[Bug other/59893] Use LTO for libgcc.a, libstdc++.a, etc

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59893

--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Tue, 21 Jan 2014, glisse at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59893
> 
> --- Comment #2 from Marc Glisse <glisse at gcc dot gnu.org> ---
> (In reply to joseph@codesourcery.com from comment #1)
> > Are LTO objects now independent of the compiler host (see bug 41526) (so 
> > that such libraries will work properly when copied from one host to 
> > another as part of a Canadian cross build)?
> 
> Thanks for the link (I don't know much about the implementation of LTO). Maybe
> restricting my proposition to the case build==host would be safer? If only
> native builds work, I am still ok with that, but I won't be surprised if there
> are bugs preventing it...

My point is not just that a Canadian cross build where the target 
libraries get rebuilt would rebuild them with the build-x-target compiler 
(producing results not actually usable on the host), but that the normal 
case for a Canadian cross build would copy the libraries from the 
build-x-target compiler - which was built with build = host - rather than 
rebuilding them at all (using make all-host when building the Canadian 
cross compiler).

Essentially, I'm suggesting that host-dependence of LTO information *is* a 
reason to consider use of LTO in GCC's libraries as something experimental 
and not appropriate to enable by default.