/// <summary>
/// Get list of dead definitions at the point right before a specified instruction.
/// </summary>
/// <param name="BasicBlock">Basic block.</param>
/// <param name="Index">Index of target instruction.</param>
/// <param name="DeadDefinitionList">Optional. List of dead definitions at the end of the basic block.</param>
/// <returns>List of dead definitions before instruction with specified <paramref name="Index"/>.</returns>
public static LocationList BeforeInstruction(BasicBlock BasicBlock, int Index, LocationList DeadDefinitionList)
{
if (Index < 0)
{
throw new ArgumentOutOfRangeException("Index");
}
if (DeadDefinitionList == null)
{
DeadDefinitionList = new LocationList();
}
else
{
DeadDefinitionList = new LocationList(DeadDefinitionList);
}
for (int i = BasicBlock.Instructions.Count - 1; i >= Index; i--)
{
Instruction Instruction = BasicBlock.Instructions[i];
LocationUsage LocationUsage = LocationUsage.ForInstruction(Instruction);
foreach (Location Location in LocationUsage.DefinedLocations)
{
if (Location.LocationType == LocationType.CilStack || Location.LocationType == LocationType.LocalVariable || Location.LocationType == LocationType.Argument)
{
DeadDefinitionList.Add(Location);
}
}
foreach (Location Location in LocationUsage.UsedLocations)
{
if (Location.LocationType == LocationType.CilStack || Location.LocationType == LocationType.LocalVariable || Location.LocationType == LocationType.Argument)
{
DeadDefinitionList.Remove(Location);
}
}
}
return(DeadDefinitionList);
}
private static bool ForBlock(BasicBlock BasicBlock, ref List <Location> DeadDefinitionList)
{
if (DeadDefinitionList == null)
{
DeadDefinitionList = new List <Location>();
}
bool InstructionsDeleted = false;
for (int i = BasicBlock.Instructions.Count - 1; i >= 0; i--)
{
Instruction Instruction = BasicBlock.Instructions[i];
bool IsDeadAssignment = false;
if (Instruction.InstructionType == InstructionType.Assignment &&
Instruction.Result != null && Instruction.Result.NodeType == NodeType.Location)
{
Location Location = ((LocationNode)Instruction.Result).Location;
// Work around default equality check for stack locations. We only
// care about the stack index, not the data type here...
if (Location.LocationType == LocationType.CilStack)
{
foreach (Location Other in DeadDefinitionList)
{
if (Other.LocationType == LocationType.CilStack && ((StackLocation)Other).Index == ((StackLocation)Location).Index)
{
IsDeadAssignment = true;
break;
}
}
}
else if (DeadDefinitionList.Contains(Location))
{
IsDeadAssignment = true;
}
}
// TODO: check for side effects...
if (IsDeadAssignment && HasSideEffects(Instruction.Argument))
{
Instruction.Result = null;
}
else if (IsDeadAssignment)
{
BasicBlock.Instructions.RemoveAt(i);
InstructionsDeleted = true;
continue;
}
LocationUsage LocationUsage = LocationUsage.ForInstruction(Instruction);
foreach (Location Location in LocationUsage.DefinedLocations)
{
if (!DeadDefinitionList.Contains(Location))
{
DeadDefinitionList.Add(Location);
}
}
foreach (Location Location in LocationUsage.UsedLocations)
{
DeadDefinitionList.Remove(Location);
}
}
return(InstructionsDeleted);
}