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Re: Dropping of old loop optimizer
- From: <tm_gccmail at mail dot kloo dot net>
- To: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>
- Cc: gcc at gcc dot gnu dot org, m dot hayes at elec dot canterbury dot ac dot nz, rth at redhat dot com,law at redhat dot com, dan at dberlin dot org, jh at suse dot cz
- Date: Wed, 26 Feb 2003 19:16:42 -0800 (PST)
- Subject: Re: Dropping of old loop optimizer
On Thu, 27 Feb 2003, Zdenek Dvorak wrote:
> Hello,
>
> > > I would like to know your opinion on this subject. Why I believe old
> > > loop optimizer should be dropped as soon as possible:
...
> > The "old" loop optimizer does BIV-to-GIV flattening which is important on
> > processors without double-register addressing modes such as the SH,
> > MIPS16, Thumb, and a few others.
> >
> > Does the new loop optimizer support this feature?
>
> no; as I said, anything related to iv's is problem.
Then I personally (and probably most users of the SH) would prefer the old
loop optimizer be retained until the new loop optimizer supports BIV
flattening.
This one optimization is extremely important; if we don't have it, the
compiler will generate a move/shift/add operation for each IV-related
load/store within the loop, which kills performance.
> Zdenek
Toshi