/// <summary>
/// Merges another state into this state by taking the set unions of all their respective reaching definitions
/// </summary>
/// <param name="other">another state</param>
/// <returns>indication whether this state was changed by the merging procedure</returns>
public EMergeResult Merge(VarAssignmentSet other)
{
EMergeResult result = _succMerge ? EMergeResult.NoChange : EMergeResult.Change;
_succMerge = true;
for (int i = 0; i < other._asmts.Length; i++)
{
if (_fixedLocals[i])
{
continue;
}
HashSet <int> rhss = other._asmts[i];
if (rhss != null)
{
foreach (int rhs in rhss)
{
if (_asmts.Add(i, rhs))
{
result = EMergeResult.Change;
}
}
}
if (other._sideFx[i] && !_sideFx[i])
{
_sideFx[i] = true;
result = EMergeResult.Change;
}
}
return(result);
}
private void DetectEliminableAccesses()
{
_writeToRead = new Dictionary <int, int>();
_eliminableLocals = new HashSet <int>();
_writtenAndNeverRead = new HashSet <int>();
for (int localIndex = 0; localIndex < _numLocals; localIndex++)
{
if (IsEliminationInhibited(localIndex))
{
continue;
}
HashSet <int> storePoints = _storePoints[localIndex];
int numEliminatedAccesses = 0;
foreach (int storePoint in storePoints)
{
if (storePoint < 0)
{
continue;
}
var storeBB = Code.GetBasicBlockContaining(storePoint);
HashSet <int> uses = _varUses.Get(storePoint);
// Assignment never used?
if (DetectWriteAndNeverRead && uses.Count == 0)
{
_writtenAndNeverRead.Add(storePoint);
numEliminatedAccesses++;
}
// Used exactly once?
else if (DetectReadAfterWrite && uses.Count == 1)
{
int readPoint = uses.Single();
var readBB = Code.GetBasicBlockContaining(readPoint);
// If variable is read within a different basic block than is
// is stored, do not optimize.
if (DoNotOptimizeAcrossBasicBlocks && !readBB.Equals(storeBB))
{
continue;
}
VarAssignmentSet preCond = _preConds[readPoint];
if (preCond.HasSideEffects(localIndex))
{
continue;
}
IEnumerable <int> readPointStores = preCond.GetStorePoints(localIndex);
// Variable definition must be unambiguous
if (readPointStores.Count() != 1)
{
continue;
}
Debug.Assert(readPointStores.Single() == storePoint);
//_readAfterWritePairs.Add(new ReadAfterWritePair(storePoint, readPoint));
_writeToRead[storePoint] = readPoint;
numEliminatedAccesses++;
}
}
if (numEliminatedAccesses == storePoints.Count)
{
// All variable accesses could be eliminated
// ==> local variable is completely superfluous
_eliminableLocals.Add(localIndex);
}
}
}
private void IterateToFixPoint()
{
List <Ti> instrs = Code.Instructions;
_preConds = new VarAssignmentSet[instrs.Count];
_postConds = new VarAssignmentSet[instrs.Count];
_refPoints = new int[instrs.Count];
_refUses = new Dictionary <int, List <int> >();
_inhibitElimination = new bool[_numLocals];
Queue <int> q = new Queue <int>();
_loadPoints = new HashSet <int> [_numLocals];
_storePoints = new HashSet <int> [_numLocals];
for (int i = 0; i < _numLocals; i++)
{
if (Code.IsLocalPinned(i))
{
InhitbitElimination(i);
}
_loadPoints[i] = new HashSet <int>();
_storePoints[i] = new HashSet <int>();
}
for (int i = 0; i < instrs.Count; i++)
{
_preConds[i] = new VarAssignmentSet(_numLocals);
_postConds[i] = new VarAssignmentSet(_numLocals);
_refPoints[i] = -1;
}
int startIndex = Code.EntryCB.StartIndex;
_preConds[startIndex].SetInitial();
q.Enqueue(startIndex);
IExtendedInstructionInfo <Ti> xinfo = InstructionInfo as IExtendedInstructionInfo <Ti>;
while (q.Count > 0)
{
int iidx = q.Dequeue();
_curILI = Code.Instructions[iidx];
_curPreCond = _preConds[iidx];
_curPostCond = _postConds[iidx];
_curPostCond.Merge(_curPreCond);
ProcessInstruction();
if (xinfo != null)
{
ProcessInstructionExtended();
}
Ti[] succs = Code.GetSuccessorsOf(_curILI);
foreach (Ti succ in succs)
{
int siidx = succ.Index;
if (_preConds[siidx].Merge(_curPostCond) ==
VarAssignmentSet.EMergeResult.Change)
{
q.Enqueue(siidx);
}
}
}
// Post-process to make sure each variable has at least one assignment location
// Variables which are not assigned in the course of the program are assumed
// to possess a "virtual assignment" location at IL index -1.
for (int i = 0; i < _numLocals; i++)
{
if (_storePoints[i].Count == 0)
{
_storePoints[i].Add(-1);
}
}
}
