https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94696
Bug ID: 94696
Summary: std::search with a parallel policy calls predicate
with wrong argument types
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: schlong at cock dot li
Target Milestone: ---
Created attachment 48325
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48325&action=edit
search with parallel execution policy
When `std::search` is called with a parallel execution policy
(`std::execution::par`, `std::execution::par_unseq`, `std::execution::unseq`)
and a binary predicate as the compare function, it tries to invoke the
predicate with wrong argument types.
```
// snippet is also attached as a file to the bug report
#include <algorithm>
#include <execution>
struct A{};
struct B{};
bool fn(A, B)
{
return true;
}
int main()
{
A a[1]{};
B b[1]{};
std::search(std::execution::par,
a, a + 1,
b, b + 1,
fn);
}
```
Compile with
```
g++ -std=c++20
```
or c++2a if using an older version of gcc (Error also occurs in older versions
of gcc).
gcc -v
```
Target: x86_64-linux-gnu
Configured with: ../gcc-trunk-20200421/configure
--prefix=/opt/compiler-explorer/gcc-build/staging --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu --disable-bootstrap
--enable-multiarch --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --enable-clocale=gnu --enable-languages=c,c++,fortran,ada,d
--enable-ld=yes --enable-gold=yes --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-linker-build-id --enable-lto
--enable-plugins --enable-threads=posix
--with-pkgversion=Compiler-Explorer-Build
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.0.1 20200420 (experimental) (Compiler-Explorer-Build)
```
Output
```
In file included from
/opt/compiler-explorer/gcc-trunk-20200421/include/c++/10.0.1/algorithm:61,
from <source>:2:
/opt/compiler-explorer/gcc-trunk-20200421/include/c++/10.0.1/bits/stl_algobase.h:
In instantiation of 'constexpr bool std::equal(_IIter1, _IIter1, _IIter2,
_BinaryPredicate) [with _IIter1 = B*; _IIter2 = A*; _BinaryPredicate = bool
(*)(A, B)]':
/opt/compiler-explorer/gcc-trunk-20200421/include/c++/10.0.1/pstl/algorithm_impl.h:449:22:
required from 'bool __pstl::__internal::__brick_equal(_ForwardIterator1,
_ForwardIterator1, _ForwardIterator2, _BinaryPredicate, std::false_type) [with
_ForwardIterator1 = B*; _ForwardIterator2 = A*; _BinaryPredicate = bool (*)(A,
B); std::false_type = std::integral_constant<bool, false>]'
/opt/compiler-explorer/gcc-trunk-20200421/include/c++/10.0.1/pstl/algorithm_impl.h:571:38:
required from '_RandomAccessIterator1
__pstl::__internal::__find_subrange(_RandomAccessIterator1,
_RandomAccessIterator1, _RandomAccessIterator1, _RandomAccessIterator2,
_RandomAccessIterator2, _BinaryPredicate, bool, _IsVector) [with
_RandomAccessIterator1 = A*; _RandomAccessIterator2 = B*; _BinaryPredicate =
bool (*)(A, B); _IsVector = std::integral_constant<bool, false>]'
/opt/compiler-explorer/gcc-trunk-20200421/include/c++/10.0.1/pstl/algorithm_impl.h:780:55:
required from '_ForwardIterator1
__pstl::__internal::__pattern_search(_ExecutionPolicy&&, _ForwardIterator1,
_ForwardIterator1, _ForwardIterator2, _ForwardIterator2, _BinaryPredicate,
_IsVector, std::true_type) [with _ExecutionPolicy = const
__pstl::execution::v1::parallel_policy&; _ForwardIterator1 = A*;
_ForwardIterator2 = B*; _BinaryPredicate = bool (*)(A, B); _IsVector =
std::integral_constant<bool, false>; std::true_type =
std::integral_constant<bool, true>]'
/opt/compiler-explorer/gcc-trunk-20200421/include/c++/10.0.1/pstl/glue_algorithm_impl.h:214:40:
required from
'__pstl::__internal::__enable_if_execution_policy<_ExecutionPolicy,
_ForwardIterator> std::search(_ExecutionPolicy&&, _ForwardIterator1,
_ForwardIterator1, _ForwardIterator2, _ForwardIterator2, _BinaryPredicate)
[with _ExecutionPolicy = const __pstl::execution::v1::parallel_policy&;
_ForwardIterator1 = A*; _ForwardIterator2 = B*; _BinaryPredicate = bool (*)(A,
B); __pstl::__internal::__enable_if_execution_policy<_ExecutionPolicy,
_ForwardIterator> = A*]'
<source>:21:7: required from here
/opt/compiler-explorer/gcc-trunk-20200421/include/c++/10.0.1/bits/stl_algobase.h:1437:25:
error: could not convert '* __first1' from 'B' to 'A'
1437 | if (!bool(__binary_pred(*__first1, *__first2)))
| ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
| |
| B
Compiler returned: 1
```
The snippet compiles with MSVC v19.24.
The snippet compiles when not using an execution policy.
The snippet compiles when using `std::execution::seq`.
