[Bug c/39330] Bad program bahavior with -O2 optimization in plain C

[ebotcazou at gcc dot gnu dot org]

------- Comment #4 from ebotcazou at gcc dot gnu dot org  2009-03-01 08:07 -------
> There is a bug in the gcc compiler for the C code that changes the behavior of
> a simple program with -O2 optimizations, but not with -O1 or -O0.

-O2 enables -fstrict-aliasing so the code must be written in ISO C as far as
aliasing is concerned, otherwise the behavior is undefined.

Your code is not written in ISO C:

#define VL(X) (*((uint32*)(X)))

is a direct violation of ISO C.  See the -fstrict-aliasing entry in the GCC
manual or the ISO standard.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39330