How to understand gcc source code?

["梁?" <liangkun1983 at gmail dot com>]

Hello, everyone :
I am learning compiler techniques. I want a live example. I also want to do my
contributions to open source. So I turn to gcc.

Last year I have added some instruction templates to one specific gcc
backend as a task in work.
I have read a little of "Using and Porting GCC".

But still, I cannot manage the source code of gcc.
I don't know how to start reading it.

My plan is: reading the book "Advanced Compiler Design and
Implementation" and reading the corresponding code in gcc at the same time.
But I even cannot find the "corresponding code" ( TT )

Last night I want to read the code of symbol table used in gcc, I searched in
google, I greped in the source code. At last, I still have no idea
where those code is.

I searched in google trying to find an article describing gcc's source
code, and I cannot find anything valuable.

Any advice to be invovled in development of gcc ?
Thank you very much.
Sorry for disturbing.

-- 

Yours

        Alex L.K