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/Constants.h"
19 #include "llvm/Instructions.h"
20 #include "llvm/Analysis/Dominators.h"
21 #include "llvm/Assembly/Writer.h"
22 #include "llvm/Support/CFG.h"
23 #include "Support/DepthFirstIterator.h"
27 static RegisterAnalysis<LoopInfo>
28 X("loops", "Natural Loop Construction", true);
30 //===----------------------------------------------------------------------===//
31 // Loop implementation
33 bool Loop::contains(const BasicBlock *BB) const {
34 return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
37 bool Loop::isLoopExit(const BasicBlock *BB) const {
38 for (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
46 /// getNumBackEdges - Calculate the number of back edges to the loop header.
48 unsigned Loop::getNumBackEdges() const {
49 unsigned NumBackEdges = 0;
50 BasicBlock *H = getHeader();
52 for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
59 void Loop::print(std::ostream &OS, unsigned Depth) const {
60 OS << std::string(Depth*2, ' ') << "Loop Containing: ";
62 for (unsigned i = 0; i < getBlocks().size(); ++i) {
64 WriteAsOperand(OS, getBlocks()[i], false);
66 if (!ExitBlocks.empty()) {
67 OS << "\tExitBlocks: ";
68 for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
70 WriteAsOperand(OS, getExitBlocks()[i], false);
76 for (iterator I = begin(), E = end(); I != E; ++I)
77 (*I)->print(OS, Depth+2);
80 void Loop::dump() const {
85 //===----------------------------------------------------------------------===//
86 // LoopInfo implementation
88 void LoopInfo::stub() {}
90 bool LoopInfo::runOnFunction(Function &) {
92 Calculate(getAnalysis<DominatorSet>()); // Update
96 void LoopInfo::releaseMemory() {
97 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
98 E = TopLevelLoops.end(); I != E; ++I)
99 delete *I; // Delete all of the loops...
101 BBMap.clear(); // Reset internal state of analysis
102 TopLevelLoops.clear();
106 void LoopInfo::Calculate(const DominatorSet &DS) {
107 BasicBlock *RootNode = DS.getRoot();
109 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
110 NE = df_end(RootNode); NI != NE; ++NI)
111 if (Loop *L = ConsiderForLoop(*NI, DS))
112 TopLevelLoops.push_back(L);
114 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
115 TopLevelLoops[i]->setLoopDepth(1);
118 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
119 AU.setPreservesAll();
120 AU.addRequired<DominatorSet>();
123 void LoopInfo::print(std::ostream &OS) const {
124 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
125 TopLevelLoops[i]->print(OS);
127 for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
128 E = BBMap.end(); I != E; ++I)
129 OS << "BB '" << I->first->getName() << "' level = "
130 << I->second->LoopDepth << "\n";
134 static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
135 if (SubLoop == 0) return true;
136 if (SubLoop == ParentLoop) return false;
137 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
140 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
141 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
143 std::vector<BasicBlock *> TodoStack;
145 // Scan the predecessors of BB, checking to see if BB dominates any of
146 // them. This identifies backedges which target this node...
147 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
148 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
149 TodoStack.push_back(*I);
151 if (TodoStack.empty()) return 0; // No backedges to this block...
153 // Create a new loop to represent this basic block...
154 Loop *L = new Loop(BB);
157 BasicBlock *EntryBlock = &BB->getParent()->getEntryBlock();
159 while (!TodoStack.empty()) { // Process all the nodes in the loop
160 BasicBlock *X = TodoStack.back();
161 TodoStack.pop_back();
163 if (!L->contains(X) && // As of yet unprocessed??
164 DS.dominates(EntryBlock, X)) { // X is reachable from entry block?
165 // Check to see if this block already belongs to a loop. If this occurs
166 // then we have a case where a loop that is supposed to be a child of the
167 // current loop was processed before the current loop. When this occurs,
168 // this child loop gets added to a part of the current loop, making it a
169 // sibling to the current loop. We have to reparent this loop.
170 if (Loop *SubLoop = const_cast<Loop*>(getLoopFor(X)))
171 if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
172 // Remove the subloop from it's current parent...
173 assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
174 Loop *SLP = SubLoop->ParentLoop; // SubLoopParent
175 std::vector<Loop*>::iterator I =
176 std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
177 assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
178 SLP->SubLoops.erase(I); // Remove from parent...
180 // Add the subloop to THIS loop...
181 SubLoop->ParentLoop = L;
182 L->SubLoops.push_back(SubLoop);
185 // Normal case, add the block to our loop...
186 L->Blocks.push_back(X);
188 // Add all of the predecessors of X to the end of the work stack...
189 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
193 // If there are any loops nested within this loop, create them now!
194 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
195 E = L->Blocks.end(); I != E; ++I)
196 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
197 L->SubLoops.push_back(NewLoop);
198 NewLoop->ParentLoop = L;
201 // Add the basic blocks that comprise this loop to the BBMap so that this
202 // loop can be found for them.
204 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
205 E = L->Blocks.end(); I != E; ++I) {
206 std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
207 if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet...
208 BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
211 // Now that we have a list of all of the child loops of this loop, check to
212 // see if any of them should actually be nested inside of each other. We can
213 // accidentally pull loops our of their parents, so we must make sure to
214 // organize the loop nests correctly now.
216 std::map<BasicBlock*, Loop*> ContainingLoops;
217 for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
218 Loop *Child = L->SubLoops[i];
219 assert(Child->getParentLoop() == L && "Not proper child loop?");
221 if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) {
222 // If there is already a loop which contains this loop, move this loop
223 // into the containing loop.
224 MoveSiblingLoopInto(Child, ContainingLoop);
225 --i; // The loop got removed from the SubLoops list.
227 // This is currently considered to be a top-level loop. Check to see if
228 // any of the contained blocks are loop headers for subloops we have
229 // already processed.
230 for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
231 Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]];
232 if (BlockLoop == 0) { // Child block not processed yet...
234 } else if (BlockLoop != Child) {
235 Loop *SubLoop = BlockLoop;
236 // Reparent all of the blocks which used to belong to BlockLoops
237 for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
238 ContainingLoops[SubLoop->Blocks[j]] = Child;
240 // There is already a loop which contains this block, that means
241 // that we should reparent the loop which the block is currently
242 // considered to belong to to be a child of this loop.
243 MoveSiblingLoopInto(SubLoop, Child);
244 --i; // We just shrunk the SubLoops list.
251 // Now that we know all of the blocks that make up this loop, see if there are
252 // any branches to outside of the loop... building the ExitBlocks list.
253 for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
254 BE = L->Blocks.end(); BI != BE; ++BI)
255 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
256 if (!L->contains(*I)) // Not in current loop?
257 L->ExitBlocks.push_back(*I); // It must be an exit block...
262 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
263 /// the NewParent Loop, instead of being a sibling of it.
264 void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) {
265 Loop *OldParent = NewChild->getParentLoop();
266 assert(OldParent && OldParent == NewParent->getParentLoop() &&
267 NewChild != NewParent && "Not sibling loops!");
269 // Remove NewChild from being a child of OldParent
270 std::vector<Loop*>::iterator I =
271 std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
272 assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
273 OldParent->SubLoops.erase(I); // Remove from parent's subloops list
274 NewChild->ParentLoop = 0;
276 InsertLoopInto(NewChild, NewParent);
279 /// InsertLoopInto - This inserts loop L into the specified parent loop. If the
280 /// parent loop contains a loop which should contain L, the loop gets inserted
282 void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) {
283 BasicBlock *LHeader = L->getHeader();
284 assert(Parent->contains(LHeader) && "This loop should not be inserted here!");
286 // Check to see if it belongs in a child loop...
287 for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
288 if (Parent->SubLoops[i]->contains(LHeader)) {
289 InsertLoopInto(L, Parent->SubLoops[i]);
293 // If not, insert it here!
294 Parent->SubLoops.push_back(L);
295 L->ParentLoop = Parent;
298 /// changeLoopFor - Change the top-level loop that contains BB to the
299 /// specified loop. This should be used by transformations that restructure
300 /// the loop hierarchy tree.
301 void LoopInfo::changeLoopFor(BasicBlock *BB, Loop *L) {
302 Loop *&OldLoop = BBMap[BB];
303 assert(OldLoop && "Block not in a loop yet!");
307 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
308 /// list with the indicated loop.
309 void LoopInfo::changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) {
310 std::vector<Loop*>::iterator I = std::find(TopLevelLoops.begin(),
311 TopLevelLoops.end(), OldLoop);
312 assert(I != TopLevelLoops.end() && "Old loop not at top level!");
314 assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 &&
315 "Loops already embedded into a subloop!");
318 //===----------------------------------------------------------------------===//
319 // APIs for simple analysis of the loop.
322 /// getLoopPreheader - If there is a preheader for this loop, return it. A
323 /// loop has a preheader if there is only one edge to the header of the loop
324 /// from outside of the loop. If this is the case, the block branching to the
325 /// header of the loop is the preheader node.
327 /// This method returns null if there is no preheader for the loop.
329 BasicBlock *Loop::getLoopPreheader() const {
330 // Keep track of nodes outside the loop branching to the header...
333 // Loop over the predecessors of the header node...
334 BasicBlock *Header = getHeader();
335 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
337 if (!contains(*PI)) { // If the block is not in the loop...
338 if (Out && Out != *PI)
339 return 0; // Multiple predecessors outside the loop
343 // Make sure there is only one exit out of the preheader...
344 succ_iterator SI = succ_begin(Out);
346 if (SI != succ_end(Out))
347 return 0; // Multiple exits from the block, must not be a preheader.
350 // If there is exactly one preheader, return it. If there was zero, then Out
355 /// getCanonicalInductionVariable - Check to see if the loop has a canonical
356 /// induction variable: an integer recurrence that starts at 0 and increments by
357 /// one each time through the loop. If so, return the phi node that corresponds
360 PHINode *Loop::getCanonicalInductionVariable() const {
361 BasicBlock *H = getHeader();
363 BasicBlock *Incoming = 0, *Backedge = 0;
364 pred_iterator PI = pred_begin(H);
365 assert(PI != pred_end(H) && "Loop must have at least one backedge!");
367 if (PI == pred_end(H)) return 0; // dead loop
369 if (PI != pred_end(H)) return 0; // multiple backedges?
371 if (contains(Incoming)) {
372 if (contains(Backedge))
374 std::swap(Incoming, Backedge);
375 } else if (!contains(Backedge))
378 // Loop over all of the PHI nodes, looking for a canonical indvar.
379 for (BasicBlock::iterator I = H->begin();
380 PHINode *PN = dyn_cast<PHINode>(I); ++I)
381 if (Instruction *Inc =
382 dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
383 if (Inc->getOpcode() == Instruction::Add && Inc->getOperand(0) == PN)
384 if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
385 if (CI->equalsInt(1))
391 /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
392 /// the canonical induction variable value for the "next" iteration of the loop.
393 /// This always succeeds if getCanonicalInductionVariable succeeds.
395 Instruction *Loop::getCanonicalInductionVariableIncrement() const {
396 if (PHINode *PN = getCanonicalInductionVariable()) {
397 bool P1InLoop = contains(PN->getIncomingBlock(1));
398 return cast<Instruction>(PN->getIncomingValue(P1InLoop));
403 /// getTripCount - Return a loop-invariant LLVM value indicating the number of
404 /// times the loop will be executed. Note that this means that the backedge of
405 /// the loop executes N-1 times. If the trip-count cannot be determined, this
408 Value *Loop::getTripCount() const {
409 // Canonical loops will end with a 'setne I, V', where I is the incremented
410 // canonical induction variable and V is the trip count of the loop.
411 Instruction *Inc = getCanonicalInductionVariableIncrement();
412 PHINode *IV = cast<PHINode>(Inc->getOperand(0));
414 BasicBlock *BackedgeBlock =
415 IV->getIncomingBlock(contains(IV->getIncomingBlock(1)));
417 if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator()))
418 if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
419 if (SCI->getOperand(0) == Inc)
420 if (BI->getSuccessor(0) == getHeader()) {
421 if (SCI->getOpcode() == Instruction::SetNE)
422 return SCI->getOperand(1);
423 } else if (SCI->getOpcode() == Instruction::SetEQ) {
424 return SCI->getOperand(1);
431 //===-------------------------------------------------------------------===//
432 // APIs for updating loop information after changing the CFG
435 /// addBasicBlockToLoop - This function is used by other analyses to update loop
436 /// information. NewBB is set to be a new member of the current loop. Because
437 /// of this, it is added as a member of all parent loops, and is added to the
438 /// specified LoopInfo object as being in the current basic block. It is not
439 /// valid to replace the loop header with this method.
441 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
442 assert((Blocks.empty() || LI[getHeader()] == this) &&
443 "Incorrect LI specified for this loop!");
444 assert(NewBB && "Cannot add a null basic block to the loop!");
445 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
447 // Add the loop mapping to the LoopInfo object...
448 LI.BBMap[NewBB] = this;
450 // Add the basic block to this loop and all parent loops...
453 L->Blocks.push_back(NewBB);
454 L = L->getParentLoop();
458 /// changeExitBlock - This method is used to update loop information. All
459 /// instances of the specified Old basic block are removed from the exit list
460 /// and replaced with New.
462 void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
463 assert(Old != New && "Cannot changeExitBlock to the same thing!");
464 assert(Old && New && "Cannot changeExitBlock to or from a null node!");
465 assert(hasExitBlock(Old) && "Old exit block not found!");
466 std::vector<BasicBlock*>::iterator
467 I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
468 while (I != ExitBlocks.end()) {
470 I = std::find(I+1, ExitBlocks.end(), Old);
474 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
475 /// the OldChild entry in our children list with NewChild, and updates the
476 /// parent pointers of the two loops as appropriate.
477 void Loop::replaceChildLoopWith(Loop *OldChild, Loop *NewChild) {
478 assert(OldChild->ParentLoop == this && "This loop is already broken!");
479 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
480 std::vector<Loop*>::iterator I = std::find(SubLoops.begin(), SubLoops.end(),
482 assert(I != SubLoops.end() && "OldChild not in loop!");
484 OldChild->ParentLoop = 0;
485 NewChild->ParentLoop = this;
487 // Update the loop depth of the new child.
488 NewChild->setLoopDepth(LoopDepth+1);
491 /// addChildLoop - Add the specified loop to be a child of this loop.
493 void Loop::addChildLoop(Loop *NewChild) {
494 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
495 NewChild->ParentLoop = this;
496 SubLoops.push_back(NewChild);
498 // Update the loop depth of the new child.
499 NewChild->setLoopDepth(LoopDepth+1);
503 static void RemoveFromVector(std::vector<T*> &V, T *N) {
504 typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N);
505 assert(I != V.end() && "N is not in this list!");
509 /// removeChildLoop - This removes the specified child from being a subloop of
510 /// this loop. The loop is not deleted, as it will presumably be inserted
511 /// into another loop.
512 Loop *Loop::removeChildLoop(iterator I) {
513 assert(I != SubLoops.end() && "Cannot remove end iterator!");
515 assert(Child->ParentLoop == this && "Child is not a child of this loop!");
516 SubLoops.erase(SubLoops.begin()+(I-begin()));
517 Child->ParentLoop = 0;
522 /// removeBlockFromLoop - This removes the specified basic block from the
523 /// current loop, updating the Blocks and ExitBlocks lists as appropriate. This
524 /// does not update the mapping in the LoopInfo class.
525 void Loop::removeBlockFromLoop(BasicBlock *BB) {
526 RemoveFromVector(Blocks, BB);
528 // If this block branched out of this loop, remove any exit blocks entries due
530 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
531 if (!contains(*SI) && *SI != BB)
532 RemoveFromVector(ExitBlocks, *SI);
534 // If any blocks in this loop branch to BB, add it to the exit blocks set.
535 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
537 ExitBlocks.push_back(BB);