313 lines
11 KiB
C
313 lines
11 KiB
C
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//===- llvm/ADT/PostOrderIterator.h - PostOrder iterator --------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file builds on the ADT/GraphTraits.h file to build a generic graph
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// post order iterator. This should work over any graph type that has a
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// GraphTraits specialization.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ADT_POSTORDERITERATOR_H
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#define LLVM_ADT_POSTORDERITERATOR_H
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#include "llvm/ADT/GraphTraits.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/iterator_range.h"
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#include <iterator>
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#include <set>
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#include <utility>
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#include <vector>
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namespace llvm {
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// The po_iterator_storage template provides access to the set of already
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// visited nodes during the po_iterator's depth-first traversal.
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//
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// The default implementation simply contains a set of visited nodes, while
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// the External=true version uses a reference to an external set.
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//
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// It is possible to prune the depth-first traversal in several ways:
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//
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// - When providing an external set that already contains some graph nodes,
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// those nodes won't be visited again. This is useful for restarting a
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// post-order traversal on a graph with nodes that aren't dominated by a
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// single node.
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//
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// - By providing a custom SetType class, unwanted graph nodes can be excluded
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// by having the insert() function return false. This could for example
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// confine a CFG traversal to blocks in a specific loop.
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//
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// - Finally, by specializing the po_iterator_storage template itself, graph
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// edges can be pruned by returning false in the insertEdge() function. This
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// could be used to remove loop back-edges from the CFG seen by po_iterator.
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//
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// A specialized po_iterator_storage class can observe both the pre-order and
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// the post-order. The insertEdge() function is called in a pre-order, while
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// the finishPostorder() function is called just before the po_iterator moves
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// on to the next node.
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/// Default po_iterator_storage implementation with an internal set object.
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template<class SetType, bool External>
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class po_iterator_storage {
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SetType Visited;
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public:
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// Return true if edge destination should be visited.
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template <typename NodeRef>
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bool insertEdge(Optional<NodeRef> From, NodeRef To) {
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return Visited.insert(To).second;
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}
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// Called after all children of BB have been visited.
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template <typename NodeRef> void finishPostorder(NodeRef BB) {}
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};
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/// Specialization of po_iterator_storage that references an external set.
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template<class SetType>
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class po_iterator_storage<SetType, true> {
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SetType &Visited;
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public:
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po_iterator_storage(SetType &VSet) : Visited(VSet) {}
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po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {}
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// Return true if edge destination should be visited, called with From = 0 for
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// the root node.
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// Graph edges can be pruned by specializing this function.
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template <class NodeRef> bool insertEdge(Optional<NodeRef> From, NodeRef To) {
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return Visited.insert(To).second;
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}
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// Called after all children of BB have been visited.
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template <class NodeRef> void finishPostorder(NodeRef BB) {}
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};
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template <class GraphT,
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class SetType =
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SmallPtrSet<typename GraphTraits<GraphT>::NodeRef, 8>,
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bool ExtStorage = false, class GT = GraphTraits<GraphT>>
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class po_iterator
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: public std::iterator<std::forward_iterator_tag, typename GT::NodeRef>,
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public po_iterator_storage<SetType, ExtStorage> {
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using super = std::iterator<std::forward_iterator_tag, typename GT::NodeRef>;
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using NodeRef = typename GT::NodeRef;
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using ChildItTy = typename GT::ChildIteratorType;
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// VisitStack - Used to maintain the ordering. Top = current block
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// First element is basic block pointer, second is the 'next child' to visit
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SmallVector<std::pair<NodeRef, ChildItTy>, 8> VisitStack;
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po_iterator(NodeRef BB) {
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this->insertEdge(Optional<NodeRef>(), BB);
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VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
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traverseChild();
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}
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po_iterator() = default; // End is when stack is empty.
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po_iterator(NodeRef BB, SetType &S)
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: po_iterator_storage<SetType, ExtStorage>(S) {
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if (this->insertEdge(Optional<NodeRef>(), BB)) {
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VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
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traverseChild();
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}
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}
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po_iterator(SetType &S)
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: po_iterator_storage<SetType, ExtStorage>(S) {
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} // End is when stack is empty.
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void traverseChild() {
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while (VisitStack.back().second != GT::child_end(VisitStack.back().first)) {
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NodeRef BB = *VisitStack.back().second++;
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if (this->insertEdge(Optional<NodeRef>(VisitStack.back().first), BB)) {
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// If the block is not visited...
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VisitStack.push_back(std::make_pair(BB, GT::child_begin(BB)));
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}
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}
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}
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public:
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using pointer = typename super::pointer;
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// Provide static "constructors"...
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static po_iterator begin(GraphT G) {
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return po_iterator(GT::getEntryNode(G));
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}
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static po_iterator end(GraphT G) { return po_iterator(); }
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static po_iterator begin(GraphT G, SetType &S) {
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return po_iterator(GT::getEntryNode(G), S);
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}
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static po_iterator end(GraphT G, SetType &S) { return po_iterator(S); }
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bool operator==(const po_iterator &x) const {
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return VisitStack == x.VisitStack;
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}
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bool operator!=(const po_iterator &x) const { return !(*this == x); }
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const NodeRef &operator*() const { return VisitStack.back().first; }
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// This is a nonstandard operator-> that dereferences the pointer an extra
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// time... so that you can actually call methods ON the BasicBlock, because
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// the contained type is a pointer. This allows BBIt->getTerminator() f.e.
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//
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NodeRef operator->() const { return **this; }
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po_iterator &operator++() { // Preincrement
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this->finishPostorder(VisitStack.back().first);
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VisitStack.pop_back();
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if (!VisitStack.empty())
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traverseChild();
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return *this;
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}
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po_iterator operator++(int) { // Postincrement
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po_iterator tmp = *this;
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++*this;
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return tmp;
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}
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};
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// Provide global constructors that automatically figure out correct types...
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//
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template <class T>
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po_iterator<T> po_begin(const T &G) { return po_iterator<T>::begin(G); }
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template <class T>
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po_iterator<T> po_end (const T &G) { return po_iterator<T>::end(G); }
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template <class T> iterator_range<po_iterator<T>> post_order(const T &G) {
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return make_range(po_begin(G), po_end(G));
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}
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// Provide global definitions of external postorder iterators...
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template <class T, class SetType = std::set<typename GraphTraits<T>::NodeRef>>
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struct po_ext_iterator : public po_iterator<T, SetType, true> {
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po_ext_iterator(const po_iterator<T, SetType, true> &V) :
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po_iterator<T, SetType, true>(V) {}
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};
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template<class T, class SetType>
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po_ext_iterator<T, SetType> po_ext_begin(T G, SetType &S) {
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return po_ext_iterator<T, SetType>::begin(G, S);
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}
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template<class T, class SetType>
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po_ext_iterator<T, SetType> po_ext_end(T G, SetType &S) {
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return po_ext_iterator<T, SetType>::end(G, S);
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}
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template <class T, class SetType>
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iterator_range<po_ext_iterator<T, SetType>> post_order_ext(const T &G, SetType &S) {
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return make_range(po_ext_begin(G, S), po_ext_end(G, S));
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}
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// Provide global definitions of inverse post order iterators...
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template <class T, class SetType = std::set<typename GraphTraits<T>::NodeRef>,
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bool External = false>
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struct ipo_iterator : public po_iterator<Inverse<T>, SetType, External> {
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ipo_iterator(const po_iterator<Inverse<T>, SetType, External> &V) :
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po_iterator<Inverse<T>, SetType, External> (V) {}
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};
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template <class T>
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ipo_iterator<T> ipo_begin(const T &G) {
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return ipo_iterator<T>::begin(G);
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}
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template <class T>
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ipo_iterator<T> ipo_end(const T &G){
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return ipo_iterator<T>::end(G);
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}
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template <class T>
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iterator_range<ipo_iterator<T>> inverse_post_order(const T &G) {
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return make_range(ipo_begin(G), ipo_end(G));
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}
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// Provide global definitions of external inverse postorder iterators...
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template <class T, class SetType = std::set<typename GraphTraits<T>::NodeRef>>
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struct ipo_ext_iterator : public ipo_iterator<T, SetType, true> {
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ipo_ext_iterator(const ipo_iterator<T, SetType, true> &V) :
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ipo_iterator<T, SetType, true>(V) {}
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ipo_ext_iterator(const po_iterator<Inverse<T>, SetType, true> &V) :
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ipo_iterator<T, SetType, true>(V) {}
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};
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template <class T, class SetType>
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ipo_ext_iterator<T, SetType> ipo_ext_begin(const T &G, SetType &S) {
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return ipo_ext_iterator<T, SetType>::begin(G, S);
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}
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template <class T, class SetType>
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ipo_ext_iterator<T, SetType> ipo_ext_end(const T &G, SetType &S) {
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return ipo_ext_iterator<T, SetType>::end(G, S);
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}
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template <class T, class SetType>
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iterator_range<ipo_ext_iterator<T, SetType>>
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inverse_post_order_ext(const T &G, SetType &S) {
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return make_range(ipo_ext_begin(G, S), ipo_ext_end(G, S));
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}
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//===--------------------------------------------------------------------===//
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// Reverse Post Order CFG iterator code
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//===--------------------------------------------------------------------===//
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//
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// This is used to visit basic blocks in a method in reverse post order. This
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// class is awkward to use because I don't know a good incremental algorithm to
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// computer RPO from a graph. Because of this, the construction of the
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// ReversePostOrderTraversal object is expensive (it must walk the entire graph
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// with a postorder iterator to build the data structures). The moral of this
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// story is: Don't create more ReversePostOrderTraversal classes than necessary.
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//
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// Because it does the traversal in its constructor, it won't invalidate when
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// BasicBlocks are removed, *but* it may contain erased blocks. Some places
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// rely on this behavior (i.e. GVN).
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//
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// This class should be used like this:
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// {
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// ReversePostOrderTraversal<Function*> RPOT(FuncPtr); // Expensive to create
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// for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
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// ...
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// }
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// for (rpo_iterator I = RPOT.begin(); I != RPOT.end(); ++I) {
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// ...
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// }
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// }
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//
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template<class GraphT, class GT = GraphTraits<GraphT>>
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class ReversePostOrderTraversal {
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using NodeRef = typename GT::NodeRef;
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std::vector<NodeRef> Blocks; // Block list in normal PO order
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void Initialize(NodeRef BB) {
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std::copy(po_begin(BB), po_end(BB), std::back_inserter(Blocks));
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}
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public:
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using rpo_iterator = typename std::vector<NodeRef>::reverse_iterator;
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using const_rpo_iterator = typename std::vector<NodeRef>::const_reverse_iterator;
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ReversePostOrderTraversal(GraphT G) { Initialize(GT::getEntryNode(G)); }
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// Because we want a reverse post order, use reverse iterators from the vector
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rpo_iterator begin() { return Blocks.rbegin(); }
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const_rpo_iterator begin() const { return Blocks.crbegin(); }
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rpo_iterator end() { return Blocks.rend(); }
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const_rpo_iterator end() const { return Blocks.crend(); }
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};
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} // end namespace llvm
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#endif // LLVM_ADT_POSTORDERITERATOR_H
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