GCC prerequisites for building LLVM head?

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1

Is there is minimum required version for GCC to build LLVM from the head revision?

I have GCC v4.9.3, but ‘Tools/sancov/sancov.cc’ won’t build because ‘std::to_string’ does not exist. When running CMake it did not flag GCC v4.9.3 as too old, and it is passing the ‘-std=gnu++11’ option, but apparently this version of GCC is not fully C++ 11 compliant, or at least its C++ library isn’t.

Everything else builds.

Thanks,

MartinO

2

Is there is minimum required version for GCC to build LLVM from the head
revision?

Last I checked it was 4.7. The CMake files also tell me that's correct:

modules/CheckCompilerVersion.cmake:
# Check if the host compiler is new enough. LLVM requires at least GCC 4.7,

I have GCC v4.9.3, but ‘Tools/sancov/sancov.cc’ won’t build because
‘std::to_string’ does not exist. When running CMake it did not flag GCC
v4.9.3 as too old, and it is passing the ‘-std=gnu++11’ option, but
apparently this version of GCC is not fully C++ 11 compliant, or at least
its C++ library isn’t.

This sounds odd. I have buildbots with 4.8.2 and 4.9.2 working perfectly.

Could this be a problem in your setup?

cheers,
--renato

3

I just checked with '-E' and I am picking up '<string>' from:

    /usr/lib/gcc/i686-pc/cygwin/4.9.3/include/c++/string

all other C++ headers are coming from the same place. The 'std::to_string' functions are not present in '<string>', but they are located in '<bits/basic_string.h>' - which is included. Perhaps it is a broken Cygwin v4.9.3 package, but this is odd since the source should be identical for the Cygwin versus Linux distros? I can't try this on Linux until tomorrow as I am working from home and don't have a Linux setup that uses v4.9.3.

The 'std::to_string' functions are provided in a block that is conditionally included as follows (line #2847 in my copy):

    #if __cplusplus >= 201103L && defined(_GLIBCXX_USE_C99)

    #include <ext/string_conversions.h>

    namespace std _GLIBCXX_VISIBILITY(default)
    {
    _GLIBCXX_BEGIN_NAMESPACE_VERSION

The test '__cplusplus >= 201103L' evaluates true in all previous cases, so it would appear that '_GLIBCXX_USE_C99' is not being defined - I can add this explicitly when I am configuring LLVM with CMake, but it seems a bit strange that I need to.

Thanks,

  MartinO

4

Looks like a broken package. I don't know how Cygwin builds their own
packages, but I wouldn't be surprised if they have their own
convoluted build system that hacks stuff together, like every other
distribution. :slight_smile:

We do test it on large number of Linux distributions, on ARM, AArch64
and x86_64, and we have found no problems at all with 4.8 or 4.9.

cheers,
--renato

5

Sorry for the delay, I had to experiment and build everything to be sure.

I am actually getting the same problem with GCC v4.9.3 on CentOS, but for both Cygwin and Linux adding '-D_GLIBCXX_USE_C99' to the '-DCMAKE_CXX_FLAGS:STRING=' flag during configuration cured the problem.

  MartinO

6

Right, I don't use that flag, why do you need that?

cheers,
--renato

7

We usually avoid using std::to_string AFAIK because not supported on every platform we support.
Twine or llvm::utostr are good replacements for that, see r267829 or r257857 for instance.

8

I've no idea, but without it, the 'std::to_string' definitions are not enabled!

9

Looks like known libstdc++ problem. See
58393 – Please relax feature check for std::to_string and std::sto* for uClibc and around.

10

That is a useful URL thanks, and the versions of GCC I am using predate the fix in the ticket.

Curious though, because both Linux and Cygwin are building LLVM using the host configuration, and both provide a full 'glibc' implementation. This could be a CMake/Cygwin problem that I am experiencing - I had to build CMake v3.5.2 from source using the usual 'configure/make/install' process, but it is not an official build from either Kitware (not available) or from the Cygwin distribution (too old).

I did try to build LLVM at revision #272991 on Linux (CentOS) but our setup has GCC v4.8.5 20150623 and not v4.9.3 as I previously thought. It did not get as far as building 'sancov.cc' though, and died with:

  [ 57%] Copying clang's immintrin.h...
  make[4]: *** No rule to make target `/work/dub44/martino/WORK/Compilers/llvmHead/llvm/tools/clang/lib/Headers/intrin.h', needed by `lib/clang/3.9.0/include/intrin.h'. Stop.

I haven't investigated this yet, but it is quite likely that the snapshot I took at revision #272991 was not yet BuildBot clean, so I will update to the head revision tomorrow and merge over the weekend and try again.

Thanks,

  MartinO