> > > For example, I have such fragment:
> > > for (j = 0; j < length; j++) {
> > >
> > > for (i = ip[j]; i <= ip[j+1]-1; i++) {
> > >
> > > b[ia[i]] = b[ia[i]] + a[i]*x[j];
> > >
> > > }
> > >
> > > }
> > >
> > > And I want to collect information only about array /b/. How can this be
> > > done?
> >
> > Short answer is, like this
> >
> > for (j = 0; j < length; j++) {
> >
> > for (i = ip[j]; i <= ip[j+1]-1; i++) {
> >
> > long ia_i = ia[i];
> > double tmp = a[i] * x[j]; // or whatever type it
> > is b[ia_i] += tmp;
> >
> > }
> >
> > }
>
The second version might be faster too. For the compiler to transform
the first version into the second version will require a lot of praying
to the gods of Common Subexpression Elimination and Alias Analysis.
J
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