RTL Representation
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Most of the work of the compiler is done on an intermediate
representation called register transfer language. In this language,
the instructions to be output are described, pretty much one by one, in
an algebraic form that describes what the instruction does.
RTL is inspired by Lisp lists. It has both an internal form, made
up of structures that point at other structures, and a textual form
that is used in the machine description and in printed debugging dumps.
The textual form uses nested parentheses to indicate the pointers in
the internal form.