* LTO and adding extra information from extra passes
@ 2009-09-02 20:06 Basile STARYNKEVITCH
2009-09-02 20:18 ` Richard Guenther
2009-09-03 12:50 ` Diego Novillo
0 siblings, 2 replies; 6+ messages in thread
From: Basile STARYNKEVITCH @ 2009-09-02 20:06 UTC (permalink / raw)
To: GCC Mailing List
Hello All,
My feeling is that the Link Time Optimisation (LTO) effort should be
soon (=is expected to be, or is already) merged inside GCC trunk (future
4.5).
Several years ago, I asked if there is any possibility for an additional
pass to profit of LTO infrastructure to add some extra data into LTO
stuff (which is probably DWARF related inside ELF object files, but I am
not sure) and to retrieve it. I remember that the answer was of course not.
Now we have a working plugin infrastructure, and I believe it would be
very sensible for some plugin to register passes which add persistent
information (as does LTO with its Gimple related representation) into
object files and to retrieve it.
Is there is still a major objection against that, or is there some API
usable from plguins for that purpose?
Even the mere ability to add inside the LTO data a chunk of bytes
identified by the name of the plugin would be great. Of course, some
more features could be welcome (e.g. the ability to add data specific to
each compiled function or cgraph_node or whatever, or even to each
gimple...).
I could imagine that a plugin might be interested in adding say some
information into the object file (when ordinary compilation for LTO of a
single compilation unit happens) and later retrieve it (when link time
optimisation occur merging several object files.)
A dream case example would be a plugin for whole program static analysis.
Regards.
--
Basile STARYNKEVITCH http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
8, rue de la Faiencerie, 92340 Bourg La Reine, France
*** opinions {are only mines, sont seulement les miennes} ***
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: LTO and adding extra information from extra passes
2009-09-02 20:06 LTO and adding extra information from extra passes Basile STARYNKEVITCH
@ 2009-09-02 20:18 ` Richard Guenther
2009-09-02 20:24 ` Basile STARYNKEVITCH
2009-09-03 12:50 ` Diego Novillo
1 sibling, 1 reply; 6+ messages in thread
From: Richard Guenther @ 2009-09-02 20:18 UTC (permalink / raw)
To: Basile STARYNKEVITCH; +Cc: GCC Mailing List
On Wed, Sep 2, 2009 at 10:06 PM, Basile
STARYNKEVITCH<basile@starynkevitch.net> wrote:
> Hello All,
>
> My feeling is that the Link Time Optimisation (LTO) effort should be soon
> (=is expected to be, or is already) merged inside GCC trunk (future 4.5).
>
> Several years ago, I asked if there is any possibility for an additional
> pass to profit of LTO infrastructure to add some extra data into LTO stuff
> (which is probably DWARF related inside ELF object files, but I am not sure)
> and to retrieve it. I remember that the answer was of course not.
>
> Now we have a working plugin infrastructure, and I believe it would be very
> sensible for some plugin to register passes which add persistent information
> (as does LTO with its Gimple related representation) into object files and
> to retrieve it.
>
> Is there is still a major objection against that, or is there some API
> usable from plguins for that purpose?
>
> Even the mere ability to add inside the LTO data a chunk of bytes identified
> by the name of the plugin would be great. Of course, some more features
> could be welcome (e.g. the ability to add data specific to each compiled
> function or cgraph_node or whatever, or even to each gimple...).
>
> I could imagine that a plugin might be interested in adding say some
> information into the object file (when ordinary compilation for LTO of a
> single compilation unit happens) and later retrieve it (when link time
> optimisation occur merging several object files.)
>
> A dream case example would be a plugin for whole program static analysis.
The IPA pass infrastructure has all the necessary bits for this.
Richard.
> Regards.
> --
> Basile STARYNKEVITCH http://starynkevitch.net/Basile/
> email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
> 8, rue de la Faiencerie, 92340 Bourg La Reine, France
> *** opinions {are only mines, sont seulement les miennes} ***
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: LTO and adding extra information from extra passes
2009-09-02 20:18 ` Richard Guenther
@ 2009-09-02 20:24 ` Basile STARYNKEVITCH
2009-09-02 20:35 ` Richard Guenther
0 siblings, 1 reply; 6+ messages in thread
From: Basile STARYNKEVITCH @ 2009-09-02 20:24 UTC (permalink / raw)
To: Richard Guenther; +Cc: GCC Mailing List
Richard Guenther wrote:
> On Wed, Sep 2, 2009 at 10:06 PM, Basile
> STARYNKEVITCH<basile@starynkevitch.net> wrote:
>> Hello All,
>>
>> My feeling is that the Link Time Optimisation (LTO) effort should be soon
>> (=is expected to be, or is already) merged inside GCC trunk (future 4.5).
>>
>> Several years ago, I asked if there is any possibility for an additional
>> pass to profit of LTO infrastructure to add some extra data into LTO stuff
>> (which is probably DWARF related inside ELF object files, but I am not sure)
>> and to retrieve it. I remember that the answer was of course not.
[...]
>>
>> I could imagine that a plugin might be interested in adding say some
>> information into the object file (when ordinary compilation for LTO of a
>> single compilation unit happens) and later retrieve it (when link time
>> optimisation occur merging several object files.)
>>
>> A dream case example would be a plugin for whole program static analysis.
>
> The IPA pass infrastructure has all the necessary bits for this.
How do you deal with several compilation units?
I was thinking LTO is designed for that?
Regards.
--
Basile STARYNKEVITCH http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
8, rue de la Faiencerie, 92340 Bourg La Reine, France
*** opinions {are only mines, sont seulement les miennes} ***
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: LTO and adding extra information from extra passes
2009-09-02 20:24 ` Basile STARYNKEVITCH
@ 2009-09-02 20:35 ` Richard Guenther
2009-09-02 20:37 ` Basile STARYNKEVITCH
0 siblings, 1 reply; 6+ messages in thread
From: Richard Guenther @ 2009-09-02 20:35 UTC (permalink / raw)
To: Basile STARYNKEVITCH; +Cc: GCC Mailing List
On Wed, Sep 2, 2009 at 10:24 PM, Basile
STARYNKEVITCH<basile@starynkevitch.net> wrote:
> Richard Guenther wrote:
>>
>> On Wed, Sep 2, 2009 at 10:06 PM, Basile
>> STARYNKEVITCH<basile@starynkevitch.net> wrote:
>>>
>>> Hello All,
>>>
>>> My feeling is that the Link Time Optimisation (LTO) effort should be soon
>>> (=is expected to be, or is already) merged inside GCC trunk (future 4.5).
>>>
>>> Several years ago, I asked if there is any possibility for an additional
>>> pass to profit of LTO infrastructure to add some extra data into LTO
>>> stuff
>>> (which is probably DWARF related inside ELF object files, but I am not
>>> sure)
>>> and to retrieve it. I remember that the answer was of course not.
>
> [...]
>
>>>
>>> I could imagine that a plugin might be interested in adding say some
>>> information into the object file (when ordinary compilation for LTO of a
>>> single compilation unit happens) and later retrieve it (when link time
>>> optimisation occur merging several object files.)
>>>
>>> A dream case example would be a plugin for whole program static analysis.
>>
>> The IPA pass infrastructure has all the necessary bits for this.
>
> How do you deal with several compilation units?
>
> I was thinking LTO is designed for that?
I of course mean the IPA pass infrastructure on the LTO branch.
Richard.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: LTO and adding extra information from extra passes
2009-09-02 20:35 ` Richard Guenther
@ 2009-09-02 20:37 ` Basile STARYNKEVITCH
0 siblings, 0 replies; 6+ messages in thread
From: Basile STARYNKEVITCH @ 2009-09-02 20:37 UTC (permalink / raw)
To: Richard Guenther; +Cc: GCC Mailing List
Richard Guenther wrote:
>>>>
>>>> A dream case example would be a plugin for whole program static analysis.
>>> The IPA pass infrastructure has all the necessary bits for this.
>> How do you deal with several compilation units?
>>
>> I was thinking LTO is designed for that?
>
> I of course mean the IPA pass infrastructure on the LTO branch.
What include files describes the API?
Regards.
--
Basile STARYNKEVITCH http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
8, rue de la Faiencerie, 92340 Bourg La Reine, France
*** opinions {are only mines, sont seulement les miennes} ***
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: LTO and adding extra information from extra passes
2009-09-02 20:06 LTO and adding extra information from extra passes Basile STARYNKEVITCH
2009-09-02 20:18 ` Richard Guenther
@ 2009-09-03 12:50 ` Diego Novillo
1 sibling, 0 replies; 6+ messages in thread
From: Diego Novillo @ 2009-09-03 12:50 UTC (permalink / raw)
To: Basile STARYNKEVITCH; +Cc: GCC Mailing List
On Wed, Sep 2, 2009 at 16:06, Basile
STARYNKEVITCH<basile@starynkevitch.net> wrote:
> Hello All,
>
> My feeling is that the Link Time Optimisation (LTO) effort should be soon
> (=is expected to be, or is already) merged inside GCC trunk (future 4.5).
>
> Several years ago, I asked if there is any possibility for an additional
> pass to profit of LTO infrastructure to add some extra data into LTO stuff
> (which is probably DWARF related inside ELF object files, but I am not sure)
> and to retrieve it. I remember that the answer was of course not.
Note that the gimple streamer does not use dwarf encoding. It uses
its own bytecode format. There is no dwarf in the ELF files, unless
you use -g.
> Now we have a working plugin infrastructure, and I believe it would be very
> sensible for some plugin to register passes which add persistent information
> (as does LTO with its Gimple related representation) into object files and
> to retrieve it.
Yes. That's been my plan all along. Once LTO is merged in trunk, we
should add some plugin events to allow interaction with the streamer
as it writes and reads the callgraph.
> Even the mere ability to add inside the LTO data a chunk of bytes identified
> by the name of the plugin would be great. Of course, some more features
> could be welcome (e.g. the ability to add data specific to each compiled
> function or cgraph_node or whatever, or even to each gimple...).
Passes can add their own data to the bytecode. A couple of IPA passes
are already doing that in the branch (notably, the inliner).
> A dream case example would be a plugin for whole program static analysis.
Note that gimple may not be an appropriate IL to do some kinds of
static analysis. In gimple we have lost many front end attributes
that a static analyzer may want to use. However, combined with -g,
this could be partially reconstructed.
Regardless, I agree that there are some analyses that are still
possible and useful that can be done right after the compiler has
built the complete callgraph.
Diego.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2009-09-02 20:06 LTO and adding extra information from extra passes Basile STARYNKEVITCH
2009-09-02 20:18 ` Richard Guenther
2009-09-02 20:24 ` Basile STARYNKEVITCH
2009-09-02 20:35 ` Richard Guenther
2009-09-02 20:37 ` Basile STARYNKEVITCH
2009-09-03 12:50 ` Diego Novillo
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