[cfe-dev] Unexpected check-libcxx failures on FreeBSD
Eric Fiselier via cfe-dev
cfe-dev at lists.llvm.org
Fri Oct 7 18:59:19 PDT 2016
> Does anyone know what the problem may be?
FreeBSD ships std::pair with explicitly defined copy and move constructors
as opposed to explicitly defaulted ones. Mistakenly these constructors have
not been marked constexpr in C++14.
FreeBSD provides these old constructors is because switching to defaulted
copy/move constructors is an ABI break because it makes std::pair
non-trivial and changes how it's passed to functions according to the
Itanium ABI.
Fixing this requires either (A) marking the fallback constructors constexpr
in C++14, or (B) convincing FreeBSD to take the ABI break.
The easiest and simplistic fix is (A). However my concern with (A) is that
the fallback constructors don't SFINAE away if they are ill-formed. This
means that applying constexpr to them could break existing code by causing
the eager instantiation of the ill-formed constructors, instantiations that
would not occur if the constructors were non-constexpr. For this reason I
think fix (B) is more correct, and greatly preferable.
Since we have plenty of time until the next release I'll go ahead and
commit (A) for now, keeping my ear to the ground for breakage.
/Eric
On Fri, Oct 7, 2016 at 7:23 PM, Krzysztof Parzyszek via cfe-dev <
cfe-dev at lists.llvm.org> wrote:
> I'm running this on FreeBSD 11 (stable). It has clang-3.8.0 as the system
> compiler. LLVM/Clang/et al. compiled without problems, but I'm seeing
> failures in check-libcxx. Example below.
>
> Does anyone know what the problem may be?
>
>
> clang version 4.0.0 (http://llvm.org/git/clang.git
> a85c03256cfc0812e268f5e0f1b804910e75e673) (http://llvm.org/git/llvm.git
> c95d4ff692323bde64fc8ef45e174b19450779af)
> Target: x86_64-unknown-freebsd11.0
> Thread model: posix
> InstalledDir: /w/c/org/bin
> "/w/c/org/bin/clang-4.0" -cc1 -triple x86_64-unknown-freebsd11.0
> -emit-obj -mrelax-all -disable-free -main-file-name
> minmax_init_list_comp.pass.cpp -mrelocation-model static -mthread-model
> posix -mdisable-fp-elim -masm-verbose -mconstructor-aliases -munwind-tables
> -target-cpu x86-64 -v -v -dwarf-column-info -debugger-tuning=gdb
> -coverage-notes-file /w/bld/org/projects/libcxx/tes
> t/std/algorithms/alg.sorting/alg.min.max/Output/minmax_init_list_comp.pass.cpp.gcno
> -nostdinc++ -resource-dir /w/c/org/bin/../lib/clang/4.0.0 -include /w/src/
> llvm.org/projects/libcxx/test/support/nasty_macros.hpp -I /w/src/
> llvm.org/projects/libcxx/include -I /w/src/llvm.org/projects/libcx
> x/test/support -D LIBCXX_FILESYSTEM_STATIC_TEST_ROOT=/w/src/
> llvm.org/projects/libcxx/test/std/experimental/f
> ilesystem/Inputs/static_test_env -D LIBCXX_FILESYSTEM_DYNAMIC_TEST
> _ROOT=/w/bld/org/projects/libcxx/test/filesystem/Output/dynamic_env -D
> LIBCXX_FILESYSTEM_DYNAMIC_TEST_HELPER=/usr/local/bin/python2.7 /w/src/
> llvm.org/projects/libcxx/test/support/filesystem_dynamic_test_helper.py
> -Werror=thread-safety -std=c++1z -fdeprecated-macro -fdebug-compilation-dir
> /w/src/llvm.org -ferror-limit 19 -fmessage-length 210
> -fobjc-runtime=gnustep -fcxx-exceptions -fexceptions
> -fdiagnostics-show-option -fcolor-diagnostics -o
> /w/bld/org/projects/libcxx/test/std/algorithms/alg.sorting/
> alg.min.max/Output/minmax_init_list_comp.pass.cpp.o -x c++ /w/src/
> llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp
> clang -cc1 version 4.0.0 based upon LLVM 4.0.0svn default target
> x86_64-unknown-freebsd11.0
> #include "..." search starts here:
> #include <...> search starts here:
> /w/src/llvm.org/projects/libcxx/include
> /w/src/llvm.org/projects/libcxx/test/support
> /w/c/org/bin/../lib/clang/4.0.0/include
> /usr/include
> End of search list.
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:68:19: error:
> static_assert expression is not an integral constant expression
> static_assert((std::minmax({1, 2, 3}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
>
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /w/src/llvm.org/projects/libcxx/include/algorithm:2823:12: note:
> non-constexpr constructor 'pair' cannot be used in a constant expression
> return __result;
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:68:20: note: in call
> to 'minmax({&{1, 2, 3}[0], 3}, {{}})'
> static_assert((std::minmax({1, 2, 3}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
> ^
> /w/src/llvm.org/projects/libcxx/include/utility:316:5: note: declared here
> pair(pair&& __p) _NOEXCEPT_(is_nothrow_move_constructible<first_type>::value
> &&
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:69:19: error:
> static_assert expression is not an integral constant expression
> static_assert((std::minmax({1, 3, 2}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
>
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /w/src/llvm.org/projects/libcxx/include/algorithm:2823:12: note:
> non-constexpr constructor 'pair' cannot be used in a constant expression
> return __result;
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:69:20: note: in call
> to 'minmax({&{1, 3, 2}[0], 3}, {{}})'
> static_assert((std::minmax({1, 3, 2}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
> ^
> /w/src/llvm.org/projects/libcxx/include/utility:316:5: note: declared here
> pair(pair&& __p) _NOEXCEPT_(is_nothrow_move_constructible<first_type>::value
> &&
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:70:19: error:
> static_assert expression is not an integral constant expression
> static_assert((std::minmax({2, 1, 3}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
>
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /w/src/llvm.org/projects/libcxx/include/algorithm:2823:12: note:
> non-constexpr constructor 'pair' cannot be used in a constant expression
> return __result;
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:70:20: note: in call
> to 'minmax({&{2, 1, 3}[0], 3}, {{}})'
> static_assert((std::minmax({2, 1, 3}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
> ^
> /w/src/llvm.org/projects/libcxx/include/utility:316:5: note: declared here
> pair(pair&& __p) _NOEXCEPT_(is_nothrow_move_constructible<first_type>::value
> &&
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:71:19: error:
> static_assert expression is not an integral constant expression
> static_assert((std::minmax({2, 3, 1}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
>
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /w/src/llvm.org/projects/libcxx/include/algorithm:2823:12: note:
> non-constexpr constructor 'pair' cannot be used in a constant expression
> return __result;
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:71:20: note: in call
> to 'minmax({&{2, 3, 1}[0], 3}, {{}})'
> static_assert((std::minmax({2, 3, 1}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
> ^
> /w/src/llvm.org/projects/libcxx/include/utility:316:5: note: declared here
> pair(pair&& __p) _NOEXCEPT_(is_nothrow_move_constructible<first_type>::value
> &&
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:72:19: error:
> static_assert expression is not an integral constant expression
> static_assert((std::minmax({3, 1, 2}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
>
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /w/src/llvm.org/projects/libcxx/include/algorithm:2823:12: note:
> non-constexpr constructor 'pair' cannot be used in a constant expression
> return __result;
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:72:20: note: in call
> to 'minmax({&{3, 1, 2}[0], 3}, {{}})'
> static_assert((std::minmax({3, 1, 2}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
> ^
> /w/src/llvm.org/projects/libcxx/include/utility:316:5: note: declared here
> pair(pair&& __p) _NOEXCEPT_(is_nothrow_move_constructible<first_type>::value
> &&
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:73:19: error:
> static_assert expression is not an integral constant expression
> static_assert((std::minmax({3, 2, 1}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
>
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /w/src/llvm.org/projects/libcxx/include/algorithm:2823:12: note:
> non-constexpr constructor 'pair' cannot be used in a constant expression
> return __result;
> ^
> /w/src/llvm.org/projects/libcxx/test/std/algorithms/alg.
> sorting/alg.min.max/minmax_init_list_comp.pass.cpp:73:20: note: in call
> to 'minmax({&{3, 2, 1}[0], 3}, {{}})'
> static_assert((std::minmax({3, 2, 1}, std::greater<int>()) ==
> std::pair<int, int>(3, 1)), "");
> ^
> /w/src/llvm.org/projects/libcxx/include/utility:316:5: note: declared here
> pair(pair&& __p) _NOEXCEPT_(is_nothrow_move_constructible<first_type>::value
> &&
> ^
> 6 errors generated.
>
>
> -Krzysztof
>
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