What's the function of semantic analysis in a compiler?

Semantic analysis in a compiler checks the source code for semantic errors and maintains the semantic consistency of the code.

Semantic analysis is a vital stage in the compilation process. After the lexical and syntax analysis, the compiler moves on to the semantic analysis phase. This phase is responsible for checking the source code for semantic errors, which are errors in logic or meaning. For instance, it checks if the variables are declared before use, if the function calls match the definitions, if the operators are applicable to the given operands, and so on.

The semantic analysis phase also ensures the semantic consistency of the code. This means it verifies that the code makes sense in the context of the programming language's rules and the program's logic. For example, it checks if the types on either side of an assignment operation are compatible, if the number and types of arguments in a function call match the function definition, and if the return statements in a function match the function's return type.

The semantic analysis phase uses the symbol table, which is a data structure created during the lexical analysis phase that contains information about identifiers (like variables and functions) used in the program. The semantic analyser uses this information to check if the identifiers are used correctly and consistently.

If the semantic analyser finds any errors, it generates error messages that help the programmer understand what's wrong with their code. These error messages are usually more meaningful and helpful than the ones generated during the lexical and syntax analysis phases, as they relate to the logic and meaning of the code, rather than just its structure and format.

In summary, the semantic analysis phase of a compiler plays a crucial role in ensuring that the source code is logically correct and semantically consistent, thereby preventing many potential runtime errors and making the code more reliable and robust.