[LLVMdev] Leaks in PBQPBuilderWithCoalescing::build ?

[David Blaikie]

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.
>

Committed in 217563.

Running the PBQP test without my change under valgrind didn't show any
memory leak, but hopefully with Arnaud's change and valgrind he can see the
leak and then verify that my change addresses it... *fingers crossed*


>
> 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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