GTY(()) in gcc source

[yuya...@gmail.com]

Hello, everyone,

I am confused by the explaination of GTY in gcc internal.
According to the description at
http://gcc.gnu.org/onlinedocs/gccint/Type-Information.html#Type-Infor...,

"special markers are used to determine what parts of the
source to look at. All struct and union declarations that
define data structures that are allocated under control of the
garbage collector must be marked."

Where is the garbage collector? Why gcc's source code is
also compiled by gcc, I tried to manually preprocess some
.h/.c files that contain GTY macro, but those macros disappear
after preprocessing with gcc -E option.

Any remarks on this?

Thanks a lot!

-Andy