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Re: Source Code for Profile Guided Code Positioning
- From: Maxim Ostapenko <m dot ostapenko at partner dot samsung dot com>
- To: Sriraman Tallam <tmsriram at google dot com>, Yury Gribov <y dot gribov at samsung dot com>
- Cc: vivek pandya <vivekvpandya at gmail dot com>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Pavel Kopyl <p dot kopyl at samsung dot com>
- Date: Thu, 21 Jan 2016 14:41:36 +0300
- Subject: Re: Source Code for Profile Guided Code Positioning
- Authentication-results: sourceware.org; auth=none
- References: <CAHYgpoLhosGmQZJb6OHiD6SmJ6Y_BTuEh_8Pj6z1DeHp_b0C4A at mail dot gmail dot com> <56992CFC dot 7050207 at samsung dot com> <CAHYgpoJ9mqxcAiLLrAdPyiwmzms+Vcz3yk9f2uN_39AjHFuqhw at mail dot gmail dot com> <56993187 dot 7050409 at samsung dot com> <CAAs8Hmz7GM07cA-kxGDb6xkTKn1G05b7DJAi-p=JiNAnvbLHLw at mail dot gmail dot com>
On 20/01/16 10:08, Sriraman Tallam wrote:
On Fri, Jan 15, 2016 at 9:51 AM, Yury Gribov <email@example.com> wrote:
On 01/15/2016 08:44 PM, vivek pandya wrote:
Thanks Yury for
https://gcc.gnu.org/ml/gcc-patches/2011-09/msg01440.html this link.
It implements procedure reordering as linker plugin.
I have some questions :
1 ) Can you point me to some documentation for "how to write plugin
for linkers " I am I have not seen doc for structs with 'ld_' prefix
(i.e defined in plugin-api.h )
2 ) There is one more algorithm for Basic Block ordering with
execution frequency count in PH paper . Is there any implementation
available for it ?
Quite frankly - I don't know (I've only learned about Google implementation
I've added Sriram to maybe comment.
Sorry for the late response. The google/gcc_4_9 branch has the source
of function reordering linker Plugin. It is available in the
function_reordering_plugin directory under the top level gcc
The function reordering plugin constructs a callgraph and uses profile
information to do a Pettis Hansen style function reordering. This
plugin does not do basic block re-ordering.
There is no documentation as such that I am aware of to write a linker
plugin. Here is a very brief overview. The linker calls the
plugin's "onload" function when registering the plugin and the plugin
inturn can register two call-backs with the linker, "claim_file_hook"
and the "all_symbols_read_hook". "claim_file_hook" is called for
each object file that the linker prcesses and the
"all_symbols_read_hook" is called after all the symbols have been read
by the linker. These are just two different interesting points in the
course of a link.
The plugin can also get handles to linker functions like
"get_input_section_name" which it can use to process sections given
their handle. You can also check the gold linker tests for simpler
Very interesting, thank you! Actually, I see -freorder-functions switch
in GCC that allows perform pretty the same optimizations in linker,
right? Just wondering if you achieved to get performance improvements
against -freorder-functions with your plugin.