[llvm-dev] RFC: LLVM Build System Future Direction

[Chris Bieneman via llvm-dev]

Reid, I think your breakdown makes a lot of sense. Generally I think instrumentation tools (profile & xray) could be grouped with the sanitizers. More broadly those are all "developer tool" libraries.

Pulling crt, builtins, and blocks into a separate top-level project is, IMO, the right goal.

-Chris

> On Oct 29, 2019, at 1:37 PM, Reid Kleckner <rnk at google.com> wrote:
> 
> Thanks for organizing the discussion and summarizing it. I haven't been involved, but it all seems like it's going in the right direction.
> 
> On Tue, Oct 29, 2019 at 10:10 AM Chris Bieneman via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> There are also problems related to cross-runtime dependencies which have come up recently. Some of these problems can be addressed more cleanly with modern CMake generator expressions, and other issues may require a larger restructuring of code. For years there have been discussions thrown around about breaking the builtins libraries out of compiler-rt. Maybe now is the time to consider doing that.
> 
> Why split out builtins from compiler-rt? They were the original compiler runtime library. Should we go the other direction instead? For a long time, I've wondered if we should have split the sanitizer runtimes out of compiler-rt. GCC maintains a forked copy of some of the sanitizer runtimes in a libsanitizer subdirectory next to libgcc:
> https://github.com/gcc-mirror/gcc/tree/master/libsanitizer <https://github.com/gcc-mirror/gcc/tree/master/libsanitizer>
> I think we put the sanitizers in compiler-rt mainly because it is a "compiler runtime", a runtime to which the compiler generates calls, but the same applies to libcxxabi, OpenMP, I assume libcl, and other things. The sanitizers are the biggest piece of compiler-rt by far, so maybe they deserve their own top level directory.
> 
> Here are the contents of compiler-rt/lib, with my categorizations:
> 
> Platform building blocks:
> - crt
> - builtins
> - BlocksRuntime
> 
> Instrumentation tools:
> - profile
> - xray
> 
> Sanitizer or security things:
> - cfi
> - asan
> - tsan
> - ubsan
> - ubsan_minimal
> - dfsan
> - fuzzer
> - gwp_asan
> - hwasan
> - interception
> - lsan
> - msan
> - safestack
> - sanitizer_common
> - stats
> - scudo
> 
> ---
> 
> All of the above said, I don't see any particularly strong reasons to change anything at the moment, but maybe you have a good reason to separate builtins and instrumentation that I haven't thought of.

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