On Tue, Mar 01, 2016 at 05:55:07PM +0100, Michael Matz wrote:
> Hi,
>
> On Tue, 1 Mar 2016, Richard Biener wrote:
>
> > > What about the example I gave above? Is it unrealistic for compilers
> > > do ever do something like this, or is it just unlikely to gain much
> > > performance, or is it just that GCC does not do this today?
> >
> > GCC does not do this today with the exception of value-profiling. GCC
> > in other cases does not establish equivalences but only relations (a <
> > b, etc.) that are not a problem as far as I can see because those do not
> > allow to change expressions using a to use b.
>
> Made up example using relations:
>
> int32 a, b;
> a = (b >> 31) & 1;
>
> -->
>
> if (b < 0)
> a = 1;
> else
> a = 0;
>
> data-dep to control-dep and only relations :) (I think this is taken care
> of by Pauls wording, ignoring the fact that these aren't pointers anyway
> and hence don't carry a dependency through them, only onto them at max)
Agreed, these are not pointers, and therefore do not carry dependencies.
Thanx, Paul
