[Mesa-dev] [PATCH 24/24] automake: ask the linker to do garbage collection

[Emil Velikov]

On 28/03/14 08:35, Lauri Kasanen wrote:
> On Thu, 27 Mar 2014 21:00:39 +0000
> Emil Velikov <emil.l.velikov at gmail.com> wrote:
> 
>> By doing GC the linker removes all the symbols that are not referenced
>> and/or used by the final library. This results in a saving of ~100K
>> up-to ~600K per (stripped) binary (classic vs gallium drivers).
>>
>> If interested one can ask the compiler to print the sections that are
>> removed using -Wl,--print-gc-sections.
> 
> I didn't see where you add the corresponding flags to CFLAGS/CXXFLAGS.
> 
What do you have in mind with "the corresponding flags" ?

> Without -ffunction-sections -fdata-sections in compile flags the garbage
> collection is handicapped - add those by default too, and see much
> greater gains.
> 
"Handicapped" or not it produces very nice results at this point. AFAICS both
options that you've mentioned have some interesting side effects, from which I
would rather opt out at this stage. Speaking of "much greather gains" do you
have any numbers in mind (wrt mesa) ?

> I should also add that this is a GNUism, so it should be detected for
Ouch good point.

> in configure in case people use other compilers/linkers. It's also
> redundant if LTO is used.
As mentioned by Marc, LTO is somewhat broken + adds a substantial delay to the
build process. Thus I'd rather not enforce it on people.

> 
> In one of my projects I detect as such:
> 
> if -flto supported, use it (needs to be added to all three CFLAGS
> CXXFLAGS LDFLAGS)
> else if sections supported, use it
> else print a message they're missing out
> 


Thanks
-Emil
> - Lauri
>