From: Ilya Enkovich <enkovich.gnu@gmail.com>
To: Jan Hubicka <hubicka@ucw.cz>
Cc: gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [CHKP, PATCH] Fix LTO cgraph merge for instrumented functions
Date: Mon, 06 Apr 2015 13:57:00 -0000 [thread overview]
Message-ID: <CAMbmDYYmSMVZrJk709pFtss3_ML+dx8TW3VMZgW-vdnaPY_H5A@mail.gmail.com> (raw)
In-Reply-To: <20150403184915.GS21276@atrey.karlin.mff.cuni.cz>
2015-04-03 21:49 GMT+03:00 Jan Hubicka <hubicka@ucw.cz>:
>> Assembler name of instrumented function is a transparent alias of
>> original function's name. Alias chains are not taken into account by
>> analysis. Thus we see no conflict between instrumented function's name
>> and a variable name but emit them with the same assembler name. To
>> detect name conflict I keep original function node alive.
>
> Hmm, so lets see if I understand your situation. You always have transparent alias TA
> and function F connected by IPA_REF_CHKP and because TA is represented as thunk
> you also have a fake call from TA to F?
>
> I do not understand how you can miss the link these days. I extended lto-cgraph to
> always keep thunk and its target in every unit that reffers to thunk. That should
> solve you problem? How IPA_REF_CHKP can link get lost?
References are not streamed out for nodes which are referenced in a
partition but don't belong to it ('continue' condition in output_refs
loop).
>
> I suppose we still need to
> 1) write_symbol and lto-symtab should know that transparent aliases are not real
> symbols and ignore them. We have predicate symtab_node::real_symbol_p,
> I suppose it should return true.
>
> I think cgraph_merge and varpool_merge in lto-symtab needs to know what to do
> when merging two symbols with transparent aliases.
> 2) At some point we need to populate transparent alias links as discussed in the
> other thread.
> 3) For safety, I guess we want symbol_table::change_decl_assembler_name to either
> sanity check there are no trasparent alias links pointing to old assembler
> names or update it.
Wouldn't search for possible referring via transparent aliases nodes
be too expensive?
> 4) I think we want verify_node to check that transparent alias links and chkp points
> as intended and only on those symbols where they need to be
>
> There is also logic in lto-partition to always insert alias target
>> > OK, so you have the chkp references that links to instrumented_version.
>> > You do not stream them for boundary symbols but for some reason they are needed,
>> > but when you can end up with wrong CHKP link?
>>
>> Wrong links may appear when cgraph nodes are merged.
>
> I see, I think you really want to fix these at merging time as sugested in 1).
> In this case even the node->instrumented_version pointer may be out of date and
> point to a node that lost in merging?
node->instrumented_version is redirected and never points to lost
symbol. But during merge we may have situations when
(node->instrumented_version->instrumented_version != node) because of
multiple not merged (yet) symbols referencing the same merged target.
Thanks,
Ilya
>
> Honza
>>
>> Thanks
>> Ilya
next prev parent reply other threads:[~2015-04-06 13:57 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-12 12:10 Ilya Enkovich
2015-03-19 8:35 ` Ilya Enkovich
2015-04-02 14:52 ` Ilya Enkovich
2015-04-02 17:01 ` Jan Hubicka
2015-04-03 7:54 ` Ilya Enkovich
2015-04-03 18:49 ` Jan Hubicka
2015-04-06 13:57 ` Ilya Enkovich [this message]
2015-04-10 1:15 ` Jan Hubicka
2015-04-14 9:16 ` Ilya Enkovich
2015-05-05 8:06 ` Ilya Enkovich
2015-05-19 9:40 ` Ilya Enkovich
2015-05-26 13:09 ` Ilya Enkovich
2015-05-29 6:33 ` Jan Hubicka
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