c++ - 生成 LLVM C++ API 代码作为后端

Question

Online LLVM demo page 可以选择从源代码生成 LLVM C++ API 代码作为后端。但是，该演示页面现在已禁用。我想知道我们如何使用可用的 LLVM 工具自己做到这一点。

我尝试了以下

clang++ -c -emit-llvm input.cpp -o input.ll
llc -march=cpp -o input.ll.cpp input.ll

出现以下错误

llc: error: invalid target 'cpp'.

我使用的是 LLVM/Clang 3.2 版。

Answer 1

在构建 LLVM 时，必须在配置期间启用 LLVM C++ 后端。它在 configure (autotools) 构建中默认启用，但在 Windows 上构建时不会在 CMake 构建中启用。您可以通过在使用 CMake 进行配置时设置适当的标志来启用它。见 this page了解更多信息。

引用:

LLVM_TARGETS_TO_BUILD:STRING Semicolon-separated list of targets to build, or all for building all targets. Case-sensitive. For Visual C++ defaults to X86. On the other cases defaults to all. Example: -DLLVM_TARGETS_TO_BUILD="X86;PowerPC".

更新

自 3.9 版 起，CppBackend 不再是有效目标。由于生成的代码存在一些问题，因此他们已从代码中删除。

Check this commit

Remove bit-rotten CppBackend.

This backend was supposed to generate C++ code which will re-construct
the LLVM IR passed as input. This seems to me to have very marginal
usefulness in the first place.

However, the code has never been updated to use IRBuilder, which makes
its current value negative -- people who look at the output may be
steered to use the *wrong* C++ APIs to construct IR.

Furthermore, it's generated code that doesn't compile since at least
2013.

Differential Revision: http://reviews.llvm.org/D19942

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268631 91177308-0d34-0410-b5e6-96231b3b80d8