[Bug c++/26767] New: Optimization level -O3 changes the program behavior

[Bug c++/26767] New: Optimization level -O3 changes the program behavior

[mor_gopal at yahoo dot com]

Following program generates different outputs for -O1 and -O3 optimization
levels.

#include <stdio.h>

typedef struct _airInfo{
        unsigned int craftNo : 16;
        unsigned int onAir:1;
        unsigned int numCrew:2;
        unsigned int numPassenger:2;
        unsigned int onLand:1;
        unsigned int fuelTank:2;
        unsigned int height: 8;
} airInfo_t ;

#pragma pack(1)
typedef struct _atmosphere {
        int temp:24;
        int humidity:24;
        int pressure:24;
        int altitude:24;
}atmosphere_t;

typedef struct _mixedInfo {
        airInfo_t    ai;
        atmosphere_t atm;
}mixedInfo_t;

#pragma pack()

int main() {
        mixedInfo_t mi ;

        mi.ai.height       = 17;
        mi.ai.craftNo      = 1;
        mi.ai.onAir        = 0;
        mi.ai.numCrew      = 2;
        mi.ai.numPassenger = 2;
        mi.ai.onLand       = 0;
        mi.ai.fuelTank     = 0;

        printf("ai in num = %u\n", (*((unsigned int *)(&mi.ai)))) ;
        return 0 ;
}

// Output from program when compiled with -O1
$ g++ -O1 test1.cxx ; ./a.out 
ai in num = 286523393

// Output from program when compiled with -O3
$ g++ -O3 test1.cxx ; ./a.out 
ai in num = 1310720


-- 
           Summary: Optimization level -O3 changes the program behavior
           Product: gcc
           Version: 3.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mor_gopal at yahoo dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26767

[Bug c++/26767] Optimization level -O3 changes the program behavior

[mor_gopal at yahoo dot com]

------- Comment #1 from mor_gopal at yahoo dot com  2006-03-20 10:00 -------
Following details are added.
// g++ version info
$ g++ -v
Reading specs from /usr/lib/gcc/x86_64-redhat-linux/3.4.3/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--disable-checking --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-java-awt=gtk --host=x86_64-redhat-linux
Thread model: posix
gcc version 3.4.3 20050227 (Red Hat 3.4.3-22.1)

// System info
$uname -a
Linux NEW1_dev_opteron 2.6.9-11.EL #1 Fri May 20 18:15:25 EDT 2005 x86_64
x86_64 x86_64 GNU/Linux


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26767

[Bug c++/26767] Optimization level -O3 changes the program behavior

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2006-03-20 10:08 -------


*** This bug has been marked as a duplicate of 21920 ***


-- 

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=26767

[Bug c++/26767] Optimization level -O3 changes the program behavior

[mor_gopal at yahoo dot com]

------- Comment #3 from mor_gopal at yahoo dot com  2006-03-22 05:25 -------
The following keywords are added to this page, so that developers facing
similar problem can search (hopefully) this page using search engines.

bitfield problem bug gcc g++ optimization bit field strict aliasing ISO C


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26767