On Wednesday 2013-12-04 16:36 -0500, Ehsan Akhgari wrote: > On Tue, Dec 3, 2013 at 2:47 PM, L. David Baron <[email protected]> wrote: > > I'd certainly hope that nearly all of the difference in size of > > libxul.so is debugging info that wouldn't be present in a non-debug > > build. But it's worth testing, because if that's not the case, > > there are some serious improvements that could be made in the C/C++ > > toolchain... > > Well, not really. In the case of unified builds, the compiler sees larger > translation units, so it has better opportunity for optimizations such as > inlining, DCE, etc.
I did a set of builds on changeset 8648aa476eef, on 64-bit Linux
with gcc, to test these theories.
Neither -DDEBUG -DDEBUG optimized
nor optimized
The sizes I get from the build (with -g) are:
Nonunified 834700176 905487728 907369496
Unified 520194760 563257880 554848888
If I run "strip --strip-debug" on these, this removes the vast
majority of the size difference:
Nonunified 155896907 176296907 87984550
Unified 152048885 168215761 87616359
And if I further run "strip" on these, I get:
Nonunified 111273928 128967104 65150320
Unified 109413312 123112424 64863456
readelf -WS (on the "optimized" pair) showed size differences in
many of the sections, but the largest differences were the .debug_*
ones.
So indeed, *most* of the size difference is debugging info. But
there is indeed still a small size difference without the debugging
info (about 0.5% for optimized and not -DDEBUG, more without
optimization or with -DDEBUG).
(I still have all of the above binaries if people are interested in
more information from them.)
-David
--
𝄞 L. David Baron http://dbaron.org/ 𝄂
𝄢 Mozilla https://www.mozilla.org/ 𝄂
Before I built a wall I'd ask to know
What I was walling in or walling out,
And to whom I was like to give offense.
- Robert Frost, Mending Wall (1914)
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