[Bug c++/92687] New: decltype of a structured binding to a tuple component is a reference type inside a template function
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92687
Bug ID: 92687
Summary: decltype of a structured binding to a tuple component
is a reference type inside a template function
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vis...@royal-caliber.com
Target Milestone: ---
Created attachment 47370
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47370&action=edit
preprocessed file
Hello,
The code below shows an inconsistency in the handling of decltype for
structured bindings within template functions vs. non-template functions - the
static_assert in foo() triggers, but not in bar(). I think the handling in
bar() is correct, as per the notes at
https://en.cppreference.com/w/cpp/language/structured_binding.
This may or may not be related to bug 81176. Details of the compilation command
are listed below the source.
Thank you,
Vishal
#include
#include
template
void foo()
{
auto [x, y] = std::tuple{0, 2};
static_assert(!std::is_reference::value);
}
void bar()
{
auto [x, y] = std::tuple{0, 2};
static_assert(!std::is_reference::value);
}
int main()
{
foo<>();
bar();
}
---
g++-9.2.0 -v -save-temps -pedantic -Wall -Wextra -std=c++17 test.cpp
Using built-in specs.
COLLECT_GCC=g++-9.2.0
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/9.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-9.2.0/work/gcc-9.2.0/configure
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr
--bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/9.2.0
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/9.2.0
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/9.2.0/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/9.2.0/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/9.2.0/python
--enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt
--disable-werror --with-system-zlib --enable-nls --without-included-gettext
--enable-checking=release --with-bugurl=https://bugs.gentoo.org/
--with-pkgversion='Gentoo 9.2.0 p1' --disable-esp --enable-libstdcxx-time
--enable-shared --enable-threads=posix --enable-__cxa_atexit
--enable-clocale=gnu --disable-multilib --with-multilib-list=m64
--disable-altivec --disable-fixed-point --enable-targets=all --enable-libgomp
--disable-libmudflap --disable-libssp --disable-systemtap
--enable-vtable-verify --enable-lto --without-isl --enable-default-pie
--enable-default-ssp
Thread model: posix
gcc version 9.2.0 (Gentoo 9.2.0 p1)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wpedantic' '-Wall' '-Wextra'
'-std=c++17' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/libexec/gcc/x86_64-pc-linux-gnu/9.2.0/cc1plus -E -quiet -v -D_GNU_SOURCE
test.cpp -mtune=generic -march=x86-64 -std=c++17 -Wpedantic -Wall -Wextra
-fpch-preprocess -o test.ii
ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9
/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9/x86_64-pc-linux-gnu
/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9/backward
/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include
/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wpedantic' '-Wall' '-Wextra'
'-std=c++17' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/libexec/gcc/x86_64-pc-linux-gnu/9.2.0/cc1plus -fpreprocessed test.ii
-quiet -dumpbase test.cpp -mtune=generic -march=x86-64 -auxbase test -Wpedantic
-Wall -Wextra -std=c++17 -version -o test.s
GNU C++17 (Gentoo 9.2.0 p1) version 9.2.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 9.2.0, GMP version 6.1.2, MPFR version 3.1.6,
MPC version 1.0.3, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++17 (Gentoo 9.2.0 p1) version 9.2.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 9.2.0, GMP version 6.1.2, MPFR version 3.1.6,
MPC version 1.0.3, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 2f11227cf3606c8ecdab2bd17fc2bf18
test.cpp: In function ‘void foo()’:
test.cpp:9:17: error: static assertion failed
9 | static_assert(!std::is_reference::value);
| ^~
[Bug c++/85311] New: const& aggregate parameter with empty default brace initializer results in undefined references to std containers
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85311
Bug ID: 85311
Summary: const& aggregate parameter with empty default brace
initializer results in undefined references to std
containers
Product: gcc
Version: 7.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vis...@royal-caliber.com
Target Milestone: ---
Created attachment 43890
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43890&action=edit
preprocessed output
Hello,
The following code fails to link:
--test.cpp--
#include
struct Foo
{
std::vector x;
};
void foo(const Foo& = {})
{
}
int main()
{
foo();
}
---
$ g++ test.cpp
/tmp/ccJsJY1c.o: In function `main':
test.cpp:(.text+0x2a): undefined reference to `std::vector >::vector()'
collect2: error: ld returned 1 exit status
The problem is triggered by the default value for the parameter to foo(). It
can be avoided by either changing the prototype of foo() to not have a default
value, or by actually providing a value in the call to foo().
The same behavior occurs with several other std containers inside the aggregate
such as deque and list. It can be reproduced in gcc versions 6.4.0, 7.2.0 and
7.3.0 and libstdc++ versions 6.0.22 and 6.0.24.
The preprocessed file is attached. The output of g++ -v follows.
Thank you,
Vishal
Output of "g++-7.3 -v -save-temps test.cpp"
Using built-in specs.
COLLECT_GCC=g++-7.3
COLLECT_LTO_WRAPPER=/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --enable-languages=c,c++
--prefix=/home/vishal/localbuild --program-suffix=-7.3 --disable-multilib
Thread model: posix
gcc version 7.3.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/cc1plus -E
-quiet -v -D_GNU_SOURCE test.cpp -mtune=generic -march=x86-64 -fpch-preprocess
-o test.ii
ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory
"/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0
/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/x86_64-pc-linux-gnu
/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/backward
/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include
/home/vishal/localbuild/include
/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/cc1plus
-fpreprocessed test.ii -quiet -dumpbase test.cpp -mtune=generic -march=x86-64
-auxbase test -version -o test.s
GNU C++14 (GCC) version 7.3.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 7.3.0, GMP version 6.1.0, MPFR version
3.1.3-p4, MPC version 1.0.2, isl version none
warning: GMP header version 6.1.0 differs from library version 6.1.2.
warning: MPFR header version 3.1.3-p4 differs from library version 3.1.6.
warning: MPC header version 1.0.2 differs from library version 1.0.3.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++14 (GCC) version 7.3.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 7.3.0, GMP version 6.1.0, MPFR version
3.1.3-p4, MPC version 1.0.2, isl version none
warning: GMP header version 6.1.0 differs from library version 6.1.2.
warning: MPFR header version 3.1.3-p4 differs from library version 3.1.6.
warning: MPC header version 1.0.2 differs from library version 1.0.3.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: e93c907a87f28f1e65d001f94ea5afa5
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
as -v --64 -o test.o test.s
GNU assembler version 2.29.1 (x86_64-pc-linux-gnu) using BFD version (Gentoo
2.29.1 p3) 2.29.1
COMPILER_PATH=/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/:/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.3.0/:/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/:/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/7.3.0/:/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-gnu/
LIBRARY_PATH=/home/vishal/localbuild/lib/gcc/x86_64-pc-linux-g
[Bug c++/80935] New: [C++1z] incorrect error 'uninitialized variable in constexpr function' when conditionally declaring variable inside lambda inside template class
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80935
Bug ID: 80935
Summary: [C++1z] incorrect error 'uninitialized variable in
constexpr function' when conditionally declaring
variable inside lambda inside template class
Product: gcc
Version: 7.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vis...@royal-caliber.com
Target Milestone: ---
Created attachment 41445
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41445&action=edit
preprocessed file generated by g++ -std=c++1z -v -save-temps
The following code fails to compile with g++ 7.1.0 with flags -std=c++1z. It
compiles with -std=c++14 or -std=c++11. I believe expected behavior is to
compile cleanly. clang-4.0 also has no problem with this code.
struct S
{
int x;
int y;
};
template
struct Foo
{
void foo()
{
auto f = [](int x)
{
if (x)
{
S s;
s.x = 20;
s.y = 10;
(void) s;
}
};
f(10);
}
};
int main()
{
Foo f;
f.foo();
}
When compiled with g++ -std=c++1z, the following error is raised:
test.cpp: In instantiation of ‘Foo::foo():: [with T = int]’:
test.cpp:26:15: required from ‘struct Foo::foo() [with T =
int]::’
test.cpp:26:10: required from ‘void Foo::foo() [with T = int]’
test.cpp:45:9: required from here
test.cpp:30:11: error: uninitialized variable ‘s’ in ‘constexpr’ function
S s;
^
test.cpp:14:8: note: ‘struct S’ has no user-provided default constructor
struct S
^
test.cpp:16:7: note: and the implicitly-defined constructor does not initialize
‘int S::x’
int x;
The gcc build information is as follows:
Using built-in specs.
COLLECT_GCC=g++-7.1
COLLECT_LTO_WRAPPER=/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --prefix=/home/vishal/localbuild
--enable-languages=c,c++ --program-suffix=-7.1 --disable-multilib
Thread model: posix
gcc version 7.1.0 (GCC)
COLLECT_GCC_OPTIONS='-std=c++1z' '-Wall' '-Wextra' '-v' '-save-temps'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/cc1plus
-fpreprocessed test.ii -quiet -dumpbase test.cpp -mtune=generic -march=x86-64
-auxbase test -Wall -Wextra -std=c++1z -version -o test.s
GNU C++14 (GCC) version 7.1.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 7.1.0, GMP version 6.1.0, MPFR version
3.1.3-p4, MPC version 1.0.2, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++14 (GCC) version 7.1.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 7.1.0, GMP version 6.1.0, MPFR version
3.1.3-p4, MPC version 1.0.2, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
