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 "llvm/ADT/DepthFirstIterator.h"
29 static RegisterAnalysis<LoopInfo>
30 X("loops", "Natural Loop Construction", true);
32 //===----------------------------------------------------------------------===//
33 // Loop implementation
35 bool Loop::contains(const BasicBlock *BB) const {
36 return std::find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
39 bool Loop::isLoopExit(const BasicBlock *BB) const {
40 for (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
48 /// getNumBackEdges - Calculate the number of back edges to the loop header.
50 unsigned Loop::getNumBackEdges() const {
51 unsigned NumBackEdges = 0;
52 BasicBlock *H = getHeader();
54 for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
61 /// isLoopInvariant - Return true if the specified value is loop invariant
63 bool Loop::isLoopInvariant(Value *V) const {
64 if (Instruction *I = dyn_cast<Instruction>(V))
65 return !contains(I->getParent());
66 return true; // All non-instructions are loop invariant
69 void Loop::print(std::ostream &OS, unsigned Depth) const {
70 OS << std::string(Depth*2, ' ') << "Loop Containing: ";
72 for (unsigned i = 0; i < getBlocks().size(); ++i) {
74 WriteAsOperand(OS, getBlocks()[i], false);
78 for (iterator I = begin(), E = end(); I != E; ++I)
79 (*I)->print(OS, Depth+2);
82 void Loop::dump() const {
87 //===----------------------------------------------------------------------===//
88 // LoopInfo implementation
90 void LoopInfo::stub() {}
92 bool LoopInfo::runOnFunction(Function &) {
94 Calculate(getAnalysis<DominatorSet>()); // Update
98 void LoopInfo::releaseMemory() {
99 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
100 E = TopLevelLoops.end(); I != E; ++I)
101 delete *I; // Delete all of the loops...
103 BBMap.clear(); // Reset internal state of analysis
104 TopLevelLoops.clear();
108 void LoopInfo::Calculate(const DominatorSet &DS) {
109 BasicBlock *RootNode = DS.getRoot();
111 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
112 NE = df_end(RootNode); NI != NE; ++NI)
113 if (Loop *L = ConsiderForLoop(*NI, DS))
114 TopLevelLoops.push_back(L);
117 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
118 AU.setPreservesAll();
119 AU.addRequired<DominatorSet>();
122 void LoopInfo::print(std::ostream &OS, const Module* ) 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->getLoopDepth() << "\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.
253 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
254 /// the NewParent Loop, instead of being a sibling of it.
255 void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) {
256 Loop *OldParent = NewChild->getParentLoop();
257 assert(OldParent && OldParent == NewParent->getParentLoop() &&
258 NewChild != NewParent && "Not sibling loops!");
260 // Remove NewChild from being a child of OldParent
261 std::vector<Loop*>::iterator I =
262 std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
263 assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
264 OldParent->SubLoops.erase(I); // Remove from parent's subloops list
265 NewChild->ParentLoop = 0;
267 InsertLoopInto(NewChild, NewParent);
270 /// InsertLoopInto - This inserts loop L into the specified parent loop. If the
271 /// parent loop contains a loop which should contain L, the loop gets inserted
273 void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) {
274 BasicBlock *LHeader = L->getHeader();
275 assert(Parent->contains(LHeader) && "This loop should not be inserted here!");
277 // Check to see if it belongs in a child loop...
278 for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
279 if (Parent->SubLoops[i]->contains(LHeader)) {
280 InsertLoopInto(L, Parent->SubLoops[i]);
284 // If not, insert it here!
285 Parent->SubLoops.push_back(L);
286 L->ParentLoop = Parent;
289 /// changeLoopFor - Change the top-level loop that contains BB to the
290 /// specified loop. This should be used by transformations that restructure
291 /// the loop hierarchy tree.
292 void LoopInfo::changeLoopFor(BasicBlock *BB, Loop *L) {
293 Loop *&OldLoop = BBMap[BB];
294 assert(OldLoop && "Block not in a loop yet!");
298 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
299 /// list with the indicated loop.
300 void LoopInfo::changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) {
301 std::vector<Loop*>::iterator I = std::find(TopLevelLoops.begin(),
302 TopLevelLoops.end(), OldLoop);
303 assert(I != TopLevelLoops.end() && "Old loop not at top level!");
305 assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 &&
306 "Loops already embedded into a subloop!");
309 /// removeLoop - This removes the specified top-level loop from this loop info
310 /// object. The loop is not deleted, as it will presumably be inserted into
312 Loop *LoopInfo::removeLoop(iterator I) {
313 assert(I != end() && "Cannot remove end iterator!");
315 assert(L->getParentLoop() == 0 && "Not a top-level loop!");
316 TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin()));
320 /// removeBlock - This method completely removes BB from all data structures,
321 /// including all of the Loop objects it is nested in and our mapping from
322 /// BasicBlocks to loops.
323 void LoopInfo::removeBlock(BasicBlock *BB) {
324 std::map<BasicBlock *, Loop*>::iterator I = BBMap.find(BB);
325 if (I != BBMap.end()) {
326 for (Loop *L = I->second; L; L = L->getParentLoop())
327 L->removeBlockFromLoop(BB);
334 //===----------------------------------------------------------------------===//
335 // APIs for simple analysis of the loop.
338 /// getExitBlocks - Return all of the successor blocks of this loop. These
339 /// are the blocks _outside of the current loop_ which are branched to.
341 void Loop::getExitBlocks(std::vector<BasicBlock*> &ExitBlocks) const {
342 for (std::vector<BasicBlock*>::const_iterator BI = Blocks.begin(),
343 BE = Blocks.end(); BI != BE; ++BI)
344 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
345 if (!contains(*I)) // Not in current loop?
346 ExitBlocks.push_back(*I); // It must be an exit block...
350 /// getLoopPreheader - If there is a preheader for this loop, return it. A
351 /// loop has a preheader if there is only one edge to the header of the loop
352 /// from outside of the loop. If this is the case, the block branching to the
353 /// header of the loop is the preheader node.
355 /// This method returns null if there is no preheader for the loop.
357 BasicBlock *Loop::getLoopPreheader() const {
358 // Keep track of nodes outside the loop branching to the header...
361 // Loop over the predecessors of the header node...
362 BasicBlock *Header = getHeader();
363 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
365 if (!contains(*PI)) { // If the block is not in the loop...
366 if (Out && Out != *PI)
367 return 0; // Multiple predecessors outside the loop
371 // Make sure there is only one exit out of the preheader...
372 succ_iterator SI = succ_begin(Out);
374 if (SI != succ_end(Out))
375 return 0; // Multiple exits from the block, must not be a preheader.
378 // If there is exactly one preheader, return it. If there was zero, then Out
383 /// getCanonicalInductionVariable - Check to see if the loop has a canonical
384 /// induction variable: an integer recurrence that starts at 0 and increments by
385 /// one each time through the loop. If so, return the phi node that corresponds
388 PHINode *Loop::getCanonicalInductionVariable() const {
389 BasicBlock *H = getHeader();
391 BasicBlock *Incoming = 0, *Backedge = 0;
392 pred_iterator PI = pred_begin(H);
393 assert(PI != pred_end(H) && "Loop must have at least one backedge!");
395 if (PI == pred_end(H)) return 0; // dead loop
397 if (PI != pred_end(H)) return 0; // multiple backedges?
399 if (contains(Incoming)) {
400 if (contains(Backedge))
402 std::swap(Incoming, Backedge);
403 } else if (!contains(Backedge))
406 // Loop over all of the PHI nodes, looking for a canonical indvar.
407 for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
408 PHINode *PN = cast<PHINode>(I);
409 if (Instruction *Inc =
410 dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
411 if (Inc->getOpcode() == Instruction::Add && Inc->getOperand(0) == PN)
412 if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
413 if (CI->equalsInt(1))
419 /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
420 /// the canonical induction variable value for the "next" iteration of the loop.
421 /// This always succeeds if getCanonicalInductionVariable succeeds.
423 Instruction *Loop::getCanonicalInductionVariableIncrement() const {
424 if (PHINode *PN = getCanonicalInductionVariable()) {
425 bool P1InLoop = contains(PN->getIncomingBlock(1));
426 return cast<Instruction>(PN->getIncomingValue(P1InLoop));
431 /// getTripCount - Return a loop-invariant LLVM value indicating the number of
432 /// times the loop will be executed. Note that this means that the backedge of
433 /// the loop executes N-1 times. If the trip-count cannot be determined, this
436 Value *Loop::getTripCount() const {
437 // Canonical loops will end with a 'setne I, V', where I is the incremented
438 // canonical induction variable and V is the trip count of the loop.
439 Instruction *Inc = getCanonicalInductionVariableIncrement();
440 if (Inc == 0) return 0;
441 PHINode *IV = cast<PHINode>(Inc->getOperand(0));
443 BasicBlock *BackedgeBlock =
444 IV->getIncomingBlock(contains(IV->getIncomingBlock(1)));
446 if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator()))
447 if (BI->isConditional())
448 if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
449 if (SCI->getOperand(0) == Inc)
450 if (BI->getSuccessor(0) == getHeader()) {
451 if (SCI->getOpcode() == Instruction::SetNE)
452 return SCI->getOperand(1);
453 } else if (SCI->getOpcode() == Instruction::SetEQ) {
454 return SCI->getOperand(1);
461 //===-------------------------------------------------------------------===//
462 // APIs for updating loop information after changing the CFG
465 /// addBasicBlockToLoop - This function is used by other analyses to update loop
466 /// information. NewBB is set to be a new member of the current loop. Because
467 /// of this, it is added as a member of all parent loops, and is added to the
468 /// specified LoopInfo object as being in the current basic block. It is not
469 /// valid to replace the loop header with this method.
471 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
472 assert((Blocks.empty() || LI[getHeader()] == this) &&
473 "Incorrect LI specified for this loop!");
474 assert(NewBB && "Cannot add a null basic block to the loop!");
475 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
477 // Add the loop mapping to the LoopInfo object...
478 LI.BBMap[NewBB] = this;
480 // Add the basic block to this loop and all parent loops...
483 L->Blocks.push_back(NewBB);
484 L = L->getParentLoop();
488 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
489 /// the OldChild entry in our children list with NewChild, and updates the
490 /// parent pointers of the two loops as appropriate.
491 void Loop::replaceChildLoopWith(Loop *OldChild, Loop *NewChild) {
492 assert(OldChild->ParentLoop == this && "This loop is already broken!");
493 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
494 std::vector<Loop*>::iterator I = std::find(SubLoops.begin(), SubLoops.end(),
496 assert(I != SubLoops.end() && "OldChild not in loop!");
498 OldChild->ParentLoop = 0;
499 NewChild->ParentLoop = this;
502 /// addChildLoop - Add the specified loop to be a child of this loop.
504 void Loop::addChildLoop(Loop *NewChild) {
505 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
506 NewChild->ParentLoop = this;
507 SubLoops.push_back(NewChild);
511 static void RemoveFromVector(std::vector<T*> &V, T *N) {
512 typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N);
513 assert(I != V.end() && "N is not in this list!");
517 /// removeChildLoop - This removes the specified child from being a subloop of
518 /// this loop. The loop is not deleted, as it will presumably be inserted
519 /// into another loop.
520 Loop *Loop::removeChildLoop(iterator I) {
521 assert(I != SubLoops.end() && "Cannot remove end iterator!");
523 assert(Child->ParentLoop == this && "Child is not a child of this loop!");
524 SubLoops.erase(SubLoops.begin()+(I-begin()));
525 Child->ParentLoop = 0;
530 /// removeBlockFromLoop - This removes the specified basic block from the
531 /// current loop, updating the Blocks and ExitBlocks lists as appropriate. This
532 /// does not update the mapping in the LoopInfo class.
533 void Loop::removeBlockFromLoop(BasicBlock *BB) {
534 RemoveFromVector(Blocks, BB);