The Load Function

  An additional function is associated with the compiled output for all operators. This is the load function, which coordinates the use of the router for that operator. It serves a number of purposes:

• It loads any necessary router information before beginning to use the operator.
• Its arguments are the values for any (runtime) operands, and it is responsible for updating the router when those values change.
• For the first operator after a phase change, it coordinates any necessary overhead in changing from the previous phase (such as barriers or required delays).

The I/O functions could be overloaded to handle all of this, by adding additional arguments for run-time operators, then testing when the values change, or when the operator is used for the first time, and updating the router as necessary. However, this seemed inelegant and inefficient, since the HLL compiler knows where to insert the code to perform these tasks before calling any I/O functions.

For a sequential operator, the load function must be placed before the operator's first use of its I/O function(s), and after the last use of the previous operator's I/O function(s). Where sequential operators are placed into the same phase, only the first sequential operator will load the router code for that phase. For parallel operators, the load functions for the operators must all be called before the HLL compiler calls any of the I/O functions for the operators.

As is mentioned above, loop constructs also have a label. This label is used by the compiler to generate a load function for the loop; such a load function may contain router reprogramming commands that can be hoisted out of the loop, and thus executed only once per entering the loop. No I/O functions are associated with loop labels.