[LLVMdev] Leaks in PBQPBuilderWithCoalescing::build ?

[Alexey Samsonov]

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
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>>>
>>
>
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>


-- 
Alexey Samsonov
vonosmas at gmail.com
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