[Boost-bugs] [Boost C++ Libraries] #13513: Nvidia cuda compiler 9 does not work with boost::mp11

Subject: [Boost-bugs] [Boost C++ Libraries] #13513: Nvidia cuda compiler 9 does not work with boost::mp11
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2018-04-05 12:19:47

#13513: Nvidia cuda compiler 9 does not work with boost::mp11
---------------------------------------------+-------------------------
 Reporter:  Alexander Matthes <a.matthes@…>  |      Owner:  (none)
     Type:  Bugs                             |     Status:  new
Milestone:  To Be Determined                 |  Component:  None
  Version:  Boost 1.66.0                     |   Severity:  Showstopper
 Keywords:                                   |
---------------------------------------------+-------------------------
 I am working with cuda and I choose to use boost::mp11 for my projects.
 However cuda 9 does not work with boost::mp11, even this simple
 application fails:

 {{{
 #include <boost/mp11.hpp>
 int main() {}
 }}}

 To be fair, this seems to be a bug in the nvidia compiler not boost, but
 this is a showstopper for using boost::mp11 together with a recent cuda
 version. Everything works fine with cuda 8.

 I already figured out, what fails in the background in the nvcc (details
 are
 [https://github.com/ComputationalRadiationPhysics/alpaka/issues/459#issuecomment-377678240
 here]), but now also found a work around for boost::mp11:

 The problem occurs on code like this:

 {{{
 template<template<class...> class F, class... T> using mp_defer =
 mp_if<mp_valid<F, T...>, detail::mp_defer_impl<F, T...>,
 detail::mp_no_type>;
 }}}

 Everytime mp_if is used, the nvcc preprocessor tries to be "smart" and
 starts recursively replacing stuff so that in the end
 detail::mp_no_type... is given to the compiler.

 I figured out I can prevent nvcc from doing this with invoking another
 struct inbetween like this:

 {{{
 template<template<class...> class F, class... T>
 struct cuda_workaround
 {
     using type = mp_if<mp_valid<F, T...>, detail::mp_defer_impl<F, T...>,
 detail::mp_no_type>;
 };

 template<template<class...> class F, class... T>
 using mp_defer = typename cuda_workaround< F, T... >::type;
 }}}

 This work around is needed on 5 places in the boost mp11:
 * mp_append.hpp
 {{{
 template<class... L> struct mp_append_impl: mp_if_c<(sizeof...(L) > 111),
 mp_quote<append_inf_impl>, mp_if_c<(sizeof...(L) > 11),
 mp_quote<append_111_impl>, mp_quote<append_11_impl> > >::template fn<L...>
 }}}
 * algorithm.hpp
 {{{
 template<template<class...> class F, class... L> using mp_transform =
 typename mp_if<mp_same<mp_size<L>...>, detail::mp_transform_impl<F, L...>,
 detail::list_size_mismatch>::type;
 }}}
 {{{
 template<class L, std::size_t I> using mp_at_c = typename mp_if_c<(I <
 mp_size<L>::value), detail::mp_at_c_impl<L, I>, void>::type;
 }}}
 {{{
     using type = typename mp_cond<

         mp_bool<(I < N1)>, mp_nth_element_impl<L1, I, P>,
         mp_bool<(I == N1)>, mp_identity<T1>,
         mp_true, mp_nth_element_impl<L2, I - N1 - 1, P>

     >::type;
 }}}
 * utility.hpp
 {{{
 template<template<class...> class F, class... T> using mp_defer =
 mp_if<mp_valid<F, T...>, detail::mp_defer_impl<F, T...>,
 detail::mp_no_type>;
 }}}

 I added an intermediate struct as seen above for every case if cuda 9 is
 used and now my code compiles with nvcc 9.

 So I suggest to add such a work around for cuda 9 and above. I can also do
 this myself, what would be the best way? Providing a patch for the most
 recent version on github or directly opening a pull request?

-- 
Ticket URL: <https://svn.boost.org/trac10/ticket/13513>
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