https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91058
Bug ID: 91058
Summary: Crash involving std::variant, std::visit, templates,
and static constexpr
Product: gcc
Version: 7.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: tom.smeding at gmail dot com
Target Milestone: ---
Created attachment 46545
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46545&action=edit
Preprocessed output of the code using GCC 7.4.0
In GCC 7.4.0 in C++17 mode, the following code crashes the compiler with a
segmentation fault:
#include <variant>
class some_class
{
public:
void encode() const {}
};
// This template is necessary to trigger the bug.
template <class encoder_t>
void process() noexcept
{
// This variable needs to be both static and constexpr to trigger the
bug.
static constexpr some_class magic;
// The useless visit here is necessary to trigger the bug.
std::visit([](auto &&key) {
// This encode function must be a member function to trigger the
bug.
magic.encode();
}, std::variant<int>{});
}
// Instantiate the template above
template void process<int>() noexcept;
In particular, if the attachment is called a.cpp and 'g++' refers to the C++
frontend of GCC 7.4.0, the following command crashes:
g++ -std=c++17 a.cpp
The compiler output is as follows:
a.cpp: In instantiation of ‘process()::<lambda(auto:1&&)> [with auto:1 = int;
encoder_t = int]’:
/usr/include/c++/7/variant:1252:44: required from ‘constexpr decltype(auto)
std::visit(_Visitor&&, _Variants&& ...) [with _Visitor = process() [with
encoder_t = int]::<lambda(auto:1&&)>; _Variants = {std::variant<int>}]’
a.cpp:16:15: required from ‘void process() [with encoder_t = int]’
a.cpp:23:30: required from here
a.cpp:18:21: internal compiler error: Segmentation fault
magic.encode();
~~~~~~~~~~~~^~
Please submit a full bug report,
with preprocessed source if appropriate.
See <file:///usr/share/doc/gcc-7/README.Bugs> for instructions.
Platform: stock Ubuntu 18.04.2
'g++ -v' output:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
7.4.0-1ubuntu1~18.04.1' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04.1)
