[cfe-dev] [llvm-dev] Disk space and RAM requirements in docs

[Sean Silva via cfe-dev]

It would be great if our build system could default to gold or LLD if
available.

On Tue, Apr 30, 2019, 1:58 AM Alex Bradbury via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> On Tue, 30 Apr 2019 at 07:38, Petr Penzin via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> >
> > Hi,
> >
> > Have anybody recently built LLVM in Debug mode within space requirements
> from the Getting Started doc?
> >
> > https://llvm.org/docs/GettingStarted.html#hardware
> >
> > > An LLVM-only build will need about 1-3 GB of space. A full build of
> LLVM and Clang will need around 15-20 GB of disk space.
> >
> > From my experience this numbers looks drastically low. On FreeBSD my
> recent builds consumed more than 70 GB and on Linux - more than 60. I am
> building LLVM, Clang, and LLD with all default targets and default
> settings. On FreeBSD I am also building Polly. Also, building `clang-check`
> target adds around to 20 GB to the build directory size.
> >
> > Apologies for the long snippet, but here is top 20 lines from `du -h |
> sort -rh` on my FreeBSD directory (full log is attached):
> >
> >  91G    build
> >  40G    build/bin
> >  25G    build/tools
> >  25G    build/lib
> >  24G    build/tools/clang
> >  15G    build/tools/clang/unittests
> > 5.0G    build/tools/clang/lib
> > 3.9G    build/lib/Target
> > 3.1G    build/tools/clang/unittests/Tooling
> > 3.1G    build/tools/clang/test
> > 2.8G
> build/tools/clang/test/Tooling/Output/clang-check-mac-libcxx-fixed-compilation-db.cpp.tmp/mock-libcxx/bin
> > 2.8G
> build/tools/clang/test/Tooling/Output/clang-check-mac-libcxx-fixed-compilation-db.cpp.tmp/mock-libcxx
> > 2.8G
> build/tools/clang/test/Tooling/Output/clang-check-mac-libcxx-fixed-compilation-db.cpp.tmp
> > 2.8G    build/tools/clang/test/Tooling/Output
> > 2.8G    build/tools/clang/test/Tooling
> > 1.9G    build/tools/clang/unittests/Frontend
> > 1.6G    build/tools/clang/unittests/Driver
> > 1.5G    build/tools/clang/unittests/ASTMatchers
> > 1.4G    build/tools/clang/lib/StaticAnalyzer
> > 1.3G    build/lib/CodeGen
> >
> > Note that Clang's `unittest` and `test` directory together occupy more
> than 18 GB (which is about the size manual assigns for the entire build),
> with most of the space in `test` taken up by output of tooling tests (is
> that for MacOS, by the way?). Also, looks like five of the unittest
> directories for clang components are taking more than a gigabyte each (with
> Tooling using more than 3 GB).
> >
> > Is this expected or am I doing something wrong? If it is expected,
> should the manual be fixed?
> >
> > There are no RAM requirements in the doc, from my observation linker
> process  on Linux or FreeBSD needs about 10 GB at the moment (and this has
> been growing for a while). Should this be also reflected in hardware
> requirements as well?
>
> I think it would be worth strongly recommending the use of LLD or gold
> to link. I've helped out a number of students/newcomers getting LLVM
> to build for the first time and encountering issues due to binutils ld
> OOMing is a common issue.
>
> > And lastly is there a way to reduce the space consumption by Clang
> unittests and Tooling tests aside of disabling those?
>
> Setting -DBUILD_SHARED_LIBS=True will reduce space requirements by
> using shared libraries rather than static libraries. It will impact
> the time taken to run LLVM and Clang tests though, due to greater
> startup time.
>
> Best,
>
> Alex
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