[Bug c/45852] New: volatile structs are broken!

[regehr at cs dot utah.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45852

           Summary: volatile structs are broken!
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: reg...@cs.utah.edu
                CC: cheny...@cs.utah.edu


gcc should not be optimizing away the read from or write to this struct.

reg...@john-home:~$ current-gcc -v
Using built-in specs.
COLLECT_GCC=current-gcc
COLLECT_LTO_WRAPPER=/home/regehr/z/compiler-install/gcc-r164818-install/libexec/gcc/i686-pc-linux-gnu/4.6.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ../configure --with-libelf=/usr/local --enable-lto
--prefix=/home/regehr/z/compiler-install/gcc-r164818-install
--program-prefix=r164818- --enable-languages=c,c++
Thread model: posix
gcc version 4.6.0 20100930 (experimental) (GCC) 

reg...@john-home:~$ current-gcc -S -o - -O1 small.c 

        .file   "small.c"
        .text
        .globl  func_1
        .type   func_1, @function
func_1:
.LFB0:
        .cfi_startproc
        rep
        ret
        .cfi_endproc
.LFE0:
        .size   func_1, .-func_1
        .globl  g_18
        .data
        .align 4
        .type   g_18, @object
        .size   g_18, 4
g_18:
        .long   -6
        .ident  "GCC: (GNU) 4.6.0 20100930 (experimental)"
        .section        .note.GNU-stack,"",@progbits

reg...@john-home:~$ cat small.c

struct S1
{
  int f0;
};

volatile struct S1 g_18 = { -6 };

void
func_1 (void)
{
  g_18 = g_18;
}