[patch] Dead-strip binaries by default on OS X and posix (was: Reduce size of clang-format by 87% on OS X)

[Chandler Carruth]

On Fri, Dec 27, 2013 at 2:12 PM, Nico Weber <thakis at chromium.org> wrote:

> On Thu, Dec 26, 2013 at 10:04 PM, Chandler Carruth <chandlerc at google.com>wrote:
>
>>
>> On Fri, Dec 27, 2013 at 1:02 AM, Chandler Carruth <chandlerc at google.com>wrote:
>>
>>> Have you checked the other binary size reductions? I wonder why we
>>> didn't do this sooner.
>>>
>>
>> Oh, of course, you did this just for clang-format.
>>
>> Can we instead do this for all LLVM projects by default, and opt maybe
>> 'clang', 'opt', 'llc', and 'bugpoint' out of it to support dlopen'ed passes
>> and plugins?
>>
>
> Something like the attached patch? (Make-only again, but now including the
> linux bits. If folks like it, I can do the cmake part as a followup.)
>
> This adds -ffunction-sections -fdata-sections unconditionally, since most
> tools have few source files anyways and mostly link in static libs. This
> reduces the size of e.g. diagtool from 21 MB to 2.8 MB and clang-format
> from 22 MB to 1.8 MB (these numbers are on Linux). libclang.so drops from
> 29MB to 20MB, but from skimming through `vim -d <(nm old-libclang.so) <(nm
> new-libclang.so)` only mangled symbols are getting dropped, and the
> libclang makefile sets EXPORTED_SYMBOL_FILE, and tests pass, so hopefully
> nothing necessary is getting dropped.
>
> The size of libclang.a grows from 1.6 MB to 2 MB, as you'd expect with
> -ffunction-sections. The size of other .a files increases similarly:
> libclangARCMigrate goes from 5.9 MB to 8.9 MB, libclangAST.a from 8.1 MB to
> 11 MB, and so on. This is probably acceptable?
>

This seems very reasonable to me for the advantages it poses. I even expect
link times to go *down* as a consequence. Rock!

Feel free to submit, and submit the cmake variant whenever you have it. The
bots can catch the fallout. =D
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