clang简介

摘抄自官方手册

clang is a C, C++, and Objective-C compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking. Depending on which high-level mode setting is passed, Clang will stop before doing a full link. While Clang is highly integrated, it is important to understand the stages of compilation, to understand how to invoke it. These stages are:

Driver（驱动）

The clang executable is actually a small driver which controls the overall execution of other tools such as the compiler, assembler and linker. Typically you do not need to interact with the driver, but you transparently use it to run the other tools.

Preprocessing（预处理）

This stage handles tokenization of the input source file, macro expansion, #include expansion and handling of other preprocessor directives. The output of this stage is typically called a “.i” (for C), “.ii” (for C++), “.mi” (for Objective-C), or “.mii” (for Objective-C++) file.

Parsing and Semantic Analysis（解析与语义分析）

This stage parses the input file, translating preprocessor tokens into a parse tree. Once in the form of a parse tree, it applies semantic analysis to compute types for expressions as well and determine whether the code is well formed. This stage is responsible for generating most of the compiler warnings as well as parse errors. The output of this stage is an “Abstract Syntax Tree” (AST).

Code Generation and Optimization（代码生成与优化）

This stage translates an AST into low-level intermediate code (known as “LLVM IR”) and ultimately to machine code. This phase is responsible for optimizing the generated code and handling target-specific code generation. The output of this stage is typically called a “.s” file or “assembly” file.

Clang also supports the use of an integrated assembler, in which the code generator produces object files directly. This avoids the overhead of generating the “.s” file and of calling the target assembler.

Assembler（汇编）

This stage runs the target assembler to translate the output of the compiler into a target object file. The output of this stage is typically called a “.o” file or “object” file.

Linker（链接）

This stage runs the target linker to merge multiple object files into an executable or dynamic library. The output of this stage is typically called an “a.out”, “.dylib” or “.so” file.

在了解了ANTLR4及其他的语法分析工具后，还是对C/C++的编译预处理与语法解析存在一些误解，这个需要通过语言的规约说明来理解这两个独立的过程。
简单的说，预处理应该是纯token级文本匹配操作的，不涉及过多复杂的分析，不过是不是还需要再深入一些，待后续填补。