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home / developersection / forums / what is a compiler? what are the different phases of a compiler?
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Utpal Vishwas
Utpal Vishwas

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I am Utpal Vishwas from Uttar Pradesh. Have completed my B. Tech. course from MNNIT campus Prayagraj in 2022. I have good knowledge of computer networking.

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2 Answers

Aryan Kumar
Aryan Kumar 17 Apr 2023
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A compiler is software that translates the code written in one programming language to another. Ex, g++ from GNU family of compilers, PowerBASIC, etc. There are 6 phases in the compiler, namely, lexical analysis, syntax analysis, semantics analysis, intermediate code generation, code optimization, and code generation.

  1. Lexical Analysis: The first phase of a compiler is the lexical analysis, also called scanning. In this phase, the source code is divided into a sequence of tokens, which are the basic building blocks of the language. The tokens are identified by analyzing the characters in the source code and grouping them into meaningful units.
  2. Syntax Analysis: The second phase of a compiler is the syntax analysis, also called parsing. In this phase, the tokens produced by the lexical analysis are organized into a parse tree that represents the structure of the program. The parse tree is generated according to the rules of the language's grammar.
  3. Semantic Analysis: The third phase of a compiler is the semantic analysis. In this phase, the parse tree is checked for semantic correctness, which means that the compiler checks whether the program follows the rules of the language and whether it is well-formed.
  4. Intermediate Code Generation: The fourth phase of a compiler is the intermediate code generation. In this phase, the compiler generates an intermediate code that is a low-level representation of the program. The intermediate code is independent of the target machine and can be optimized before it is translated into machine code.
  5. Code Optimization: The fifth phase of a compiler is the code optimization. In this phase, the intermediate code is analyzed and optimized to improve its efficiency and reduce its size.
  6. Code Generation: The final phase of a compiler is the code generation. In this phase, the compiler translates the optimized intermediate code into machine code that can be executed by the target machine. The machine code is specific to the target machine's architecture and operating system.
    Each phase of the compiler performs a specific task to transform the source code into machine code. The output of one phase is the input of the next phase, and the compiler performs these phases in a sequence to produce the final machine code.
Krishnapriya Rajeev
Krishnapriya Rajeev 07 Apr 2023
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A compiler is a computer program that translates source code in one language into an equivalent program in another language. It also identifies errors in the source code during the translation process. 

The conversion process is completed after the source code goes through a sequence of stages including:

  • Lexical Analysis: The first stage is called lexical analysis or scanning, which involves grouping characters in the source code into meaningful sequences known as lexemes. The lexical analyzer then generates tokens of the form <token-name, attribute-value> for each lexeme and passes them on to the next stage, syntax analysis.
  • Syntax Analysis: The second stage is syntax analysis or parsing, which uses the first components of the tokens produced by the lexical analyzer to create a tree-like representation that shows the grammatical structure of the token stream.
  • Semantic Analysis: The semantic analyzer uses the syntax tree and the information in the symbol table to check the source code for consistency with the language definition. Type checking and type conversion are crucial parts of semantic analysis.
  • Intermediate Code Generation: In translating the source code into the target code, the compiler may create one or more intermediate representations, which can take different forms. The intermediate code should be straightforward to produce and translate into the target machine.
  • Code Optimization: The machine-independent code-optimization stage aims to improve the intermediate code to generate better target code. Optimization can be performed for faster execution, shorter code, or target code that consumes less power.
  • Code Generation: The code generator takes the intermediate representation of the source code as input and maps it into the target language. The intermediate instructions are converted into sequences of machine instructions that perform the same function.
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