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Re: [PATCH, rs6000] Add expansions for min/max vector reductions

From: Alan Lawrence <alan dot lawrence at arm dot com>
To: Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
Cc: "dje dot gcc at gmail dot com" <dje dot gcc at gmail dot com>
Date: Wed, 16 Sep 2015 16:29:22 +0100
Subject: Re: [PATCH, rs6000] Add expansions for min/max vector reductions
Authentication-results: sourceware.org; auth=none
References: <1442413689 dot 2896 dot 45 dot camel at gnopaine>

On 16/09/15 15:28, Bill Schmidt wrote:

2015-09-16  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

         * config/rs6000/altivec.md (UNSPEC_REDUC_SMAX, UNSPEC_REDUC_SMIN,
         UNSPEC_REDUC_UMAX, UNSPEC_REDUC_UMIN, UNSPEC_REDUC_SMAX_SCAL,
         UNSPEC_REDUC_SMIN_SCAL, UNSPEC_REDUC_UMAX_SCAL,
         UNSPEC_REDUC_UMIN_SCAL): New enumerated constants.
         (reduc_smax_v2di): New define_expand.
         (reduc_smax_scal_v2di): Likewise.
         (reduc_smin_v2di): Likewise.
         (reduc_smin_scal_v2di): Likewise.
         (reduc_umax_v2di): Likewise.
         (reduc_umax_scal_v2di): Likewise.
         (reduc_umin_v2di): Likewise.
         (reduc_umin_scal_v2di): Likewise.
         (reduc_smax_v4si): Likewise.
         (reduc_smin_v4si): Likewise.
         (reduc_umax_v4si): Likewise.
         (reduc_umin_v4si): Likewise.
         (reduc_smax_v8hi): Likewise.
         (reduc_smin_v8hi): Likewise.
         (reduc_umax_v8hi): Likewise.
         (reduc_umin_v8hi): Likewise.
         (reduc_smax_v16qi): Likewise.
         (reduc_smin_v16qi): Likewise.
         (reduc_umax_v16qi): Likewise.
         (reduc_umin_v16qi): Likewise.
         (reduc_smax_scal_<mode>): Likewise.
         (reduc_smin_scal_<mode>): Likewise.
         (reduc_umax_scal_<mode>): Likewise.
         (reduc_umin_scal_<mode>): Likewise.

You shouldn't need the non-_scal reductions. Indeed, they shouldn't be used ifthe _scal are present. The non-_scal's were previously defined as producing avector with one element holding the result and the other elements all zero, andthis was only ever used with a vec_extract immediately after; the _scal patternnow includes the vec_extract as well. Hence the non-_scal patterns aredeprecated / considered legacy, as per md.texi.

I proposed a patch to migrate PPC off the old patterns, but have forgotten toping it recently - last athttps://gcc.gnu.org/ml/gcc-patches/2014-12/msg01024.html ... (ping?!)


--Alan

Follow-Ups:
- Re: [PATCH, rs6000] Add expansions for min/max vector reductions
  - From: Bill Schmidt
- Re: [PATCH, rs6000] Add expansions for min/max vector reductions
  - From: Bill Schmidt

References:
- [PATCH, rs6000] Add expansions for min/max vector reductions
  - From: Bill Schmidt

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