1 //===--------- LoopIterator.h - Iterate over loop blocks --------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
9 // This file defines iterators to visit the basic blocks within a loop.
11 // These iterators currently visit blocks within subloops as well.
12 // Unfortunately we have no efficient way of summarizing loop exits which would
13 // allow skipping subloops during traversal.
15 // If you want to visit all blocks in a loop and don't need an ordered traveral,
16 // use Loop::block_begin() instead.
18 // This is intentionally designed to work with ill-formed loops in which the
19 // backedge has been deleted. The only prerequisite is that all blocks
20 // contained within the loop according to the most recent LoopInfo analysis are
21 // reachable from the loop header.
22 //===----------------------------------------------------------------------===//
24 #ifndef LLVM_ANALYSIS_LOOPITERATOR_H
25 #define LLVM_ANALYSIS_LOOPITERATOR_H
27 #include "llvm/ADT/PostOrderIterator.h"
28 #include "llvm/Analysis/LoopInfo.h"
32 class LoopBlocksTraversal;
34 /// Store the result of a depth first search within basic blocks contained by a
37 /// TODO: This could be generalized for any CFG region, or the entire CFG.
40 /// Postorder list iterators.
41 typedef std::vector<BasicBlock*>::const_iterator POIterator;
42 typedef std::vector<BasicBlock*>::const_reverse_iterator RPOIterator;
44 friend class LoopBlocksTraversal;
49 /// Map each block to its postorder number. A block is only mapped after it is
50 /// preorder visited by DFS. It's postorder number is initially zero and set
51 /// to nonzero after it is finished by postorder traversal.
52 DenseMap<BasicBlock*, unsigned> PostNumbers;
53 std::vector<BasicBlock*> PostBlocks;
56 LoopBlocksDFS(Loop *Container) :
57 L(Container), PostNumbers(NextPowerOf2(Container->getNumBlocks())) {
58 PostBlocks.reserve(Container->getNumBlocks());
61 Loop *getLoop() const { return L; }
63 /// Traverse the loop blocks and store the DFS result.
64 void perform(LoopInfo *LI);
66 /// Return true if postorder numbers are assigned to all loop blocks.
67 bool isComplete() const { return PostBlocks.size() == L->getNumBlocks(); }
69 /// Iterate over the cached postorder blocks.
70 POIterator beginPostorder() const {
71 assert(isComplete() && "bad loop DFS");
72 return PostBlocks.begin();
74 POIterator endPostorder() const { return PostBlocks.end(); }
76 /// Reverse iterate over the cached postorder blocks.
77 RPOIterator beginRPO() const {
78 assert(isComplete() && "bad loop DFS");
79 return PostBlocks.rbegin();
81 RPOIterator endRPO() const { return PostBlocks.rend(); }
83 /// Return true if this block has been preorder visited.
84 bool hasPreorder(BasicBlock *BB) const { return PostNumbers.count(BB); }
86 /// Return true if this block has a postorder number.
87 bool hasPostorder(BasicBlock *BB) const {
88 DenseMap<BasicBlock*, unsigned>::const_iterator I = PostNumbers.find(BB);
89 return I != PostNumbers.end() && I->second;
92 /// Get a block's postorder number.
93 unsigned getPostorder(BasicBlock *BB) const {
94 DenseMap<BasicBlock*, unsigned>::const_iterator I = PostNumbers.find(BB);
95 assert(I != PostNumbers.end() && "block not visited by DFS");
96 assert(I->second && "block not finished by DFS");
100 /// Get a block's reverse postorder number.
101 unsigned getRPO(BasicBlock *BB) const {
102 return 1 + PostBlocks.size() - getPostorder(BB);
111 /// Specialize po_iterator_storage to record postorder numbers.
112 template<> class po_iterator_storage<LoopBlocksTraversal, true> {
113 LoopBlocksTraversal &LBT;
115 po_iterator_storage(LoopBlocksTraversal &lbs) : LBT(lbs) {}
116 // These functions are defined below.
117 bool insertEdge(BasicBlock *From, BasicBlock *To);
118 void finishPostorder(BasicBlock *BB);
121 /// Traverse the blocks in a loop using a depth-first search.
122 class LoopBlocksTraversal {
124 /// Graph traversal iterator.
125 typedef po_iterator<BasicBlock*, LoopBlocksTraversal, true> POTIterator;
132 LoopBlocksTraversal(LoopBlocksDFS &Storage, LoopInfo *LInfo) :
133 DFS(Storage), LI(LInfo) {}
135 /// Postorder traversal over the graph. This only needs to be done once.
136 /// po_iterator "automatically" calls back to visitPreorder and
137 /// finishPostorder to record the DFS result.
138 POTIterator begin() {
139 assert(DFS.PostBlocks.empty() && "Need clear DFS result before traversing");
140 assert(DFS.L->getNumBlocks() && "po_iterator cannot handle an empty graph");
141 return po_ext_begin(DFS.L->getHeader(), *this);
144 // po_ext_end interface requires a basic block, but ignores its value.
145 return po_ext_end(DFS.L->getHeader(), *this);
148 /// Called by po_iterator upon reaching a block via a CFG edge. If this block
149 /// is contained in the loop and has not been visited, then mark it preorder
150 /// visited and return true.
152 /// TODO: If anyone is interested, we could record preorder numbers here.
153 bool visitPreorder(BasicBlock *BB) {
154 if (!DFS.L->contains(LI->getLoopFor(BB)))
157 return DFS.PostNumbers.insert(std::make_pair(BB, 0)).second;
160 /// Called by po_iterator each time it advances, indicating a block's
162 void finishPostorder(BasicBlock *BB) {
163 assert(DFS.PostNumbers.count(BB) && "Loop DFS skipped preorder");
164 DFS.PostBlocks.push_back(BB);
165 DFS.PostNumbers[BB] = DFS.PostBlocks.size();
169 inline bool po_iterator_storage<LoopBlocksTraversal, true>::
170 insertEdge(BasicBlock *From, BasicBlock *To) {
171 return LBT.visitPreorder(To);
174 inline void po_iterator_storage<LoopBlocksTraversal, true>::
175 finishPostorder(BasicBlock *BB) {
176 LBT.finishPostorder(BB);
179 } // End namespace llvm