[Bug lto/48094] ld: warning: section has unexpectedly large size errors in objc/obj-c++ lto

["iains at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48094

--- Comment #17 from Iain Sandoe <iains at gcc dot gnu.org> ---
Created attachment 30514
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30514&action=edit
proposed fix.

So the problem here is that when we bind multiple objects together (each of
which has an anonymous image_info section) LTO (unlike the system linker)
doens't know that these should be coalesced - and, TBH, I doubt we're going to
teach it about a darwin-specific section ... 

Luckily, the content of the image_info section only depends on command line
flags.

So this is a proposed solution.

1. allow the requisite ObjC flags to be recognized by lto1.

2. don't generate the image_info section in the FE instead ..

3. take note of the flag values, and (IFF there is some ObjC metadata present
in the object) emit the image_info section from the back end.

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I've checked that this flies on Darwin12 with XCode 4.6.3 [with lto enabled] -
but I don't have the XCode 4.2 configuration on Darwin10.  

(it has also been tested on older versions of the tool-chain).

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Mike - opinions on the solution?

others: wider testing please