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RE: RFC: GIMPLE tuples. Design and implementation proposal
On Tue, 2007-04-10 at 20:39 +0100, Dave Korn wrote:
> On 10 April 2007 20:02, Diego Novillo wrote:
>
> >> The obvious way to make the proposed tuples position independent would
> >> be to use array offsets rather than pointers. This has the obvious
> >> disadvantage that every access through a pointer requires an
> >> additional memory reference. On the other hand, it has some other
> >> advantages: it may no longer be necessary to keep a previous pointer
> >
> > I doubt this. We had started with single-linked chains but reverse
> > traversals do occur, and they were very painful and slow.
>
> Reverse-traversing an array really isn't all that painful or slow!
I don't think we're talking about traversing an array, but rather a
linked list which uses an array index rather than a pointer. You don't
want to go moving around array slices everytime you add instructions.
You will still need a PREV index if you want to avoid finding prev's by
starting at the beginning of a BB and scanning forward. We've already
done this in tree-ssa and it is a big loss on passes which work on the
instruction stream in reverse.
Andrew