It uses something they call IRA and LRA on the RTL representation. But bottom line is: it's graph colouring. https://gcc.gnu.org/onlinedocs/gccint/RTL-passes.h

It uses something they call IRA and LRA on the RTL representation. But bottom line is: it's graph colouring. https://gcc.gnu.org/onlinedocs/gccint/RTL-passes.html https://gcc.gnu.org/onlinedocs/gccint/RTL-passes.html There's really quite a lot of documentation and published papers when you actually look: https://github.com/gcc-mirror/gcc/blob/751f306688508b08842d0ab967dee8e6c3b91351/gcc/ira.cc#L21-L363 https://github.com/gcc-mirror/gcc/blob/751f306688508b08842d0...