tips for understanding the GCC codebase?

[Jonathan Wilson]

I have read the GCC manuals (including the internals manual) but GCC is 
still next to impossible to understand.

For example, I have looked everywhere and I STILL cant figure out how to 
tell GCC that the i[34567]86-pc-mingw target supports TLS and __thread.

And I cant figure out how to tell GCC which variables can and cant be 
marked __thread on win32 (to be fair, I dont know myself what is and isnt 
valid when it comes to TLS on win32 :)

And I cant figure out how to tell GCC how to spit out the right code for 
these variables :(