To read an RTL object from a file, call read_rtx. It takes one
argument, a stdio stream, and returns a single RTL object. This routine
is defined in read-rtl.c. It is not available in the compiler
itself, only the various programs that generate the compiler back end
from the machine description.
People frequently have the idea of using RTL stored as text in a file as an interface between a language front end and the bulk of GCC. This idea is not feasible.
GCC was designed to use RTL internally only. Correct RTL for a given program is very dependent on the particular target machine. And the RTL does not contain all the information about the program.
The proper way to interface GCC to a new language front end is with the “tree” data structure, described in the files tree.h and tree.def. The documentation for this structure (see GENERIC) is incomplete.