The current R version comes also with a 64-bit version so its not necessary to compile it from source anymore, but you do need to tell ESS how to use the 64bit version
So today I compiled 64 bit R 2.91 on Mac OS X 10.5.7 in order to get maximum speed for my analyses. The speed increase I got was 15-25 %, when I ran some tests with matrix calculation and intensive loops. Note that you can also download optimized binaries from http://r.research.att.com/, although they are not the latest version. It took me some effort and googling to get it done so I'm going to post the instructions here, so that I know how to do it next time and I hope that it also benefits others. After I got the installation done I ran into a problem getting ESS to recognize my 64 bit version, but I managed to solve that as well. So here is how I did it:
First I installed the necessary developer tools from http://r.research.att.com/tools/. I already had gcc 4.2 from apple so installed gfortran and libreadline readline-5.2-1-quad.tar.gz. Readline is a precompiled binary and you extract is using
sudo tar fvxz readline-5.2-1-quad.tar.gz -C /
After installing the depencies I extracted R-2.9.1.tar.gz downloaded from cran and executed configure in the extracted directory with the following options (a bit modified from http://r.research.att.com/building.html):
./configure SHELL='/bin/bash' r_arch=x86_64 \ CC='gcc -arch x86_64 -std=gnu99' CXX='g++ -arch x86_64' \ OBJC='gcc -arch x86_64' F77='gfortran -arch x86_64' \ FC='gfortran -arch x86_64' --with-system-zlib --with-blas='-framework vecLib' \ --with-lapack --host=x86_64-apple-darwin9.7.0 --build=x86_64-apple-darwin9.7.0
After running "make" and "make install" I had a working installation that can be started using:
R --arch x86_64
Just running R tries to run 32 bit version of R which I don't have, so I made an alias R='R--arch=x86_64' to .profile and R starts form terminal with just the familiar R.
Ok, all was well so far but then I discovered that ESS can't find R anymore, because it is trying to execute the 32 bit version and doesn't work. So after looking at the ESS source I discovered that you can modify R startup options in the file "essd-r.el". I use Carbon Emacs, but this methods should work with other Emacs variants. If you are wondering how to install ESS on OS X have a look at this post. First give yourself a permission to modify the file:
chmod u+w essd-r.el
Then open it and look for a line that says:
inferior-R-args " " ; add space just in case
And chance it to:
inferior-R-args "--arch x86_64 " ; add space just in case
Thats it, you should now have a working ESS set up with a 64 bit R!