[Bug tree-optimization/22000] New: Read from volatile member of struct is optimized away

["rpedersen at atmel dot com" <gcc-bugzilla at gcc dot gnu dot org>]

In the code below the read "(int)ptr->b;" gets optimized away.
It appears to be optimized away before the RTL stages, so I guess
it must be because of the tree optimalisation.

I think that the C standard says C that the "name" of variable 
becomes an rvalue (the actual value) thus requires that the variable 
is accessed.

Code:

struct test {
  volatile int a;
  volatile int b;
};

int main(int argc, char *argv[]){

 struct test *ptr = (struct test *)0x10000000;

 ptr->b = 10;
 (int)ptr->b;

 return 1;
}

-- 
           Summary: Read from volatile member of struct is optimized away
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rpedersen at atmel dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: arm-unknown-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22000