[Bug c++/71964] New: Move constructor of std::set does not move allocator

[rbd at debian dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71964

            Bug ID: 71964
           Summary: Move constructor of std::set does not move allocator
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rbd at debian dot org
  Target Milestone: ---

My understanding of allocator aware containers (of which std::set is one) is
that moving the container should move the allocator.  However the following
code shows that std::set copies the allocator:

$ cat a.cpp
#include <set>
#include <memory>
#include <utility>
#include <stdio.h>

template<typename T>
struct my_allocator : public std::allocator<T>
{
        typedef std::true_type propagate_on_container_move_assignment;

        typedef size_t size_type;
        typedef T * pointer;
        typedef const T * const_pointer;

        template<typename _Tp1>
        struct rebind
        {
                typedef my_allocator<_Tp1> other;
        };

        my_allocator() : std::allocator<T>() { }

        my_allocator(const my_allocator & a) noexcept : std::allocator<T>(a)
        {
                fprintf(stderr, "copy constructor called\n");
        }

        my_allocator(const my_allocator && a) noexcept :
std::allocator<T>(std::move(a))
        {
                fprintf(stderr, "move constructor called\n");
        }
};

int main(int argc, char *argv[])
{
        std::set<int, std::less<int>, my_allocator<int> > x;
        std::set<int, std::less<int>, my_allocator<int> > y{ std::move(x) };

        return 0;
}

$ g++ --std=c++11 -v a.cpp
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
5.4.0-6ubuntu1~16.04.1' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --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 --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-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 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.1) 
COLLECT_GCC_OPTIONS='-std=c++11' '-v' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/5/cc1plus -quiet -v -imultiarch x86_64-linux-gnu
-D_GNU_SOURCE a.cpp -quiet -dumpbase a.cpp -mtune=generic -march=x86-64
-auxbase a -std=c++11 -version -fstack-protector-strong -Wformat
-Wformat-security -o /tmp/ccxdEpTy.s
GNU C++11 (Ubuntu 5.4.0-6ubuntu1~16.04.1) version 5.4.0 20160609
(x86_64-linux-gnu)
        compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR
version 3.1.4, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring duplicate directory "/usr/include/x86_64-linux-gnu/c++/5"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/5/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/5
 /usr/include/x86_64-linux-gnu/c++/5
 /usr/include/c++/5/backward
 /usr/lib/gcc/x86_64-linux-gnu/5/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/5/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
GNU C++11 (Ubuntu 5.4.0-6ubuntu1~16.04.1) version 5.4.0 20160609
(x86_64-linux-gnu)
        compiled by GNU C version 5.4.0 20160609, GMP version 6.1.0, MPFR
version 3.1.4, MPC version 1.0.3
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 54c46ecad36e047174be4f497c131a62
COLLECT_GCC_OPTIONS='-std=c++11' '-v' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 as -v --64 -o /tmp/cc9xwjYg.o /tmp/ccxdEpTy.s
GNU assembler version 2.26.1 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Ubuntu) 2.26.1
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/5/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/5/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-std=c++11' '-v' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/5/collect2 -plugin
/usr/lib/gcc/x86_64-linux-gnu/5/liblto_plugin.so
-plugin-opt=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
-plugin-opt=-fresolution=/tmp/ccAJN93Y.res -plugin-opt=-pass-through=-lgcc_s
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --sysroot=/
--build-id --eh-frame-hdr -m elf_x86_64 --hash-style=gnu --as-needed
-dynamic-linker /lib64/ld-linux-x86-64.so.2 -z relro
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crt1.o
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crti.o
/usr/lib/gcc/x86_64-linux-gnu/5/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/5
-L/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu
-L/usr/lib/gcc/x86_64-linux-gnu/5/../../../../lib -L/lib/x86_64-linux-gnu
-L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib
-L/usr/lib/gcc/x86_64-linux-gnu/5/../../.. /tmp/cc9xwjYg.o -lstdc++ -lm -lgcc_s
-lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/5/crtend.o
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crtn.o

$ ./a.out
copy constructor called

I tried with std::vector and std::list as got the the expected "move
constructor called".  Also gcc 4.8 std::set moves the allocator - the
regression seems to have occurred in gcc 4.9.