/// <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);
}
/// <summary>
/// Perform intra-block copy propagation.
/// </summary>
/// <param name="Graph">HlGraph.</param>
/// <returns>TRUE if any changes have occured, FALSE otherwise.</returns>
public static bool Do(HlGraph Graph)
{
bool Changed = false;
CpState State = new CpState();
Dictionary <Location, LocDef> InsertedDict = new Dictionary <Location, LocDef>();
List <Location> RemoveKeys = new List <Location>();
List <KeyValuePair <Location, LocDef> > NewDefs = new List <KeyValuePair <Location, LocDef> >();
//
// Get the list of undefined locations at the end of each basic block
//
DataFlow <LocationList> .Result DfResult = DeadAssignmentElimination.DoDF(Graph);
//
// Iterate through basic blocks
//
foreach (BasicBlock BB in Graph.BasicBlocks)
{
//
// Iterate through instructions
//
State.Defs.Clear();
for (int InstructionIndex = 0; InstructionIndex < BB.Instructions.Count; InstructionIndex++)
{
Instruction Instruction = BB.Instructions[InstructionIndex];
//
// Query lists of used and defined locations for the current instruction. If it uses
// a location that is present in the CpState, the definition can only be pasted if:
//
// 1) The definition is not of the form "x := f(..., x, ...)"; i.e., the location
// does not depend on an equally-named one at the defining site,
//
// OR
//
// 2) The definition is of the form "x := f(..., x, ...)", and the definition is dead after
// the current instruction.
//
// NOTE: Pasting the definition in case (2) duplicates evaluation of "f" at the current
// instruction, as dead assignment elimination will not be able to remove the original
// defining site due to location x being used here. Therefore, in this case, we need to
// remove the instruction itself if the definition is pasted, but we can only do so if the
// value is not used afterwards.
//
LocationUsage LocationUsage = LocationUsage.ForInstruction(Instruction);
foreach (Location Location in LocationUsage.UsedLocations)
{
LocDef LocDef;
if (State.Defs.TryGetValue(Location, out LocDef) && LocDef.SelfRef)
{
LocationList DeadList = DeadAssignmentElimination.BeforeInstruction(BB, InstructionIndex + 1, DfResult.ExitState[BB]);
if (!DeadList.Contains(Location))
{
State.Defs.Remove(Location);
}
}
}
//
// Rewrite trees
//
Instruction.Argument = ForTree(BB, Instruction, State, Instruction.Argument, false, ref Changed, InsertedDict);
Instruction.Result = ForTree(BB, Instruction, State, Instruction.Result, true, ref Changed, InsertedDict);
//
// Change CpState to reflect any newly defined locations
//
foreach (Location Location in LocationUsage.DefinedLocations)
{
State.Defs.Remove(Location);
if (Location.LocationType == LocationType.CilStack || Location.LocationType == LocationType.LocalVariable)
{
System.Diagnostics.Debug.Assert(Instruction.InstructionType == InstructionType.Assignment);
if (Instruction.Result != null && Instruction.Result.NodeType == NodeType.Location)
{
LocDef NewLocDef = new LocDef(BB, Instruction, Location, Instruction.Argument);
NewDefs.Add(new KeyValuePair <Location, LocDef>(Location, NewLocDef));
}
}
//
// Remove other definition entries that have been invalidated by redefining one of their inputs
//
foreach (KeyValuePair <Location, LocDef> Entry in State.Defs)
{
if (Entry.Value.UsedLocations.Contains(Location))
{
RemoveKeys.Add(Entry.Key);
}
}
}
//
// Remove and add entries to CpState as necessary
//
if (RemoveKeys != null && RemoveKeys.Count != 0)
{
foreach (Location RemoveLocation in RemoveKeys)
{
State.Defs.Remove(RemoveLocation);
}
RemoveKeys.Clear();
}
if (NewDefs != null && NewDefs.Count != 0)
{
foreach (KeyValuePair <Location, LocDef> Entry in NewDefs)
{
State.Defs.Add(Entry.Key, Entry.Value);
}
NewDefs.Clear();
}
//
// Remove instructions at defining sites that have become obsolete. This is only
// true for CilStack locations, as they are the only ones guaranteed to be consumed
// at most once. All other obsolete instructions are taken care of by dead code
// elimination.
//
// BUGBUG: this fails for the DUP instruction...
//
if (InsertedDict.Count != 0 && LocationUsage.UsedLocations.Count != 0)
{
foreach (Location Location in LocationUsage.UsedLocations)
{
LocDef RemoveLocDef;
if (Location.LocationType == LocationType.CilStack && InsertedDict.TryGetValue(Location, out RemoveLocDef))
{
bool OK = RemoveLocDef.BasicBlock.Instructions.Remove(RemoveLocDef.Instruction);
//System.Diagnostics.Debug.Assert(OK);
System.Diagnostics.Debug.Assert(object.ReferenceEquals(RemoveLocDef.BasicBlock, BB));
if (object.ReferenceEquals(RemoveLocDef.BasicBlock, BB) && OK)
{
System.Diagnostics.Debug.Assert(object.ReferenceEquals(BB.Instructions[InstructionIndex - 1], Instruction));
InstructionIndex--;
}
}
}
}
InsertedDict.Clear();
}
}
return(Changed);
}