[LLVMdev] Preserving accurate stack traces with optimization?

[Eric Christopher]

On Oct 30, 2013 7:25 PM, "Philip Reames" <listmail at philipreames.com> wrote:
>
> On 10/30/13 7:09 PM, Philip Reames wrote:
>>
>> David, Quentin - Thanks for the feedback.  Responses inline.
>>
>> On 10/30/13 11:21 AM, David Blaikie wrote:
>>>
>>> Actually CCing Eric.
>>>
>>>
>>> On Wed, Oct 30, 2013 at 11:00 AM, Quentin Colombet <qcolombet at apple.com>
wrote:
>>>>
>>>> Philip,
>>>>
>>>> Thanks for the clarification.
>>>>
>>>> As far as I can tell, there is currently no way to preserve a full and
accurate stack trace while utilizing most of LLVM’s optimization abilities.
>>>>
>>>> The work on debug information may help you get the information you
need, but I do not think we will provide information on stack frames that
have been removed via inlining or tail call.
>>>
>>>
>>> In theory, at -gmlt we should emit enough debug info to give you
accurate stack traces including inlined frames. Tail calls I assume we
can't do anything about.
>>
>> Tail calls I'm not too worried about.  I'm reasonably sure that our
existing optimizer doesn't do any tail call optimizations.  Given that,
turning them off doesn't worry me too much performance wise.
>>
>> First, thank for you for mentioning the -gmit option.  I had been
completely unaware of that.  I'll have to dig into the implementation and
usage a bit.  Can you point me to any documentation?  A quick google search
didn't turn up anything.
>>
>> Can you clarify two things for me?  First, is the intent that -gmit
*always* provide accurate stack traces?  (modulo bugs of course)  If so,
what is your subjective opinion on how close it comes to meeting that goal
today?  (i.e. how much help would we need to contribute to get it to a
solid state?)
>
> David - Redoing my google searching with "gmlt" (i.e. the correct
spelling) I see more useful links.  From what I can gather, -gmlt emits a
strict subset of the debug information you'd see at -g.  Are you saying
that "-g" should always be sufficient for accurate stack traces - even in
the face of inlining?  This would be ideal for us.
>

It should yes. Any time where it can't is a bug in either our
implementation or in DWARF itself. :)

-eric
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