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 (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
36 /// getNumBackEdges - Calculate the number of back edges to the loop header.
38 unsigned Loop::getNumBackEdges() const {
39 unsigned NumBackEdges = 0;
40 BasicBlock *H = getHeader();
42 for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
49 void Loop::print(std::ostream &OS, unsigned Depth) const {
50 OS << std::string(Depth*2, ' ') << "Loop Containing: ";
52 for (unsigned i = 0; i < getBlocks().size(); ++i) {
54 WriteAsOperand(OS, getBlocks()[i], false);
56 if (!ExitBlocks.empty()) {
57 OS << "\tExitBlocks: ";
58 for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
60 WriteAsOperand(OS, getExitBlocks()[i], false);
66 for (unsigned i = 0, e = getSubLoops().size(); i != e; ++i)
67 getSubLoops()[i]->print(OS, Depth+2);
70 void Loop::dump() const {
75 //===----------------------------------------------------------------------===//
76 // LoopInfo implementation
78 void LoopInfo::stub() {}
80 bool LoopInfo::runOnFunction(Function &) {
82 Calculate(getAnalysis<DominatorSet>()); // Update
86 void LoopInfo::releaseMemory() {
87 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
88 E = TopLevelLoops.end(); I != E; ++I)
89 delete *I; // Delete all of the loops...
91 BBMap.clear(); // Reset internal state of analysis
92 TopLevelLoops.clear();
96 void LoopInfo::Calculate(const DominatorSet &DS) {
97 BasicBlock *RootNode = DS.getRoot();
99 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
100 NE = df_end(RootNode); NI != NE; ++NI)
101 if (Loop *L = ConsiderForLoop(*NI, DS))
102 TopLevelLoops.push_back(L);
104 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
105 TopLevelLoops[i]->setLoopDepth(1);
108 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
109 AU.setPreservesAll();
110 AU.addRequired<DominatorSet>();
113 void LoopInfo::print(std::ostream &OS) const {
114 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
115 TopLevelLoops[i]->print(OS);
117 for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
118 E = BBMap.end(); I != E; ++I)
119 OS << "BB '" << I->first->getName() << "' level = "
120 << I->second->LoopDepth << "\n";
124 static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
125 if (SubLoop == 0) return true;
126 if (SubLoop == ParentLoop) return false;
127 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
130 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
131 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
133 std::vector<BasicBlock *> TodoStack;
135 // Scan the predecessors of BB, checking to see if BB dominates any of
136 // them. This identifies backedges which target this node...
137 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
138 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
139 TodoStack.push_back(*I);
141 if (TodoStack.empty()) return 0; // No backedges to this block...
143 // Create a new loop to represent this basic block...
144 Loop *L = new Loop(BB);
147 while (!TodoStack.empty()) { // Process all the nodes in the loop
148 BasicBlock *X = TodoStack.back();
149 TodoStack.pop_back();
151 if (!L->contains(X)) { // As of yet unprocessed??
152 // Check to see if this block already belongs to a loop. If this occurs
153 // then we have a case where a loop that is supposed to be a child of the
154 // current loop was processed before the current loop. When this occurs,
155 // this child loop gets added to a part of the current loop, making it a
156 // sibling to the current loop. We have to reparent this loop.
157 if (Loop *SubLoop = const_cast<Loop*>(getLoopFor(X)))
158 if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
159 // Remove the subloop from it's current parent...
160 assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
161 Loop *SLP = SubLoop->ParentLoop; // SubLoopParent
162 std::vector<Loop*>::iterator I =
163 std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
164 assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
165 SLP->SubLoops.erase(I); // Remove from parent...
167 // Add the subloop to THIS loop...
168 SubLoop->ParentLoop = L;
169 L->SubLoops.push_back(SubLoop);
172 // Normal case, add the block to our loop...
173 L->Blocks.push_back(X);
175 // Add all of the predecessors of X to the end of the work stack...
176 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
180 // If there are any loops nested within this loop, create them now!
181 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
182 E = L->Blocks.end(); I != E; ++I)
183 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
184 L->SubLoops.push_back(NewLoop);
185 NewLoop->ParentLoop = L;
188 // Add the basic blocks that comprise this loop to the BBMap so that this
189 // loop can be found for them.
191 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
192 E = L->Blocks.end(); I != E; ++I) {
193 std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
194 if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet...
195 BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
198 // Now that we have a list of all of the child loops of this loop, check to
199 // see if any of them should actually be nested inside of each other. We can
200 // accidentally pull loops our of their parents, so we must make sure to
201 // organize the loop nests correctly now.
203 std::map<BasicBlock*, Loop*> ContainingLoops;
204 for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
205 Loop *Child = L->SubLoops[i];
206 assert(Child->getParentLoop() == L && "Not proper child loop?");
208 if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) {
209 // If there is already a loop which contains this loop, move this loop
210 // into the containing loop.
211 MoveSiblingLoopInto(Child, ContainingLoop);
212 --i; // The loop got removed from the SubLoops list.
214 // This is currently considered to be a top-level loop. Check to see if
215 // any of the contained blocks are loop headers for subloops we have
216 // already processed.
217 for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
218 Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]];
219 if (BlockLoop == 0) { // Child block not processed yet...
221 } else if (BlockLoop != Child) {
222 Loop *SubLoop = BlockLoop;
223 // Reparent all of the blocks which used to belong to BlockLoops
224 for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
225 ContainingLoops[SubLoop->Blocks[j]] = Child;
227 // There is already a loop which contains this block, that means
228 // that we should reparent the loop which the block is currently
229 // considered to belong to to be a child of this loop.
230 MoveSiblingLoopInto(SubLoop, Child);
231 --i; // We just shrunk the SubLoops list.
238 // Now that we know all of the blocks that make up this loop, see if there are
239 // any branches to outside of the loop... building the ExitBlocks list.
240 for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
241 BE = L->Blocks.end(); BI != BE; ++BI)
242 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
243 if (!L->contains(*I)) // Not in current loop?
244 L->ExitBlocks.push_back(*I); // It must be an exit block...
249 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
250 /// the NewParent Loop, instead of being a sibling of it.
251 void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) {
252 Loop *OldParent = NewChild->getParentLoop();
253 assert(OldParent && OldParent == NewParent->getParentLoop() &&
254 NewChild != NewParent && "Not sibling loops!");
256 // Remove NewChild from being a child of OldParent
257 std::vector<Loop*>::iterator I =
258 std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
259 assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
260 OldParent->SubLoops.erase(I); // Remove from parent's subloops list
261 NewChild->ParentLoop = 0;
263 InsertLoopInto(NewChild, NewParent);
266 /// InsertLoopInto - This inserts loop L into the specified parent loop. If the
267 /// parent loop contains a loop which should contain L, the loop gets inserted
269 void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) {
270 BasicBlock *LHeader = L->getHeader();
271 assert(Parent->contains(LHeader) && "This loop should not be inserted here!");
273 // Check to see if it belongs in a child loop...
274 for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
275 if (Parent->SubLoops[i]->contains(LHeader)) {
276 InsertLoopInto(L, Parent->SubLoops[i]);
280 // If not, insert it here!
281 Parent->SubLoops.push_back(L);
282 L->ParentLoop = Parent;
287 /// getLoopPreheader - If there is a preheader for this loop, return it. A
288 /// loop has a preheader if there is only one edge to the header of the loop
289 /// from outside of the loop. If this is the case, the block branching to the
290 /// header of the loop is the preheader node. The "preheaders" pass can be
291 /// "Required" to ensure that there is always a preheader node for every loop.
293 /// This method returns null if there is no preheader for the loop (either
294 /// because the loop is dead or because multiple blocks branch to the header
295 /// node of this loop).
297 BasicBlock *Loop::getLoopPreheader() const {
298 // Keep track of nodes outside the loop branching to the header...
301 // Loop over the predecessors of the header node...
302 BasicBlock *Header = getHeader();
303 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
305 if (!contains(*PI)) { // If the block is not in the loop...
306 if (Out && Out != *PI)
307 return 0; // Multiple predecessors outside the loop
311 // Make sure there is only one exit out of the preheader...
312 succ_iterator SI = succ_begin(Out);
314 if (SI != succ_end(Out))
315 return 0; // Multiple exits from the block, must not be a preheader.
318 // If there is exactly one preheader, return it. If there was zero, then Out
323 /// addBasicBlockToLoop - This function is used by other analyses to update loop
324 /// information. NewBB is set to be a new member of the current loop. Because
325 /// of this, it is added as a member of all parent loops, and is added to the
326 /// specified LoopInfo object as being in the current basic block. It is not
327 /// valid to replace the loop header with this method.
329 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
330 assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
331 assert(NewBB && "Cannot add a null basic block to the loop!");
332 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
334 // Add the loop mapping to the LoopInfo object...
335 LI.BBMap[NewBB] = this;
337 // Add the basic block to this loop and all parent loops...
340 L->Blocks.push_back(NewBB);
341 L = L->getParentLoop();
345 /// changeExitBlock - This method is used to update loop information. All
346 /// instances of the specified Old basic block are removed from the exit list
347 /// and replaced with New.
349 void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
350 assert(Old != New && "Cannot changeExitBlock to the same thing!");
351 assert(Old && New && "Cannot changeExitBlock to or from a null node!");
352 assert(hasExitBlock(Old) && "Old exit block not found!");
353 std::vector<BasicBlock*>::iterator
354 I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
355 while (I != ExitBlocks.end()) {
357 I = std::find(I+1, ExitBlocks.end(), Old);