[Bug c++/60367] New: Default argument object is not getting constructed

["rob.desbois at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60367

            Bug ID: 60367
           Summary: Default argument object is not getting constructed
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rob.desbois at gmail dot com

Created attachment 32234
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32234&action=edit
Preprocessed, minimal testcase triggering unexpected behaviour

The attached minimal testcase has the following function with
default-constructed default argument:
    void do_something( foo f = {} )
    {
    std::cout << "default argument is at " << &f << std::endl;
    }

The constructor for foo outputs its address; I got the following output from a
single run:
    constructed foo @ 0x7ffff10bdb7f
    default argument is at 0x7ffff10bdb60

It shows that only 1 foo was constructed, and not at the same address as that
of the default argument. It's been a loooong week, but I can't see anything
wrong with the code. In the real code on which this was based, a segfault was
occurring when running the destructor of a foo that was move-constructed from
the default argument, because the underlying memory was seemingly
uninitialised.


build command & output
----------------------
[rob@localhost tests]$ g++ -v -save-temps -Wall -Wextra --std=c++0x
-fno-strict-aliasing -fwrapv -fno-aggressive-loop-optimizations
default-args-fail.cpp -o ./default-args-fail
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-isl=/builddir/build/BUILD/gcc-4.8.2-20131212/obj-x86_64-redhat-linux/isl-install
--with-cloog=/builddir/build/BUILD/gcc-4.8.2-20131212/obj-x86_64-redhat-linux/cloog-install
--with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.8.2 20131212 (Red Hat 4.8.2-7) (GCC) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-std=c++11'
'-fno-strict-aliasing' '-fwrapv' '-fno-aggressive-loop-optimizations' '-o'
'./default-args-fail' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/4.8.2/cc1plus -E -quiet -v -D_GNU_SOURCE
default-args-fail.cpp -mtune=generic -march=x86-64 -std=c++11 -Wall -Wextra
-fno-strict-aliasing -fwrapv -fno-aggressive-loop-optimizations
-fpch-preprocess -o default-args-fail.ii
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include-fixed"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../x86_64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2

/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/x86_64-redhat-linux
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/backward
 /usr/lib/gcc/x86_64-redhat-linux/4.8.2/include
 /usr/local/include
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-std=c++11'
'-fno-strict-aliasing' '-fwrapv' '-fno-aggressive-loop-optimizations' '-o'
'./default-args-fail' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/4.8.2/cc1plus -fpreprocessed
default-args-fail.ii -quiet -dumpbase default-args-fail.cpp -mtune=generic
-march=x86-64 -auxbase default-args-fail -Wall -Wextra -std=c++11 -version
-fno-strict-aliasing -fwrapv -fno-aggressive-loop-optimizations -o
default-args-fail.s
GNU C++ (GCC) version 4.8.2 20131212 (Red Hat 4.8.2-7) (x86_64-redhat-linux)
        compiled by GNU C version 4.8.2 20131212 (Red Hat 4.8.2-7), GMP version
5.1.2, MPFR version 3.1.2, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++ (GCC) version 4.8.2 20131212 (Red Hat 4.8.2-7) (x86_64-redhat-linux)
        compiled by GNU C version 4.8.2 20131212 (Red Hat 4.8.2-7), GMP version
5.1.2, MPFR version 3.1.2, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 36de953cba87bab1ad58280401e36d59
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-std=c++11'
'-fno-strict-aliasing' '-fwrapv' '-fno-aggressive-loop-optimizations' '-o'
'./default-args-fail' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
 as -v --64 -o default-args-fail.o default-args-fail.s
GNU assembler version 2.23.2 (x86_64-redhat-linux) using BFD version version
2.23.2
COMPILER_PATH=/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/:/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/:/usr/libexec/gcc/x86_64-redhat-linux/:/usr/lib/gcc/x86_64-redhat-linux/4.8.2/:/usr/lib/gcc/x86_64-redhat-linux/
LIBRARY_PATH=/usr/lib/gcc/x86_64-redhat-linux/4.8.2/:/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-Wextra' '-std=c++11'
'-fno-strict-aliasing' '-fwrapv' '-fno-aggressive-loop-optimizations' '-o'
'./default-args-fail' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/4.8.2/collect2 --build-id --no-add-needed
--eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker
/lib64/ld-linux-x86-64.so.2 -o ./default-args-fail
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/crt1.o
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/crti.o
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/crtbegin.o
-L/usr/lib/gcc/x86_64-redhat-linux/4.8.2
-L/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64 -L/lib/../lib64
-L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../..
default-args-fail.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/crtend.o
/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/crtn.o