问题描述
最近在看sqlite3的源代码.在合并版本中，只有四个文件.在官方网站上，他们说:
I'm recently reading the source code of sqlite3. In the amalgamation version, there are only four files. On the official website, they say that:
合并也让它运行得更快"
当我们使用合并来编译 SQLite 而不是单独的源文件时，我们测量了 5% 到 10% 的性能改进."
"We have measured performance improvements of between 5 and 10% when we use the amalgamation to compile SQLite rather than individual source files."
我不明白他们是怎么做到的，为什么.有没有人有任何想法?我们是否有任何工具可用于执行此操作?
I don't understand how they make it and why. Does anyone have any ideas? Do we have any tools available for doing that?
推荐答案
如果你解析所有 .c 文件，提取所有 #include ，然后构建一个大文件，你会得到类似的结果列出所有包含，然后列出那些 .c 文件的所有其他内容.
You can have similar result if you parse all .c file, extract all #includes, then build a huge file that first lists all includes, then lists all the other content of those .c files.
通过这种方式，您可以将所有代码放在一个翻译单元中，这样编译器就可以一次查看所有代码并执行更好的优化.这与大多数 C 编译器相关，但最新的编译器具有所谓的 链接时代码生成功能 允许编译器一次查看多个翻译单元的代码(在链接时)，即使没有合并技巧也能生成更好的代码.
This way you have all code in a single translation unit which allows the compiler to see all code at once and perform better optimizations. This is relevant for most C compilers yet newest compilers feature so-called link-time code generation that allows the compiler to see code of multiple translation units at once (at link time) and generate better code even without the amalgamation trick.
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