What are the phases of compiler design?

The phases of compiler design are lexical analysis, syntax analysis, semantic analysis, intermediate code generation, code optimisation, and code generation.

The first phase of compiler design is lexical analysis, also known as scanning. In this phase, the compiler breaks down the source program into a sequence of atomic units called tokens. These tokens are the smallest individual units in a program, such as identifiers, keywords, operators, and delimiters. The lexical analyser also removes any white spaces or comments in the source program.

The second phase is syntax analysis or parsing. Here, the compiler checks the tokens produced by the lexical analyser against the grammar of the programming language to ensure they form a correct syntactic structure. This phase produces a parse tree, which is a tree representation of the syntactic structure of the source program. To better understand the algorithms involved in parsing, you may refer to our detailed notes on Understanding and Applying Standard Algorithms.

The third phase is semantic analysis. In this phase, the compiler checks the parse tree for semantic errors and gathers type information for the subsequent code generation phase. This includes checking that identifiers are declared before use, that variables are of the correct type, and that operators are used with compatible operands. The compiler's activities during this phase are similar to some of the fundamental programming constructs outlined in Introduction to Fundamental Programming Constructs.

The fourth phase is intermediate code generation. The compiler translates the source program into an intermediate representation that is easier to translate into the target machine language. This intermediate code is machine-independent, which allows the same intermediate representation to be used for different target machines.

The fifth phase is code optimisation. The compiler attempts to improve the intermediate code so that the resulting machine code runs more efficiently. This can involve removing unnecessary instructions, reducing the size of the code, or improving the speed of the code.

The final phase is code generation. The compiler translates the optimised intermediate code into the machine language of the target machine. This involves allocating memory for variables and generating machine instructions. The output of this phase is the object code, which is a binary file that can be executed by the machine. To further explore how compilers are part of the broader programming environment, check the resources on the Need for Language Translators and Interpreters.

A-Level Computer Science Tutor Summary: In compiler design, there are six main phases: lexical analysis, syntax analysis, semantic analysis, intermediate code generation, code optimisation, and code generation. These steps transform source code into machine language. They involve breaking down the code into tokens, checking its structure, ensuring it makes sense, converting it to an intermediate form, optimising this form for efficiency, and finally translating it into a format the computer can execute.