llvm dev - Dec 2017 - [RFC] - Deduplication of debug information in linkers (LLD).

>Wasn't our (lld/ELF's) position on debug info size that we should
focus on providing a great split-dwarf workflow and not try go too far out of
our way to deduplicate >or otherwise reduce debug info size inside LLD? I
recall there being some patches that made linking of large debug binaries like
1.5GB+ clang faster, but we decided to >reject those changes because
split-dwarf was the "right" solution.
>
>Rafael, Rui?
>
>(I even recall Rafael saying at one point that a great split-dwarf workflow
was one of the key things he considered as necessary for him to consider LLD
"done")
>
>-- Sean Silva
I probably not the right person to suggest (still mostly learning here for now,
so would like to be on a fence in general),
but it looks for me that splitting DWARF and deduplicating DWARF is a bit
othogonal things.
It feels for me that there is a room to do both things and have a benefit from
combinatiion ?

George.
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On Sat, Dec 16, 2017 at 4:08 AM George Rimar <grimar at accesssoftek.com>
wrote:
> >Wasn't our (lld/ELF's) position on debug info size that we
should focus
> on providing a great split-dwarf workflow and not try go too far out of our
> way to deduplicate >or otherwise reduce debug info size inside LLD? I
> recall there being some patches that made linking of large debug binaries
> like 1.5GB+ clang faster, but we decided to >reject those changes
because
> split-dwarf was the "right" solution.
> >
> >Rafael, Rui?
> >
> >(I even recall Rafael saying at one point that a great split-dwarf
> workflow was one of the key things he considered as necessary for him to
> consider LLD "done")
> >
> >-- Sean Silva
>
> I probably not the right person to suggest (still mostly learning here for
> now, so would like to be on a fence in general),
> but it looks for me that splitting DWARF and deduplicating DWARF is a
> bit othogonal things.
> It feels for me that there is a room to do both things and have a benefit
> from combinatiion ?
>
The two features/directions don't really compose - if the DWARF is split,
then the linker never sees the DWARF (it's not in the object files), so has
no deduplication to do. (llvm-dwp might see it, so the deduplication can
happen there)

>
> George.
>
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?But could not we for example do split dwarf, but for example do dedup of types
?

I do not mean right now, but in a theory ?


Best regards,
George | Developer | Access Softek, Inc
________________________________
От: David Blaikie <dblaikie at gmail.com>
Отправлено: 16 декабря 2017 г. 22:25
Кому: George Rimar
Копия: Sean Silva; llvm-dev at lists.llvm.org; Rui Ueyama; Rafael Espindola
Тема: Re: [llvm-dev] [RFC] - Deduplication of debug information in linkers
(LLD).



On Sat, Dec 16, 2017 at 4:08 AM George Rimar <grimar at
accesssoftek.com<mailto:grimar at accesssoftek.com>> wrote:
>Wasn't our (lld/ELF's) position on debug info size that we should
focus on providing a great split-dwarf workflow and not try go too far out of
our way to deduplicate >or otherwise reduce debug info size inside LLD? I
recall there being some patches that made linking of large debug binaries like
1.5GB+ clang faster, but we decided to >reject those changes because
split-dwarf was the "right" solution.
>
>Rafael, Rui?
>
>(I even recall Rafael saying at one point that a great split-dwarf workflow
was one of the key things he considered as necessary for him to consider LLD
"done")
>
>-- Sean Silva
I probably not the right person to suggest (still mostly learning here for now,
so would like to be on a fence in general),
but it looks for me that splitting DWARF and deduplicating DWARF is a bit
othogonal things.
It feels for me that there is a room to do both things and have a benefit from
combinatiion ?

The two features/directions don't really compose - if the DWARF is split,
then the linker never sees the DWARF (it's not in the object files), so has
no deduplication to do. (llvm-dwp might see it, so the deduplication can happen
there)


George.
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