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

[David Blaikie via llvm-dev]

On Sat, Dec 16, 2017 at 11:27 AM George Rimar <grimar at accesssoftek.com>
wrote:

> ​But could not we for example do split dwarf, but for example do dedup of
> types ?
>
Yep, that is already supported - but the type deduplication happens in the
DWP tool/generation, not in the linker. The linker inputs (.o files) don't
contain any of the type information, only the .dwo files contain the type
information, etc, in a Fission build.

> 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>
> 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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