[Bug c++/16590] [3.4 regression] Incorrect execution when compiling with -O2

["bangerth at dealii dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From bangerth at dealii dot org  2004-07-16 15:39 -------
Confirmed. Here's a very fragile testcase (if you change a bit, the 
bug goes away): 
------------------------ 
extern "C" void abort(); 
 
struct iterator { 
    char * p; 
    int *dummy; 
}; 
 
static iterator pend(char * start) { 
  iterator p = {start, 0}; 
  if (p.p == start) p.p = start+5; 
  --p.p; 
  return p; 
} 
 
int main() { 
  char mem[4+1]; 
 
  if(pend(mem).p != mem+4) 
    abort (); 
} 
------------------------ 
g/x> /home/bangerth/bin/gcc-3.4-pre/bin/c++ x.cc ; ./a.out  
g/x> /home/bangerth/bin/gcc-3.4-pre/bin/c++ -O2 x.cc ; ./a.out  
Aborted 
 
The bug doesn't happen with 3.3.4 and mainline, but who knows whether this 
is due to a fix or just by chance. It's a regression in any case, so 
should be investigated, then we can see whether the same fix is 
necessary on other branches than 3.4.x as well. 
 
W. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |critical
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |wrong-code
      Known to fail|                            |3.4.0
      Known to work|                            |3.3.4 3.5.0
   Last reconfirmed|0000-00-00 00:00:00         |2004-07-16 15:39:46
               date|                            |
            Summary|Incorrect execution when    |[3.4 regression] Incorrect
                   |compiling with -O2          |execution when compiling
                   |                            |with -O2
   Target Milestone|---                         |3.4.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16590