Messages in this thread | | | Date | Wed, 20 May 2015 07:03:43 -0700 | From | "Paul E. McKenney" <> | Subject | Re: Compilers and RCU readers: Once more unto the breach! |
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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@linux.vnet.ibm.com> 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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