Re: Compilers and RCU readers: Once more unto the breach!

[Paul E. McKenney]

On Wed, May 20, 2015 at 02:44:30PM +0100, Ramana Radhakrishnan wrote:
> 
> 
> On 20/05/15 14:37, David Howells wrote:
> >Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> >
> >>I was thinking of "y" as a simple variable, but if it is something more
> >>complex, then the compiler could do this, right?
> >>
> >>	char *x;
> >>
> >>	y;
> >>	x = z;
> >
> >Yeah.  I presume it has to maintain the ordering, though.
> 
> The scheduler for e.g. is free to reorder if it can prove there is
> no dependence (or indeed side-effects for y) between insns produced
> for y and `x = z'.

So for example, if y is independent of z, the compiler can do the
following:

	char *x;

	x = z;
	y;

But the dependency ordering is still maintained from z to x, so this
is not a problem.

Or am I missing something subtle here?

							Thanx, Paul

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