[Bug c++/31398] New: When O2 optimization option is set, the execution flow is changed.

[Bug c++/31398] New: When O2 optimization option is set, the execution flow is changed.

[windows2000d at gmail dot com]

Look out the output:
1. When no O2 option set, the output is:
   send out: 500000 Time: 1165250900
   192.168.1.1     100000

2. When -O2 option is set, the output is:
   192.168.1.1     send out: 500000 Time: 1165250934
   100000

It proves that the execution sequence has been changed. I think it's a block
bug, due to the reason that I can not control the execution flow, I had
disabled -O2 optimization, but that's a big performance discount to my program.


Source Code: 

#include <iostream>
#include <ctime>

float
CalcDownSpeed()
{
        // fake define
        int nStartTime = 100;
        int nTotalSendOut = 500000;
        int nLastCalc = 10000000;

        int now = time(NULL);

        std::cout << "send out: " << nTotalSendOut << " Time: " << now -
nLastCalc << std::endl;

        float downspeed = 100000;

        return downspeed;
}

int main()
{
        std::cout << "192.168.1.1" << "\t" << CalcDownSpeed() << std::endl;
        return 0;
}


-- 
           Summary: When O2 optimization option is set, the execution flow
                    is changed.
           Product: gcc
           Version: 3.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: windows2000d at gmail dot com
  GCC host triplet: Intel platform
GCC target triplet: Red hat linux, 2.6.9-5.EL


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31398

[Bug c++/31398] When O2 optimization option is set, the execution flow is changed.

[windows2000d at gmail dot com]

------- Comment #1 from windows2000d at gmail dot com  2007-03-30 11:47 -------
Created an attachment (id=13301)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13301&action=view)
The sample code show the bug.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31398

[Bug c++/31398] When O2 optimization option is set, the execution flow is changed.

[windows2000d at gmail dot com]

-- 

windows2000d at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |blocker


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31398

[Bug c++/31398] When O2 optimization option is set, the execution flow is changed.

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2007-03-30 13:03 -------
You are relying on undefined behavior.

*** This bug has been marked as a duplicate of 11751 ***


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31398