1 //===- LoopInfo.cpp - Natural Loop Calculator -------------------------------=//
3 // This file defines the LoopInfo class that is used to identify natural loops
4 // and determine the loop depth of various nodes of the CFG. Note that the
5 // loops identified may actually be several natural loops that share the same
6 // header node... not just a single natural loop.
8 //===----------------------------------------------------------------------===//
10 #include "llvm/Analysis/LoopInfo.h"
11 #include "llvm/Analysis/Dominators.h"
12 #include "llvm/Support/CFG.h"
13 #include "llvm/Assembly/Writer.h"
14 #include "Support/DepthFirstIterator.h"
17 static RegisterAnalysis<LoopInfo>
18 X("loops", "Natural Loop Construction", true);
20 //===----------------------------------------------------------------------===//
21 // Loop implementation
23 bool Loop::contains(const BasicBlock *BB) const {
24 return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
27 bool Loop::isLoopExit(const BasicBlock *BB) const {
28 for (BasicBlock::succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
36 unsigned Loop::getNumBackEdges() const {
37 unsigned numBackEdges = 0;
38 BasicBlock *header = Blocks.front();
40 for (std::vector<BasicBlock*>::const_iterator i = Blocks.begin(), e = Blocks.end();
42 for (BasicBlock::succ_iterator Successor = succ_begin(*i), SEnd = succ_end(*i);
43 Successor != SEnd; ++Successor) {
44 if (header == *Successor)
51 void Loop::print(std::ostream &OS) const {
52 OS << std::string(getLoopDepth()*2, ' ') << "Loop Containing: ";
54 for (unsigned i = 0; i < getBlocks().size(); ++i) {
56 WriteAsOperand(OS, (const Value*)getBlocks()[i]);
60 for (unsigned i = 0, e = getSubLoops().size(); i != e; ++i)
61 getSubLoops()[i]->print(OS);
64 //===----------------------------------------------------------------------===//
65 // LoopInfo implementation
67 void LoopInfo::stub() {}
69 bool LoopInfo::runOnFunction(Function &) {
71 Calculate(getAnalysis<DominatorSet>()); // Update
75 void LoopInfo::releaseMemory() {
76 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
77 E = TopLevelLoops.end(); I != E; ++I)
78 delete *I; // Delete all of the loops...
80 BBMap.clear(); // Reset internal state of analysis
81 TopLevelLoops.clear();
85 void LoopInfo::Calculate(const DominatorSet &DS) {
86 BasicBlock *RootNode = DS.getRoot();
88 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
89 NE = df_end(RootNode); NI != NE; ++NI)
90 if (Loop *L = ConsiderForLoop(*NI, DS))
91 TopLevelLoops.push_back(L);
93 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
94 TopLevelLoops[i]->setLoopDepth(1);
97 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
99 AU.addRequired<DominatorSet>();
102 void LoopInfo::print(std::ostream &OS) const {
103 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
104 TopLevelLoops[i]->print(OS);
107 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
108 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
110 std::vector<BasicBlock *> TodoStack;
112 // Scan the predecessors of BB, checking to see if BB dominates any of
114 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
115 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
116 TodoStack.push_back(*I);
118 if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
120 // Create a new loop to represent this basic block...
121 Loop *L = new Loop(BB);
124 while (!TodoStack.empty()) { // Process all the nodes in the loop
125 BasicBlock *X = TodoStack.back();
126 TodoStack.pop_back();
128 if (!L->contains(X)) { // As of yet unprocessed??
129 L->Blocks.push_back(X);
131 // Add all of the predecessors of X to the end of the work stack...
132 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
136 // Add the basic blocks that comprise this loop to the BBMap so that this
137 // loop can be found for them. Also check subsidary basic blocks to see if
138 // they start subloops of their own.
140 for (std::vector<BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
141 E = L->Blocks.rend(); I != E; ++I) {
143 // Check to see if this block starts a new loop
144 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
145 L->SubLoops.push_back(NewLoop);
146 NewLoop->ParentLoop = L;
149 if (BBMap.find(*I) == BBMap.end())
150 BBMap.insert(std::make_pair(*I, L));
156 /// getLoopPreheader - If there is a preheader for this loop, return it. A
157 /// loop has a preheader if there is only one edge to the header of the loop
158 /// from outside of the loop. If this is the case, the block branching to the
159 /// header of the loop is the preheader node. The "preheaders" pass can be
160 /// "Required" to ensure that there is always a preheader node for every loop.
162 /// This method returns null if there is no preheader for the loop (either
163 /// because the loop is dead or because multiple blocks branch to the header
164 /// node of this loop).
166 BasicBlock *Loop::getLoopPreheader() const {
167 // Keep track of nodes outside the loop branching to the header...
170 // Loop over the predecessors of the header node...
171 BasicBlock *Header = getHeader();
172 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
174 if (!contains(*PI)) { // If the block is not in the loop...
175 if (Out && Out != *PI)
176 return 0; // Multiple predecessors outside the loop
180 // If there is exactly one preheader, return it. If there was zero, then Out
185 /// addBasicBlockToLoop - This function is used by other analyses to update loop
186 /// information. NewBB is set to be a new member of the current loop. Because
187 /// of this, it is added as a member of all parent loops, and is added to the
188 /// specified LoopInfo object as being in the current basic block. It is not
189 /// valid to replace the loop header with this method.
191 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
192 assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
193 assert(NewBB && "Cannot add a null basic block to the loop!");
194 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
196 // Add the loop mapping to the LoopInfo object...
197 LI.BBMap[NewBB] = this;
199 // Add the basic block to this loop and all parent loops...
202 L->Blocks.push_back(NewBB);
203 L = L->getParentLoop();