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Pacific++ 2017: Chandler Carruth "LLVM: A Modern, Open C++ Toolchain"
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All the comments and stories posted to Hacker News that reference this video.For those who haven't explored LLVM, it's an incredibly powerful technology and rather approachable for getting started with.A few of my favorite LLVM discoveries:
- If you want to build Clang (LLVM C/C++ Compiler), it's really simple to pull down and build with little external development tooling (only a compiler and CMake). Shown here [0].
- You can pull LLVM/Clang master and use that for a "bleeding-edge" toolchain with a high degree of stability. [0].
- Clang is used to compile Chromium and Firefox on all platforms. Both have seen great performance gains from Clang's link time optimization. [1] [2]
- Klee is built on LLVM infrastructure and is used for automatic generation of test cases. [3] See some of their papers for how powerful their results are.
- Clang can now produce ABI compatible binaries with MSVC and has support for the Visual Studio debugger. [4]
- Lots of interesting research projects leveraging LLVM [5]
[0] https://www.youtube.com/watch?v=uZI_Qla4pNA
[1] http://blog.llvm.org/2018/03/clang-is-now-used-to-build-chro...
[2] https://glandium.org/blog/?p=3888
[4] http://blog.llvm.org/2017/08/llvm-on-windows-now-supports-pd...
[5] https://scholar.google.com/scholar?as_ylo=2017&q=LLVM&hl=en&...
⬐ jclayMy list is mostly C++ focused, but the LLVM tooling for clang-tidy/clang-query is also worth a mention. There are a big set of refactors that you can apply across your codebase if you wanted to migrate to new C++ features for example. You can also write your own if you wanted to refactor to use the API of an updated dependency for example. It's a lower-level version of Javascript's "codemods" for C/C++.There's some work being done to build some tooling around interactively creating AST matchers and applying refactors across an entire codebase. [0]
[0] https://steveire.wordpress.com/2018/11/11/future-development...
⬐ eslaughtKlee is also a great example of the cost of LLVM's never-backwards-compatible approach: according to their home page, the stable release of Klee runs on 3.4 and 3.8 is "experimental". (The LLVM releases since then have included: 3.9, 4.0, 5.0, 6.0, and 7.0.)Don't get me wrong, LLVM is great, but I really wish that as the project matured they had made more of an effort to provide some level of compatibility. As it is, it's a massive pain for open source projects to follow along.
⬐ jcranmerIf you compile a bitcode file from anywhere around LLVM 3.3 or later, you can generally read it in the most up-to-date version of LLVM (you may have to first strip debugging metadata though).The LLVM-C API also maintains compatibility, but that comes at the steep cost of preventing you from using most of the power: LLVM-C is basically limited to reading/writing LLVM code, running passes largely at the -O1/-O2/-O3 level of granularity, and executing the JIT. Writing a pass with that API is very difficult, and pretty much impossible if you want to use any analyses.
⬐ jclayThat's a good point. Most of the large LLVM projects I've used (such as Root's Cling) seem to lag behind LLVM's versions rather drastically.⬐ drmeisterCounterpoint - I implemented a Common Lisp compiler that uses llvm as the back end (https://github.com/clasp-developers/clasp). I've kept up with the versions from 3.6 to 6.0 and I'm about to upgrade to 7.0.I'm not sure why other projects find this difficult but I have noticed that if I get too far behind it does get a bit more difficult.
I exposed the C++ API to Common Lisp and write all of the compiler in Common Lisp. The Clang C++ compiler tells me what is broken when I upgrade to a new version of llvm and then I fix it. I talk about it here https://www.youtube.com/watch?reload=9&v=mbdXeRBbgDM&feature... at about 13:30