On 5/4/23 15:37, Qing Zhao wrote:
On May 4, 2023, at 9:05 AM, Martin Liška <mli...@suse.cz> wrote:
On 5/4/23 14:54, Qing Zhao wrote:
On May 4, 2023, at 4:30 AM, Martin Liška <mli...@suse.cz> wrote:
On 5/3/23 21:10, Qing Zhao via Gcc-patches wrote:
Hi, Jan,
You added the following patch into gcc10:
From 34fbe3f0946f88828765184ed6581bda62cdf49f Mon Sep 17 00:00:00 2001
From: Jan Hubicka <hubi...@ucw.cz>
Date: Thu, 5 Dec 2019 19:12:51 +0100
Subject: [PATCH] cgraphclones.c (localize_profile): New function.
* cgraphclones.c (localize_profile): New function.
(cgraph_node::create_clone): Use it for partial profiles.
* common.opt (fprofile-partial-training): New flag.
* doc/invoke.texi (-fprofile-partial-training): Document.
* ipa-cp.c (update_profiling_info): For partial profiles do not
set function profile to zero.
* profile.c (compute_branch_probabilities): With partial profile
watch if edge count is zero and turn all probabilities to guessed.
(compute_branch_probabilities): For partial profiles do not apply
profile when entry count is zero.
* tree-profile.c (tree_profiling): Only do value_profile_transformations
when profile is read.
My question is:
Hello.
Why would anybody backport such change to unsupported code-stream of GCC 8?
Generally speaking, I discourage from doing that.
Yes, I agree.
However, many users still use GCC8 right now, and some of them are asking for
more performance
from PGO recently. That’s the reason I am studying this right now.
I understand there are products that are based on GCC8, but as the branch is
officially unsupported, I don't
see a reason to backport a new feature from newer release. It's just asking for
troubles. If your clients are
interested in more performance, then they should use a recent supported release.
We are trying to persuade them to use newer GCC, but it’s quite hard...
From my understanding, -fprofile-partial-training is one important option for
PGO performance.
I don't think so, speed benefit would be rather small I guess.
I saw some articles online to introduce this option for gcc10,
https://documentation.suse.com/sbp/all/html/SBP-GCC-10/index.html#sec-gcc10-pgo
Hi.
Ah, I see.
And also based on my previous experience in Studio compiler, I guess that this
one might have
Some good performance impact on PGO. Is there any old performance data on this
option? (I cannot find online)
Maybe Honza can chime in here? Or Martin who is the author of the white paper.
Martin
thanks.
Qing
I’d like
to see any big technique difficult to prevent it from being back ported to GCC8.
There might be of course some patch dependencies and I don't see a point why
should we waste
time with that.
Cheers,
Martin
Thanks.
Qing
Martin
Can this patch be back ported to GCC8 easily? I am wondering any significant
Change between GCC8 and GCC10 that might make the backporting very hard>
Thanks a lot for your help.
Qing
