| //===- llvm/ADT/SuffixTree.h - Tree for substrings --------------*- 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // A data structure for fast substring queries. |
| // |
| // Suffix trees represent the suffixes of their input strings in their leaves. |
| // A suffix tree is a type of compressed trie structure where each node |
| // represents an entire substring rather than a single character. Each leaf |
| // of the tree is a suffix. |
| // |
| // A suffix tree can be seen as a type of state machine where each state is a |
| // substring of the full string. The tree is structured so that, for a string |
| // of length N, there are exactly N leaves in the tree. This structure allows |
| // us to quickly find repeated substrings of the input string. |
| // |
| // In this implementation, a "string" is a vector of unsigned integers. |
| // These integers may result from hashing some data type. A suffix tree can |
| // contain 1 or many strings, which can then be queried as one large string. |
| // |
| // The suffix tree is implemented using Ukkonen's algorithm for linear-time |
| // suffix tree construction. Ukkonen's algorithm is explained in more detail |
| // in the paper by Esko Ukkonen "On-line construction of suffix trees. The |
| // paper is available at |
| // |
| // https://www.cs.helsinki.fi/u/ukkonen/SuffixT1withFigs.pdf |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_SUPPORT_SUFFIXTREE_H |
| #define LLVM_SUPPORT_SUFFIXTREE_H |
| |
| #include "llvm/ADT/ArrayRef.h" |
| #include "llvm/Support/Allocator.h" |
| #include "llvm/Support/SuffixTreeNode.h" |
| |
| namespace llvm { |
| class SuffixTree { |
| public: |
| /// Each element is an integer representing an instruction in the module. |
| ArrayRef<unsigned> Str; |
| |
| /// A repeated substring in the tree. |
| struct RepeatedSubstring { |
| /// The length of the string. |
| unsigned Length; |
| |
| /// The start indices of each occurrence. |
| SmallVector<unsigned> StartIndices; |
| }; |
| |
| private: |
| /// Maintains internal nodes in the tree. |
| SpecificBumpPtrAllocator<SuffixTreeInternalNode> InternalNodeAllocator; |
| /// Maintains leaf nodes in the tree. |
| SpecificBumpPtrAllocator<SuffixTreeLeafNode> LeafNodeAllocator; |
| |
| /// The root of the suffix tree. |
| /// |
| /// The root represents the empty string. It is maintained by the |
| /// \p NodeAllocator like every other node in the tree. |
| SuffixTreeInternalNode *Root = nullptr; |
| |
| /// The end index of each leaf in the tree. |
| unsigned LeafEndIdx = SuffixTreeNode::EmptyIdx; |
| |
| /// Helper struct which keeps track of the next insertion point in |
| /// Ukkonen's algorithm. |
| struct ActiveState { |
| /// The next node to insert at. |
| SuffixTreeInternalNode *Node = nullptr; |
| |
| /// The index of the first character in the substring currently being added. |
| unsigned Idx = SuffixTreeNode::EmptyIdx; |
| |
| /// The length of the substring we have to add at the current step. |
| unsigned Len = 0; |
| }; |
| |
| /// The point the next insertion will take place at in the |
| /// construction algorithm. |
| ActiveState Active; |
| |
| /// Allocate a leaf node and add it to the tree. |
| /// |
| /// \param Parent The parent of this node. |
| /// \param StartIdx The start index of this node's associated string. |
| /// \param Edge The label on the edge leaving \p Parent to this node. |
| /// |
| /// \returns A pointer to the allocated leaf node. |
| SuffixTreeNode *insertLeaf(SuffixTreeInternalNode &Parent, unsigned StartIdx, |
| unsigned Edge); |
| |
| /// Allocate an internal node and add it to the tree. |
| /// |
| /// \param Parent The parent of this node. Only null when allocating the root. |
| /// \param StartIdx The start index of this node's associated string. |
| /// \param EndIdx The end index of this node's associated string. |
| /// \param Edge The label on the edge leaving \p Parent to this node. |
| /// |
| /// \returns A pointer to the allocated internal node. |
| SuffixTreeInternalNode *insertInternalNode(SuffixTreeInternalNode *Parent, |
| unsigned StartIdx, unsigned EndIdx, |
| unsigned Edge); |
| |
| /// Allocate the root node and add it to the tree. |
| /// |
| /// \returns A pointer to the root. |
| SuffixTreeInternalNode *insertRoot(); |
| |
| /// Set the suffix indices of the leaves to the start indices of their |
| /// respective suffixes. |
| void setSuffixIndices(); |
| |
| /// Construct the suffix tree for the prefix of the input ending at |
| /// \p EndIdx. |
| /// |
| /// Used to construct the full suffix tree iteratively. At the end of each |
| /// step, the constructed suffix tree is either a valid suffix tree, or a |
| /// suffix tree with implicit suffixes. At the end of the final step, the |
| /// suffix tree is a valid tree. |
| /// |
| /// \param EndIdx The end index of the current prefix in the main string. |
| /// \param SuffixesToAdd The number of suffixes that must be added |
| /// to complete the suffix tree at the current phase. |
| /// |
| /// \returns The number of suffixes that have not been added at the end of |
| /// this step. |
| unsigned extend(unsigned EndIdx, unsigned SuffixesToAdd); |
| |
| public: |
| /// Construct a suffix tree from a sequence of unsigned integers. |
| /// |
| /// \param Str The string to construct the suffix tree for. |
| SuffixTree(const ArrayRef<unsigned> &Str); |
| |
| /// Iterator for finding all repeated substrings in the suffix tree. |
| struct RepeatedSubstringIterator { |
| private: |
| /// The current node we're visiting. |
| SuffixTreeNode *N = nullptr; |
| |
| /// The repeated substring associated with this node. |
| RepeatedSubstring RS; |
| |
| /// The nodes left to visit. |
| SmallVector<SuffixTreeInternalNode *> InternalNodesToVisit; |
| |
| /// The minimum length of a repeated substring to find. |
| /// Since we're outlining, we want at least two instructions in the range. |
| /// FIXME: This may not be true for targets like X86 which support many |
| /// instruction lengths. |
| const unsigned MinLength = 2; |
| |
| /// Move the iterator to the next repeated substring. |
| void advance(); |
| |
| public: |
| /// Return the current repeated substring. |
| RepeatedSubstring &operator*() { return RS; } |
| |
| RepeatedSubstringIterator &operator++() { |
| advance(); |
| return *this; |
| } |
| |
| RepeatedSubstringIterator operator++(int I) { |
| RepeatedSubstringIterator It(*this); |
| advance(); |
| return It; |
| } |
| |
| bool operator==(const RepeatedSubstringIterator &Other) const { |
| return N == Other.N; |
| } |
| bool operator!=(const RepeatedSubstringIterator &Other) const { |
| return !(*this == Other); |
| } |
| |
| RepeatedSubstringIterator(SuffixTreeInternalNode *N) : N(N) { |
| // Do we have a non-null node? |
| if (!N) |
| return; |
| // Yes. At the first step, we need to visit all of N's children. |
| // Note: This means that we visit N last. |
| InternalNodesToVisit.push_back(N); |
| advance(); |
| } |
| }; |
| |
| typedef RepeatedSubstringIterator iterator; |
| iterator begin() { return iterator(Root); } |
| iterator end() { return iterator(nullptr); } |
| }; |
| |
| } // namespace llvm |
| |
| #endif // LLVM_SUPPORT_SUFFIXTREE_H |