[LLVMdev] Leaks in PBQPBuilderWithCoalescing::build ?

[Lang Hames]

Thanks Alexey!

Arnaud - apologies for misleading you: It looks like the vectors are pooled
too.

Hopefully Dave's patch fixes this up, otherwise I'll try to take a look at
this soon.

- Lang.


On Wed, Sep 10, 2014 at 4:35 PM, Alexey Samsonov <vonosmas at gmail.com> wrote:

> FTR, similar leak was recently reported by LSan on our bootstrap bot:
> http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap/builds/4506/steps/check-llvm%20asan/logs/stdio
>
> On Wed, Sep 10, 2014 at 4:21 PM, Lang Hames <lhames at gmail.com> wrote:
>
>> Oooh. Neat. Thanks Dave. Please go ahead and commit that.
>>
>> Arnaud - I have no idea whether Dave's patch will help with this bug, but
>> it's certainly worth testing.
>>
>> - Lang.
>>
>> On Wed, Sep 10, 2014 at 4:10 PM, David Blaikie <dblaikie at gmail.com>
>> wrote:
>>
>>> While I'm not sure where the leak is, using some pre-canned memory
>>> management might help...
>>>
>>> Attached is a patch that changes this allocation to use shared_ptr,
>>> perhaps it'll address the bug?
>>>
>>> (ideally we shouldn't need the intrusive ref counting
>>> (std::enable_shared_from_this) but instead have a weak_set that has
>>> std::weak_ptr in it & implicitly removes elements as they become null
>>> (probably on a harvesting schedule, rather than with a direct callback as
>>> is currently implemented))​
>>>  pbqp_leak.diff
>>> <https://docs.google.com/file/d/0B0jpkch3iC_7TXFVU2hCcUpfZXM/edit?usp=drive_web>
>>> ​
>>>
>>> On Wed, Sep 10, 2014 at 3:19 PM, Arnaud A. de Grandmaison <
>>> arnaud.degrandmaison at arm.com> wrote:
>>>
>>>> Hi Lang,
>>>>
>>>>
>>>>
>>>> In PBQPBuilderWithCoalescing::build, around line 360, we have code
>>>> looking like:
>>>>
>>>>
>>>>
>>>> …
>>>>
>>>> PBQP::Vector newCosts(g.getNodeCosts(node));
>>>>
>>>> addPhysRegCoalesce(newCosts, pregOpt, cBenefit);
>>>>
>>>> g.setNodeCosts(node, newCosts);
>>>>
>>>> …
>>>>
>>>>
>>>>
>>>> I suspect the leak occurs around the setNodeCosts method, and I have
>>>> trouble understanding how it handles the case where the node already has
>>>> costs.
>>>>
>>>>
>>>>
>>>> It seems to me that:
>>>>
>>>> - we make of copy of the node’s costs (probably because someone else
>>>> can refer to it ?)
>>>>
>>>> - we modify the copy
>>>>
>>>> - we set the node’s new costs. But what is supposed to happen there,
>>>> especially in the CostAllocator part ?
>>>>
>>>>
>>>>
>>>> Could you shed some light there ?
>>>>
>>>>
>>>>
>>>> Thanks,
>>>>
>>>> Arnaud
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> *From:* Lang Hames [mailto:lhames at gmail.com]
>>>> *Sent:* 10 September 2014 19:26
>>>> *To:* Arnaud De Grandmaison
>>>> *Subject:* Re: Leaks in PBQPBuilderWithCoalescing::build ?
>>>>
>>>>
>>>>
>>>> Thanks Arnaud!
>>>>
>>>>
>>>>
>>>> - Lang.
>>>>
>>>>
>>>>
>>>> On Wed, Sep 10, 2014 at 11:23 AM, Arnaud A. de Grandmaison <
>>>> arnaud.degrandmaison at arm.com> wrote:
>>>>
>>>> Hi Lang,
>>>>
>>>>
>>>>
>>>> For your information, the leak sanitizer found something when I
>>>> committed my patch:
>>>>
>>>>
>>>>
>>>>
>>>> http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap/builds/4506/steps/check-llvm%20asan/logs/stdio
>>>>
>>>>
>>>>
>>>> I will try to have a look at it.
>>>>
>>>>
>>>>
>>>> Cheers,
>>>>
>>>> --
>>>>
>>>> Arnaud A. de Grandmaison
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
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>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
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>>>>
>>>>
>>>
>>
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>>
>
>
> --
> Alexey Samsonov
> vonosmas at gmail.com
>
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