CompilerFrontends

Compiler frontends are the parts of a compiler that process source code from a programming language and translate it into an intermediate form for further processing by the rest of the toolchain. They perform lexical analysis, syntax analysis, and semantic analysis, and handle preprocessing, module or header resolution, and other language-specific transformations. The frontend is responsible for turning raw text into a structured representation that the rest of the compiler can work with.

Key functions of a frontend include tokenizing input, parsing it into a structured form such as an abstract syntax tree, and performing semantic checks. This involves name resolution and symbol table construction, scope and type checking, and the desugaring or normalization of language features into a core set understood by the backend. Frontends also report syntax and semantic errors and warnings to the user, often with precise source locations.

Frontends are typically language-specific, designed to understand the grammar, syntax, and semantic rules of a particular language. They usually produce an intermediate representation or annotated AST that is suitable for a language-agnostic middle-end or backend, such as an intermediate language or control-flow graph. This separation allows multiple frontends to target the same backend, enabling code generation for different languages from a common analysis and optimization pipeline.

In contemporary compiler design, the frontend, middle-end, and backend may be modular. Examples include Clang as a frontend for C-family languages targeting the LLVM backend, and the architecture of compilers like GCC, which employs separate language-specific frontends. The use of a standard intermediate form, such as LLVM IR, facilitates reuse of optimization and code-generation components across languages.