編譯器：高階語言轉中間碼 - j0c
在前面的文章中，我們首先介紹了整體架構，接著設計出了 CPU0 的指令集，然後寫出了 AS0 組譯器與 VM0 虛擬機：
但是、直到目前為止，我們都還沒有為開放電腦計畫打造出「高階語言」，因此本文將設計出一個 名為 J0 的高階語言 (代表JavaScript 的精簡版)，並採用 JavaScript 去實作，然後在 node.js 平台中執行。
有了 J0 語言與 J0C 編譯器之後，我們就可以創建出以下的工具鏈：
J0 語言 ( j0c 編譯器) => IR0 中間碼 (ir2as 轉換器) => CPU0 組合語言 (AS0 組譯器) => CPU0 機器碼 (VM0 虛擬機執行或 CPU0 FPGA 執行)
JavaScript 簡化版 – J0 語言
以下是一個 J0 語言的程式範例，支援了 function, while, if, for 等語句，並且支援了「陣列與字典」等資料結構。
檔案：test.j0
s = sum(10);
function sum(n) {
s = 0;
i=1;
while (i<=10) {
s = s + i;
i++;
}
return s;
}
m = max(3,5);
function max(a, b) {
if (a > b)
return a;
else
return b;
}
function total(a) {
s = 0;
for (i in a) {
s = s + a[i];
}
return s;
}
a = [ 1, 3, 7, 2, 6];
t = total(a);
word = { e:"dog", c:"狗" };
原始碼
接著我們用 node.js + javascript 實作出 j0c 編譯器，該編譯器可以將 J0 語言的程式，編譯成一種平坦化的中間碼格式，我們稱這種格式為 IR0，也就是 Intermediate Representation 0 的意思，以下是 j0c 編譯器的完整程式碼。
檔案：j0c.js
// j0c 編譯器，用法範例： node j0c test.j0
var fs = require("fs");
var util = require("util");
var log = console.log; // 將 console.log 名稱縮短一點
var format = util.format; // 字串格式化
var tokens = [];
var tokenIdx = 0;
var end = "$END";
var funcName = "main";
var funcStack = [ funcName ];
var irText = "";
var symTable = {};
symTable[funcName] = { type:"function", name:"main", pcodes:[] };
var scan=function(text) {
var re = new RegExp(/(\/\*[\s\S]*?\*\/)|(\/\/[^\r\n])|(".*?")|(\d+(\.\d*)?)|([a-zA-Z]\w*)|([>=<!\+\-\*\/&%|]+)|(\s+)|(.)/gm);
var types = [ "", "COMMENT", "COMMENT", "STRING", "INTEGER", "FLOAT", "ID", "OP2", "SPACE", "CH" ];
tokens = [];
tokenIdx = 0;
var lines = 1, m;
while((m = re.exec(text)) !== null) {
var token = m[0], type;
for (i=1; i<=9; i++) {
if (m[i] !== undefined)
type = types[i];
}
if (!token.match(/^[\s\r\n]/) && type!="COMMENT") {
tokens.push({ "token":token, "type":type, "lines":lines });
}
lines += token.split(/\n/).length-1;
}
tokens.push({ "token": end, "type":end, "lines":lines });
return tokens;
}
var error=function(expect) {
var token = tokens[tokenIdx];
log("Error: line=%d token (%s) do not match expect (%s)!", token.lines, token.token, expect);
log(new Error().stack);
process.exit(1);
}
var skip=function(o) { if (isNext(o)) next(o); }
var next=function(o) {
if (o==null || isNext(o)) {
return tokens[tokenIdx++].token;
}
error(o);
}
var isNext=function(o) {
if (tokenIdx >= tokens.length)
return false;
var token = tokens[tokenIdx].token;
if (o instanceof RegExp) {
return token.match(o);
} else
return (token == o);
}
var nextType=function(o) {
if (o==null || isNextType(o)) {
return tokens[tokenIdx++].token;
}
error(o);
}
var isNextType=function(pattern) {
var type = tokens[tokenIdx].type;
return (("|"+pattern+"|").indexOf("|"+type+"|")>=0);
}
var pcode=function(label, op, p, p1, p2) {
symTable[funcName].pcodes.push({"label":label, "op":op, "p":p, "p1":p1, "p2":p2});
var irCode = format("%s\t%s\t%s\t%s\t%s", label, op, p, p1, p2);
log(irCode);
irText += irCode+"\n";
}
var tempIdx = 1;
var nextTemp=function() {
var name="T"+tempIdx++;
symTable[name] = { type:"var", name:name };
return name;
}
var labelIdx = 1;
var nextLabel=function() { return "L"+labelIdx++; }
var elseIdx = 1;
var nextElse=function() { return "else"+elseIdx++; }
var compile=function(text) {
scan(text);
PROG();
}
// PROG = STMTS
var PROG=function() {
STMTS();
}
// STMTS = STMT*
var STMTS=function() {
while (!isNext("}") && !isNext(end))
STMT();
}
// BLOCK = { STMTS }
var BLOCK=function() {
next("{");
STMTS();
next("}");
}
// STMT = FOR | WHILE | IF | FUNCTION | return EXP ; | ASSIGN ; | BLOCK
var STMT=function() {
if (isNext("for")) {
FOR();
} else if (isNext("while")) {
WHILE();
} else if (isNext("if")) {
IF();
} else if (isNext("function")) {
FUNCTION();
} else if (isNext("return")) {
next("return");
var e = EXP();
pcode("", "return", e, "", "");
next(";");
} else if (isNext("{")) {
BLOCK();
} else {
ASSIGN();
next(";");
}
}
// FOR = for (ID in EXP) BLOCK
var FOR=function() {
var startLabel = nextLabel(), exitLabel = nextLabel();
next("for");
next("(");
var id = nextType("ID");
pcode("", "=", id, "0", "");
next("in");
var e=EXP();
next(")");
var t = nextTemp();
pcode(startLabel, "<", t, id, e+".length");
pcode("", "if0", t, exitLabel, "");
BLOCK();
pcode("", "goto", startLabel, "", "");
pcode(exitLabel, "", "", "", "");
}
// WHILE = while (EXP) BLOCK
var WHILE=function() {
var startLabel = nextLabel(), exitLabel=nextLabel();
pcode(startLabel, "", "", "", "");
next("while");
next("(");
var e = EXP();
next(")");
pcode("", "if0", e, exitLabel, "");
BLOCK();
pcode("", "goto", startLabel, "", "");
pcode(exitLabel, "", "", "", "");
}
// IF = if (EXP) STMT (else STMT)?
var IF=function() {
next("if");
next("(");
var e = EXP();
next(")");
var elseLabel = nextLabel();
pcode("", "if0", e, elseLabel, "");
STMT();
if (isNext("else")) {
next("else");
pcode(elseLabel, "", "", "", "");
STMT();
}
}
// ASSIGN = ID[++|--]?(=EXP?)?
var ASSIGN=function() {
var id, op, hasNext = false;
if (isNextType("ID")) {
id = nextType("ID");
symTable[id] = { type:"var", name:id };
if (isNext("++") || isNext("--")) {
var op = next(null);
pcode("", op, id, "", "");
}
hasNext = true;
}
if (isNext("=")) {
next("=");
var e = EXP();
if (id != undefined)
pcode("", "=", id, e, "");
hasNext = true;
}
if (!hasNext)
return EXP();
}
// EXP=TERM (OP2 TERM)?
var EXP=function() {
t1 = TERM();
if (isNextType("OP2")) {
var op2 = next(null);
t2 = TERM();
var t = nextTemp();
pcode("", op2, t, t1, t2);
t1 = t;
}
return t1;
}
// TERM=STRING | INTEGER | FLOAT | ARRAY | TABLE | ID (TERMS)? | ID [TERMS]?| ( EXP )
var TERM=function() {
if (isNextType("STRING|INTEGER|FLOAT")) {
return next(null);
} else if (isNext("[")) {
return ARRAY();
} else if (isNext("{")) {
return TABLE();
} else if (isNextType("ID")) { // function call
var id = next(null);
if (isNext("(")) {
next("(");
while (!isNext(")")) {
// TERM();
var arg = next(null);
pcode("", "arg", arg, "", "");
skip(",");
}
next(")");
var ret = nextTemp();
pcode("", "call", ret, id, "");
return ret;
}
var array = id;
if (isNext("[")) {
next("[");
while (!isNext("]")) {
var idx = TERM();
var t = nextTemp();
pcode("", "[]", t, array, idx);
skip(",");
array = t;
}
next("]");
return array;
}
return id;
} else if (isNext("(")) {
next("(");
var e = EXP();
next(")");
return e;
} else error();
}
// FUNCTION = function ID(ARGS) BLOCK
var FUNCTION = function() {
next("function");
funcName = nextType("ID");
funcStack.push(funcName);
symTable[funcName] = { type:"function", name:funcName, pcodes: [] };
pcode(funcName, "function", "", "", "");
next("(");
while (!isNext(")")) {
var arg=nextType("ID");
pcode("", "param", arg, "", "");
skip(",");
}
next(")");
BLOCK();
pcode("", "endf", "", "", "");
funcStack.pop();
funcName = funcStack[funcStack.length-1];
}
// ARRAY = [ TERMS ];
var ARRAY = function() {
next("[");
var array = nextTemp();
pcode(array, "array", "", "", "");
while (!isNext("]")) {
var t = TERM();
pcode("", "push", array, t, "");
skip(",");
}
next("]");
return array;
}
// TABLE = { (TERM:TERM)* }
var TABLE = function() {
next("{");
var table = nextTemp();
pcode(table, "table", "", "", "");
while (!isNext("}")) {
var key = TERM();
next(":");
var value = TERM();
skip(",");
pcode("", "map", table, key, value);
}
next("}");
return table;
}
var source = fs.readFileSync(process.argv[2], "utf8");
compile(source);
執行結果
然後、我們可以用 node.js 來執行上述程式，並且編譯指定的 J0 程式檔，例如以下指令就用 j0c 編譯器去編譯了 test.j0 這個輸入檔，接著畫面上所輸出的就是 IR0 的中間碼。
D:\Dropbox\Public\web\oc\code\js>node j0c test.j0
arg 10
call T1 sum
= s T1
sum function
param n
= s 0
= i 1
L1
<= T2 i 10
if0 T2 L2
+ T3 s i
= s T3
++ i
goto L1
L2
return s
endf
arg 3
arg 5
call T4 max
= m T4
max function
param a
param b
> T5 a b
if0 T5 L3
return a
L3
return b
endf
total function
param a
= s 0
= i 0
L4 < T6 i a.length
if0 T6 L5
[] T7 a i
+ T8 s T7
= s T8
goto L4
L5
return s
endf
T9 array
push T9 1
push T9 3
push T9 7
push T9 2
push T9 6
= a T9
arg a
call T10 total
= t T10
T11 table
map T11 e "dog"
map T11 c "狗"
= word T11
結語
在開放電腦計劃中，我們希望透過 J0 語言，以及 j0c 編譯器，用簡易的程式揭露「高階語言與編譯器」的設計原理。
在下期中，我們將撰寫程式去將上述 IR0 中間碼轉換為 CPU0 的組合語言，這樣就可以接上先前所作的組譯器 AS0 與虛擬機 VM0，以形成一套簡易但完整的工具鏈。
透過這樣的工具鏈，我們希望能讓程式人輕易的學會「電腦軟硬體的設計原理」。