On Thu, Dec 05, 2013 at 10:50:42AM +0100, Ingo Molnar wrote:
>
> * Paul E. McKenney <[email protected]> wrote:
>
> > + (*) The compiler is within its rights to reload a variable, for example,
> > + in cases where high register pressure prevents the compiler from
> > + keeping all data of interest in registers. The compiler might
> > + therefore optimize the variable tmp out of our previous example:
> > +
> > + while (tmp = a)
> > + do_something_with(tmp);
> > +
> > + This could result in the following code, which is perfectly safe in
> > + single-threaded code, but can be fatal in concurrent code:
> > +
> > + while (a)
> > + do_something_with(a);
> > +
> > + For example, the optimized version of this code could result in
> > + passing a zero to do_something_with() in the case where the variable
> > + a was modified by some other CPU between the "while" statement and
> > + the call to do_something_with().
>
> Nit: I guess references to variable names such as 'a' should be quoted
> (same for 'tmp', 'b', etc):
>
> For example, the optimized version of this code could result in
> passing a zero to do_something_with() in the case where the variable
> 'a' was modified by some other CPU between the "while" statement and
> the call to do_something_with().
>
> which makes reading it less ambiguous and more fluid IMO. This
> observation applies to the whole document as 'a' is used in many
> places.
Good point, fixed.
Thanx, Paul
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