Peter Zijlstra wrote:
quoted text
> Not sure - I think all barrier clobber the full register and memory set.
> So if you access a variable after a barrier it will have to issue a
> load.
>   

IIRC a barrier only clobbers memory.  gcc must reload a variable from 
memory unless it can prove the variable's address has not escaped anywhere.

So:

void f()
{
    int v;

    v = g();
    barrier();
    do_domething_with(v);
}

Need not reload v from memory (indeed, v can be in a register for its 
entire lifetime), but

void f()
{
    int v;

    v = g();
    h(&v);
    barrier();
    do_domething_with(v);
}
 
Will force v into memory, and reload it after the barrier.

-- 
error compiling committee.c: too many arguments to function

--
unsubscribe notice
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/