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"
28 static RegisterAnalysis<LoopInfo>
29 X("loops", "Natural Loop Construction", true);
31 //===----------------------------------------------------------------------===//
32 // Loop implementation
34 bool Loop::contains(const BasicBlock *BB) const {
35 return std::find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
38 bool Loop::isLoopExit(const BasicBlock *BB) const {
39 for (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
47 /// getNumBackEdges - Calculate the number of back edges to the loop header.
49 unsigned Loop::getNumBackEdges() const {
50 unsigned NumBackEdges = 0;
51 BasicBlock *H = getHeader();
53 for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
60 /// isLoopInvariant - Return true if the specified value is loop invariant
62 bool Loop::isLoopInvariant(Value *V) const {
63 if (Instruction *I = dyn_cast<Instruction>(V))
64 return !contains(I->getParent());
65 return true; // All non-instructions are loop invariant
68 void Loop::print(std::ostream &OS, unsigned Depth) const {
69 OS << std::string(Depth*2, ' ') << "Loop Containing: ";
71 for (unsigned i = 0; i < getBlocks().size(); ++i) {
73 WriteAsOperand(OS, getBlocks()[i], false);
77 for (iterator I = begin(), E = end(); I != E; ++I)
78 (*I)->print(OS, Depth+2);
81 void Loop::dump() const {
86 //===----------------------------------------------------------------------===//
87 // LoopInfo implementation
89 bool LoopInfo::runOnFunction(Function &) {
91 Calculate(getAnalysis<ETForest>()); // 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(ETForest &EF) {
106 BasicBlock *RootNode = EF.getRoot();
108 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
109 NE = df_end(RootNode); NI != NE; ++NI)
110 if (Loop *L = ConsiderForLoop(*NI, EF))
111 TopLevelLoops.push_back(L);
114 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
115 AU.setPreservesAll();
116 AU.addRequired<ETForest>();
119 void LoopInfo::print(std::ostream &OS, const Module* ) const {
120 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
121 TopLevelLoops[i]->print(OS);
123 for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
124 E = BBMap.end(); I != E; ++I)
125 OS << "BB '" << I->first->getName() << "' level = "
126 << I->second->getLoopDepth() << "\n";
130 static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
131 if (SubLoop == 0) return true;
132 if (SubLoop == ParentLoop) return false;
133 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
136 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, ETForest &EF) {
137 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
139 std::vector<BasicBlock *> TodoStack;
141 // Scan the predecessors of BB, checking to see if BB dominates any of
142 // them. This identifies backedges which target this node...
143 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
144 if (EF.dominates(BB, *I)) // If BB dominates it's predecessor...
145 TodoStack.push_back(*I);
147 if (TodoStack.empty()) return 0; // No backedges to this block...
149 // Create a new loop to represent this basic block...
150 Loop *L = new Loop(BB);
153 BasicBlock *EntryBlock = &BB->getParent()->getEntryBlock();
155 while (!TodoStack.empty()) { // Process all the nodes in the loop
156 BasicBlock *X = TodoStack.back();
157 TodoStack.pop_back();
159 if (!L->contains(X) && // As of yet unprocessed??
160 EF.dominates(EntryBlock, X)) { // X is reachable from entry block?
161 // Check to see if this block already belongs to a loop. If this occurs
162 // then we have a case where a loop that is supposed to be a child of the
163 // current loop was processed before the current loop. When this occurs,
164 // this child loop gets added to a part of the current loop, making it a
165 // sibling to the current loop. We have to reparent this loop.
166 if (Loop *SubLoop = const_cast<Loop*>(getLoopFor(X)))
167 if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
168 // Remove the subloop from it's current parent...
169 assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
170 Loop *SLP = SubLoop->ParentLoop; // SubLoopParent
171 std::vector<Loop*>::iterator I =
172 std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
173 assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
174 SLP->SubLoops.erase(I); // Remove from parent...
176 // Add the subloop to THIS loop...
177 SubLoop->ParentLoop = L;
178 L->SubLoops.push_back(SubLoop);
181 // Normal case, add the block to our loop...
182 L->Blocks.push_back(X);
184 // Add all of the predecessors of X to the end of the work stack...
185 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
189 // If there are any loops nested within this loop, create them now!
190 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
191 E = L->Blocks.end(); I != E; ++I)
192 if (Loop *NewLoop = ConsiderForLoop(*I, EF)) {
193 L->SubLoops.push_back(NewLoop);
194 NewLoop->ParentLoop = L;
197 // Add the basic blocks that comprise this loop to the BBMap so that this
198 // loop can be found for them.
200 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
201 E = L->Blocks.end(); I != E; ++I) {
202 std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
203 if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet...
204 BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
207 // Now that we have a list of all of the child loops of this loop, check to
208 // see if any of them should actually be nested inside of each other. We can
209 // accidentally pull loops our of their parents, so we must make sure to
210 // organize the loop nests correctly now.
212 std::map<BasicBlock*, Loop*> ContainingLoops;
213 for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
214 Loop *Child = L->SubLoops[i];
215 assert(Child->getParentLoop() == L && "Not proper child loop?");
217 if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) {
218 // If there is already a loop which contains this loop, move this loop
219 // into the containing loop.
220 MoveSiblingLoopInto(Child, ContainingLoop);
221 --i; // The loop got removed from the SubLoops list.
223 // This is currently considered to be a top-level loop. Check to see if
224 // any of the contained blocks are loop headers for subloops we have
225 // already processed.
226 for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
227 Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]];
228 if (BlockLoop == 0) { // Child block not processed yet...
230 } else if (BlockLoop != Child) {
231 Loop *SubLoop = BlockLoop;
232 // Reparent all of the blocks which used to belong to BlockLoops
233 for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
234 ContainingLoops[SubLoop->Blocks[j]] = Child;
236 // There is already a loop which contains this block, that means
237 // that we should reparent the loop which the block is currently
238 // considered to belong to to be a child of this loop.
239 MoveSiblingLoopInto(SubLoop, Child);
240 --i; // We just shrunk the SubLoops list.
250 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
251 /// the NewParent Loop, instead of being a sibling of it.
252 void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) {
253 Loop *OldParent = NewChild->getParentLoop();
254 assert(OldParent && OldParent == NewParent->getParentLoop() &&
255 NewChild != NewParent && "Not sibling loops!");
257 // Remove NewChild from being a child of OldParent
258 std::vector<Loop*>::iterator I =
259 std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
260 assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
261 OldParent->SubLoops.erase(I); // Remove from parent's subloops list
262 NewChild->ParentLoop = 0;
264 InsertLoopInto(NewChild, NewParent);
267 /// InsertLoopInto - This inserts loop L into the specified parent loop. If the
268 /// parent loop contains a loop which should contain L, the loop gets inserted
270 void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) {
271 BasicBlock *LHeader = L->getHeader();
272 assert(Parent->contains(LHeader) && "This loop should not be inserted here!");
274 // Check to see if it belongs in a child loop...
275 for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
276 if (Parent->SubLoops[i]->contains(LHeader)) {
277 InsertLoopInto(L, Parent->SubLoops[i]);
281 // If not, insert it here!
282 Parent->SubLoops.push_back(L);
283 L->ParentLoop = Parent;
286 /// changeLoopFor - Change the top-level loop that contains BB to the
287 /// specified loop. This should be used by transformations that restructure
288 /// the loop hierarchy tree.
289 void LoopInfo::changeLoopFor(BasicBlock *BB, Loop *L) {
290 Loop *&OldLoop = BBMap[BB];
291 assert(OldLoop && "Block not in a loop yet!");
295 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
296 /// list with the indicated loop.
297 void LoopInfo::changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) {
298 std::vector<Loop*>::iterator I = std::find(TopLevelLoops.begin(),
299 TopLevelLoops.end(), OldLoop);
300 assert(I != TopLevelLoops.end() && "Old loop not at top level!");
302 assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 &&
303 "Loops already embedded into a subloop!");
306 /// removeLoop - This removes the specified top-level loop from this loop info
307 /// object. The loop is not deleted, as it will presumably be inserted into
309 Loop *LoopInfo::removeLoop(iterator I) {
310 assert(I != end() && "Cannot remove end iterator!");
312 assert(L->getParentLoop() == 0 && "Not a top-level loop!");
313 TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin()));
317 /// removeBlock - This method completely removes BB from all data structures,
318 /// including all of the Loop objects it is nested in and our mapping from
319 /// BasicBlocks to loops.
320 void LoopInfo::removeBlock(BasicBlock *BB) {
321 std::map<BasicBlock *, Loop*>::iterator I = BBMap.find(BB);
322 if (I != BBMap.end()) {
323 for (Loop *L = I->second; L; L = L->getParentLoop())
324 L->removeBlockFromLoop(BB);
331 //===----------------------------------------------------------------------===//
332 // APIs for simple analysis of the loop.
335 /// getExitBlocks - Return all of the successor blocks of this loop. These
336 /// are the blocks _outside of the current loop_ which are branched to.
338 void Loop::getExitBlocks(std::vector<BasicBlock*> &ExitBlocks) const {
339 for (std::vector<BasicBlock*>::const_iterator BI = Blocks.begin(),
340 BE = Blocks.end(); BI != BE; ++BI)
341 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
342 if (!contains(*I)) // Not in current loop?
343 ExitBlocks.push_back(*I); // It must be an exit block...
347 /// getLoopPreheader - If there is a preheader for this loop, return it. A
348 /// loop has a preheader if there is only one edge to the header of the loop
349 /// from outside of the loop. If this is the case, the block branching to the
350 /// header of the loop is the preheader node.
352 /// This method returns null if there is no preheader for the loop.
354 BasicBlock *Loop::getLoopPreheader() const {
355 // Keep track of nodes outside the loop branching to the header...
358 // Loop over the predecessors of the header node...
359 BasicBlock *Header = getHeader();
360 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
362 if (!contains(*PI)) { // If the block is not in the loop...
363 if (Out && Out != *PI)
364 return 0; // Multiple predecessors outside the loop
368 // Make sure there is only one exit out of the preheader.
369 assert(Out && "Header of loop has no predecessors from outside loop?");
370 succ_iterator SI = succ_begin(Out);
372 if (SI != succ_end(Out))
373 return 0; // Multiple exits from the block, must not be a preheader.
375 // If there is exactly one preheader, return it. If there was zero, then Out
380 /// getLoopLatch - If there is a latch block for this loop, return it. A
381 /// latch block is the canonical backedge for a loop. A loop header in normal
382 /// form has two edges into it: one from a preheader and one from a latch
384 BasicBlock *Loop::getLoopLatch() const {
385 BasicBlock *Header = getHeader();
386 pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
387 if (PI == PE) return 0; // no preds?
389 BasicBlock *Latch = 0;
393 if (PI == PE) return 0; // only one pred?
396 if (Latch) return 0; // multiple backedges
400 if (PI != PE) return 0; // more than two preds
405 /// getCanonicalInductionVariable - Check to see if the loop has a canonical
406 /// induction variable: an integer recurrence that starts at 0 and increments by
407 /// one each time through the loop. If so, return the phi node that corresponds
410 PHINode *Loop::getCanonicalInductionVariable() const {
411 BasicBlock *H = getHeader();
413 BasicBlock *Incoming = 0, *Backedge = 0;
414 pred_iterator PI = pred_begin(H);
415 assert(PI != pred_end(H) && "Loop must have at least one backedge!");
417 if (PI == pred_end(H)) return 0; // dead loop
419 if (PI != pred_end(H)) return 0; // multiple backedges?
421 if (contains(Incoming)) {
422 if (contains(Backedge))
424 std::swap(Incoming, Backedge);
425 } else if (!contains(Backedge))
428 // Loop over all of the PHI nodes, looking for a canonical indvar.
429 for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
430 PHINode *PN = cast<PHINode>(I);
431 if (Instruction *Inc =
432 dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
433 if (Inc->getOpcode() == Instruction::Add && Inc->getOperand(0) == PN)
434 if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
435 if (CI->equalsInt(1))
441 /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
442 /// the canonical induction variable value for the "next" iteration of the loop.
443 /// This always succeeds if getCanonicalInductionVariable succeeds.
445 Instruction *Loop::getCanonicalInductionVariableIncrement() const {
446 if (PHINode *PN = getCanonicalInductionVariable()) {
447 bool P1InLoop = contains(PN->getIncomingBlock(1));
448 return cast<Instruction>(PN->getIncomingValue(P1InLoop));
453 /// getTripCount - Return a loop-invariant LLVM value indicating the number of
454 /// times the loop will be executed. Note that this means that the backedge of
455 /// the loop executes N-1 times. If the trip-count cannot be determined, this
458 Value *Loop::getTripCount() const {
459 // Canonical loops will end with a 'setne I, V', where I is the incremented
460 // canonical induction variable and V is the trip count of the loop.
461 Instruction *Inc = getCanonicalInductionVariableIncrement();
462 if (Inc == 0) return 0;
463 PHINode *IV = cast<PHINode>(Inc->getOperand(0));
465 BasicBlock *BackedgeBlock =
466 IV->getIncomingBlock(contains(IV->getIncomingBlock(1)));
468 if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator()))
469 if (BI->isConditional())
470 if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
471 if (SCI->getOperand(0) == Inc)
472 if (BI->getSuccessor(0) == getHeader()) {
473 if (SCI->getOpcode() == Instruction::SetNE)
474 return SCI->getOperand(1);
475 } else if (SCI->getOpcode() == Instruction::SetEQ) {
476 return SCI->getOperand(1);
482 /// isLCSSAForm - Return true if the Loop is in LCSSA form
483 bool Loop::isLCSSAForm() const {
484 for (Loop::block_iterator BB = block_begin(), E = block_end();
486 for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
487 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
489 BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
490 if (!isa<PHINode>(*UI) && !contains(UserBB)) {
499 //===-------------------------------------------------------------------===//
500 // APIs for updating loop information after changing the CFG
503 /// addBasicBlockToLoop - This function is used by other analyses to update loop
504 /// information. NewBB is set to be a new member of the current loop. Because
505 /// of this, it is added as a member of all parent loops, and is added to the
506 /// specified LoopInfo object as being in the current basic block. It is not
507 /// valid to replace the loop header with this method.
509 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
510 assert((Blocks.empty() || LI[getHeader()] == this) &&
511 "Incorrect LI specified for this loop!");
512 assert(NewBB && "Cannot add a null basic block to the loop!");
513 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
515 // Add the loop mapping to the LoopInfo object...
516 LI.BBMap[NewBB] = this;
518 // Add the basic block to this loop and all parent loops...
521 L->Blocks.push_back(NewBB);
522 L = L->getParentLoop();
526 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
527 /// the OldChild entry in our children list with NewChild, and updates the
528 /// parent pointers of the two loops as appropriate.
529 void Loop::replaceChildLoopWith(Loop *OldChild, Loop *NewChild) {
530 assert(OldChild->ParentLoop == this && "This loop is already broken!");
531 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
532 std::vector<Loop*>::iterator I = std::find(SubLoops.begin(), SubLoops.end(),
534 assert(I != SubLoops.end() && "OldChild not in loop!");
536 OldChild->ParentLoop = 0;
537 NewChild->ParentLoop = this;
540 /// addChildLoop - Add the specified loop to be a child of this loop.
542 void Loop::addChildLoop(Loop *NewChild) {
543 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
544 NewChild->ParentLoop = this;
545 SubLoops.push_back(NewChild);
549 static void RemoveFromVector(std::vector<T*> &V, T *N) {
550 typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N);
551 assert(I != V.end() && "N is not in this list!");
555 /// removeChildLoop - This removes the specified child from being a subloop of
556 /// this loop. The loop is not deleted, as it will presumably be inserted
557 /// into another loop.
558 Loop *Loop::removeChildLoop(iterator I) {
559 assert(I != SubLoops.end() && "Cannot remove end iterator!");
561 assert(Child->ParentLoop == this && "Child is not a child of this loop!");
562 SubLoops.erase(SubLoops.begin()+(I-begin()));
563 Child->ParentLoop = 0;
568 /// removeBlockFromLoop - This removes the specified basic block from the
569 /// current loop, updating the Blocks and ExitBlocks lists as appropriate. This
570 /// does not update the mapping in the LoopInfo class.
571 void Loop::removeBlockFromLoop(BasicBlock *BB) {
572 RemoveFromVector(Blocks, BB);
575 // Ensure this file gets linked when LoopInfo.h is used.
576 DEFINING_FILE_FOR(LoopInfo)