/** Inserts PHI functions at the beginning of basic blocks. */
private void insertPhiFunctions() {
// See Figure 11
// http://www.cs.utexas.edu/~pingali/CS380C/2010/papers/ssaCytron.pdf
int iterCount = 0;
Map<BasicBlock, Integer> hasAlready = Maps.newHashMap();
Map<BasicBlock, Integer> work = Maps.newHashMap();
for (BasicBlock X : cfg.getLiveBasicBlocks()) {
hasAlready.put(X, 0);
work.put(X, 0);
}
Queue<BasicBlock> W = Lists.newLinkedList();
for (Variable V : cfg.variables()) {
iterCount = iterCount + 1;
for (BasicBlock X :
Iterables.filter(cfg.getLiveBasicBlocks(), CfgPredicates.containsAssignmentTo(V))) {
work.put(X, iterCount);
W.add(X);
}
while (!W.isEmpty()) {
BasicBlock X = W.poll();
for (BasicBlock Y : dtree.getFrontier(X)) {
if (X != cfg.getExit()) {
if (hasAlready.get(Y) < iterCount) {
Y.insertPhiFunction(V, cfg.getPredecessors(Y).size());
// place (V <- phi(V,..., V)) at Y
hasAlready.put(Y, iterCount);
if (work.get(Y) < iterCount) {
work.put(Y, iterCount);
W.add(Y);
}
}
}
}
}
}
}
