[PATCH] D36388: [X86][SandyBridge] Additional updates to the SNB instructions scheduling information

[Haber, Gadi via llvm-commits]

Code alignment in X86 is indeed an issue.
There are currently two pending reviews for patches that start providing a fix for this.
The reviews are in a pending state for quite some time now.

The 1st patch: https://reviews.llvm.org/D34393 is an NFC that provides the needed infrastructure for adding padding code aimed only for performance stability.

The 2nd patch: https://reviews.llvm.org/D34396 uses the above infrastructure to handle the 1st case of regression caused by branches to same target addresses which can cause misprediction – resolved by appropriate code padding.

From: Chandler Carruth [mailto:chandlerc at gmail.com]
Sent: Wednesday, August 16, 2017 13:05
To: reviews+D36388+public+604ca58e3311abc8 at reviews.llvm.org; Gadi Haber via Phabricator <reviews at reviews.llvm.org>; Haber, Gadi <gadi.haber at intel.com>; Rackover, Zvi <zvi.rackover at intel.com>; llvm-dev at redking.me.uk; chandlerc at gmail.com; Breger, Igor <igor.breger at intel.com>; Zuckerman, Michael <michael.zuckerman at intel.com>; craig.topper at gmail.com; Musa, Ayman <ayman.musa at intel.com>; dimitry at andric.com
Cc: llvm-commits at lists.llvm.org
Subject: Re: [PATCH] D36388: [X86][SandyBridge] Additional updates to the SNB instructions scheduling information

It does look like code alignment. =/ But we're still not sure how to fix it. =[ The code alignment issues we're hitting on Sandybridge and Haswell is getting ... insane.

On Wed, Aug 16, 2017 at 3:03 AM Gadi Haber via Phabricator via llvm-commits <llvm-commits at lists.llvm.org<mailto:llvm-commits at lists.llvm.org>> wrote:
gadi.haber added a comment.

20% is high. Try to verify if this is not code alignment related.


Repository:
  rL LLVM

https://reviews.llvm.org/D36388



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