[Bug c++/55993] [C++11] derived-to-base conversion fails in constant expression

["splinterofchaos at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55993

splinterofchaos at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |splinterofchaos at gmail dot com

--- Comment #11 from splinterofchaos at gmail dot com ---
I still get an error with 4.9 when using one of the less reduced cases,
although not when using the test cases in that patch.


#include <tuple>
struct A {};
constexpr auto t = std::get<0>( std::make_tuple( A(), A() ) );


$ g++ test.cpp -std=c++14 -Wall -Wextra; and ./a.out; echo $status
test.cpp:3:61:   in constexpr expansion of ‘std::get<0ul, {A, A}>((* &
std::make_tuple(_Elements&& ...) [with _Elements = {A, A}]((* & A()))))’
/usr/include/c++/4.9/tuple:774:44:   in constexpr expansion of ‘std::get<0ul,
{A, A}>((* & __t))’
/usr/include/c++/4.9/tuple:757:40:   in constexpr expansion of
‘std::__get_helper<0ul, A, {A}>((*(std::_Tuple_impl<0ul, A, A>*)(& __t)))’
/usr/include/c++/4.9/tuple:744:60:   in constexpr expansion of
‘std::_Tuple_impl<_Idx, _Head, _Tail ...>::_M_head<0ul, A, {A}>((* & __t))’
test.cpp:3:61: error: ‘(std::_Head_base<0ul, A, true>*)(& std::tuple<A, A>())’
is not a constant expression
 constexpr auto t = std::get<0>( std::make_tuple( A(), A() ) );


$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.9/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.9.1-16ubuntu6'
--with-bugurl=file:///usr/share/doc/gcc-4.9/README.Bugs
--enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.9 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.9 --libdir=/usr/lib --enable-nls
--with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-vtable-verify
--enable-plugin --with-system-zlib --disable-browser-plugin
--enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.9-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.9.1 (Ubuntu 4.9.1-16ubuntu6)
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From: "dcb314 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/64570] error: non-trivial conversion at assignment
Date: Thu, 26 Feb 2015 15:54:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idd570

--- Comment #3 from David Binderman <dcb314 at hotmail dot com> ---
(In reply to Richard Biener from comment #2)
> Fails everywhere, 4.6 rejects the testcase.  Looks more like a C++ frontend
> issue to me.

Still goes wrong over a month later with trunk dated 20150225.