I've run some statistics with various versions of gcc and sent the following message to the gcc mail list, which is archived at

http://gcc.gnu.org/ml/gcc/

Perhaps some of you may be interested.

Brad

-------- Forwarded Message --------

From: Bradley Lucier lucier@math.purdue.edu To: gcc@gcc.gnu.org Cc: Bradley Lucier lucier@math.purdue.edu Subject: Measuring FSF gcc from 4.1.2 to today on various benchmarks. Date: Fri, 29 May 2009 15:58:00 -0400

I've put at

http://www.math.purdue.edu/~lucier/bugzilla/9/

some compile-time and run-time statistics related to PR 39157 and PR 33928 and compile times and run times for the programs in the Gambit Scheme benchmark suite. The statistics are for 4.1.2 release, 4.2.4 release, 4.3.3 release, 4.4.1 20090522, 4.5.0 20090521 (revision 147758), and 4.5.0 20090521 (revision 147758) with -fno-forward-propagate; they use (mainly) the set of options

-O1 -fno-math-errno -fschedule-insns2 -fno-trapping-math -fno-strict-aliasing -fwrapv -fomit-frame-pointer -fPIC -fno-common -mieee-fp

on a Core 2 quad processor (running basically nothing else at the time).

I would conclude from the statistics that, right now, the cost of including -fforward-propagate in -O1 overrides any performance benefit that may result.

Brad