a more efficient loopForestSteensgaard

[Stephen Weeks]

> Do you have a reference to the algorithm you used (presumably
> by Steensgaard) for the implementation?  I'd be curious
> to read it.

The algorithm is not by Steensgaard.  I did a direct implementation of
section 3.2 of the Ramalingam paper (see comment below), specialized
to Steensgaard's header function in section 3.3.  It's more efficient
than the code that we had because it computes the headers more
efficiently (in time linear in the size of the graph) and constructs
new graphs for the recursive calls more efficiently.


(* This is an implementation of the G. Ramalingam loop forest construction,
 * as described in "On Loops, Dominators, and Dominance Frontiers"
 * (originally in PLDI00; revised technical report at
 * http://www.research.ibm.com/people/r/rama/Papers/ibmtr21513.revised.ps).
 *)