[Bug middle-end/67120] New: wrong code for volatile pointers at -O1 and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67120

            Bug ID: 67120
           Summary: wrong code for volatile pointers at -O1 and above on
                    x86_64-linux-gnu
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          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 both 32-bit and 64-bit modes. 

This is a regression from 5.1.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-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 6.0.0 20150804 (experimental) [trunk revision 226592] (GCC) 
$ 
$ gcc-trunk -O0 small.c; ./a.out
$ gcc-5.1 -O1 small.c; ./a.out
$ 
$ gcc-trunk -O1 small.c
$ ./a.out
Aborted (core dumped)
$ 


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


volatile int *volatile *a;
static volatile int *volatile **b = &a;

int
main ()
{
  volatile int *volatile c;
  *b = &c;

  if (a != &c) 
    __builtin_abort (); 

  return 0;
}