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 *H = getHeader();
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, getBlocks()[i], false);
57 if (!ExitBlocks.empty()) {
58 OS << "\tExitBlocks: ";
59 for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
61 WriteAsOperand(OS, getExitBlocks()[i], false);
67 for (unsigned i = 0, e = getSubLoops().size(); i != e; ++i)
68 getSubLoops()[i]->print(OS);
72 //===----------------------------------------------------------------------===//
73 // LoopInfo implementation
75 void LoopInfo::stub() {}
77 bool LoopInfo::runOnFunction(Function &) {
79 Calculate(getAnalysis<DominatorSet>()); // Update
83 void LoopInfo::releaseMemory() {
84 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
85 E = TopLevelLoops.end(); I != E; ++I)
86 delete *I; // Delete all of the loops...
88 BBMap.clear(); // Reset internal state of analysis
89 TopLevelLoops.clear();
93 void LoopInfo::Calculate(const DominatorSet &DS) {
94 BasicBlock *RootNode = DS.getRoot();
96 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
97 NE = df_end(RootNode); NI != NE; ++NI)
98 if (Loop *L = ConsiderForLoop(*NI, DS))
99 TopLevelLoops.push_back(L);
101 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
102 TopLevelLoops[i]->setLoopDepth(1);
105 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
106 AU.setPreservesAll();
107 AU.addRequired<DominatorSet>();
110 void LoopInfo::print(std::ostream &OS) const {
111 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
112 TopLevelLoops[i]->print(OS);
114 for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
115 E = BBMap.end(); I != E; ++I)
116 OS << "BB '" << I->first->getName() << "' level = "
117 << I->second->LoopDepth << "\n";
121 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
122 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
124 std::vector<BasicBlock *> TodoStack;
126 // Scan the predecessors of BB, checking to see if BB dominates any of
128 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
129 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
130 TodoStack.push_back(*I);
132 if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
134 // Create a new loop to represent this basic block...
135 Loop *L = new Loop(BB);
138 while (!TodoStack.empty()) { // Process all the nodes in the loop
139 BasicBlock *X = TodoStack.back();
140 TodoStack.pop_back();
142 if (!L->contains(X)) { // As of yet unprocessed??
143 L->Blocks.push_back(X);
145 // Add all of the predecessors of X to the end of the work stack...
146 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
150 // If there are any loops nested within this loop, create them now!
151 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
152 E = L->Blocks.end(); I != E; ++I)
153 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
154 L->SubLoops.push_back(NewLoop);
155 NewLoop->ParentLoop = L;
159 // Add the basic blocks that comprise this loop to the BBMap so that this
160 // loop can be found for them.
162 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
163 E = L->Blocks.end(); I != E; ++I) {
164 std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
165 if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet...
166 BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
169 // Now that we know all of the blocks that make up this loop, see if there are
170 // any branches to outside of the loop... building the ExitBlocks list.
171 for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
172 BE = L->Blocks.end(); BI != BE; ++BI)
173 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
174 if (!L->contains(*I)) // Not in current loop?
175 L->ExitBlocks.push_back(*I); // It must be an exit block...
180 /// getLoopPreheader - If there is a preheader for this loop, return it. A
181 /// loop has a preheader if there is only one edge to the header of the loop
182 /// from outside of the loop. If this is the case, the block branching to the
183 /// header of the loop is the preheader node. The "preheaders" pass can be
184 /// "Required" to ensure that there is always a preheader node for every loop.
186 /// This method returns null if there is no preheader for the loop (either
187 /// because the loop is dead or because multiple blocks branch to the header
188 /// node of this loop).
190 BasicBlock *Loop::getLoopPreheader() const {
191 // Keep track of nodes outside the loop branching to the header...
194 // Loop over the predecessors of the header node...
195 BasicBlock *Header = getHeader();
196 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
198 if (!contains(*PI)) { // If the block is not in the loop...
199 if (Out && Out != *PI)
200 return 0; // Multiple predecessors outside the loop
204 // Make sure there is only one exit out of the preheader...
205 succ_iterator SI = succ_begin(Out);
207 if (SI != succ_end(Out))
208 return 0; // Multiple exits from the block, must not be a preheader.
211 // If there is exactly one preheader, return it. If there was zero, then Out
216 /// addBasicBlockToLoop - This function is used by other analyses to update loop
217 /// information. NewBB is set to be a new member of the current loop. Because
218 /// of this, it is added as a member of all parent loops, and is added to the
219 /// specified LoopInfo object as being in the current basic block. It is not
220 /// valid to replace the loop header with this method.
222 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
223 assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
224 assert(NewBB && "Cannot add a null basic block to the loop!");
225 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
227 // Add the loop mapping to the LoopInfo object...
228 LI.BBMap[NewBB] = this;
230 // Add the basic block to this loop and all parent loops...
233 L->Blocks.push_back(NewBB);
234 L = L->getParentLoop();
238 /// changeExitBlock - This method is used to update loop information. All
239 /// instances of the specified Old basic block are removed from the exit list
240 /// and replaced with New.
242 void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
243 assert(Old != New && "Cannot changeExitBlock to the same thing!");
244 assert(Old && New && "Cannot changeExitBlock to or from a null node!");
245 assert(hasExitBlock(Old) && "Old exit block not found!");
246 std::vector<BasicBlock*>::iterator
247 I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
248 while (I != ExitBlocks.end()) {
250 I = std::find(I+1, ExitBlocks.end(), Old);