protected void eliminateDeadCode(JilMethod method) {
HashMap<String, Integer> labels = new HashMap();
List<JilStmt> body = method.body();
Stack<Integer> worklist = new Stack();
HashSet<Integer> visited = new HashSet();
// first, initialiser label map
int pos = 0;
for (JilStmt s : body) {
if (s instanceof JilStmt.Label) {
JilStmt.Label lab = (JilStmt.Label) s;
labels.put(lab.label(), pos);
}
pos++;
}
worklist.push(0);
visited.add(0);
while (!worklist.isEmpty()) {
int idx = worklist.pop();
if (idx != body.size()) {
JilStmt stmt = body.get(idx);
addSuccessors(worklist, visited, labels, stmt, idx);
}
}
// Ok, now eliminate any dead statements (if there are any)
if (visited.size() <= body.size()) {
pos = 0;
int size = body.size();
for (int i = 0; i != size; ++i) {
if (!visited.contains(i)) {
body.remove(pos);
} else {
pos = pos + 1;
}
}
}
}
protected void addSuccessors(
Stack<Integer> worklist,
HashSet<Integer> visited,
HashMap<String, Integer> labels,
JilStmt stmt,
int offset) {
// First, add sequential exit if there is one.
if (stmt instanceof JilStmt.Goto) {
JilStmt.Goto gto = (JilStmt.Goto) stmt;
int target = labels.get(gto.label());
if (!visited.contains(target)) {
worklist.add(target);
visited.add(target);
}
} else if (stmt instanceof JilStmt.Switch) {
JilStmt.Switch swt = (JilStmt.Switch) stmt;
for (Pair<JilExpr.Number, String> c : swt.cases()) {
int target = labels.get(c.second());
if (!visited.contains(target)) {
worklist.add(target);
visited.add(target);
}
}
// And, don't forget the default label!
int deftarget = labels.get(swt.defaultLabel());
if (!visited.contains(deftarget)) {
worklist.add(deftarget);
visited.add(deftarget);
}
} else if (!(stmt instanceof JilStmt.Return || stmt instanceof JilStmt.Throw)) {
// this is a statement with a sequential exit
if (!visited.contains(offset + 1)) {
worklist.add(offset + 1);
visited.add(offset + 1);
}
}
// Second, check for conditional branch
if (stmt instanceof JilStmt.IfGoto) {
JilStmt.IfGoto gto = (JilStmt.IfGoto) stmt;
int target = labels.get(gto.label());
if (!visited.contains(target)) {
worklist.add(target);
visited.add(target);
}
}
// Third, add any exceptional edges
for (Pair<Type.Clazz, String> ex : stmt.exceptions()) {
int target = labels.get(ex.second());
if (!visited.contains(target)) {
worklist.add(target);
visited.add(target);
}
}
}