Efficient building and placing of gating functions

In this paper, we present an almost-linear time algorithm for constructing Gated Single Assignment (GSA), which is SSA augmented with gating functions at ø-nodes. The gating functions specify the control dependences for each reaching definition at a ø-node. We introduce a new concept of gating path, which is path in the control flow graph from the immediate dominator u of a node v to v, such that every node in the path is dominated by u. Previous algorithms start with ø-function placement, and then traverse the control flow graph to compute the gating functions. By formulating the problem into gating path construction, we are able to identify not only a ø-node, but also a gating path expression which defines a gating function for the ø-node.