id
        cfw.stopMethod((short)4);
    }

    private void generateFunctionInit(ClassFileWriter cfw,
                                      OptFunctionNode ofn)
    {
        final int CONTEXT_ARG = 1;
        final int SCOPE_ARG = 2;
        cfw.startMethod(getFunctionInitMethodName(ofn),
                        FUNCTION_INIT_SIGNATURE,
                        (short)(ClassFileWriter.ACC_PRIVATE
                                | ClassFileWriter.ACC_FINAL));

        // Call NativeFunction.initScriptFunction
        cfw.addLoadThis();
        cfw.addALoad(CONTEXT_ARG);
        cfw.addALoad(SCOPE_ARG);
        cfw.addInvoke(ByteCode.INVOKEVIRTUAL,
                      "org/mozilla/javascript/NativeFunction",
                      "initScriptFunction",
                      "(Lorg/mozilla/javascript/Context;"
                      +"Lorg/mozilla/javascript/Scriptable;"
                      +")V");

        // precompile all regexp literals
        int regexpCount = ofn.fnode.getRegexpCount();
        if (regexpCount != 0) {
            cfw.addLoadThis();
            pushRegExpArray(cfw, ofn.fnode, CONTEXT_ARG, SCOPE_ARG);
            cfw.add(ByteCode.PUTFIELD, mainClassName,
                    REGEXP_ARRAY_FIELD_NAME, REGEXP_ARRAY_FIELD_TYPE);
        }

        cfw.add(ByteCode.RETURN);
        // 3 = (scriptThis/functionRef) + scope + context
        cfw.stopMethod((short)3);
    }

    private void generateNativeFunctionOverrides(ClassFileWriter cfw,
                                                 String encodedSource)
    {
        // Override NativeFunction.getLanguageVersion() with
        // public int getLanguageVersion() { return <version-constant>; }

        cfw.startMethod("getLanguageVersion", "()I",
                        ClassFileWriter.ACC_PUBLIC);

        cfw.addPush(compilerEnv.getLanguageVersion());
        cfw.add(ByteCode.IRETURN);

        // 1: this and no argument or locals
        cfw.stopMethod((short)1);

        // The rest of NativeFunction overrides require specific code for each
        // script/function id

        final int Do_getFunctionName      = 0;
        final int Do_getParamCount        = 1;
        final int Do_getParamAndVarCount  = 2;
        final int Do_getParamOrVarName    = 3;
        final int Do_getEncodedSource     = 4;
        final int Do_getParamOrVarConst   = 5;
        final int SWITCH_COUNT            = 6;

        for (int methodIndex = 0; methodIndex != SWITCH_COUNT; ++methodIndex) {
            if (methodIndex == Do_getEncodedSource && encodedSource == null) {
                continue;
            }

            // Generate:
            //   prologue;
            //   switch over function id to implement function-specific action
            //   epilogue

            short methodLocals;
            switch (methodIndex) {
              case Do_getFunctionName:
                methodLocals = 1; // Only this
                cfw.startMethod("getFunctionName", "()Ljava/lang/String;",
                                ClassFileWriter.ACC_PUBLIC);
                break;
              case Do_getParamCount:
                methodLocals = 1; // Only this
                cfw.startMethod("getParamCount", "()I",
                                ClassFileWriter.ACC_PUBLIC);
                break;
              case Do_getParamAndVarCount:
                methodLocals = 1; // Only this
                cfw.startMethod("getParamAndVarCount", "()I",
                                ClassFileWriter.ACC_PUBLIC);
                break;
              case Do_getParamOrVarName:
                methodLocals = 1 + 1; // this + paramOrVarIndex
                cfw.startMethod("getParamOrVarName", "(I)Ljava/lang/String;",
                                ClassFileWriter.ACC_PUBLIC);
                break;
              case Do_getParamOrVarConst:
                methodLocals = 1 + 1 + 1; // this + paramOrVarName
                cfw.startMethod("getParamOrVarConst", "(I)Z",
                                ClassFileWriter.ACC_PUBLIC);
                break;
              case Do_getEncodedSource:
                methodLocals = 1; // Only this
                cfw.startMethod("getEncodedSource", "()Ljava/lang/String;",
                                ClassFileWriter.ACC_PUBLIC);
                cfw.addPush(encodedSource);
                break;
              default:
                throw Kit.codeBug();
            }

            int count = scriptOrFnNodes.length;

            int switchStart = 0;
            int switchStackTop = 0;
            if (count > 1) {
                // Generate switch but only if there is more then one
                // script/function
                cfw.addLoadThis();
                cfw.add(ByteCode.GETFIELD, cfw.getClassName(),
                        ID_FIELD_NAME, "I");

                // do switch from 1 .. count - 1 mapping 0 to the default case
                switchStart = cfw.addTableSwitch(1, count - 1);
            }

            for (int i = 0; i != count; ++i) {
                ScriptOrFnNode n = scriptOrFnNodes[i];
                if (i == 0) {
                    if (count > 1) {
                        cfw.markTableSwitchDefault(switchStart);
                        switchStackTop = cfw.getStackTop();
                    }
                } else {
                    cfw.markTableSwitchCase(switchStart, i - 1,
                                            switchStackTop);
                }

                // Impelemnet method-specific switch code
                switch (methodIndex) {
                  case Do_getFunctionName:
                    // Push function name
                    if (n.getType() == Token.SCRIPT) {
                        cfw.addPush("");
                    } else {
                        String name = ((FunctionNode)n).getFunctionName();
                        cfw.addPush(name);
                    }
                    cfw.add(ByteCode.ARETURN);
                    break;

                  case Do_getParamCount:
                    // Push number of defined parameters
                    cfw.addPush(n.getParamCount());
                    cfw.add(ByteCode.IRETURN);
                    break;

                  case Do_getParamAndVarCount:
                    // Push number of defined parameters and declared variables
                    cfw.addPush(n.getParamAndVarCount());
                    cfw.add(ByteCode.IRETURN);
                    break;

                  case Do_getParamOrVarName:
                    // Push name of parameter using another switch
                    // over paramAndVarCount
                    int paramAndVarCount = n.getParamAndVarCount();
                    if (paramAndVarCount == 0) {
                        // The runtime should never call the method in this
                        // case but to make bytecode verifier happy return null
                        // as throwing execption takes more code
                        cfw.add(ByteCode.ACONST_NULL);
                        cfw.add(ByteCode.ARETURN);
                    } else if (paramAndVarCount == 1) {
                        // As above do not check for valid index but always
                        // return the name of the first param
                        cfw.addPush(n.getParamOrVarName(0));
                        cfw.add(ByteCode.ARETURN);
                    } else {
                        // Do switch over getParamOrVarName
                        cfw.addILoad(1); // param or var index
                        // do switch from 1 .. paramAndVarCount - 1 mapping 0
                        // to the default case
                        int paramSwitchStart = cfw.addTableSwitch(
                                                   1, paramAndVarCount - 1);
                        for (int j = 0; j != paramAndVarCount; ++j) {
                            if (cfw.getStackTop() != 0) Kit.codeBug();
                            String s = n.getParamOrVarName(j);
                            if (j == 0) {
                                cfw.markTableSwitchDefault(paramSwitchStart);
                            } else {
                                cfw.markTableSwitchCase(paramSwitchStart, j - 1,
                                                        0);
                            }
                            cfw.addPush(s);
                            cfw.add(ByteCode.ARETURN);
                        }
                    }
                    break;

                    case Do_getParamOrVarConst:
                        // Push name of parameter using another switch
                        // over paramAndVarCount
                        paramAndVarCount = n.getParamAndVarCount();
                        boolean [] constness = n.getParamAndVarConst();
                        if (paramAndVarCount == 0) {
                            // The runtime should never call the method in this
                            // case but to make bytecode verifier happy return null
                            // as throwing execption takes more code
                            cfw.add(ByteCode.ICONST_0);
                            cfw.add(ByteCode.IRETURN);
                        } else if (paramAndVarCount == 1) {
                            // As above do not check for valid index but always
                            // return the name of the first param
                            cfw.addPush(constness[0]);
                            cfw.add(ByteCode.IRETURN);
                        } else {
                            // Do switch over getParamOrVarName
                            cfw.addILoad(1); // param or var index
                            // do switch from 1 .. paramAndVarCount - 1 mapping 0
                            // to the default case
                            int paramSwitchStart = cfw.addTableSwitch(
                                                       1, paramAndVarCount - 1);
                            for (int j = 0; j != paramAndVarCount; ++j) {
                                if (cfw.getStackTop() != 0) Kit.codeBug();
                                if (j == 0) {
                                    cfw.markTableSwitchDefault(paramSwitchStart);
                                } else {
                                    cfw.markTableSwitchCase(paramSwitchStart, j - 1,
                                                            0);
                                }
                                cfw.addPush(constness[j]);
                                cfw.add(ByteCode.IRETURN);
                            }
                        }
                      break;

                  case Do_getEncodedSource:
                    // Push number encoded source start and end
                    // to prepare for encodedSource.substring(start, end)
                    cfw.addPush(n.getEncodedSourceStart());
                    cfw.addPush(n.getEncodedSourceEnd());
                    cfw.addInvoke(ByteCode.INVOKEVIRTUAL,
                                  "java/lang/String",
                                  "substring",
                                  "(II)Ljava/lang/String;");
                    cfw.add(ByteCode.ARETURN);
                    break;

                  default:
                    throw Kit.codeBug();
                }
            }

            cfw.stopMethod(methodLocals);
        }
    }

    private void emitRegExpInit(ClassFileWriter cfw)
    {
        // precompile all regexp literals

        int totalRegCount = 0;
        for (int i = 0; i != scriptOrFnNodes.length; ++i) {
            totalRegCount += scriptOrFnNodes[i].getRegexpCount();
        }
        if (totalRegCount == 0) {
            return;
        }

        cfw.startMethod(REGEXP_INIT_METHOD_NAME, REGEXP_INIT_METHOD_SIGNATURE,
            (short)(ClassFileWriter.ACC_STATIC | ClassFileWriter.ACC_PRIVATE
                    | ClassFileWriter.ACC_SYNCHRONIZED));
        cfw.addField("_reInitDone", "Z",
                     (short)(ClassFileWriter.ACC_STATIC
                             | ClassFileWriter.ACC_PRIVATE));
        cfw.add(ByteCode.GETSTATIC, mainClassName, "_reInitDone", "Z");
        int doInit = cfw.acquireLabel();
        cfw.add(ByteCode.IFEQ, doInit);
        cfw.add(ByteCode.RETURN);
        cfw.markLabel(doInit);

        for (int i = 0; i != scriptOrFnNodes.length; ++i) {
            ScriptOrFnNode n = scriptOrFnNodes[i];
            int regCount = n.getRegexpCount();
            for (int j = 0; j != regCount; ++j) {
                String reFieldName = getCompiledRegexpName(n, j);
                String reFieldType = "Ljava/lang/Object;";
                String reString = n.getRegexpString(j);
                String reFlags = n.getRegexpFlags(j);
                cfw.addField(reFieldName, reFieldType,