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[PATCH, i386]: Fine tune prefetchw emission (PR 77270)

From: Uros Bizjak <ubizjak at gmail dot com>
To: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
Cc: "Kumar, Venkataramanan" <Venkataramanan dot Kumar at amd dot com>, NightStrike StrikeNight <nightstrike at gmail dot com>
Date: Sun, 21 Aug 2016 21:06:08 +0200
Subject: [PATCH, i386]: Fine tune prefetchw emission (PR 77270)
Authentication-results: sourceware.org; auth=none

Hello!

Attached patch fine-tunes the condition when prefetchw write prefetch
insns are emitted. prefetchw is preferred for non-SSE2 K7 athlons
(this is covered by i386-prefetch.exp tests), on the other hand, SSE
prefetches are preferred for K8 targets, as measured and reported in
PR 77270.

For newer targets, PRFCHW cpuid bit is respected, and -march=native
correctly emits prefetchw, when PRFCHW cpuid bit is set. (on a related
note, PTA_PRFCHW should probably be set for amdfam10+ targets,
Venkataramanan is looking into this issue).

2016-08-21  Uros Bizjak  <ubizjak@gmail.com>

    PR target/77270
    * config/i386/i386.md (prefetch): When TARGET_PRFCHW or
    TARGET_PREFETCHWT1 are disabled, emit 3dNOW! write prefetches for
    non-SSE2 athlons only, otherwise prefer SSE prefetches.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Committed to mainline SVN.

Uros.

Attachment: p.diff.txt
Description: Text document

Follow-Ups:
- RE: [PATCH, i386]: Fine tune prefetchw emission (PR 77270)
  - From: Kumar, Venkataramanan

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