ARM VERSION 1.2 - Manual (Page 349)

Directives Reference
ARM DUI 0068B Copyright © 2000, 2001 ARM Limited. All rights reserved. 7-67
7.7.19 RN
The RN directive defines a register name for a specified register.
Syntax
name RN expr
where:
name is the name to be assigned to the register. name cannot be the same as any
of the predefined names listed in Predefined register and coprocessor
names on page 3-9.
expr evaluates to a register number from 0 to 15.
Usage
Use RN to allocate convenient names to registers, to help you to remember what you use
each register for. Be careful to avoid conflicting uses of the same register under different
names.
Examples
regname RN 11 ; defines regname for register 11
sqr4 RN r6 ; defines sqr4 for register 6