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Re: [RS6000] cost SLOW_UNALIGNED_ACCESS
- From: Segher Boessenkool <segher at kernel dot crashing dot org>
- To: Alan Modra <amodra at gmail dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Tue, 2 Aug 2016 10:31:33 -0500
- Subject: Re: [RS6000] cost SLOW_UNALIGNED_ACCESS
- Authentication-results: sourceware.org; auth=none
- References: <20160802143506.GG20904@bubble.grove.modra.org>
On Wed, Aug 03, 2016 at 12:05:07AM +0930, Alan Modra wrote:
> As noted in the last patch, rs6000_rtx_costs ought to cost slow
> unaligned mems. This stops combine merging loads/stores with a
> mode-changing SET subreg, if the load/store in the subreg mode would
> be slow. Costing slow mems at 100 insns is just an order of magnitude
> estimate. (The alignment interrupt does cost quite a lot.
> Experiments on power8 with a misaligned lwarx showed taking the
> alignment interrupt cost roughly 300 insns.)
Okay for trunk. Do you have a testcase, too?
Segher