NCC

2016春季学期系统方向综合实验组成部分

目标

将类 C 的高级语言编译生成 x86 二进制可执行文件，由 NEMU 加载运行。

TODO

• 增加预处理机制
• 增加对全局变量的支持
• 增加对函数声明的支持

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Naive C-like Compiler

The code is derived from Wonicon's compiler lab code in school. This NCC generates x86 assembly codes in AT&T format instead of MIP32 ones.

Supported Syntax

Some significant limitations are shown below:

1. No declaration, all functions should be defined before called;
2. No global variables (parsed but cannot generate code);
3. No preprocessor;
4. Basic type only consists of int (float is parsed but cannot generate code);
5. All local variables should be defined at the beginning of a function;
6. Struct is passed by reference, and returning a struct is dangerous.

The top level of a program should look like this:

// one-line comment

/**
 * multi-line comment
 * can be /* nested */
 * ignore everything after //
 * like // */
 * like // /*
 * like // *//*
 * like // /*_*/
 */ // This is the end of this multi-line commet!

// int read()
// write(int x)
// are provided functions to support input and output

int echo(int e)
{
    write(e);
    return read();
}

struct A {
    int a;
    int b;
};

int main()
{
    /* Local definitions, like follows */

    int foo;
    int bar = 3;
    int vec[2];
    char hello[5];
    struct A a;

    /* character array */
    hello[0] = 'h';
    hello[1] = 'e';
    hello[2] = 'l';
    hello[3] = 'k' + 1;    //char and calculate with int
    hello[4] = 'o';

    /* Statements, like follows */

    if (/* Expression */) {
        /* Statements */
    }
    else if (/* Expression */) {
        /* Statements */
    }
    else {
        /* Statements */
    }

    while (/* Expression */) {
        /* Statements */
    }

    // the three parts of for-loop cannot be omitted currently
    for (foo = 0; foo < 5; foo = foo + 1) {
        writec(hello[foo]);
    }

    /* Expressions */

    foo = bar;  // Assignment
    foo + 1;    // Binary operation: +, -, *, /
    foo < bar;  // Comparing operation: <, <=, >, >=, ==, !=
    !foo;       // Unary operation: -, !
    a.a         // field access
    (foo);
    foo = echo(vec[0]);  // Function call, array access

    return 0;
}