[wwwdocs] gcc-4.9/changes.html: Mention that LTO now generates slim objects

[Tobias Burnus]

On Fri, Mar 21, 2014 at 10:40:26AM +0100, Richard Biener wrote:
> On Fri, 21 Mar 2014, Tobias Burnus wrote:
> > This patch mentions that -flto now generates slim objects. That's especially
> > relevant for static libraries as one can there run into surprises, if one
> > does not know about gcc-ar.
> 
> Please adjust slightly to "When using a linker-plugin,
> compiling with the <code>-flto</code> option now generates slim 
> object files by default ..." as the change doesn't affect _all_
> configurations but only those with HAVE_LTO_PLUGIN set (thus
> -fno-use-linker-plugin overrides the default as well).
> 
> I'd also mention gcc-nm which needs to be used to inspect archives
> with thin LTO files.

Thanks for the suggestions - updated patch below.


Tobias

--- changes.html        8 Mar 2014 20:45:54 -0000       1.63
+++ changes.html        21 Mar 2014 12:43:44 -0000
@@ -65,6 +65,16 @@
       <li>Function bodies are now loaded on-demand and released early improving
          overall memory usage at link time.</li>
       <li>C++ hidden keyed methods can now be optimized out.</li>
+      <li>When using a linker plugin, compiling with the <code>-flto</code>
+          option now generates slim objects files (<code>.o</code>) which only
+          contain intermediate language representation for LTO. Use
+          <code>-ffat-lto-objects</code> to create files which contain
+          additionally the object code.  To generate static libraries suitable
+          for LTO processing, use <code>gcc-ar</code> and
+         <code>gcc-ranlib</code>; to list symbols from a slim object file use
+         <code>gcc-nm</code>. (Requires that <code>ar</code>,
+         <code>ranlib</code> and <code>nm</code> have been compiled with
+         plugin support.)</li>
     </ul>
     Memory usage building Firefox with debug enabled was reduced from 15GB to
     3.5GB; link time from 1700 seconds to 350 seconds.