#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/SmallPtrSet.h"
#include <set>
-#include <stack>
#include <vector>
namespace llvm {
-template<class SetType, bool External> // Non-external set
+// The po_iterator_storage template provides access to the set of already
+// visited nodes during the po_iterator's depth-first traversal.
+//
+// The default implementation simply contains a set of visited nodes, while
+// the Extended=true version uses a reference to an external set.
+//
+// It is possible to prune the depth-first traversal in several ways:
+//
+// - When providing an external set that already contains some graph nodes,
+// those nodes won't be visited again. This is useful for restarting a
+// post-order traversal on a graph with nodes that aren't dominated by a
+// single node.
+//
+// - By providing a custom SetType class, unwanted graph nodes can be excluded
+// by having the insert() function return false. This could for example
+// confine a CFG traversal to blocks in a specific loop.
+//
+// - Finally, by specializing the po_iterator_storage template itself, graph
+// edges can be pruned by returning false in the insertEdge() function. This
+// could be used to remove loop back-edges from the CFG seen by po_iterator.
+//
+// A specialized po_iterator_storage class can observe both the pre-order and
+// the post-order. The insertEdge() function is called in a pre-order, while
+// the finishPostorder() function is called just before the po_iterator moves
+// on to the next node.
+
+/// Default po_iterator_storage implementation with an internal set object.
+template<class SetType, bool External>
class po_iterator_storage {
-public:
SetType Visited;
+public:
+ // Return true if edge destination should be visited.
+ template<typename NodeType>
+ bool insertEdge(NodeType *From, NodeType *To) {
+ return Visited.insert(To);
+ }
+
+ // Called after all children of BB have been visited.
+ template<typename NodeType>
+ void finishPostorder(NodeType *BB) {}
};
+/// Specialization of po_iterator_storage that references an external set.
template<class SetType>
class po_iterator_storage<SetType, true> {
+ SetType &Visited;
public:
po_iterator_storage(SetType &VSet) : Visited(VSet) {}
po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {}
- SetType &Visited;
+
+ // Return true if edge destination should be visited, called with From = 0 for
+ // the root node.
+ // Graph edges can be pruned by specializing this function.
+ template<class NodeType>
+ bool insertEdge(NodeType *From, NodeType *To) { return Visited.insert(To); }
+
+ // Called after all children of BB have been visited.
+ template<class NodeType>
+ void finishPostorder(NodeType *BB) {}
};
template<class GraphT,
// VisitStack - Used to maintain the ordering. Top = current block
// First element is basic block pointer, second is the 'next child' to visit
- std::stack<std::pair<NodeType *, ChildItTy> > VisitStack;
+ std::vector<std::pair<NodeType *, ChildItTy> > VisitStack;
void traverseChild() {
- while (VisitStack.top().second != GT::child_end(VisitStack.top().first)) {
- NodeType *BB = *VisitStack.top().second++;
- if (!this->Visited.count(BB)) { // If the block is not visited...
- this->Visited.insert(BB);
- VisitStack.push(std::make_pair(BB, GT::child_begin(BB)));
+ while (VisitStack.back().second != GT::child_end(VisitStack.back().first)) {
+ NodeType *BB = *VisitStack.back().second++;
+ if (this->insertEdge(VisitStack.back().first, BB)) {
+ // If the block is not visited...
+ VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
}
}
}
inline po_iterator(NodeType *BB) {
- this->Visited.insert(BB);
- VisitStack.push(std::make_pair(BB, GT::child_begin(BB)));
+ this->insertEdge((NodeType*)nullptr, BB);
+ VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
traverseChild();
}
inline po_iterator() {} // End is when stack is empty.
inline po_iterator(NodeType *BB, SetType &S) :
po_iterator_storage<SetType, ExtStorage>(S) {
- if(!S.count(BB)) {
- this->Visited.insert(BB);
- VisitStack.push(std::make_pair(BB, GT::child_begin(BB)));
+ if (this->insertEdge((NodeType*)nullptr, BB)) {
+ VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
traverseChild();
}
}
inline bool operator!=(const _Self& x) const { return !operator==(x); }
inline pointer operator*() const {
- return VisitStack.top().first;
+ return VisitStack.back().first;
}
// This is a nonstandard operator-> that dereferences the pointer an extra
inline NodeType *operator->() const { return operator*(); }
inline _Self& operator++() { // Preincrement
- VisitStack.pop();
+ this->finishPostorder(VisitStack.back().first);
+ VisitStack.pop_back();
if (!VisitStack.empty())
traverseChild();
return *this;
return ipo_iterator<T>::end(G);
}
-//Provide global definitions of external inverse postorder iterators...
+// Provide global definitions of external inverse postorder iterators...
template <class T,
class SetType = std::set<typename GraphTraits<T>::NodeType*> >
struct ipo_ext_iterator : public ipo_iterator<T, SetType, true> {
ipo_ext_iterator(const ipo_iterator<T, SetType, true> &V) :
- ipo_iterator<T, SetType, true>(&V) {}
+ ipo_iterator<T, SetType, true>(V) {}
ipo_ext_iterator(const po_iterator<Inverse<T>, SetType, true> &V) :
- ipo_iterator<T, SetType, true>(&V) {}
+ ipo_iterator<T, SetType, true>(V) {}
};
template <class T, class SetType>
typedef typename GT::NodeType NodeType;
std::vector<NodeType*> Blocks; // Block list in normal PO order
inline void Initialize(NodeType *BB) {
- copy(po_begin(BB), po_end(BB), back_inserter(Blocks));
+ std::copy(po_begin(BB), po_end(BB), std::back_inserter(Blocks));
}
public:
typedef typename std::vector<NodeType*>::reverse_iterator rpo_iterator;
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