Modification of the AST-tree of the GCC compiler

It is needed to gather the necessary information about the translation unit using the plugin for GCC and to modify AST on its base. I've already understood how to gather information. But I haven't unde开发者_高级运维rstand yet how to modify AST before it's passed into CRT. Very little information is available on this subject. Tell me plese what should I read on this subject? Share thoughts, links.

Thank's.

P.S. I've already read everything on these links:

http://en.wikibooks.org/wiki/GNU_C_Compiler_Internals/Print_version http://developer.apple.com/library/mac/#documentation/DeveloperTools/gcc-4.2.1/gccint/index.html#Top

The GCC test suite contains a basic examples of such modifications. See http://gcc.gnu.org/viewcvs/gcc/trunk/gcc/testsuite/gcc.dg/plugin/finish_unit_plugin.c and start_unit_plugin.c shows how to create a var. Unfortunately for more serious modifications the GCC source code are probably your best bet.

Are you tied to GCC for this endeavor? The ROSE compiler is built specifically for performing source-level modification, then handing the resulting code off to a backend compiler.