[llvm] r202486 - [docs] Add a big section with details about how to go about acquiring

[Hal Finkel]

----- Original Message -----
> From: "Chandler Carruth" <chandlerc at gmail.com>
> To: llvm-commits at cs.uiuc.edu
> Sent: Friday, February 28, 2014 4:56:58 AM
> Subject: [llvm] r202486 - [docs] Add a big section with details about how to	go about acquiring
> 
> Author: chandlerc
> Date: Fri Feb 28 04:56:57 2014
> New Revision: 202486
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=202486&view=rev
> Log:
> [docs] Add a big section with details about how to go about acquiring
> a more modern host C++ toolchain for Linux distros where folks
> sometimes
> don't have a good option to get one as part of their system.
> 
> This is a first cut, so feedback, testing, and suggestions are very,
> very welcom. This is one of the last real documentation changes that
> was
> specifically requested prior to switching LLVM and Clang to build in
> C++11 mode by default.

Why are we advocating downloading gcc 4.8.2 to build Clang/LLVM? Should we not first suggest downloading Clang/LLVM 3.4?

 -Hal

> 
> Modified:
>     llvm/trunk/docs/GettingStarted.rst
> 
> Modified: llvm/trunk/docs/GettingStarted.rst
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/GettingStarted.rst?rev=202486&r1=202485&r2=202486&view=diff
> ==============================================================================
> --- llvm/trunk/docs/GettingStarted.rst (original)
> +++ llvm/trunk/docs/GettingStarted.rst Fri Feb 28 04:56:57 2014
> @@ -275,6 +275,71 @@ contained `a bug <http://gcc.gnu.org/bug
>  causes Clang to refuse to compile condition_variable header file.
>   At the time
>  of writing, this breaks LLD build.
>  
> +Getting a Modern Host C++ Toolchain
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +This section mostly applies to Linux and BSDs. On Mac OS X, you
> should have
> +a sufficiently modern Xcode, or you will likely need to upgrade
> until you do.
> +On Windows, just use Visual Studio 2012 as the host compiler, it is
> explicitly
> +supported and widely available.
> +
> +However, on Linux and BSDs there are some notable distributions
> which have
> +extremely old versions of GCC. These steps attempt to help you
> upgrade you
> +compiler even on such a system. However, if at all possible, we
> encourage you
> +to use a recent version of a distribution with a modern system
> compiler that
> +meets these requirements. Note that it is tempting to to install a
> prior
> +version of Clang and libc++ to be the host compiler, however libc++
> was not
> +well tested or set up to build on Linux until relatively recently.
> As
> +a consequence, this guide suggests just using libstdc++ and a modern
> GCC as the
> +initial host in a bootstrap, and then using Clang (and potentially
> libc++).
> +
> +The first step is to get a recent GCC toolchain installed. The most
> common
> +distribution on which users have struggled with the version
> requirements is
> +Ubuntu Precise, 12.04 LTS. For this distribution, one easy option is
> to install
> +the `toolchain testing PPA
> +<https://launchpad.net/~ubuntu-toolchain-r/+archive/test>` and use
> it to
> +install a modern GCC. There is a really nice discussions of this on
> the `ask
> +ubuntu stack exchange
> +<http://askubuntu.com/questions/271388/how-to-install-gcc-4-8-in-ubuntu-12-04-from-the-terminal>`.
> +However, not all users can use PPAs and there are many other
> distros, so it may
> +be necessory (or just useful, if you're here you *are* doing
> compiler
> +development after all) to build and install GCC from source. It is
> also quite
> +easy to do these days.
> +
> +Easy steps for installing GCC 4.8.2:
> +
> +.. code-block:: console
> +
> +  wget ftp://ftp.gnu.org/gnu/gcc/gcc-4.8.2/gcc-4.8.2.tar.bz2
> +  tar -xvjf gcc-4.8.2.tar.bz2
> +  cd gcc-4.8.2
> +  ./contrib/download_prerequisites
> +  cd ..
> +  mkdir gcc-4.8.2-build
> +  cd gcc-4.8.2-build
> +  %PWD/../gcc-4.8.2/configure --prefix=$HOME/toolchains
> --enable-languages=c,c++
> +  make -j$(nproc)
> +  make install
> +
> +For more details, check out the `excellent GCC wiki entry
> +<http://gcc.gnu.org/wiki/InstallingGCC>`, where I got most of this
> information
> +from.
> +
> +Once you have a GCC toolchain, use it as your host compiler. Things
> should
> +generally "just work". You may need to pass a special linker flag,
> +``-Wl,-rpath,$HOME/toolchains/lib`` or some variant thereof to get
> things to
> +find the libstdc++ DSO in this toolchain.
> +
> +When you build Clang, you will need to give *it* access to modern
> C++11
> +standard library in order to use it as your new host in part of a
> bootstrap.
> +There are two easy ways to do this, either build (and install)
> libc++ along
> +with Clang and then use it with the ``-stdlib=libc++`` compile and
> link flag,
> +or install Clang into the same prefix (``$HOME/toolchains`` above)
> as GCC.
> +Clang will look within its own prefix for libstdc++ and use it if
> found. You
> +can also add an explicit prefix for Clang to look in for a GCC
> toolchain with
> +the ``--gcc-toolchain=/opt/my/gcc/prefix`` flag, passing it to both
> compile and
> +link commands when using your just-built-Clang to bootstrap.
> +
>  .. _Getting Started with LLVM:
>  
>  Getting Started with LLVM
> 
> 
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-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory