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Re: [patch] Fix computing address costs in ivopts
- From: David Edelsohn <dje at watson dot ibm dot com>
- To: Zdenek Dvorak <dvorakz at suse dot cz>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Fri, 19 Nov 2004 17:55:47 -0500
- Subject: Re: [patch] Fix computing address costs in ivopts
- References: <200411190545.iAJ5jfD29606@makai.watson.ibm.com>
The use of target_spill_cost in tree-ssa-loop-ivopts.c looks
questionable to me. It appears that the algorithm adds the cost of a
spill to many cost computations without any analysis of the need for a
spill. That might be correct for a register-starved architecture, but
exagerates the costs on architectures without that constraint.
In the generated assembly for 301.apsi, the current code with the
inflated costs appears to be using more registers, causing more spills and
more increments of the additional IVs.