[Bug c++/80129] New: wrong code with ternary struct assignment to const

[richard.gcc at rhughes dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80129

            Bug ID: 80129
           Summary: wrong code with ternary struct assignment to const
           Product: gcc
           Version: 6.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: richard.gcc at rhughes dot net
  Target Milestone: ---

$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/6/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 6.3.0-6'
--with-bugurl=file:///usr/share/doc/gcc-6/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-6 --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 --disable-browser-plugin --enable-java-awt=gtk
--enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-6-amd64/jre
--enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-6-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-6-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--with-target-system-zlib --enable-objc-gc=auto --enable-multiarch
--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 6.3.0 20170205 (Debian 6.3.0-6)

$ cat foo.cc
struct pair
{
    bool first;
    unsigned second;
};

static pair ext()
{
    return {false, 0u};
}

static void test(bool b)
{
    const pair x = b ? pair{true, 64u} : ext();
    if (x.first)
        __builtin_abort();
}

int main()
{
    test(false);
}

$ g++ -O0 -std=gnu++11 foo.cc
$ ./a.out
Segmentation fault

$ g++ -O1 -std=gnu++11 foo.cc
$ ./a.out
Aborted

Expected result: Completion with no output

Also reproduced on 4.9.2 and 4.7.2 (Debian Jessie and Wheezy)


Note that an earlier, less-reduced test case was:

#include <stdlib.h>
#include <utility>

__attribute__((noinline)) static std::pair<bool,unsigned> ext()
{
    std::pair<bool,unsigned> r(false, 0u);
    return r;
}

static void test(bool b)
{
    const std::pair<bool,unsigned> x = b ? std::make_pair(true, 64u) : ext();
    if (x.first)
        abort();
}

int main()
{
    test(false);
}

This worked on previous versions but (presumably due to libstdc++ changes,
maybe constexpr additions?) aborts at -O1 and above with gcc 6. It also works
when compiled with -std=gnu++03