[RFC] Faster linking (-gsplit-dwarf, gold)

[Luboš Luňák]

 Hello,

 I've switched my LO debug build to use -gsplit-dwarf and together with using 
the gold linker this makes the build noticeably smaller and faster to link, 
for a negligible cost when starting gdb. So at 
https://gerrit.libreoffice.org/#/c/56416/ and 
https://gerrit.libreoffice.org/#/c/56417/ there are support 
for --enable-split-debug and --enable-gold that I intend to push.

 However, the actual reason for this mail is that I think that this should be 
the default for whoever can use it. I've been using it for a while on 
openSUSE42.3 (a year-old distro) with Clang5 and it seems that everything 
works just fine (including gdb and valgrind). Gold has been around for a 
couple of years and so has -gsplit-dwarf, so I'd naively expect that any 
distro capable of building current LO should have a decent support there as 
well.

 Has somebody any problematic experience with either of these? I've been 
pointed to 
http://document-foundation-mail-archive.969070.n3.nabble.com/configuring-gold-as-your-linker-td4217690.html 
by Noel, but the problems mentioned there are old and not very convincing.

 And note that I'm talking only about developer builds here 
(i.e. --enable-debug/dbgutil). I expect that distros would have problems with 
handling split debug info and the performance of gold doesn't really matter 
for them either.

Some numbers:
                        normal  | split
total debug build size   19120M |  14294M
CXXObject dir size       10320M |   8137M
libsclo.so size         461669K | 207951K
libsclo bfd link time   32.433s | 20.697s
libsclo gold link time  10.394s |  6.159s
gdb symbols load time       49s |     51s

-- 
 Luboš Luňák
 l.lunak at collabora.com