[llvm-dev] Compiler support in libc++

[Mehdi AMINI via llvm-dev]

On Wed, Mar 3, 2021 at 5:34 PM Michael Kruse <llvmdev at meinersbur.de> wrote:

> Am Mi., 3. März 2021 um 13:18 Uhr schrieb Mehdi AMINI via llvm-dev
> <llvm-dev at lists.llvm.org>:
> > That's a good point:
> >  - stage1: build just clang with host clang-8/libstdc++
> > - stage1.5: build libc++ with stage1 clang
> > - stage 2: assemble toolchain with clang from stage1 and libc++ from
> stage2
> > - stage3: build test "anything" using stage2 (`ninja check-all` in the
> monorepo for example, but applicable to any other external project)
>
> Stage 1.5 is exactly what cmake
> -DLLVM_ENABLE_RUNTIMES=libcxxabi;libcxx should do.


Fantastic! It looks like the cmake option I was suggesting already exists
actually :)

I had to read our CMake scripts to figure out how to use it though, looking
at https://llvm.org/docs/BuildingADistribution.html#relevant-cmake-options
it mentions the CMake option, but just running locally `ninja` does not get
them to be built, I had to explicitly call `ninja runtimes` to get libc++
to be built, I don't know if this is intended?
I also need to explicitly have `-DLLVM_ENABLE_PROJECTS=clang` by the way
otherwise `ninja runtimes` will error out obscurely at some point, the
cmake handling of this option isn't defensive about it at the moment.

Anyway, I need to update the bot config to see if this "just works", but
locally it seems promising!

Thanks Michael!

-- 
Mehdi





>
> When I last looked at it, it did work and haven't noticed work on that
> front. However, I just re-tried and it actually does work. Thanks to
> anyone who fixed it ;-)
>
> Michael
>
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