Re: Speed Impact experiment on GCJ

[Andrew Haley <aph at redhat dot com>]

Holger Hoffstaette writes:
 > On Wed, 15 Feb 2006 12:29:24 +0100, Thomas Hallgren wrote:
 > 
 > > I think that's incorrect. The 1.5 JVM and it's rt.jar is backward
 > > compatible with 1.4. And you're likely to see some performance gain if you
 > > upgrade to the latest 1.5.0_06 version. I think even a highly optimized
 > > gcj compilation will have a hard time to catch up. It would be interesting
 > > to see a comparison.
 > 
 > Even more interesting would be a comparison with a recent Mustang
 > aka 1.6 build, because that will make the 1.5 test look slow. :-)
 > The one thing where gcj used to have a very clear advantage was
 > interface-method invocation since before 1.5 that used to be up to
 > 10 (!)  times slower than direct method invocations; this was
 > reduced to a factor of ~1.8 in 1.5 and completely optimized away in
 > Mustang.

Err, how do they do that, then?  Is there a paper somewhere?

 > Mustang also sports a new register allocator that makes a
 > tremendous difference for loops and therefore
 > String/array/collection operations.  The other big change - escape
 > analysis - is very recent and supposed to help the GC but I didn't
 > benchmark that; all I know is that some large maven builds are up
 > to twice as fast with 1.6 than with 1.5. It is really fast.

gcj is going to get escape analysis sooner or later, as it's an
ongoing gcc project.  That will certainly be interesting.

>From my POV, the amazing thing about gcj is who well it does,
*despite* the fact that there really is very little in the way of
Java-specific optimization in there.

Andrew.