[Bug c/48418] Bit shift operator >>=

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48418

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

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

--- Comment #1 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-04-02 21:06:47 UTC ---
> int x=1000;
> x>>=(sizeof(int)<<3);
> 
> x is still 1000

The warning is clear:

t.cc: In function 'void foo()':
t.cc:4:22: warning: right shift count >= width of type

This invokes undefined behavior, any result is acceptable.

> In some cases bit shift operator used with variable (not constant) and compiler
> didnot show warning. My opinion is that result must be 0.

The compiler cannot warn about values computed only at run time.  If the shift
amount is >= width of type at run time, this also invokes undefined behavior.