GCC Plugin for Implementing Loop Interchange

[aditya sasongko]

I want to write a GCC Plugin that performs a simple loop interchange on a
nested for loop, so that an inner for statement is to be swapped with
its outer for statement. I am making this plugin as a practice which
is assigned by the supervisor of a project that I am working on.
To learn how to transform loop structure, I have tried experimenting
with the loop manipulation functions shown in the gcc internal manual
by calling the loops in my source code with FOR_EACH_LOOP (I tried to
remove some loop nodes).
However any manipulation that I attempted doesn't seem to be produced
in the output code. I am really new to GCC Plugin API or GCC
development in overall. So is there anyone who can tell me where to
start in making this loop interchange?