Re: IVOPT improvement patch

[Toon Moene <toon at moene dot org>]

On 05/12/2010 12:31 AM, Xinliang David Li wrote:

> On Tue, May 11, 2010 at 2:52 PM, Toon Moene<toon@moene.org>  wrote:

> > Does this also take care of induction variables of the form of:
> >
> > inv * iv + inv + const
> >
> > ?
> >
> > This was one we had to "deal with" in the second half of the '90s, as a
> > result of Fortran arrays being (by default) 1-based instead of 0-based.

> The answer depends:
>
> For this linear address expression:  inv1*iv + inv2 + const
>
> if inv1 is not compile time constant (or too big one), the cost of
> expressing it using this iv is 'infinite' in the current
> implementation, which means this expression will either be strength
> reduced (to its own iv candidate) or expressed using another iv with
> stride == inv1.  If inv1 is a constant but not one of the multiplier
> allowed in the target address, the cost of expressing is also high,
> but the final expression may end up in this form depending on other
> cost.
>
> And yes if the final expression is in this form, the reassociation
> will make the memory op into MEM_REF (inv2 + const, iv, inv1).

Thanks - that answers all my questions.

Kind regards,

--
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