https://gcc.gnu.org/onlinedocs/

https://kristerw.blogspot.com.by/2017/08/writing-gcc-backend_4.html
https://kristerw.blogspot.com.by/2017/08/the-structure-of-gcc-back-end.html
https://kristerw.blogspot.com.by/2017/08/getting-started-with-gcc-back-end.html
https://kristerw.blogspot.com.by/2017/08/gcc-low-level-ir-and-basic-code.html