[LLVMdev] Looking for a fix to memory leak in DWARF support

[Sergei Larin]

Eric,

  Let me clarify it a bit...  without type uniqueing for LTO + debug will I have a highly inefficient IR representation or incorrect debug info? If debug info for LTO is known to be non-useful or ambiguous or flat wrong -  there is no point in fixing its emission... or will it still be practical and if I manage to improve it somewhat the customer will still have some value-add by using it?

Thanks...

Sergei

---
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation


> -----Original Message-----
> From: Eric Christopher [mailto:echristo at gmail.com]
> Sent: Friday, June 13, 2014 4:32 PM
> To: Sergei Larin
> Cc: David Blaikie; LLVM Developers Mailing List
> Subject: Re: [LLVMdev] Looking for a fix to memory leak in DWARF support
> 
> On Fri, Jun 13, 2014 at 2:28 PM, Sergei Larin <slarin at codeaurora.org> wrote:
> >
> > Thanks Eric,
> >
> >
> > They are doing LTO build but with some custom modifications (think a
> library at a time as opposed to a whole program). I must admit, it is a rather
> large application as well, so as expected, any inefficiencies are multiplied
> greatly.
> >
> > From little that I have seen so far, it looks like debug metadata for an IR
> object linger behind once the object itself is eliminated (optimized). Rings a
> bell?
> >
> 
> They're going to run into all sorts of problems. They're doomed if it's a large
> C++ application (or really even if it's a C based application).
> 
> They won't get this to link likely with LTO + debug. It's unlikely to be a
> memory leak. It's just an explosion of debug info because of our lack of
> uniquing for type information. You can see my EuroLLVM 2013 talk where I
> describe this and Manman's patches to help fix the issue over the last couple
> of years.
> 
> -eric
> 
> > Thanks.
> >
> > Sergei
> >
> > ---
> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> > hosted by The Linux Foundation
> >
> >
> >> -----Original Message-----
> >> From: Eric Christopher [mailto:echristo at gmail.com]
> >> Sent: Friday, June 13, 2014 4:00 PM
> >> To: Sergei Larin
> >> Cc: David Blaikie; LLVM Developers Mailing List
> >> Subject: Re: [LLVMdev] Looking for a fix to memory leak in DWARF
> >> support
> >>
> >> On Fri, Jun 13, 2014 at 11:03 AM, Sergei Larin <slarin at codeaurora.org>
> wrote:
> >> >
> >> > David,
> >> >
> >> > Thanks for the quick response...
> >> >
> >> >
> >> > No, at this point I am just getting into the issue... I assume it
> >> > is a leak, but
> >> no clear proof yet. I was hoping it was an obvious thing since I
> >> recall a discussion about it a while ago... but maybe I am just confused.
> >> >
> >> > Was your work for compressing DWARF data  motivated by a certain
> >> inefficiency in debug info representation? Did it result in significant
> savings?
> >> >
> >>
> >> The compression isn't related to the IR level and some data is here
> >> on that
> >> compressing:
> >>
> >> https://gcc.gnu.org/wiki/DebugFission
> >>
> >> The internal representation and code have change significantly since
> >> then and there's no real way to help much. It may be a memory leak,
> >> but I don't recall one that bad back then. How is your customer compiling?
> LTO?
> >> Something else?
> >>
> >> -eric
> >>
> >> > Thanks.
> >> >
> >> > Sergei
> >> >
> >> > ---
> >> > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> >> > hosted by The Linux Foundation
> >> >
> >> >
> >> >> -----Original Message-----
> >> >> From: David Blaikie [mailto:dblaikie at gmail.com]
> >> >> Sent: Friday, June 13, 2014 12:41 PM
> >> >> To: Sergei Larin
> >> >> Cc: LLVM Developers Mailing List
> >> >> Subject: Re: Looking for a fix to memory leak in DWARF support
> >> >>
> >> >> Are you sure it's a leak, not just a large memory footprint?
> >> >>
> >> >> A lot of things have changed. Heck, even the bugs that we've fixed
> >> >> might not have existed two years ago (I've certainly created (and
> >> >> fixed) my share of bugs in debug info).
> >> >>
> >> >> Best you start with a leak tracking tool and at least be able to
> >> >> point to the major leak culprit (eg: "90% of the leaked memory was
> >> >> allocated at <stack
> >> >> trace>")
> >> >>
> >> >> On Fri, Jun 13, 2014 at 9:16 AM, Sergei Larin
> >> >> <slarin at codeaurora.org>
> >> wrote:
> >> >> >
> >> >> > David, (and everyone else)
> >> >> >
> >> >> >   I am forced to do some maintenance work on a fairly old LLVM
> >> >> > branch (likely based on release 3.1) that among other issues has
> >> >> > a major problem with memory leak somewhere around DWARF
> debug
> >> support.
> >> >> > In fact customer is unable to build with -g at all - simply
> >> >> > running out of memory on their project...
> >> >> >
> >> >> >   I seem to remember that there has been a major fix related to
> >> >> > it, but finding it hard to pinpoint. So the appeal to the
> >> >> > communal memory
> >> >> > - do you remember if  there was a single fix (since the middle
> >> >> > of
> >> >> > 2012 or so) that would have addressed such issue?
> >> >> >
> >> >> >   I know the code was drastically change since - I have seen
> >> >> > this for instance
> >> >> > llvm.org/viewvc/llvm-
> project/llvm/trunk/lib/MC/ELFObjectWriter.cpp?
> >> >> > vie
> >> >> > w=log&
> >> >> > pathrev=205990
> >> >> >
> >> >> > ...but not sure this is what I am looking for, and whether there
> >> >> > is something less drastic than I can do to plug that leak.
> >> >> >
> >> >> > Any clue would be very much appreciated.
> >> >> >
> >> >> > Thanks.
> >> >> >
> >> >> > Sergei
> >> >> >
> >> >> > ---
> >> >> > Qualcomm Innovation Center, Inc. is a member of Code Aurora
> >> >> > Forum, hosted by The Linux Foundation
> >> >> >
> >> >
> >> >
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