Register transfer language (RTL) is a kind of intermediate representation (IR) that is very close to assembly language
RTL is also the name of a specific IR used in the GNU Compiler Collection (GCC), and several other compilers, such as Zephyr or the European compiler projects CerCo and CompCert.
In GCC, RTL is generated from the GIMPLE representation, transformed by various passes in the GCC 'middle-end', and then converted to assembly language.
link http://en.wikipedia.org/wiki/Register_transfer_language