Could I get the lex&yacc files of gcc frontend?

[Xin Qi]

Dear Sir / Madam,

I am a college senior student. I have been dealing with a project
about C language and SGI WHIRL intermediate representation for my
course on Principle of Compiler. The WHIRL IR exploits a tree structure
to represent while parsing the source. I know that gcc also uses a 
tree structure as IR. So I think the code of gcc could be a very 
good reference for me.

Would you please let me know how to find the lex&yacc files for gcc 
frontend? I have got the source code of gcc front-end, but a lex or
yacc source would be more readable than just a c program generated
by lex&yacc.

Thank you very much for your help.

Sincerely yours,
Xin Qi
12/20/2002