chuanqi.xcq via llvm-dev
2021-Mar-31 02:16 UTC
[llvm-dev] Why the binary size in trunk are smaller significantly?
Hi Jeremy and David,
The most significant reduction comes from the section `.debug_loc` and
`.debug_info` section.
The size of `.debug_info` reduced about 14% and the size of of `.debug_loc`
reduced to even 69%!
I would try the patches in the link.
Thanks,
Chuanqi
------------------------------------------------------------------
From:David Blaikie <dblaikie at gmail.com>
Send Time:2021年3月31日(星期三) 00:24
To:Jeremy Morse <jeremy.morse.llvm at gmail.com>
Cc:chuanqi.xcq <yedeng.yd at linux.alibaba.com>; llvm-dev at
lists.llvm.org <llvm-dev at lists.llvm.org>
Subject:Re: [llvm-dev] Why the binary size in trunk are smaller significantly?
Yep, I'd be curious to see more data - comparisons of sections sizes (Bloaty
is a handy tool to make comparisons simpler (though for a one off might not be
worth the hassle of going and downloading/building it/etc)) & any work that
could be done isolating/reducing the test case (hopefully enough that it can be
shared) and verifying what differences might exist between the two compilations
if there's anything other than the compiler version.
On Tue, Mar 30, 2021 at 3:33 AM Jeremy Morse <jeremy.morse.llvm at
gmail.com> wrote:
Hi Chuanqi,
On Tue, Mar 30, 2021 at 9:47 AM chuanqi.xcq via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> In a private code bases, I find that the binary size produced in llvm-11
is 60M while the size produced in trunk is 51M.
>
> I tried to find the patch who made this change in git log or in
phabricator by keywords like `reduce`, 'size' or 'binary'. But I
find nothing.
Interesting -- which sections reduce in size between llvm-11 and
trunk? Assuming you're using ELF/DWARF binaries, `readelf -W -S` will
give you sections and sizes.
Since llvm-11 branched, there were some patches [0] that improved how
variable locations are represented in DWARF, I've seen some binaries
where that reduced file size by 10%. That would be reflected in the
.debug_loc section. There's also the constructor homing flag, passed
to clang with "-Xclang -fuse-ctor-homing", I'm not sure whether
it's
on by default in trunk. That would show a significant reduction in the
.debug_info section.
[0] https://reviews.llvm.org/rG0b5a8050ea39355a3876cc6bba9383d91e224e1f
--
Thanks,
Jeremy
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David Blaikie via llvm-dev
2021-Mar-31 02:28 UTC
[llvm-dev] Why the binary size in trunk are smaller significantly?
On Tue, Mar 30, 2021 at 7:16 PM chuanqi.xcq <yedeng.yd at linux.alibaba.com> wrote:> Hi Jeremy and David, > > The most significant reduction comes from the section `.debug_loc` > and `.debug_info` section. > The size of `.debug_info` reduced about 14% and the size of of > `.debug_loc` reduced to even 69%! >Surprises me a bit, but yeah, that could be debug info related, or unrelated - optimizations might make fewer variable locations because we've lost track of more variables so there are no locations - or locations might be better tracked so they're more contiguously described (so less small slices of variable locations - each slice having some overhead in its description)... but hard to say. llvm-dwarfdump --statistics might be insightful as to whether it's improvement in locations or not. But I'd make an educated guess that this probably isn't reflective of any bugs and is just roughly expected change from optimization changes and maybe debug info location improvements. But I could be wrong - it is a pretty big swing, for sure. - Dave> > I would try the patches in the link. > > Thanks, > Chuanqi > > > > ------------------------------------------------------------------ > From:David Blaikie <dblaikie at gmail.com> > Send Time:2021年3月31日(星期三) 00:24 > To:Jeremy Morse <jeremy.morse.llvm at gmail.com> > Cc:chuanqi.xcq <yedeng.yd at linux.alibaba.com>; llvm-dev at lists.llvm.org < > llvm-dev at lists.llvm.org> > Subject:Re: [llvm-dev] Why the binary size in trunk are smaller > significantly? > > Yep, I'd be curious to see more data - comparisons of sections sizes ( > Bloaty <https://github.com/google/bloaty> is a handy tool to make > comparisons simpler (though for a one off might not be worth the hassle of > going and downloading/building it/etc)) & any work that could be done > isolating/reducing the test case (hopefully enough that it can be shared) > and verifying what differences might exist between the two compilations if > there's anything other than the compiler version. > > On Tue, Mar 30, 2021 at 3:33 AM Jeremy Morse <jeremy.morse.llvm at gmail.com> > wrote: > Hi Chuanqi, > > On Tue, Mar 30, 2021 at 9:47 AM chuanqi.xcq via llvm-dev > <llvm-dev at lists.llvm.org> wrote: > > In a private code bases, I find that the binary size produced in llvm-11 > is 60M while the size produced in trunk is 51M. > > > > I tried to find the patch who made this change in git log or in > phabricator by keywords like `reduce`, 'size' or 'binary'. But I find > nothing. > > Interesting -- which sections reduce in size between llvm-11 and > trunk? Assuming you're using ELF/DWARF binaries, `readelf -W -S` will > give you sections and sizes. > > Since llvm-11 branched, there were some patches [0] that improved how > variable locations are represented in DWARF, I've seen some binaries > where that reduced file size by 10%. That would be reflected in the > .debug_loc section. There's also the constructor homing flag, passed > to clang with "-Xclang -fuse-ctor-homing", I'm not sure whether it's > on by default in trunk. That would show a significant reduction in the > .debug_info section. > > [0] https://reviews.llvm.org/rG0b5a8050ea39355a3876cc6bba9383d91e224e1f > > -- > Thanks, > Jeremy > > >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20210330/bf7ee528/attachment.html>