Morning!
I've got a transform-reduce statement that compiles with execution::seq.
When replacing the policy parameter with execution::par, I get a compile
time error. This seems odd to me and I'm seeking advice here whether to
file a bug report with gcc or not.
The environment is a gcc 10.2 on an arch linux derivate; libstdc++ has
version 6.0.28 (owned by package gcc-libs 10.2.0-3); libtbb is in use
(owned by package tbb 2020.3-1).
The statement in questions reads (in a simplified example):
Obj x = transform_reduce( execution::par, v.begin(), v.end(), Obj{0},
[](Obj &a,Obj const &b) { a.combine(b); return
move(a); },
[](int i){ return Obj{i}; } );
( overload 6: https://en.cppreference.com/w/cpp/algorithm/transform_reduce )
Pls find the compiler error at the end of this mail; seems to be in the
interface to TBB. On the compiler explorer, this behaviour is
reproducible, when TBB is selected as additional library. It compiles
(and runs) OK there without the TBB.
Might this be a bug in gcc's interface to TBB?
The complete compiler error messages follows (different name "Inte" for
example class). (If requested I can, of course, post a complete source
for the problem as well.)
Cheers, Kai
In file included from /usr/include/c++/10.2.0/pstl/parallel_backend.h:16,
from /usr/include/c++/10.2.0/pstl/algorithm_impl.h:22,
from /usr/include/c++/10.2.0/pstl/glue_execution_defs.h:50,
from /usr/include/c++/10.2.0/execution:32,
from ../demos/main.cpp:3:
/usr/include/c++/10.2.0/pstl/parallel_backend_tbb.h: In instantiation of
‘void __pstl::__par_backend::__par_trans_red_body<_Index, _Up, _Tp, _Cp,
_Rp>::operator()(const tbb::blocked_range<Index>&) [with _Index =
__gnu_cxx::__normal_iterator<int*, std::vector<int> >; _Up =
__pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >)>; _Tp = Inte; _Cp = main(int,
char**)::<lambda(Inte&, const Inte&)>; _Rp =
__pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int>
>, Inte)>]’:
/usr/include/tbb/parallel_reduce.h:150:47: required from ‘void
tbb::interface9::internal::start_reduce<Range, Body,
Partitioner>::run_body(Range&) [with Range =
tbb::blocked_range<__gnu_cxx::__normal_iterator<int*, std::vector<int> >
>; Body =
__pstl::__par_backend::__par_trans_red_body<__gnu_cxx::__normal_iterator<int*,
std::vector<int> >, __pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >)>, Inte, main(int, char**)::<lambda(Inte&, const
Inte&)>, __pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int>
>, Inte)> >; Partitioner = const tbb::auto_partitioner]’
/usr/include/tbb/partitioner.h:423:27: required from ‘void
tbb::interface9::internal::dynamic_grainsize_mode<Mode>::work_balance(StartType&,
Range&) [with StartType =
tbb::interface9::internal::start_reduce<tbb::blocked_range<__gnu_cxx::__normal_iterator<int*,
std::vector<int> > >,
__pstl::__par_backend::__par_trans_red_body<__gnu_cxx::__normal_iterator<int*,
std::vector<int> >, __pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >)>, Inte, main(int, char**)::<lambda(Inte&, const
Inte&)>, __pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int>
>, Inte)> >, const tbb::auto_partitioner>; Range =
tbb::blocked_range<__gnu_cxx::__normal_iterator<int*, std::vector<int> >
>; Mode =
tbb::interface9::internal::adaptive_mode<tbb::interface9::internal::auto_partition_type>]’
/usr/include/tbb/partitioner.h:256:28: required from ‘void
tbb::interface9::internal::partition_type_base<Partition>::execute(StartType&,
Range&) [with StartType =
tbb::interface9::internal::start_reduce<tbb::blocked_range<__gnu_cxx::__normal_iterator<int*,
std::vector<int> > >,
__pstl::__par_backend::__par_trans_red_body<__gnu_cxx::__normal_iterator<int*,
std::vector<int> >, __pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >)>, Inte, main(int, char**)::<lambda(Inte&, const
Inte&)>, __pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int>
>, Inte)> >, const tbb::auto_partitioner>; Range =
tbb::blocked_range<__gnu_cxx::__normal_iterator<int*, std::vector<int> >
>; Partition = tbb::interface9::internal::auto_partition_type]’
/usr/include/tbb/parallel_reduce.h:190:29: required from ‘tbb::task*
tbb::interface9::internal::start_reduce<Range, Body,
Partitioner>::execute() [with Range =
tbb::blocked_range<__gnu_cxx::__normal_iterator<int*, std::vector<int> >
>; Body =
__pstl::__par_backend::__par_trans_red_body<__gnu_cxx::__normal_iterator<int*,
std::vector<int> >, __pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >)>, Inte, main(int, char**)::<lambda(Inte&, const
Inte&)>, __pstl::__internal::__pattern_transform_reduce<const
__pstl::execution::v1::parallel_policy&,
__gnu_cxx::__normal_iterator<int*, std::vector<int> >, Inte, main(int,
char**)::<lambda(Inte&, const Inte&)>, main(int, char**)::<lambda(int)>,
std::integral_constant<bool, false>
>::<lambda()>::<lambda(__gnu_cxx::__normal_iterator<int*,
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int>
>, Inte)> >; Partitioner = const tbb::auto_partitioner]’
/usr/include/tbb/parallel_reduce.h:181:11: required from here
/usr/include/c++/10.2.0/pstl/parallel_backend_tbb.h:177:31: error: no
match for call to ‘(main(int, char**)::<lambda(Inte&, const Inte&)>)
(Inte, Inte)’
177 | _Tp(_M_combine(_M_u(__i), _M_u(__i + 1))); //
The condition i+1 < j is provided by the grain size of 3
| ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/10.2.0/pstl/parallel_backend_tbb.h:177:31: note:
candidate: ‘Inte (*)(Inte&, const Inte&)’ (conversion)
/usr/include/c++/10.2.0/pstl/parallel_backend_tbb.h:177:31: note:
conversion of argument 2 would be ill-formed:
/usr/include/c++/10.2.0/pstl/parallel_backend_tbb.h:177:36: error:
cannot bind non-const lvalue reference of type ‘Inte&’ to an rvalue of
type ‘Inte’
177 | _Tp(_M_combine(_M_u(__i), _M_u(__i + 1))); //
The condition i+1 < j is provided by the grain size of 3
| ~~~~^~~~~
../demos/main.cpp:41:34: note: candidate: ‘main(int,
char**)::<lambda(Inte&, const Inte&)>’ (near match)
41 | [](Inte &a,Inte const &b) /*->
Inte*/ { a.combine(b); return move(a); },
| ^
../demos/main.cpp:41:34: note: conversion of argument 1 would be
ill-formed:
In file included from /usr/include/c++/10.2.0/pstl/parallel_backend.h:16,
from /usr/include/c++/10.2.0/pstl/algorithm_impl.h:22,
from /usr/include/c++/10.2.0/pstl/glue_execution_defs.h:50,
from /usr/include/c++/10.2.0/execution:32,
from ../demos/main.cpp:3:
/usr/include/c++/10.2.0/pstl/parallel_backend_tbb.h:177:36: error:
cannot bind non-const lvalue reference of type ‘Inte&’ to an rvalue of
type ‘Inte’
177 | _Tp(_M_combine(_M_u(__i), _M_u(__i + 1))); //
The condition i+1 < j is provided by the grain size of 3
| ~~~~^~~~~
--
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D-55120 Meenz
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