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

Richard Biener rguenther@suse.de
Fri Mar 21 10:29:00 GMT 2014


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.
> 
> OK - or do you have a better suggestion?

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.

Richard.

> Tobias
> 
> 
> --- changes.html        8 Mar 2014 20:45:54 -0000       1.63
> +++ changes.html        21 Mar 2014 09:10:32 -0000
> @@ -65,6 +65,13 @@
>        <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>By default, 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> (requires that <code>ar</code> and + 
> <code>ranlib</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.



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