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

[Martin Storsjö via llvm-dev]

On Tue, 29 Oct 2019, Reid Kleckner via llvm-dev wrote:

> 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
> 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.

When building a cross toolchain from scratch, with no preexisting 
libraries for the target, I end up building compiler-rt twice: First I 
build only the builtins, which are necessary for a basic working C 
environment. With builtins in place, I build libunwind/libcxxabi/libcxx, 
to get a working C++ environment. After that, I build compiler-rt again, 
building all of it, as the sanitizers now can be built as the C++ 
environment is complete.

(I haven't dug in very deep to see how much of a C++ standard library 
actually is required by the sanitizers, or if it's just a case where I 
could tell CMake to ignore the check for a "working" C++ compiler.)

// Martin