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Re: [PATCH, rs6000] Document issues with permutes for analyze_swaps
- From: David Edelsohn <dje dot gcc at gmail dot com>
- To: Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 6 Oct 2014 10:47:29 -0400
- Subject: Re: [PATCH, rs6000] Document issues with permutes for analyze_swaps
- Authentication-results: sourceware.org; auth=none
- References: <1412546763 dot 2986 dot 126 dot camel at gnopaine>
On Sun, Oct 5, 2014 at 6:06 PM, Bill Schmidt
> I spent some time thinking about handling vperm instructions in the
> analyze_swaps pass, and convinced myself that it isn't necessarily wise
> to do so. At the least it will require adding a cost model to the pass
> to determine whether a computation involving permutes should be
> At this time I don't intend to implement this, but I want to record the
> information about how it could be done should it be deemed necessary.
> So this patch just adds a few paragraphs of documentation about the
> issue. No change in behavior intended.
> I've ensured that rs6000.c still compiles successfully on
> powerpc64le-unknown-linux-gnu. Is this ok for trunk?
> 2014-10-05 Bill Schmidt <firstname.lastname@example.org>
> * config/rs6000/rs6000.c (analyze_swaps commentary): Add
> discussion of permutes and why we don't handle them.