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);
71 void Loop::dump() const {
76 //===----------------------------------------------------------------------===//
77 // LoopInfo implementation
79 void LoopInfo::stub() {}
81 bool LoopInfo::runOnFunction(Function &) {
83 Calculate(getAnalysis<DominatorSet>()); // Update
87 void LoopInfo::releaseMemory() {
88 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
89 E = TopLevelLoops.end(); I != E; ++I)
90 delete *I; // Delete all of the loops...
92 BBMap.clear(); // Reset internal state of analysis
93 TopLevelLoops.clear();
97 void LoopInfo::Calculate(const DominatorSet &DS) {
98 BasicBlock *RootNode = DS.getRoot();
100 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
101 NE = df_end(RootNode); NI != NE; ++NI)
102 if (Loop *L = ConsiderForLoop(*NI, DS))
103 TopLevelLoops.push_back(L);
105 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
106 TopLevelLoops[i]->setLoopDepth(1);
109 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
110 AU.setPreservesAll();
111 AU.addRequired<DominatorSet>();
114 void LoopInfo::print(std::ostream &OS) const {
115 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
116 TopLevelLoops[i]->print(OS);
118 for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
119 E = BBMap.end(); I != E; ++I)
120 OS << "BB '" << I->first->getName() << "' level = "
121 << I->second->LoopDepth << "\n";
125 static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
126 if (SubLoop == 0) return true;
127 if (SubLoop == ParentLoop) return false;
128 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
131 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
132 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
134 std::vector<BasicBlock *> TodoStack;
136 // Scan the predecessors of BB, checking to see if BB dominates any of
137 // them. This identifies backedges which target this node...
138 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
139 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
140 TodoStack.push_back(*I);
142 if (TodoStack.empty()) return 0; // No backedges to this block...
144 // Create a new loop to represent this basic block...
145 Loop *L = new Loop(BB);
148 while (!TodoStack.empty()) { // Process all the nodes in the loop
149 BasicBlock *X = TodoStack.back();
150 TodoStack.pop_back();
152 if (!L->contains(X)) { // As of yet unprocessed??
153 // Check to see if this block already belongs to a loop. If this occurs
154 // then we have a case where a loop that is supposed to be a child of the
155 // current loop was processed before the current loop. When this occurs,
156 // this child loop gets added to a part of the current loop, making it a
157 // sibling to the current loop. We have to reparent this loop.
158 if (Loop *SubLoop = const_cast<Loop*>(getLoopFor(X)))
159 if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
160 // Remove the subloop from it's current parent...
161 assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
162 Loop *SLP = SubLoop->ParentLoop; // SubLoopParent
163 std::vector<Loop*>::iterator I =
164 std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
165 assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
166 SLP->SubLoops.erase(I); // Remove from parent...
168 // Add the subloop to THIS loop...
169 SubLoop->ParentLoop = L;
170 L->SubLoops.push_back(SubLoop);
173 // Normal case, add the block to our loop...
174 L->Blocks.push_back(X);
176 // Add all of the predecessors of X to the end of the work stack...
177 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
181 // If there are any loops nested within this loop, create them now!
182 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
183 E = L->Blocks.end(); I != E; ++I)
184 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
185 L->SubLoops.push_back(NewLoop);
186 NewLoop->ParentLoop = L;
190 // Add the basic blocks that comprise this loop to the BBMap so that this
191 // loop can be found for them.
193 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
194 E = L->Blocks.end(); I != E; ++I) {
195 std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
196 if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet...
197 BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
200 // Now that we know all of the blocks that make up this loop, see if there are
201 // any branches to outside of the loop... building the ExitBlocks list.
202 for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
203 BE = L->Blocks.end(); BI != BE; ++BI)
204 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
205 if (!L->contains(*I)) // Not in current loop?
206 L->ExitBlocks.push_back(*I); // It must be an exit block...
211 /// getLoopPreheader - If there is a preheader for this loop, return it. A
212 /// loop has a preheader if there is only one edge to the header of the loop
213 /// from outside of the loop. If this is the case, the block branching to the
214 /// header of the loop is the preheader node. The "preheaders" pass can be
215 /// "Required" to ensure that there is always a preheader node for every loop.
217 /// This method returns null if there is no preheader for the loop (either
218 /// because the loop is dead or because multiple blocks branch to the header
219 /// node of this loop).
221 BasicBlock *Loop::getLoopPreheader() const {
222 // Keep track of nodes outside the loop branching to the header...
225 // Loop over the predecessors of the header node...
226 BasicBlock *Header = getHeader();
227 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
229 if (!contains(*PI)) { // If the block is not in the loop...
230 if (Out && Out != *PI)
231 return 0; // Multiple predecessors outside the loop
235 // Make sure there is only one exit out of the preheader...
236 succ_iterator SI = succ_begin(Out);
238 if (SI != succ_end(Out))
239 return 0; // Multiple exits from the block, must not be a preheader.
242 // If there is exactly one preheader, return it. If there was zero, then Out
247 /// addBasicBlockToLoop - This function is used by other analyses to update loop
248 /// information. NewBB is set to be a new member of the current loop. Because
249 /// of this, it is added as a member of all parent loops, and is added to the
250 /// specified LoopInfo object as being in the current basic block. It is not
251 /// valid to replace the loop header with this method.
253 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
254 assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
255 assert(NewBB && "Cannot add a null basic block to the loop!");
256 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
258 // Add the loop mapping to the LoopInfo object...
259 LI.BBMap[NewBB] = this;
261 // Add the basic block to this loop and all parent loops...
264 L->Blocks.push_back(NewBB);
265 L = L->getParentLoop();
269 /// changeExitBlock - This method is used to update loop information. All
270 /// instances of the specified Old basic block are removed from the exit list
271 /// and replaced with New.
273 void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
274 assert(Old != New && "Cannot changeExitBlock to the same thing!");
275 assert(Old && New && "Cannot changeExitBlock to or from a null node!");
276 assert(hasExitBlock(Old) && "Old exit block not found!");
277 std::vector<BasicBlock*>::iterator
278 I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
279 while (I != ExitBlocks.end()) {
281 I = std::find(I+1, ExitBlocks.end(), Old);