How to modify the source code of gcc compiler, recompile and build it again?

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http://askubuntu.com – I have 11.10 (32 bit OS) in my computer. It has gcc-4.6 as the default compiler. As it is installed by default, I can't modify the source and rebuild it again. I want to modify the source code of the gcc compiler itself. I tried installing gcc-4.4.6 from the source package (gcc-4.4.6.tar.gz) which I downloaded from gcc official mirror site but I couldn't install it successfully. Can anyone suggest how to install any version of gcc supported by 11.10 from its .tar file.? Or suggest another way to modify the source code of gcc and then build the modified version again? (HowTos)