自定义编译器_编译器的定义和目的

灰太狼 2022-12-06 15:40 159阅读 0赞

自定义编译器

A [compiler][] is a [program][] that translates human-readable [source code][] into computer-executable machine code. To do this successfully, the human-readable code must comply with the [syntax][source code] rules of whichever programming language it is written in. The compiler is only a program and cannot fix your code for you. If you make a mistake, you have to correct the syntax or it won't compile.

甲[编译器][compiler]是一个[程序][program]即转换人类可读的[源代码][source code]到计算机可执行的机器代码。 为了成功地做到这一点，人类可读的代码必须符合所使用的任何一种编程语言的[语法][source code]规则。编译器只是一个程序，无法为您修复代码。 如果输入有误，则必须更正语法，否则将无法编译。

## 编译代码时会发生什么？ **(** What Happens When You Compile Code? **)** ##

A compiler's complexity depends on the syntax of the language and how much abstraction [that programming language][] provides. A C compiler is much simpler than a compiler for C++ or C\#.

编译器的复杂性取决于该语言的语法以及[该编程语言][that programming language]提供多少抽象。 AC编译器比C ++或C＃编译器简单得多。

## 词法分析 **(** Lexical Analysis **)** ##

When compiling, the compiler first reads a stream of characters from a source code file and generates a stream of lexical tokens. For example, the C++ code:

编译时，编译器首先从源代码文件中读取字符流，并生成词汇标记流。 例如，C ++代码：

int C= (A*B)+10;

might be analyzed as these tokens:

可能会被分析为以下标记：

*  type "int"
    
    输入“ int”
 *  variable "C"
    
    变量“ C”
 *  equals
    
    等于
 *  leftbracket
    
    左括号
 *  variable "A"
    
    变量“ A”
 *  times
    
    次
 *  variable "B"
    
    变量“ B”
 *  rightbracket
    
    右括号
 *  plus
    
    加
 *  literal "10"
    
    文字“ 10”

## 句法分析 **(** Syntactical Analysis **)** ##

The lexical output goes to the syntactical analyzer part of the compiler, which uses the rules of grammar to decide whether the input is valid or not. Unless [variables][] A and B were previously declared and were in scope, the compiler might say:

词汇输出到达编译器的语法分析器部分，该部分使用语法规则来确定输入是否有效。 除非[变量][variables] A和B先前已声明并且在范围内，否则编译器可能会说：

*  'A' : undeclared identifier.
    
    'A'：未声明的标识符。

If they were declared but not initialized. the compiler issues a warning:

如果已声明但未初始化。 编译器发出警告：

*  local variable 'A' used without being initialized.
    
    使用未初始化的局部变量“ A”。

You should never ignore compiler warnings. They can break your code in weird and unexpected ways. Always fix compiler warnings.

您永远不应忽略编译器警告。 他们可能以怪异和意外的方式破坏您的代码。 始终修复编译器警告。

## 一两遍？ **(** One Pass or Two? **)** ##

Some programming languages are written so a compiler can read the source code only once and generate the machine code. [Pascal][] is one such language. Many [compilers][compiler] require at least two passes. Sometimes, it is because of forward declarations of [functions][Pascal] or classes.

编写了一些编程语言，因此编译器只能读取一次源代码并生成机器代码。 [Pascal][]是一种这样的语言。 许多[编译器][compiler]至少需要两次通过。 有时是因为[函数][Pascal]或类的前向声明。

In C++, a class can be declared but not defined until later. The compiler is unable to work out how much memory the class needs until it compiles the body of the class. It must reread the source code before generating the correct machine code.

在C ++中，可以声明一个类，但要等到以后再定义。 在编译类主体之前，编译器无法计算出该类需要多少内存。 在生成正确的机器代码之前，它必须重新读取源代码。

## 生成机器码 **(** Generating Machine Code **)** ##

Assuming that the compiler successfully completes the lexical and syntactical analyses, the final stage is generating machine code. This is a complicated process, especially with modern CPUs.

假设编译器成功完成了词法和句法分析，最后一步就是生成机器代码。 这是一个复杂的过程，尤其是对于现代CPU。

The speed of the compiled [executable][source code] code should be as fast as possible and can vary enormously according to the quality of the generated code and how much optimization was requested.

编译后的[可执行][source code]代码的速度应尽可能快，并且会根据生成代码的质量和要求的优化程度而有很大的不同。

Most compilers let you specify the amount of optimization—typically known for quick debugging compiles and full optimization for the released code.

大多数编译器允许您指定优化的数量-通常以快速调试编译和对已发布代码的完全优化而著称。

## 代码生成具有挑战性 **(** Code Generation Is Challenging **)** ##

The compiler writer faces challenges when writing a code generator. Many processors speed up processing by using

编译器作者在编写代码生成器时面临挑战。 许多处理器通过使用来加快处理速度

*  Instruction pipelining
    
    指令流水线
 *  Internal [caches][].
    
    内部[缓存][caches] 。

If all the instructions within a code [loop][] can be held in the [CPU][compiler] cache, then that loop runs much faster than when the CPU has to fetch instructions from the main RAM. The CPU cache is a block of memory built into the CPU chip that is accessed much faster than data in the main RAM.

如果代码[循环中的][loop]所有指令都可以保留在[CPU][compiler]缓存中，则该循环的运行速度比CPU必须从主RAM中提取指令的速度快得多。 CPU高速缓存是内置在CPU芯片中的一块内存，其访问速度比主RAM中的数据快得多。

## 缓存和队列 **(** Caches and Queues **)** ##

Most CPUs have a pre-fetch queue where the CPU reads instructions into the cache before executing them. If a conditional branch happens, the CPU has to reload the queue. The code should be generated to minimize this.

大多数CPU都有一个预取队列，在该队列中，CPU在执行指令之前将其读入缓存。 如果发生条件分支，则CPU必须重新加载队列。 应该生成代码以最大程度地减少这种情况。

Many CPUs have separate parts for:

许多CPU具有以下单独的部分：

*  Integer arithmetic (whole numbers)
    
    整数算术(整数)
 *  Floating point arithmetic (fractional numbers)
    
    浮点算术(分数)

These operations can often run in parallel to increase speed.

这些操作通常可以并行运行以提高速度。

Compilers typically generate machine code into object files that are then [linked][source code] together by a linker program.

编译器通常将机器代码生成为目标文件，然后通过链接器程序将它们[链接][source code]在一起。

> 翻译自: [https://www.thoughtco.com/what-is-a-compiler-958322][https_www.thoughtco.com_what-is-a-compiler-958322]

自定义编译器

[compiler]: https://www.thoughtco.com/definition-of-compiler-958198
[program]: https://www.thoughtco.com/what-is-a-programming-language-958332
[source code]: https://www.thoughtco.com/source-code-definition-958200
[that programming language]: https://www.thoughtco.com/comparing-popular-programming-languages-958275
[variables]: https://www.thoughtco.com/definition-of-variable-958320
[Pascal]: https://www.thoughtco.com/definition-of-void-958182
[caches]: https://www.thoughtco.com/definition-of-buffer-p2-958030
[loop]: https://www.thoughtco.com/definition-of-loop-958105
[https_www.thoughtco.com_what-is-a-compiler-958322]: https://www.thoughtco.com/what-is-a-compiler-958322