[Bug rtl-optimization/70602] New: wrong code at -O1 and above on x86_64-linux-gnu in 32-bit mode (and at -Os only in 64-bit mode)

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70602

            Bug ID: 70602
           Summary: wrong code at -O1 and above on x86_64-linux-gnu in
                    32-bit mode (and at -Os only in 64-bit mode)
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The current gcc trunk miscompiles the following code on x86_64-linux-gnu at -O1
and above in the 32-bit mode and at -Os only in the 64-bit mode.

This is a regression from 5.3.x. 


$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 6.0.0 20160408 (experimental) [trunk revision 234826] (GCC) 
$ 
$ gcc-trunk -m32 -O0 small.c; ./a.out
$ gcc-5.3 -m32 -O1 small.c; ./a.out
$                  
$ gcc-trunk -m32 -O1 small.c  
$ ./a.out
Segmentation fault (core dumped)
$ 


-----------------------------------------


#pragma pack(1)
struct S0
{
  int f0:1;
  int f1:20;
};

int a, b, c;

int
main ()
{
  for (; a < 1; a++)
    {
      struct S0 e[] = { {0, 9}, {0, 9}, {0, 9}, {0, 0}, {0, 9}, {0, 9}, {0, 9}, 
                        {0, 0}, {0, 9}, {0, 9}, {0, 9}, {0, 0}, {0, 9}, {0, 9}, 
                        {0, 9}, {0, 0}, {0, 9}, {0, 9}, {0, 9}, {0, 0}, {0, 9}
};
      b = b || e[0].f0;
      c = e[0].f1;
    }
  return 0;
}