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Add Hybrid Cycle Detection to Andersen's analysis.

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Patch by Curtis Dunham.

llvm-svn: 47959
This commit is contained in:
Daniel Berlin 2008-03-05 19:31:47 +00:00
parent 8322b6fb70
commit 2a8fd44b9d
1 changed files with 272 additions and 32 deletions
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304
lib/Analysis/IPA/Andersens.cpp
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@ -31,10 +31,12 @@
// address taking.
//
// The offline constraint graph optimization portion includes offline variable
// substitution algorithms intended to computer pointer and location
// substitution algorithms intended to compute pointer and location
// equivalences. Pointer equivalences are those pointers that will have the
// same points-to sets, and location equivalences are those variables that
// always appear together in points-to sets.
// always appear together in points-to sets. It also includes an offline
// cycle detection algorithm that allows cycles to be collapsed sooner
// during solving.
//
// The inclusion constraint solving phase iteratively propagates the inclusion
// constraints until a fixed point is reached. This is an O(N^3) algorithm.
@ -48,7 +50,7 @@
// CallReturnPos. The arguments start at getNode(F) + CallArgPos.
//
// Future Improvements:
// Offline detection of online cycles. Use of BDD's.
// Use of BDD's.
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "anders-aa"
@ -418,6 +420,13 @@ namespace {
// pointer equivalent but not location equivalent variables. -1 if we have
// no representative node for this pointer equivalence class yet.
std::vector<int> PENLEClass2Node;
// Union/Find for HCD
std::vector<unsigned> HCDSCCRep;
// HCD's offline-detected cycles; "Statically DeTected"
// -1 if not part of such a cycle, otherwise a representative node.
std::vector<int> SDT;
// Whether to use SDT (UniteNodes can use it during solving, but not before)
bool SDTActive;
public:
static char ID;
@ -546,6 +555,8 @@ namespace {
void RewriteConstraints();
void HU();
void HVN();
void HCD();
void Search(unsigned Node);
void UnitePointerEquivalences();
void SolveConstraints();
bool QueryNode(unsigned Node);
@ -1985,11 +1996,141 @@ void Andersens::PrintLabels() {
}
}
/// The technique used here is described in "The Ant and the
/// Grasshopper: Fast and Accurate Pointer Analysis for Millions of
/// Lines of Code. In Programming Language Design and Implementation
/// (PLDI), June 2007." It is known as the "HCD" (Hybrid Cycle
/// Detection) algorithm. It is called a hybrid because it performs an
/// offline analysis and uses its results during the solving (online)
/// phase. This is just the offline portion; the results of this
/// operation are stored in SDT and are later used in SolveContraints()
/// and UniteNodes().
void Andersens::HCD() {
DOUT << "Starting HCD.\n";
HCDSCCRep.resize(GraphNodes.size());
for (unsigned i = 0; i < GraphNodes.size(); ++i) {
GraphNodes[i].Edges = new SparseBitVector<>;
HCDSCCRep[i] = i;
}
for (unsigned i = 0, e = Constraints.size(); i != e; ++i) {
Constraint &C = Constraints[i];
assert (C.Src < GraphNodes.size() && C.Dest < GraphNodes.size());
if (C.Type == Constraint::AddressOf) {
continue;
} else if (C.Type == Constraint::Load) {
if( C.Offset == 0 )
GraphNodes[C.Dest].Edges->set(C.Src + FirstRefNode);
} else if (C.Type == Constraint::Store) {
if( C.Offset == 0 )
GraphNodes[C.Dest + FirstRefNode].Edges->set(C.Src);
} else {
GraphNodes[C.Dest].Edges->set(C.Src);
}
}
Node2DFS.insert(Node2DFS.begin(), GraphNodes.size(), 0);
Node2Deleted.insert(Node2Deleted.begin(), GraphNodes.size(), false);
Node2Visited.insert(Node2Visited.begin(), GraphNodes.size(), false);
SDT.insert(SDT.begin(), GraphNodes.size() / 2, -1);
DFSNumber = 0;
for (unsigned i = 0; i < GraphNodes.size(); ++i) {
unsigned Node = HCDSCCRep[i];
if (!Node2Deleted[Node])
Search(Node);
}
for (unsigned i = 0; i < GraphNodes.size(); ++i)
if (GraphNodes[i].Edges != NULL) {
delete GraphNodes[i].Edges;
GraphNodes[i].Edges = NULL;
}
while( !SCCStack.empty() )
SCCStack.pop();
Node2DFS.clear();
Node2Visited.clear();
Node2Deleted.clear();
HCDSCCRep.clear();
DOUT << "HCD complete.\n";
}
// Component of HCD:
// Use Nuutila's variant of Tarjan's algorithm to detect
// Strongly-Connected Components (SCCs). For non-trivial SCCs
// containing ref nodes, insert the appropriate information in SDT.
void Andersens::Search(unsigned Node) {
unsigned MyDFS = DFSNumber++;
Node2Visited[Node] = true;
Node2DFS[Node] = MyDFS;
for (SparseBitVector<>::iterator Iter = GraphNodes[Node].Edges->begin(),
End = GraphNodes[Node].Edges->end();
Iter != End;
++Iter) {
unsigned J = HCDSCCRep[*Iter];
assert(GraphNodes[J].isRep() && "Debug check; must be representative");
if (!Node2Deleted[J]) {
if (!Node2Visited[J])
Search(J);
if (Node2DFS[Node] > Node2DFS[J])
Node2DFS[Node] = Node2DFS[J];
}
}
if( MyDFS != Node2DFS[Node] ) {
SCCStack.push(Node);
return;
}
// This node is the root of a SCC, so process it.
//
// If the SCC is "non-trivial" (not a singleton) and contains a reference
// node, we place this SCC into SDT. We unite the nodes in any case.
if (!SCCStack.empty() && Node2DFS[SCCStack.top()] >= MyDFS) {
SparseBitVector<> SCC;
SCC.set(Node);
bool Ref = (Node >= FirstRefNode);
Node2Deleted[Node] = true;
do {
unsigned P = SCCStack.top(); SCCStack.pop();
Ref |= (P >= FirstRefNode);
SCC.set(P);
HCDSCCRep[P] = Node;
} while (!SCCStack.empty() && Node2DFS[SCCStack.top()] >= MyDFS);
if (Ref) {
unsigned Rep = SCC.find_first();
assert(Rep < FirstRefNode && "The SCC didn't have a non-Ref node!");
SparseBitVector<>::iterator i = SCC.begin();
// Skip over the non-ref nodes
while( *i < FirstRefNode )
++i;
while( i != SCC.end() )
SDT[ (*i++) - FirstRefNode ] = Rep;
}
}
}
/// Optimize the constraints by performing offline variable substitution and
/// other optimizations.
void Andersens::OptimizeConstraints() {
DOUT << "Beginning constraint optimization\n";
SDTActive = false;
// Function related nodes need to stay in the same relative position and can't
// be location equivalent.
for (std::map<unsigned, unsigned>::iterator Iter = MaxK.begin();
@ -2051,12 +2192,25 @@ void Andersens::OptimizeConstraints() {
if (FindNode(i) == i) {
Node *N = &GraphNodes[i];
delete N->PointsTo;
N->PointsTo = NULL;
delete N->PredEdges;
N->PredEdges = NULL;
delete N->ImplicitPredEdges;
N->ImplicitPredEdges = NULL;
delete N->PointedToBy;
N->PointedToBy = NULL;
}
}
// perform Hybrid Cycle Detection (HCD)
HCD();
SDTActive = true;
// No longer any need for the upper half of GraphNodes (for ref nodes).
GraphNodes.erase(GraphNodes.begin() + FirstRefNode, GraphNodes.end());
// HCD complete.
DOUT << "Finished constraint optimization\n";
FirstRefNode = 0;
FirstAdrNode = 0;
@ -2221,6 +2375,14 @@ void Andersens::SolveConstraints() {
}
}
std::queue<unsigned int> TarjanWL;
#if !FULL_UNIVERSAL
// "Rep and special variables" - in order for HCD to maintain conservative
// results when !FULL_UNIVERSAL, we need to treat the special variables in
// the same way that the !FULL_UNIVERSAL tweak does throughout the rest of
// the analysis - it's ok to add edges from the special nodes, but never
// *to* the special nodes.
std::vector<unsigned int> RSV;
#endif
while( !CurrWL->empty() ) {
DOUT << "Starting iteration #" << ++NumIters << "\n";
@ -2259,6 +2421,39 @@ void Andersens::SolveConstraints() {
continue;
*(CurrNode->OldPointsTo) |= CurrPointsTo;
// Check the offline-computed equivalencies from HCD.
bool SCC = false;
unsigned Rep;
if (SDT[CurrNodeIndex] >= 0) {
SCC = true;
Rep = FindNode(SDT[CurrNodeIndex]);
#if !FULL_UNIVERSAL
RSV.clear();
#endif
for (SparseBitVector<>::iterator bi = CurrPointsTo.begin();
bi != CurrPointsTo.end(); ++bi) {
unsigned Node = FindNode(*bi);
#if !FULL_UNIVERSAL
if (Node < NumberSpecialNodes) {
RSV.push_back(Node);
continue;
}
#endif
Rep = UniteNodes(Rep,Node);
}
#if !FULL_UNIVERSAL
RSV.push_back(Rep);
#endif
NextWL->insert(&GraphNodes[Rep]);
if ( ! CurrNode->isRep() )
continue;
}
Seen.clear();
/* Now process the constraints for this node. */
@ -2301,39 +2496,74 @@ void Andersens::SolveConstraints() {
li++;
continue;
}
// TODO: hybrid cycle detection would go here, we should check
// See if we can use Hybrid Cycle Detection (that is, check
// if it was a statically detected offline equivalence that
// involves pointers , and if so, remove the redundant constraints.
// involves pointers; if so, remove the redundant constraints).
if( SCC && K == 0 ) {
#if FULL_UNIVERSAL
CurrMember = Rep;
const SparseBitVector<> &Solution = CurrPointsTo;
for (SparseBitVector<>::iterator bi = Solution.begin();
bi != Solution.end();
++bi) {
CurrMember = *bi;
// Need to increment the member by K since that is where we are
// supposed to copy to/from. Note that in positive weight cycles,
// which occur in address taking of fields, K can go past
// MaxK[CurrMember] elements, even though that is all it could point
// to.
if (K > 0 && K > MaxK[CurrMember])
continue;
else
CurrMember = FindNode(CurrMember + K);
// Add an edge to the graph, so we can just do regular bitmap ior next
// time. It may also let us notice a cycle.
#if !FULL_UNIVERSAL
if (*Dest < NumberSpecialNodes)
continue;
#endif
if (GraphNodes[*Src].Edges->test_and_set(*Dest))
if (GraphNodes[*Dest].PointsTo |= *(GraphNodes[*Src].PointsTo))
NextWL->insert(&GraphNodes[*Dest]);
#else
for (unsigned i=0; i < RSV.size(); ++i) {
CurrMember = RSV[i];
if (*Dest < NumberSpecialNodes)
continue;
if (GraphNodes[*Src].Edges->test_and_set(*Dest))
if (GraphNodes[*Dest].PointsTo |= *(GraphNodes[*Src].PointsTo))
NextWL->insert(&GraphNodes[*Dest]);
}
#endif
// since all future elements of the points-to set will be
// equivalent to the current ones, the complex constraints
// become redundant.
//
std::list<Constraint>::iterator lk = li; li++;
#if !FULL_UNIVERSAL
// In this case, we can still erase the constraints when the
// elements of the points-to sets are referenced by *Dest,
// but not when they are referenced by *Src (i.e. for a Load
// constraint). This is because if another special variable is
// put into the points-to set later, we still need to add the
// new edge from that special variable.
if( lk->Type != Constraint::Load)
#endif
GraphNodes[CurrNodeIndex].Constraints.erase(lk);
} else {
const SparseBitVector<> &Solution = CurrPointsTo;
for (SparseBitVector<>::iterator bi = Solution.begin();
bi != Solution.end();
++bi) {
CurrMember = *bi;
// Need to increment the member by K since that is where we are
// supposed to copy to/from. Note that in positive weight cycles,
// which occur in address taking of fields, K can go past
// MaxK[CurrMember] elements, even though that is all it could point
// to.
if (K > 0 && K > MaxK[CurrMember])
continue;
else
CurrMember = FindNode(CurrMember + K);
// Add an edge to the graph, so we can just do regular
// bitmap ior next time. It may also let us notice a cycle.
#if !FULL_UNIVERSAL
if (*Dest < NumberSpecialNodes)
continue;
#endif
if (GraphNodes[*Src].Edges->test_and_set(*Dest))
if (GraphNodes[*Dest].PointsTo |= *(GraphNodes[*Src].PointsTo))
NextWL->insert(&GraphNodes[*Dest]);
}
li++;
}
li++;
}
SparseBitVector<> NewEdges;
SparseBitVector<> ToErase;
@ -2351,8 +2581,8 @@ void Andersens::SolveConstraints() {
// got an edge for the representative, delete the current edge.
if (Rep == CurrNodeIndex ||
(Rep != DestVar && NewEdges.test(Rep))) {
ToErase.set(DestVar);
continue;
ToErase.set(DestVar);
continue;
}
std::pair<unsigned,unsigned> edge(CurrNodeIndex,Rep);
@ -2395,6 +2625,8 @@ void Andersens::SolveConstraints() {
delete N->OldPointsTo;
delete N->Edges;
}
SDTActive = false;
SDT.clear();
}
//===----------------------------------------------------------------------===//
@ -2461,7 +2693,15 @@ unsigned Andersens::UniteNodes(unsigned First, unsigned Second,
DEBUG(PrintNode(SecondNode));
DOUT << "\n";
// TODO: Handle SDT
if (SDTActive)
if (SDT[Second] >= 0)
if (SDT[First] < 0)
SDT[First] = SDT[Second];
else {
UniteNodes( FindNode(SDT[First]), FindNode(SDT[Second]) );
First = FindNode(First);
}
return First;
}