1 //===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the LoopInfo class that is used to identify natural loops
11 // and determine the loop depth of various nodes of the CFG. Note that the
12 // loops identified may actually be several natural loops that share the same
13 // header node... not just a single natural loop.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Analysis/LoopInfo.h"
18 #include "llvm/Analysis/Dominators.h"
19 #include "llvm/Support/CFG.h"
20 #include "llvm/Assembly/Writer.h"
21 #include "Support/DepthFirstIterator.h"
26 static RegisterAnalysis<LoopInfo>
27 X("loops", "Natural Loop Construction", true);
29 //===----------------------------------------------------------------------===//
30 // Loop implementation
32 bool Loop::contains(const BasicBlock *BB) const {
33 return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
36 bool Loop::isLoopExit(const BasicBlock *BB) const {
37 for (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
45 /// getNumBackEdges - Calculate the number of back edges to the loop header.
47 unsigned Loop::getNumBackEdges() const {
48 unsigned NumBackEdges = 0;
49 BasicBlock *H = getHeader();
51 for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
58 void Loop::print(std::ostream &OS, unsigned Depth) const {
59 OS << std::string(Depth*2, ' ') << "Loop Containing: ";
61 for (unsigned i = 0; i < getBlocks().size(); ++i) {
63 WriteAsOperand(OS, getBlocks()[i], false);
65 if (!ExitBlocks.empty()) {
66 OS << "\tExitBlocks: ";
67 for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
69 WriteAsOperand(OS, getExitBlocks()[i], false);
75 for (unsigned i = 0, e = getSubLoops().size(); i != e; ++i)
76 getSubLoops()[i]->print(OS, Depth+2);
79 void Loop::dump() const {
84 //===----------------------------------------------------------------------===//
85 // LoopInfo implementation
87 void LoopInfo::stub() {}
89 bool LoopInfo::runOnFunction(Function &) {
91 Calculate(getAnalysis<DominatorSet>()); // Update
95 void LoopInfo::releaseMemory() {
96 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
97 E = TopLevelLoops.end(); I != E; ++I)
98 delete *I; // Delete all of the loops...
100 BBMap.clear(); // Reset internal state of analysis
101 TopLevelLoops.clear();
105 void LoopInfo::Calculate(const DominatorSet &DS) {
106 BasicBlock *RootNode = DS.getRoot();
108 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
109 NE = df_end(RootNode); NI != NE; ++NI)
110 if (Loop *L = ConsiderForLoop(*NI, DS))
111 TopLevelLoops.push_back(L);
113 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
114 TopLevelLoops[i]->setLoopDepth(1);
117 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
118 AU.setPreservesAll();
119 AU.addRequired<DominatorSet>();
122 void LoopInfo::print(std::ostream &OS) const {
123 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
124 TopLevelLoops[i]->print(OS);
126 for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
127 E = BBMap.end(); I != E; ++I)
128 OS << "BB '" << I->first->getName() << "' level = "
129 << I->second->LoopDepth << "\n";
133 static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
134 if (SubLoop == 0) return true;
135 if (SubLoop == ParentLoop) return false;
136 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
139 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
140 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
142 std::vector<BasicBlock *> TodoStack;
144 // Scan the predecessors of BB, checking to see if BB dominates any of
145 // them. This identifies backedges which target this node...
146 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
147 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
148 TodoStack.push_back(*I);
150 if (TodoStack.empty()) return 0; // No backedges to this block...
152 // Create a new loop to represent this basic block...
153 Loop *L = new Loop(BB);
156 BasicBlock *EntryBlock = &BB->getParent()->getEntryBlock();
158 while (!TodoStack.empty()) { // Process all the nodes in the loop
159 BasicBlock *X = TodoStack.back();
160 TodoStack.pop_back();
162 if (!L->contains(X) && // As of yet unprocessed??
163 DS.dominates(EntryBlock, X)) { // X is reachable from entry block?
164 // Check to see if this block already belongs to a loop. If this occurs
165 // then we have a case where a loop that is supposed to be a child of the
166 // current loop was processed before the current loop. When this occurs,
167 // this child loop gets added to a part of the current loop, making it a
168 // sibling to the current loop. We have to reparent this loop.
169 if (Loop *SubLoop = const_cast<Loop*>(getLoopFor(X)))
170 if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
171 // Remove the subloop from it's current parent...
172 assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
173 Loop *SLP = SubLoop->ParentLoop; // SubLoopParent
174 std::vector<Loop*>::iterator I =
175 std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
176 assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
177 SLP->SubLoops.erase(I); // Remove from parent...
179 // Add the subloop to THIS loop...
180 SubLoop->ParentLoop = L;
181 L->SubLoops.push_back(SubLoop);
184 // Normal case, add the block to our loop...
185 L->Blocks.push_back(X);
187 // Add all of the predecessors of X to the end of the work stack...
188 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
192 // If there are any loops nested within this loop, create them now!
193 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
194 E = L->Blocks.end(); I != E; ++I)
195 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
196 L->SubLoops.push_back(NewLoop);
197 NewLoop->ParentLoop = L;
200 // Add the basic blocks that comprise this loop to the BBMap so that this
201 // loop can be found for them.
203 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
204 E = L->Blocks.end(); I != E; ++I) {
205 std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
206 if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet...
207 BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
210 // Now that we have a list of all of the child loops of this loop, check to
211 // see if any of them should actually be nested inside of each other. We can
212 // accidentally pull loops our of their parents, so we must make sure to
213 // organize the loop nests correctly now.
215 std::map<BasicBlock*, Loop*> ContainingLoops;
216 for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
217 Loop *Child = L->SubLoops[i];
218 assert(Child->getParentLoop() == L && "Not proper child loop?");
220 if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) {
221 // If there is already a loop which contains this loop, move this loop
222 // into the containing loop.
223 MoveSiblingLoopInto(Child, ContainingLoop);
224 --i; // The loop got removed from the SubLoops list.
226 // This is currently considered to be a top-level loop. Check to see if
227 // any of the contained blocks are loop headers for subloops we have
228 // already processed.
229 for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
230 Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]];
231 if (BlockLoop == 0) { // Child block not processed yet...
233 } else if (BlockLoop != Child) {
234 Loop *SubLoop = BlockLoop;
235 // Reparent all of the blocks which used to belong to BlockLoops
236 for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
237 ContainingLoops[SubLoop->Blocks[j]] = Child;
239 // There is already a loop which contains this block, that means
240 // that we should reparent the loop which the block is currently
241 // considered to belong to to be a child of this loop.
242 MoveSiblingLoopInto(SubLoop, Child);
243 --i; // We just shrunk the SubLoops list.
250 // Now that we know all of the blocks that make up this loop, see if there are
251 // any branches to outside of the loop... building the ExitBlocks list.
252 for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
253 BE = L->Blocks.end(); BI != BE; ++BI)
254 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
255 if (!L->contains(*I)) // Not in current loop?
256 L->ExitBlocks.push_back(*I); // It must be an exit block...
261 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
262 /// the NewParent Loop, instead of being a sibling of it.
263 void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) {
264 Loop *OldParent = NewChild->getParentLoop();
265 assert(OldParent && OldParent == NewParent->getParentLoop() &&
266 NewChild != NewParent && "Not sibling loops!");
268 // Remove NewChild from being a child of OldParent
269 std::vector<Loop*>::iterator I =
270 std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
271 assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
272 OldParent->SubLoops.erase(I); // Remove from parent's subloops list
273 NewChild->ParentLoop = 0;
275 InsertLoopInto(NewChild, NewParent);
278 /// InsertLoopInto - This inserts loop L into the specified parent loop. If the
279 /// parent loop contains a loop which should contain L, the loop gets inserted
281 void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) {
282 BasicBlock *LHeader = L->getHeader();
283 assert(Parent->contains(LHeader) && "This loop should not be inserted here!");
285 // Check to see if it belongs in a child loop...
286 for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
287 if (Parent->SubLoops[i]->contains(LHeader)) {
288 InsertLoopInto(L, Parent->SubLoops[i]);
292 // If not, insert it here!
293 Parent->SubLoops.push_back(L);
294 L->ParentLoop = Parent;
299 /// getLoopPreheader - If there is a preheader for this loop, return it. A
300 /// loop has a preheader if there is only one edge to the header of the loop
301 /// from outside of the loop. If this is the case, the block branching to the
302 /// header of the loop is the preheader node. The "preheaders" pass can be
303 /// "Required" to ensure that there is always a preheader node for every loop.
305 /// This method returns null if there is no preheader for the loop (either
306 /// because the loop is dead or because multiple blocks branch to the header
307 /// node of this loop).
309 BasicBlock *Loop::getLoopPreheader() const {
310 // Keep track of nodes outside the loop branching to the header...
313 // Loop over the predecessors of the header node...
314 BasicBlock *Header = getHeader();
315 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
317 if (!contains(*PI)) { // If the block is not in the loop...
318 if (Out && Out != *PI)
319 return 0; // Multiple predecessors outside the loop
323 // Make sure there is only one exit out of the preheader...
324 succ_iterator SI = succ_begin(Out);
326 if (SI != succ_end(Out))
327 return 0; // Multiple exits from the block, must not be a preheader.
330 // If there is exactly one preheader, return it. If there was zero, then Out
335 /// addBasicBlockToLoop - This function is used by other analyses to update loop
336 /// information. NewBB is set to be a new member of the current loop. Because
337 /// of this, it is added as a member of all parent loops, and is added to the
338 /// specified LoopInfo object as being in the current basic block. It is not
339 /// valid to replace the loop header with this method.
341 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
342 assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
343 assert(NewBB && "Cannot add a null basic block to the loop!");
344 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
346 // Add the loop mapping to the LoopInfo object...
347 LI.BBMap[NewBB] = this;
349 // Add the basic block to this loop and all parent loops...
352 L->Blocks.push_back(NewBB);
353 L = L->getParentLoop();
357 /// changeExitBlock - This method is used to update loop information. All
358 /// instances of the specified Old basic block are removed from the exit list
359 /// and replaced with New.
361 void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
362 assert(Old != New && "Cannot changeExitBlock to the same thing!");
363 assert(Old && New && "Cannot changeExitBlock to or from a null node!");
364 assert(hasExitBlock(Old) && "Old exit block not found!");
365 std::vector<BasicBlock*>::iterator
366 I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
367 while (I != ExitBlocks.end()) {
369 I = std::find(I+1, ExitBlocks.end(), Old);
373 } // End llvm namespace