A function provides a mechanism for static single assignment in the presence
of predicated code. Guards placed on each source operand of the function
indicate the condition under which the corresponding source operand is live and
provide correct materialization of the functions after code reordering.
For control functions c representing a confluence of live reaching
definitions at a join point in the control flow graph, the guards indicate the
basic block which is the source of the edge associated with the source operand.
The c operands are paired with the source basic block of the
incoming edge(s) along which they are live. The operands are also ordered according
to a topological ordering of their associated block. This ordering is maintained
through subsequent code transformations. In the topological ordering, the source
of the edge from which the definition was passed is defined. A predicate
function p, represents the confluence of definitions in a straight
line of code in which some of the definitions have been predicated. For p,
the guards on the source operands indicate the predicate under which the corresponding
operand is live. The order of the operands is such that the p function
can be fully materialized by inserting a copy from each source operand to the target
variable, in the corresponding order, and each predicated by the associated predicate guard.
