//===- llvm/ADT/DepthFirstIterator.h - Depth First iterator -----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file builds on the ADT/GraphTraits.h file to build generic depth
/// first graph iterator. This file exposes the following functions/types:
///
/// df_begin/df_end/df_iterator
/// * Normal depth-first iteration - visit a node and then all of its
/// children.
///
/// idf_begin/idf_end/idf_iterator
/// * Depth-first iteration on the 'inverse' graph.
///
/// df_ext_begin/df_ext_end/df_ext_iterator
/// * Normal depth-first iteration - visit a node and then all of its
/// children. This iterator stores the 'visited' set in an external set,
/// which allows it to be more efficient, and allows external clients to
/// use the set for other purposes.
///
/// idf_ext_begin/idf_ext_end/idf_ext_iterator
/// * Depth-first iteration on the 'inverse' graph.
/// This iterator stores the 'visited' set in an external set, which
/// allows it to be more efficient, and allows external clients to use
/// the set for other purposes.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_DEPTHFIRSTITERATOR_H
#define LLVM_ADT_DEPTHFIRSTITERATOR_H
#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/iterator_range.h"
#include <iterator>
#include <optional>
#include <utility>
#include <vector>
namespace llvm {
// df_iterator_storage - A private class which is used to figure out where to
// store the visited set.
template<class SetType, bool External> // Non-external set
class df_iterator_storage {
public:
SetType Visited;
};
template<class SetType>
class df_iterator_storage<SetType, true> {
public:
df_iterator_storage(SetType &VSet) : Visited(VSet) {}
df_iterator_storage(const df_iterator_storage &S) : Visited(S.Visited) {}
SetType &Visited;
};
// The visited stated for the iteration is a simple set augmented with
// one more method, completed, which is invoked when all children of a
// node have been processed. It is intended to distinguish of back and
// cross edges in the spanning tree but is not used in the common case.
template <typename NodeRef, unsigned SmallSize=8>
struct df_iterator_default_set : public SmallPtrSet<NodeRef, SmallSize> {
using BaseSet = SmallPtrSet<NodeRef, SmallSize>;
using iterator = typename BaseSet::iterator;
std::pair<iterator,bool> insert(NodeRef N) { return BaseSet::insert(N); }
template <typename IterT>
void insert(IterT Begin, IterT End) { BaseSet::insert(Begin,End); }
void completed(NodeRef) {}
};
// Generic Depth First Iterator
template <class GraphT,
class SetType =
df_iterator_default_set<typename GraphTraits<GraphT>::NodeRef>,
bool ExtStorage = false, class GT = GraphTraits<GraphT>>
class df_iterator : public df_iterator_storage<SetType, ExtStorage> {
public:
using iterator_category = std::forward_iterator_tag;
using value_type = typename GT::NodeRef;
using difference_type = std::ptrdiff_t;
using pointer = value_type *;
using reference = value_type &;
private:
using NodeRef = typename GT::NodeRef;
using ChildItTy = typename GT::ChildIteratorType;
// First element is node reference, second is the 'next child' to visit.
// The second child is initialized lazily to pick up graph changes during the
// DFS.
using StackElement = std::pair<NodeRef, std::optional<ChildItTy>>;
// VisitStack - Used to maintain the ordering. Top = current block
std::vector<StackElement> VisitStack;
inline df_iterator(NodeRef Node) {
this->Visited.insert(Node);
VisitStack.push_back(StackElement(Node, std::nullopt));
}
inline df_iterator() = default; // End is when stack is empty
inline df_iterator(NodeRef Node, SetType &S)
: df_iterator_storage<SetType, ExtStorage>(S) {
if (this->Visited.insert(Node).second)
VisitStack.push_back(StackElement(Node, std::nullopt));
}
inline df_iterator(SetType &S)
: df_iterator_storage<SetType, ExtStorage>(S) {
// End is when stack is empty
}
inline void toNext() {
do {
NodeRef Node = VisitStack.back().first;
std::optional<ChildItTy> &Opt = VisitStack.back().second;
if (!Opt)
Opt.emplace(GT::child_begin(Node));
// Notice that we directly mutate *Opt here, so that
// VisitStack.back().second actually gets updated as the iterator
// increases.
while (*Opt != GT::child_end(Node)) {
NodeRef Next = *(*Opt)++;
// Has our next sibling been visited?
if (this->Visited.insert(Next).second) {
// No, do it now.
VisitStack.push_back(StackElement(Next, std::nullopt));
return;
}
}
this->Visited.completed(Node);
// Oops, ran out of successors... go up a level on the stack.
VisitStack.pop_back();
} while (!VisitStack.empty());
}
public:
// Provide static begin and end methods as our public "constructors"
static df_iterator begin(const GraphT &G) {
return df_iterator(GT::getEntryNode(G));
}
static df_iterator end(const GraphT &G) { return df_iterator(); }
// Static begin and end methods as our public ctors for external iterators
static df_iterator begin(const GraphT &G, SetType &S) {
return df_iterator(GT::getEntryNode(G), S);
}
static df_iterator end(const GraphT &G, SetType &S) { return df_iterator(S); }
bool operator==(const df_iterator &x) const {
return VisitStack == x.VisitStack;
}
bool operator!=(const df_iterator &x) const { return !(*this == x); }
const NodeRef &operator*() const { return VisitStack.back().first; }
// This is a nonstandard operator-> that dereferences the pointer an extra
// time... so that you can actually call methods ON the Node, because
// the contained type is a pointer. This allows BBIt->getTerminator() f.e.
//
NodeRef operator->() const { return **this; }
df_iterator &operator++() { // Preincrement
toNext();
return *this;
}
/// Skips all children of the current node and traverses to next node
///
/// Note: This function takes care of incrementing the iterator. If you
/// always increment and call this function, you risk walking off the end.
df_iterator &skipChildren() {
VisitStack.pop_back();
if (!VisitStack.empty())
toNext();
return *this;
}
df_iterator operator++(int) { // Postincrement
df_iterator tmp = *this;
++*this;
return tmp;
}
// nodeVisited - return true if this iterator has already visited the
// specified node. This is public, and will probably be used to iterate over
// nodes that a depth first iteration did not find: ie unreachable nodes.
//
bool nodeVisited(NodeRef Node) const {
return this->Visited.contains(Node);
}
/// getPathLength - Return the length of the path from the entry node to the
/// current node, counting both nodes.
unsigned getPathLength() const { return VisitStack.size(); }
/// getPath - Return the n'th node in the path from the entry node to the
/// current node.
NodeRef getPath(unsigned n) const { return VisitStack[n].first; }
};
// Provide global constructors that automatically figure out correct types...
//
template <class T>
df_iterator<T> df_begin(const T& G) {
return df_iterator<T>::begin(G);
}
template <class T>
df_iterator<T> df_end(const T& G) {
return df_iterator<T>::end(G);
}
// Provide an accessor method to use them in range-based patterns.
template <class T>
iterator_range<df_iterator<T>> depth_first(const T& G) {
return make_range(df_begin(G), df_end(G));
}
// Provide global definitions of external depth first iterators...
template <class T, class SetTy = df_iterator_default_set<typename GraphTraits<T>::NodeRef>>
struct df_ext_iterator : public df_iterator<T, SetTy, true> {
df_ext_iterator(const df_iterator<T, SetTy, true> &V)
: df_iterator<T, SetTy, true>(V) {}
};
template <class T, class SetTy>
df_ext_iterator<T, SetTy> df_ext_begin(const T& G, SetTy &S) {
return df_ext_iterator<T, SetTy>::begin(G, S);
}
template <class T, class SetTy>
df_ext_iterator<T, SetTy> df_ext_end(const T& G, SetTy &S) {
return df_ext_iterator<T, SetTy>::end(G, S);
}
template <class T, class SetTy>
iterator_range<df_ext_iterator<T, SetTy>> depth_first_ext(const T& G,
SetTy &S) {
return make_range(df_ext_begin(G, S), df_ext_end(G, S));
}
// Provide global definitions of inverse depth first iterators...
template <class T,
class SetTy =
df_iterator_default_set<typename GraphTraits<T>::NodeRef>,
bool External = false>
struct idf_iterator : public df_iterator<Inverse<T>, SetTy, External> {
idf_iterator(const df_iterator<Inverse<T>, SetTy, External> &V)
: df_iterator<Inverse<T>, SetTy, External>(V) {}
};
template <class T>
idf_iterator<T> idf_begin(const T& G) {
return idf_iterator<T>::begin(Inverse<T>(G));
}
template <class T>
idf_iterator<T> idf_end(const T& G){
return idf_iterator<T>::end(Inverse<T>(G));
}
// Provide an accessor method to use them in range-based patterns.
template <class T>
iterator_range<idf_iterator<T>> inverse_depth_first(const T& G) {
return make_range(idf_begin(G), idf_end(G));
}
// Provide global definitions of external inverse depth first iterators...
template <class T, class SetTy = df_iterator_default_set<typename GraphTraits<T>::NodeRef>>
struct idf_ext_iterator : public idf_iterator<T, SetTy, true> {
idf_ext_iterator(const idf_iterator<T, SetTy, true> &V)
: idf_iterator<T, SetTy, true>(V) {}
idf_ext_iterator(const df_iterator<Inverse<T>, SetTy, true> &V)
: idf_iterator<T, SetTy, true>(V) {}
};
template <class T, class SetTy>
idf_ext_iterator<T, SetTy> idf_ext_begin(const T& G, SetTy &S) {
return idf_ext_iterator<T, SetTy>::begin(Inverse<T>(G), S);
}
template <class T, class SetTy>
idf_ext_iterator<T, SetTy> idf_ext_end(const T& G, SetTy &S) {
return idf_ext_iterator<T, SetTy>::end(Inverse<T>(G), S);
}
template <class T, class SetTy>
iterator_range<idf_ext_iterator<T, SetTy>> inverse_depth_first_ext(const T& G,
SetTy &S) {
return make_range(idf_ext_begin(G, S), idf_ext_end(G, S));
}
} // end namespace llvm
#endif // LLVM_ADT_DEPTHFIRSTITERATOR_H