Xcode 3.2.1 GCC CLANG和LLVM解构

The readme included with the new Xcode 3.2.1 this week says the following:

这周的新Xcode 3.2.1包含了readme:

Static code analysis is fully integrated within the Xcode IDE via the Build and Analyze option under the Build menu or via custom build settings
静态代码分析通过构建菜单下的Build and Analyze选项或自定义构建设置完全集成在Xcode IDE中
GCC 4.2 is the default system compiler for the 10.6 SDK
GCC 4.2是10.6 SDK的默认系统编译器
The optional LLVM compiler is included using two different front ends - the Clang compiler is a leading-edge parser that offers dramatically improved compile times. For maximum compatibility, the GCC LLVM compiler utilizes the LLVM back-end with the GCC 4.2 parser.
可选的LLVM编译器包括使用两个不同的前端——Clang编译器是一个前沿的解析器，提供了显著改进的编译时间。为了最大程度的兼容性，GCC LLVM编译器使用LLVM后端和GCC 4.2解析器。
New optional Clang-LLVM 1.0 compiler uses the much faster Clang front-end parser coupled with the LLVM back-end compiler for fast compiles and fast executable code. Many projects will benefit from this compiler combination, although GCC 4.2 is still the system default. The Clang-LLVM 1.0 compiler will fall back to using LLVM-GCC 4.2 when it encounters C++ code.
新的可选的Clang-LLVM 1.0编译器使用更快的Clang前端解析器和LLVM后端编译器来进行快速编译和快速可执行代码。许多项目将从这个编译器组合中受益，尽管GCC 4.2仍然是系统默认值。当遇到c++代码时，Clang-LLVM 1.0编译器将退回到使用LLVM-GCC 4.2。

Our company has existing projects that are pure C, Objective-C, and Objective-C++ for desktop and iphone. Can someone summarize at a high-level the differences between LLVM, GCC, CLANG, CLANG-LLVM, WordFoo et. al. and explain what they are and when we should be using each and for what? It would be nice to have links to more a detailed explanation, but I'm really just looking for a high-level overview.

我们公司现有的项目都是纯C、Objective-C和objective - c++的桌面和iphone。有人能在高层上总结一下LLVM、GCC、CLANG、CLANG-LLVM、WordFoo等之间的差异吗?如果能有更多详细解释的链接，那就太好了，但我只是在寻找一个高层次的概述。

1 个解决方案

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In a nutshell:

简而言之:

Compilers are basically split into two parts. One being the front-end that contains the parser and semantic analysis for the programming language. The front-end produces some kind of intermediate representation of your code. Then there's the backend which takes the stuff the front-end produced, optimizes it, and eventually generates assembly code.

编译器基本上分为两部分。一个是前端，包含编程语言的解析器和语义分析。前端产生某种类型的中间代码表示。然后是后端，将前端生成的东西进行优化，最终生成汇编代码。

GCC: well known compiler, contains both front-ends for various languages and back-ends for many processor architectures
GCC:众所周知的编译器，包含各种语言的前端和许多处理器体系结构的后端
LLVM: a set of back-ends for various architectures (and other low-level stuff)
LLVM:各种体系结构(以及其他底层内容)的一组后端
clang: a new front-end for C, Objective-C, and C++; uses the LLVM back-ends. You'll get more readable errors and warnings from your compiler and shorter compile times. You might also encounter incompatibilities or bugs; clang is a very young project.
clang: C、Objective-C和c++的新前端;使用LLVM后端。您将从编译器获得更多可读的错误和警告，以及更短的编译时间。您可能还会遇到不兼容或bug;clang是一个非常年轻的项目。
LLVM-GCC: GCC's front-end with LLVM's back-end. LLVM's back-end is faster than GCC's.
LLVM-GCC: GCC前端与LLVM的后端。LLVM的后端速度比GCC快。

clang's (Objective-)C++ support is far from being complete so it calls llvm-gcc when it encounters a C++ source file. It also contains the static analyzer that is now integrated into Xcode. Some people say LLVM's back-end generates better code than GCC's but your mileage may vary. LLVM also supports link-time optimizations (which you can enable in Xcode's project settings). They may produce faster code.

clang (Objective-) c++支持还远没有完成，所以当遇到c++源文件时，它会调用llvm-gcc。它还包含现在集成到Xcode中的静态分析器。有些人说LLVM的后端生成的代码比GCC的要好，但是您的里数可能不同。LLVM还支持链接时间优化(可以在Xcode的项目设置中启用)。它们可以生成更快的代码。

Apple wants to replace GCC with clang in the future because they have a policy against GPLv3 licensed code (GCC 4.2 is the last version that's licensed under GPLv2).

苹果公司希望在未来用clang取代GCC，因为他们有针对GPLv3授权代码的策略(GCC 4.2是在GPLv2下获得许可的最后一个版本)。

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