> +Mark who has done size optimization tuning with FDO. > > On Thu, Aug 4, 2011 at 7:05 AM, Mike Hommey <mhom...@mozilla.com> wrote: > > Hi, > > > > We (Mozilla) are trying to get the best of the ARM toolchain for our > > Android build. I recently built an Android Native-code Development Kit > > with GCC 4.6.1 and binutils 2.21.53, instead of GCC 4.4.3 and binutils > > 2.19 that come with the default NDK. > > > > LTO doesn't work at all, I'm getting an ICE that looks like the one from > > bug 41159. > > > > FDO however, works, but sadly, the resulting build is not only quite > > bigger, > > Is this true for both 4.6 and 4.4 gcc? There is a bug in 4.6 that > prevents cold functions from be optimized for size with FDO. The bug > was fixed in trunk recently.
You can also backport the patch to 4.6 tree. If the bug exists there, consider the patch preaproved. With FDO, -O2 and -O3 is not really that significandly different (i.e. -O2 gets all the extra inlining, but it does not get vectorization that is probably not big deal for you). -Os is however different storry. > > > > Has there been significant changes to the ARM backend that would justify > > that I try some more with current GCC HEAD? Should I maybe try some more > > with the linaro GCC branch? Are there things we can do to help getting > > better ARM performance? > > It does not hurt to try it :) One thing that is really changed is inliner heuristics. If would be very happy to have some feedback on this early, since we plan to do re-tunning of it (LTO changes many things and there are also fortran benchmarks that shows a lot of problems. Mozilla may chime in and make my life even harder with hopefully some positive results on it). As discused earlier, I think it would be very good idea to start trakcing perfomrance of Mozilla built with mainline GCC like we track other benchmarks. We don't really monitor anything of this size and thus we are quite likely to find new interesting issues by doing so. Honza > > Thanks, > > David > > > > > Cheers, > > > > Mike > >
