[Bug c/38588] New: strict-aliasing error

[Bug c/38588] New: strict-aliasing error

[baisjing at yahoo dot com dot cn]

Hi:
  use gcc4.1.2 on x86_64/linux, for example:
 main()
{
   long long int a;
   double b;
   a=4607182418800017408;
   b=*(double *)&a;
   printf("%f\n",b);
}
if using -O0/-O1 optimization, the result is 1.000000;
but if using -O2/-O3 optimization,the result is 0.000000.
i have try to close -fno-strict-aliasing in -O2/-O3, the result will be same as
-O0/-O1.

so i think the strict-aliasing may have some bug!!!


-- 
           Summary: strict-aliasing error
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: baisjing at yahoo dot com dot cn


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38588

[Bug c/38588] strict-aliasing error

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2008-12-21 01:58 -------
No this is working as designed.  GCC does warn about this case.
t.c:6: warning: dereferencing type-punned pointer will break strict-aliasing
rules


Now in 4.4.0 and above, the same result will happen at -O1 and -O2 because of
another optimization that allows for the compiler to remove the alias violation
in the IR.

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


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38588