loop combination

A program transformation where the bodies of two loops are

merged into one thus reducing the overhead of manipulating and

testing the control variable and branching. Further

optimisation of the merged code may then become possible.

In horizontal loop combination the bodies of the loops are

largely independent so only the loop overhead is saved.

Vertical loop combination applies where the results of the

first loop are used by the second. Combining the two allows

the intermediate results to be used immediately (in

registers) rather than requiring them to be stored in an

array.

The functional equivalent of horizontal and vertical loop

combination are tupling and fusion.