[Bug c++/69820] New: Test was miss compiled with -O3 option.

["vsevolod.livinskij at frtk dot ru" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69820

            Bug ID: 69820
           Summary: Test was miss compiled with -O3 option.
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vsevolod.livinskij at frtk dot ru
  Target Milestone: ---

Created attachment 37689
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37689&action=edit
Reproducer.

Test case produces incorrect result with -O3 option. Everything works fine with
gcc version 5.3.1 20160212 (Revision=233387) and gcc version 4.9.4 20160212
(prerelease) (Revision=233387).

Output: 
> g++ -march=core-avx2 -O3 repr.cpp ; ./a.out
7540928331148314342
> g++ -march=core-avx2 -O2 repr.cpp ; ./a.out
18084857435860378664

GCC version:
> g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/export/users/vlivinsk/gcc-trunk/bin/../libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /export/users/gnutester/stability/svn/trunk/configure
--with-arch=corei7 --with-cpu=corei7 --enable-clocale=gnu --with-system-zlib
--enable-shared --with-demangler-in-ld --enable-cloog-backend=isl
--with-fpmath=sse --enable-checking=release --with-pkgversion=Revision=233012
--prefix=/export/users/gnutester/stability/work/trunk/64/install
--enable-languages=c,c++,fortran,java,lto
Thread model: posix
gcc version 6.0.0 20160130 (experimental) (Revision=233012)