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(),
41 E = Blocks.end(); I != E; ++I) {
42 for (BasicBlock::succ_iterator SI = succ_begin(*I), SE = succ_end(*I);
50 void Loop::print(std::ostream &OS) const {
51 OS << std::string(getLoopDepth()*2, ' ') << "Loop Containing: ";
53 for (unsigned i = 0; i < getBlocks().size(); ++i) {
55 WriteAsOperand(OS, (const Value*)getBlocks()[i]);
59 for (unsigned i = 0, e = getSubLoops().size(); i != e; ++i)
60 getSubLoops()[i]->print(OS);
63 //===----------------------------------------------------------------------===//
64 // LoopInfo implementation
66 void LoopInfo::stub() {}
68 bool LoopInfo::runOnFunction(Function &) {
70 Calculate(getAnalysis<DominatorSet>()); // Update
74 void LoopInfo::releaseMemory() {
75 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
76 E = TopLevelLoops.end(); I != E; ++I)
77 delete *I; // Delete all of the loops...
79 BBMap.clear(); // Reset internal state of analysis
80 TopLevelLoops.clear();
84 void LoopInfo::Calculate(const DominatorSet &DS) {
85 BasicBlock *RootNode = DS.getRoot();
87 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
88 NE = df_end(RootNode); NI != NE; ++NI)
89 if (Loop *L = ConsiderForLoop(*NI, DS))
90 TopLevelLoops.push_back(L);
92 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
93 TopLevelLoops[i]->setLoopDepth(1);
96 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
98 AU.addRequired<DominatorSet>();
101 void LoopInfo::print(std::ostream &OS) const {
102 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
103 TopLevelLoops[i]->print(OS);
106 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
107 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
109 std::vector<BasicBlock *> TodoStack;
111 // Scan the predecessors of BB, checking to see if BB dominates any of
113 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
114 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
115 TodoStack.push_back(*I);
117 if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
119 // Create a new loop to represent this basic block...
120 Loop *L = new Loop(BB);
123 while (!TodoStack.empty()) { // Process all the nodes in the loop
124 BasicBlock *X = TodoStack.back();
125 TodoStack.pop_back();
127 if (!L->contains(X)) { // As of yet unprocessed??
128 L->Blocks.push_back(X);
130 // Add all of the predecessors of X to the end of the work stack...
131 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
135 // Add the basic blocks that comprise this loop to the BBMap so that this
136 // loop can be found for them. Also check subsidary basic blocks to see if
137 // they start subloops of their own.
139 for (std::vector<BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
140 E = L->Blocks.rend(); I != E; ++I)
142 // 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;
148 std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
149 if (BBMI == BBMap.end() || BBMI->first != *I) { // Not in map yet...
150 BBMap.insert(BBMI, std::make_pair(*I, L));
152 // If this is already in the BBMap then this means that we already added
153 // a loop for it, but incorrectly added the loop to a higher level loop
154 // instead of the current loop we are creating. Fix this now by moving
155 // the loop into the correct subloop.
157 Loop *SubLoop = BBMI->second;
158 Loop *OldSubLoopParent = SubLoop->getParentLoop();
159 if (OldSubLoopParent != L) {
160 // Remove SubLoop from OldSubLoopParent's list of subloops...
161 std::vector<Loop*>::iterator I =
162 std::find(OldSubLoopParent->SubLoops.begin(),
163 OldSubLoopParent->SubLoops.end(), SubLoop);
164 assert(I != OldSubLoopParent->SubLoops.end()
165 && "Loop parent doesn't contain loop?");
166 OldSubLoopParent->SubLoops.erase(I);
167 SubLoop->ParentLoop = L;
168 L->SubLoops.push_back(SubLoop);
176 /// getLoopPreheader - If there is a preheader for this loop, return it. A
177 /// loop has a preheader if there is only one edge to the header of the loop
178 /// from outside of the loop. If this is the case, the block branching to the
179 /// header of the loop is the preheader node. The "preheaders" pass can be
180 /// "Required" to ensure that there is always a preheader node for every loop.
182 /// This method returns null if there is no preheader for the loop (either
183 /// because the loop is dead or because multiple blocks branch to the header
184 /// node of this loop).
186 BasicBlock *Loop::getLoopPreheader() const {
187 // Keep track of nodes outside the loop branching to the header...
190 // Loop over the predecessors of the header node...
191 BasicBlock *Header = getHeader();
192 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
194 if (!contains(*PI)) { // If the block is not in the loop...
195 if (Out && Out != *PI)
196 return 0; // Multiple predecessors outside the loop
200 // If there is exactly one preheader, return it. If there was zero, then Out
205 /// addBasicBlockToLoop - This function is used by other analyses to update loop
206 /// information. NewBB is set to be a new member of the current loop. Because
207 /// of this, it is added as a member of all parent loops, and is added to the
208 /// specified LoopInfo object as being in the current basic block. It is not
209 /// valid to replace the loop header with this method.
211 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
212 assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
213 assert(NewBB && "Cannot add a null basic block to the loop!");
214 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
216 // Add the loop mapping to the LoopInfo object...
217 LI.BBMap[NewBB] = this;
219 // Add the basic block to this loop and all parent loops...
222 L->Blocks.push_back(NewBB);
223 L = L->getParentLoop();