register dancing
register dancing: n. Many older processor architectures suffer
from a serious shortage of general-purpose registers. This is
especially a problem for compiler-writers, because their generated
code needs places to store temporaries for things like intermediate
values in expression evaluation. Some designs with this problem,
like the Intel 80x86, do have a handful of special-purpose
registers that can be pressed into service, providing suitable care
is taken to avoid unpleasant side effects on the state of the
processor: while the special-purpose register is being used to hold
an intermediate value, a delicate minuet is required in which the
previous value of the register is saved and then restored just before
the official function (and value) of the special-purpose register is
again needed.