https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116867
Bug ID: 116867
Summary: Incorrectly report a constexpr function as
non-constant
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hzhou11 at students dot kennesaw.edu
Target Milestone: ---
Output of "gcc -v":
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/13/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
13.2.0-23ubuntu4' --with-bugurl=file:///usr/share/doc/gcc-13/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-13
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-libstdcxx-backtrace --enable-gnu-unique-object --disable-vtable-verify
--enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-13-uJ7kn6/gcc-13-13.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-13-uJ7kn6/gcc-13-13.2.0/debian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 13.2.0 (Ubuntu 13.2.0-23ubuntu4)
Now the problem:
#include<string>
#include<iostream>
#include<vector>
#include<numeric>
constexpr std::string join(std::vector<std::string> vec, char delimiter) {
auto result = std::accumulate(std::next(vec.begin()), vec.end(),
vec[0],
[&delimiter](const std::string& a, const std::string& b) {
return a + delimiter + b;
});
return result;
}
main() {
static_assert(join({ "one", "two", "three" }, ';') == "one;two;three");
}
My expectation is there should be no error because the concatenated string is
deallocated by the end of constant evaluation, but gcc gives the following
error:
main.cpp:92:56: error: non-constant condition for static assertion
92 | static_assert(join({ "one", "two", "three" }, ';') ==
"one;two;three");
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
main.cpp:92:75: in ‘constexpr’ expansion of ‘join(std::vector >, char)(59)’
main.cpp:92:75: in ‘constexpr’ expansion of ‘std::accumulate(_InputIterator,
_InputIterator, _Tp, _BinaryOperation) [with _InputIterator =
__gnu_cxx::__normal_iterator<__cxx11::basic_string*,
vector<__cxx11::basic_string > >; _Tp = __cxx11::basic_string; _BinaryOperation
= join(std::vector >, char)::](vec.std::vector >::end(),
std::__cxx11::basic_string((*(const std::__cxx11::basic_string*)(&
vec.std::vector >::operator[](0)))), join(std::vector >, char)::{delimiter})’
main.cpp:92:75: in ‘constexpr’ expansion of
‘std::__cxx11::basic_string(__init)’
main.cpp:92:56: error: accessing
‘std::__cxx11::basic_string::::_M_allocated_capacity’ member instead of
initialized ‘std::__cxx11::basic_string::::_M_local_buf’ member in constant
expression
