[Bug c++/82789] New: Invalid code generated for std::array element-wise processing with -O3

[nazarenkoal at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82789

            Bug ID: 82789
           Summary: Invalid code generated for std::array element-wise
                    processing with -O3
           Product: gcc
           Version: lto
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nazarenkoal at gmail dot com
  Target Milestone: ---

Version:
$ gcc --version
gcc (Ubuntu 7.2.0-8ubuntu3) 7.2.0

Not reproduced on:
gcc-6 (Ubuntu 6.4.0-8ubuntu1) 6.4.0 20171010
gcc-5 (Ubuntu 5.5.0-1ubuntu1) 5.4.1 20171010

OS:
$ lsb_release -a
LSB Version:   
core-9.20160110ubuntu5-amd64:core-9.20160110ubuntu5-noarch:security-9.20160110ubuntu5-amd64:security-9.20160110ubuntu5-noarch
Distributor ID: Ubuntu
Description:    Ubuntu 17.10
Release:        17.10
Codename:       artful

Commandline:
gcc -DNDEBUG -O3 ./test_opt_2.cpp -o ./test_opt_2 -std=c++14 -lstdc++

Code:
#include <array>
#include <iostream>

template <typename A>
A l_and_r( A const & l, A const & r )
{
    A res = {0};

    for ( unsigned i=0; i<l.size(); ++i )
    {
        res[ i ] = l[ i ] & r[ i ];
    }

    return res;
}

template <typename A>
__attribute__ ((noinline)) 
A noopt_proxy( A const & a )
{
    return A(a);
}

int main ()
{
    std::array<unsigned char, 4> l = {0x01, 0x02, 0x04, 0x08 };
    std::array<unsigned char, 4> r = {0x2f, 0x07, 0x0f, 0x1f };

    auto ret_1 = l_and_r( noopt_proxy(l), noopt_proxy(r) );
    std::cout << "l_and_r( l, r ): " << std::hex << (int)ret_1[0] << " "
<<(int)ret_1[1] << " " << (int)ret_1[2] << " " << (int)ret_1[3] << std::endl;

    return 0;
}

Program output with -O0, -O1, -O2
l_and_r( l, r ): 1 2 4 8

Program output with -O3
l_and_r( l, r ): 2f 2 4 8