I would like to understand how the GNU GCC compiler handles optimizations. I know its not easy but I can't seem to find any GCC internal implementation details even just to get started.
Do I have to be a contributing GNU GCC developer to view the source code and know the low/high level design? Where can a developer, who wants to contribute to GCC, find the implementation details?
You can download gcc from all over the place. The best place to start might be the official page: http://gcc.gnu.org/releases.html
A good place to read about the optimizations is in the man page, which describes a lot of flags that control individual optimizations.
GCC is open source and its source code is freely available. You can even browse it online. And its internals are documented.