Semantic analysis in a compiler is a critical stage that evaluates the source code for semantic errors and ensures semantic consistency.

This phase follows lexical and syntax analysis in the compilation process. Its primary purpose is to identify semantic errors, which are issues related to logic or meaning in the code. For example, semantic analysis checks whether variables are declared before they are used, whether function calls correspond accurately to their definitions, and whether operators are appropriate for the given operands.

In addition to identifying errors, semantic analysis ensures that the code adheres to the semantic rules of the programming language and maintains logical coherence. This includes verifying that the types of values on either side of an assignment operation are compatible, that the number and types of arguments in a function call align with its definition, and that return statements conform to the expected return type of the function.

The semantic analysis phase relies on a symbol table, a data structure created during lexical analysis that contains information about identifiers such as variables and functions utilized within the program. The semantic analyzer leverages this information to validate that identifiers are used correctly and consistently throughout the code.

When the semantic analyzer detects any errors, it generates informative error messages to assist the programmer in diagnosing issues. These messages are typically more insightful than those produced during lexical and syntax analysis, as they pertain to the logic and meaning of the code rather than merely its structure and format.

In summary, the semantic analysis phase of a compiler is essential for ensuring that the source code is logically correct and semantically consistent. This process helps prevent numerous potential runtime errors, ultimately enhancing the reliability and robustness of the code.