A type for program points.
Return the definitions that produced the topmost 'm' elements on the stack, and that reach the instruction at index 'idx' in basic block 'bb'.
Return the instructions that produced the 'm' elements on the stack, below given 'depth'.
Implements forward dataflow analysis: the transfer function is applied when inputs to a Program point change, to obtain the new output value.
the transfer function.
Return the reaching definitions corresponding to the point after idx.
the number of times we iterated before reaching a fixpoint.