Compatibility with libc++

[t-lutz]

Compatibility with libc++

[t-lutz]

Which version of clang/libcxx are you using? I cannot reproduce that on my machine with 3.6.2 and r253347:

$> clang++ -I../include -pthread -std=c++14 -o prime prime.cpp -pthread -stdlib=libc++ && echo $?
0

[maribu]

Thanks for the fast reply!

I have the problem with both libc++ in version 3.6.0 and 3.7.0. I think the order of the arguments do matter here, also the parameter -lc++abi is needed to actually link against libc++, otherwise linking fails with libc++ in version 3.6.0 or 3.7.0. Also I believe that even if linking works without -lc++abi strange things might happen at runtime if the headers from libc++ were used.

Please try again with -lc++abi added and -stdlib=libc++ coming before -I../include. I believe in this case libc++ is looked up before ParallelSTL and #include <experimental/algorithm> will use the header from libcxx instead of the one from ParallelSTL.

Thanks for your help!

[t-lutz]

This works just as well:

clang++ -std=c++14 -stdlib=libc++ -lc++abi -pthread prime.cpp -o prime -I../include

The program runs just fine.

The -v flag shows the include directories and their order:

#include "..." search starts here:
#include <...> search starts here:
 ../include
 /usr/include/c++/v1
 /usr/local/include
 /home/tlutz/local/compilers/clang/3.6.2/bin/../lib/clang/3.6.2/include
 /usr/include
End of search list.

[maribu]

Apparently I'm very stupid and forget the -I../include, so the -I switch always gets priority over the stdlib=libc++. Still this makes it impossible to use experimental/algorithm from libc++ in conjunction with ParallelSTL - which is not a problem for me. (At least when using grep on the output of clang++ -std=c++11 -stdlib=libc++ -lc++abi -pthread prime.cpp -I../include -E I do not get any matches for functions only defined in libc++'s experimental/algorithm.)

The other problem still remains: std::sort is a template in libc++ which makes it impossible to be passed as functor. This can be seen with

clang++ -std=c++14 -stdlib=libc++ -lc++abi -pthread sort.cpp -o sort -I../include

Which gives as output:

In file included from sort.cpp:6:
In file included from ../include/experimental/algorithm:7:
In file included from ../include/experimental/execution_policy:135:
In file included from ../include/experimental/bits/parallel/policy_parallel.h:607:
../include/experimental/bits/parallel/algos/par/sort.h:29:5: error: no matching function for call to 'diffract'
    detail::diffract(first, last, std::sort<RandomAccessIterator, Compare>, comp);
    ^~~~~~~~~~~~~~~~
../include/experimental/bits/parallel/algos/par/sort.h:17:18: note: in instantiation of function template specialization 'std::experimental::parallel::v1::parallel_execution_policy::sort<std::__1::__wrap_iter<unsigned int *>, std::__1::less<unsigned int> >' requested here
    return this->sort(first, last, std::less<typename iterator_traits<RandomAccessIterator>::value_type>());
                 ^
../include/experimental/algorithm:701:10: note: in instantiation of function template specialization 'std::experimental::parallel::v1::parallel_execution_policy::sort<std::__1::__wrap_iter<unsigned int *> >' requested here
    exec.sort(first, last);
         ^
sort.cpp:19:3: note: in instantiation of function template specialization 'std::experimental::parallel::v1::sort<const std::experimental::parallel::v1::parallel_execution_policy &, std::__1::__wrap_iter<unsigned int *> >' requested here
  sort(policy, begin(copy), end(copy));
  ^
sort.cpp:43:19: note: in instantiation of function template specialization 'sort<const std::experimental::parallel::v1::parallel_execution_policy &>' requested here
  auto time_par = sort(experimental::parallel::par, values);
                  ^
../include/experimental/bits/parallel/algos/par/diffract.h:81:13: note: candidate template ignored: couldn't infer template argument '__Functor'
inline void diffract(__Iterator __first, __Iterator __last, 
            ^
1 error generated.

[t-lutz]

experimental/algorithm is not a standard header and it is probably shared by various proposals. I am not sure what libcxx implements there, but it is shouldn't be any standard function.

sort is indeed a template function, but std::sort<RandomAccessIterator, Compare> passed to diffract is a reference on an instance of this template, so this should be fine. Which version of clang are you using?

[maribu]

I tested it with clang 3.7.0 & libc++ 3.7.0, with clang 3.7.0 & libc++ 3.6.0 and with clang 3.5.2 and libc++ 3.7.0. With both clang 3.7.0 and 3.5.3 it works fine without compiling against libc++.

[t-lutz]

So you are having the problem with 3.6.0 or all versions when using libc++?

[t-lutz]

Right, I managed to reproduce it. This might be a bug in clang, which seems to need an explicit cast to instantiate the template.

[maribu]

I have the same problem with both version 3.6.0 and 3.7.0 of libc++ using clang 3.7.0 and also with clang 3.5.2 and libc++ 3.7.0. I have not tested clang 3.5.2 in conjunction with libc++ 3.6.0, as I have no machine with precompiled packages of 3.5.2 and libc++ 3.6.0 available, but I could also test this if needed, it just would take a bit longer as I'd have to compile them before testing.