private static void DeadCodeElimination(IRGraph graph)
{
Dictionary <Ident, IRIdent> identAnalysis = SimpleVariableAnalysis(graph);
Queue <Ident> worklist = new Queue <Ident>(identAnalysis.Keys);
while (worklist.Count > 0)
{
Ident ident = worklist.Dequeue();
IRIdent identObj = identAnalysis[ident];
if (identObj.CountUsesites() == 0)
{
IRTuple defStatement = identObj.GetDefsite();
if (!defStatement.HasSideEffects())
{
Console.WriteLine("SSA: Deleting tuple: " + defStatement.toString() + " as it is dead code");
HashSet <Ident> usedVars = defStatement.GetUsedVars();
foreach (Ident used in usedVars)
{
IRIdent usedObj = identAnalysis[used];
usedObj.DeleteUsesite(defStatement);
worklist.Enqueue(used);
}
graph.RemoveStatement(defStatement);
}
}
}
}
// Backward pass to determine liveness at each point in the block
public void ComputeLiveouts()
{
this.liveouts.Clear();
Stack <List <string> > reversed = new Stack <List <string> >(); // Because this is a backward pass, lists will be found in reverse
HashSet <Ident> lo = new HashSet <Ident>(this.liveout);
// Extract liveness information for last statement in block
IRTuple last = this.statements[this.statements.Count - 1];
HashSet <Ident> prevdef = last.GetDefinedVars();
string deflabel = "";
foreach (Ident ident in prevdef)
{
deflabel = ident;
}
HashSet <Ident> prevused = last.GetUsedVars();
List <string> lastliveout = new List <string>();
lastliveout.Add(deflabel);
foreach (Ident ident in lo)
{
lastliveout.Add(ident);
}
reversed.Push(lastliveout);
Console.WriteLine();
for (int i = this.statements.Count - 2; i >= 0; i--) // Start from second-last statement, as we already have liveout for last one
{
IRTuple tup = this.statements[i];
if (lo.Contains(deflabel))
{
lo.Remove(deflabel); // Remove whatever is defined in the next statement
}
foreach (Ident ident in prevused)
{
if (!lo.Contains(ident))
{
lo.Add(ident); // Add whatever is used in the next statement
}
}
deflabel = "";
prevdef = tup.GetDefinedVars();
foreach (Ident ident in prevdef)
{
deflabel = ident;
}
prevused = tup.GetUsedVars();
List <string> currentliveout = new List <string>();
currentliveout.Add(deflabel);
foreach (Ident ident in lo)
{
currentliveout.Add(ident);
}
reversed.Push(currentliveout);
}
while (reversed.Count > 0)
{
this.liveouts.Add(reversed.Pop());
}
}
