Hi! I'm trying to modify the GCC source code to get something done. But
there's a difficulty in understanding how to use some functions and data
structures. Please help me with some hints.

Here is the problem: in the file GCC-source/gcc/c/c-decl.c, before
'c_decl_attributes' is called in 'start_function', I want to insert some
additional optimize attributes in 'attributes' tree to be proceed, but I
could not find the correct way to insert a new tree in it.
 Thanks in advance.