1 //===- llvm/Analysis/LoopInfo.h - Natural Loop Calculator -------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // 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. A natural loop
12 // has exactly one entry-point, which is called the header. Note that natural
13 // loops may actually be several loops that share the same header node.
15 // This analysis calculates the nesting structure of loops in a function. For
16 // each natural loop identified, this analysis identifies natural loops
17 // contained entirely within the loop and the basic blocks the make up the loop.
19 // It can calculate on the fly various bits of information, for example:
21 // * whether there is a preheader for the loop
22 // * the number of back edges to the header
23 // * whether or not a particular block branches out of the loop
24 // * the successor blocks of the loop
28 //===----------------------------------------------------------------------===//
30 #ifndef LLVM_ANALYSIS_LOOP_INFO_H
31 #define LLVM_ANALYSIS_LOOP_INFO_H
33 #include "llvm/Pass.h"
34 #include "llvm/ADT/DenseMap.h"
35 #include "llvm/ADT/DenseSet.h"
36 #include "llvm/ADT/DepthFirstIterator.h"
37 #include "llvm/ADT/GraphTraits.h"
38 #include "llvm/ADT/SmallVector.h"
39 #include "llvm/ADT/STLExtras.h"
40 #include "llvm/Analysis/Dominators.h"
41 #include "llvm/Support/CFG.h"
42 #include "llvm/Support/raw_ostream.h"
49 inline void RemoveFromVector(std::vector<T*> &V, T *N) {
50 typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N);
51 assert(I != V.end() && "N is not in this list!");
59 template<class N, class M> class LoopInfoBase;
60 template<class N, class M> class LoopBase;
62 //===----------------------------------------------------------------------===//
63 /// LoopBase class - Instances of this class are used to represent loops that
64 /// are detected in the flow graph
66 template<class BlockT, class LoopT>
69 // SubLoops - Loops contained entirely within this one.
70 std::vector<LoopT *> SubLoops;
72 // Blocks - The list of blocks in this loop. First entry is the header node.
73 std::vector<BlockT*> Blocks;
76 LoopBase(const LoopBase<BlockT, LoopT> &);
78 const LoopBase<BlockT, LoopT>&operator=(const LoopBase<BlockT, LoopT> &);
80 /// Loop ctor - This creates an empty loop.
81 LoopBase() : ParentLoop(0) {}
83 for (size_t i = 0, e = SubLoops.size(); i != e; ++i)
87 /// getLoopDepth - Return the nesting level of this loop. An outer-most
88 /// loop has depth 1, for consistency with loop depth values used for basic
89 /// blocks, where depth 0 is used for blocks not inside any loops.
90 unsigned getLoopDepth() const {
92 for (const LoopT *CurLoop = ParentLoop; CurLoop;
93 CurLoop = CurLoop->ParentLoop)
97 BlockT *getHeader() const { return Blocks.front(); }
98 LoopT *getParentLoop() const { return ParentLoop; }
100 /// setParentLoop is a raw interface for bypassing addChildLoop.
101 void setParentLoop(LoopT *L) { ParentLoop = L; }
103 /// contains - Return true if the specified loop is contained within in
106 bool contains(const LoopT *L) const {
107 if (L == this) return true;
108 if (L == 0) return false;
109 return contains(L->getParentLoop());
112 /// contains - Return true if the specified basic block is in this loop.
114 bool contains(const BlockT *BB) const {
115 return std::find(block_begin(), block_end(), BB) != block_end();
118 /// contains - Return true if the specified instruction is in this loop.
120 template<class InstT>
121 bool contains(const InstT *Inst) const {
122 return contains(Inst->getParent());
125 /// iterator/begin/end - Return the loops contained entirely within this loop.
127 const std::vector<LoopT *> &getSubLoops() const { return SubLoops; }
128 std::vector<LoopT *> &getSubLoopsVector() { return SubLoops; }
129 typedef typename std::vector<LoopT *>::const_iterator iterator;
130 typedef typename std::vector<LoopT *>::const_reverse_iterator
132 iterator begin() const { return SubLoops.begin(); }
133 iterator end() const { return SubLoops.end(); }
134 reverse_iterator rbegin() const { return SubLoops.rbegin(); }
135 reverse_iterator rend() const { return SubLoops.rend(); }
136 bool empty() const { return SubLoops.empty(); }
138 /// getBlocks - Get a list of the basic blocks which make up this loop.
140 const std::vector<BlockT*> &getBlocks() const { return Blocks; }
141 std::vector<BlockT*> &getBlocksVector() { return Blocks; }
142 typedef typename std::vector<BlockT*>::const_iterator block_iterator;
143 block_iterator block_begin() const { return Blocks.begin(); }
144 block_iterator block_end() const { return Blocks.end(); }
146 /// getNumBlocks - Get the number of blocks in this loop in constant time.
147 unsigned getNumBlocks() const {
148 return Blocks.size();
151 /// isLoopExiting - True if terminator in the block can branch to another
152 /// block that is outside of the current loop.
154 bool isLoopExiting(const BlockT *BB) const {
155 typedef GraphTraits<BlockT*> BlockTraits;
156 for (typename BlockTraits::ChildIteratorType SI =
157 BlockTraits::child_begin(const_cast<BlockT*>(BB)),
158 SE = BlockTraits::child_end(const_cast<BlockT*>(BB)); SI != SE; ++SI) {
165 /// getNumBackEdges - Calculate the number of back edges to the loop header
167 unsigned getNumBackEdges() const {
168 unsigned NumBackEdges = 0;
169 BlockT *H = getHeader();
171 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
172 for (typename InvBlockTraits::ChildIteratorType I =
173 InvBlockTraits::child_begin(const_cast<BlockT*>(H)),
174 E = InvBlockTraits::child_end(const_cast<BlockT*>(H)); I != E; ++I)
181 //===--------------------------------------------------------------------===//
182 // APIs for simple analysis of the loop.
184 // Note that all of these methods can fail on general loops (ie, there may not
185 // be a preheader, etc). For best success, the loop simplification and
186 // induction variable canonicalization pass should be used to normalize loops
187 // for easy analysis. These methods assume canonical loops.
189 /// getExitingBlocks - Return all blocks inside the loop that have successors
190 /// outside of the loop. These are the blocks _inside of the current loop_
191 /// which branch out. The returned list is always unique.
193 void getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const;
195 /// getExitingBlock - If getExitingBlocks would return exactly one block,
196 /// return that block. Otherwise return null.
197 BlockT *getExitingBlock() const;
199 /// getExitBlocks - Return all of the successor blocks of this loop. These
200 /// are the blocks _outside of the current loop_ which are branched to.
202 void getExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const;
204 /// getExitBlock - If getExitBlocks would return exactly one block,
205 /// return that block. Otherwise return null.
206 BlockT *getExitBlock() const;
209 typedef std::pair<const BlockT*, const BlockT*> Edge;
211 /// getExitEdges - Return all pairs of (_inside_block_,_outside_block_).
212 void getExitEdges(SmallVectorImpl<Edge> &ExitEdges) const;
214 /// getLoopPreheader - If there is a preheader for this loop, return it. A
215 /// loop has a preheader if there is only one edge to the header of the loop
216 /// from outside of the loop. If this is the case, the block branching to the
217 /// header of the loop is the preheader node.
219 /// This method returns null if there is no preheader for the loop.
221 BlockT *getLoopPreheader() const;
223 /// getLoopPredecessor - If the given loop's header has exactly one unique
224 /// predecessor outside the loop, return it. Otherwise return null.
225 /// This is less strict that the loop "preheader" concept, which requires
226 /// the predecessor to have exactly one successor.
228 BlockT *getLoopPredecessor() const;
230 /// getLoopLatch - If there is a single latch block for this loop, return it.
231 /// A latch block is a block that contains a branch back to the header.
232 BlockT *getLoopLatch() const;
234 //===--------------------------------------------------------------------===//
235 // APIs for updating loop information after changing the CFG
238 /// addBasicBlockToLoop - This method is used by other analyses to update loop
239 /// information. NewBB is set to be a new member of the current loop.
240 /// Because of this, it is added as a member of all parent loops, and is added
241 /// to the specified LoopInfo object as being in the current basic block. It
242 /// is not valid to replace the loop header with this method.
244 void addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LI);
246 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
247 /// the OldChild entry in our children list with NewChild, and updates the
248 /// parent pointer of OldChild to be null and the NewChild to be this loop.
249 /// This updates the loop depth of the new child.
250 void replaceChildLoopWith(LoopT *OldChild, LoopT *NewChild);
252 /// addChildLoop - Add the specified loop to be a child of this loop. This
253 /// updates the loop depth of the new child.
255 void addChildLoop(LoopT *NewChild) {
256 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
257 NewChild->ParentLoop = static_cast<LoopT *>(this);
258 SubLoops.push_back(NewChild);
261 /// removeChildLoop - This removes the specified child from being a subloop of
262 /// this loop. The loop is not deleted, as it will presumably be inserted
263 /// into another loop.
264 LoopT *removeChildLoop(iterator I) {
265 assert(I != SubLoops.end() && "Cannot remove end iterator!");
267 assert(Child->ParentLoop == this && "Child is not a child of this loop!");
268 SubLoops.erase(SubLoops.begin()+(I-begin()));
269 Child->ParentLoop = 0;
273 /// addBlockEntry - This adds a basic block directly to the basic block list.
274 /// This should only be used by transformations that create new loops. Other
275 /// transformations should use addBasicBlockToLoop.
276 void addBlockEntry(BlockT *BB) {
277 Blocks.push_back(BB);
280 /// moveToHeader - This method is used to move BB (which must be part of this
281 /// loop) to be the loop header of the loop (the block that dominates all
283 void moveToHeader(BlockT *BB) {
284 if (Blocks[0] == BB) return;
285 for (unsigned i = 0; ; ++i) {
286 assert(i != Blocks.size() && "Loop does not contain BB!");
287 if (Blocks[i] == BB) {
288 Blocks[i] = Blocks[0];
295 /// removeBlockFromLoop - This removes the specified basic block from the
296 /// current loop, updating the Blocks as appropriate. This does not update
297 /// the mapping in the LoopInfo class.
298 void removeBlockFromLoop(BlockT *BB) {
299 RemoveFromVector(Blocks, BB);
302 /// verifyLoop - Verify loop structure
303 void verifyLoop() const;
305 /// verifyLoop - Verify loop structure of this loop and all nested loops.
306 void verifyLoopNest(DenseSet<const LoopT*> *Loops) const;
308 void print(raw_ostream &OS, unsigned Depth = 0) const;
311 friend class LoopInfoBase<BlockT, LoopT>;
312 explicit LoopBase(BlockT *BB) : ParentLoop(0) {
313 Blocks.push_back(BB);
317 template<class BlockT, class LoopT>
318 raw_ostream& operator<<(raw_ostream &OS, const LoopBase<BlockT, LoopT> &Loop) {
323 // Implementation in LoopInfoImpl.h
325 __extension__ extern template class LoopBase<BasicBlock, Loop>;
328 class Loop : public LoopBase<BasicBlock, Loop> {
332 /// isLoopInvariant - Return true if the specified value is loop invariant
334 bool isLoopInvariant(Value *V) const;
336 /// hasLoopInvariantOperands - Return true if all the operands of the
337 /// specified instruction are loop invariant.
338 bool hasLoopInvariantOperands(Instruction *I) const;
340 /// makeLoopInvariant - If the given value is an instruction inside of the
341 /// loop and it can be hoisted, do so to make it trivially loop-invariant.
342 /// Return true if the value after any hoisting is loop invariant. This
343 /// function can be used as a slightly more aggressive replacement for
346 /// If InsertPt is specified, it is the point to hoist instructions to.
347 /// If null, the terminator of the loop preheader is used.
349 bool makeLoopInvariant(Value *V, bool &Changed,
350 Instruction *InsertPt = 0) const;
352 /// makeLoopInvariant - If the given instruction is inside of the
353 /// loop and it can be hoisted, do so to make it trivially loop-invariant.
354 /// Return true if the instruction after any hoisting is loop invariant. This
355 /// function can be used as a slightly more aggressive replacement for
358 /// If InsertPt is specified, it is the point to hoist instructions to.
359 /// If null, the terminator of the loop preheader is used.
361 bool makeLoopInvariant(Instruction *I, bool &Changed,
362 Instruction *InsertPt = 0) const;
364 /// getCanonicalInductionVariable - Check to see if the loop has a canonical
365 /// induction variable: an integer recurrence that starts at 0 and increments
366 /// by one each time through the loop. If so, return the phi node that
367 /// corresponds to it.
369 /// The IndVarSimplify pass transforms loops to have a canonical induction
372 PHINode *getCanonicalInductionVariable() const;
374 /// isLCSSAForm - Return true if the Loop is in LCSSA form
375 bool isLCSSAForm(DominatorTree &DT) const;
377 /// isLoopSimplifyForm - Return true if the Loop is in the form that
378 /// the LoopSimplify form transforms loops to, which is sometimes called
380 bool isLoopSimplifyForm() const;
382 /// isSafeToClone - Return true if the loop body is safe to clone in practice.
383 bool isSafeToClone() const;
385 /// hasDedicatedExits - Return true if no exit block for the loop
386 /// has a predecessor that is outside the loop.
387 bool hasDedicatedExits() const;
389 /// getUniqueExitBlocks - Return all unique successor blocks of this loop.
390 /// These are the blocks _outside of the current loop_ which are branched to.
391 /// This assumes that loop exits are in canonical form.
393 void getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const;
395 /// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one
396 /// block, return that block. Otherwise return null.
397 BasicBlock *getUniqueExitBlock() const;
402 friend class LoopInfoBase<BasicBlock, Loop>;
403 explicit Loop(BasicBlock *BB) : LoopBase<BasicBlock, Loop>(BB) {}
406 //===----------------------------------------------------------------------===//
407 /// LoopInfo - This class builds and contains all of the top level loop
408 /// structures in the specified function.
411 template<class BlockT, class LoopT>
413 // BBMap - Mapping of basic blocks to the inner most loop they occur in
414 DenseMap<BlockT *, LoopT *> BBMap;
415 std::vector<LoopT *> TopLevelLoops;
416 friend class LoopBase<BlockT, LoopT>;
417 friend class LoopInfo;
419 void operator=(const LoopInfoBase &); // do not implement
420 LoopInfoBase(const LoopInfo &); // do not implement
423 ~LoopInfoBase() { releaseMemory(); }
425 void releaseMemory() {
426 for (typename std::vector<LoopT *>::iterator I =
427 TopLevelLoops.begin(), E = TopLevelLoops.end(); I != E; ++I)
428 delete *I; // Delete all of the loops...
430 BBMap.clear(); // Reset internal state of analysis
431 TopLevelLoops.clear();
434 /// iterator/begin/end - The interface to the top-level loops in the current
437 typedef typename std::vector<LoopT *>::const_iterator iterator;
438 typedef typename std::vector<LoopT *>::const_reverse_iterator
440 iterator begin() const { return TopLevelLoops.begin(); }
441 iterator end() const { return TopLevelLoops.end(); }
442 reverse_iterator rbegin() const { return TopLevelLoops.rbegin(); }
443 reverse_iterator rend() const { return TopLevelLoops.rend(); }
444 bool empty() const { return TopLevelLoops.empty(); }
446 /// getLoopFor - Return the inner most loop that BB lives in. If a basic
447 /// block is in no loop (for example the entry node), null is returned.
449 LoopT *getLoopFor(const BlockT *BB) const {
450 return BBMap.lookup(const_cast<BlockT*>(BB));
453 /// operator[] - same as getLoopFor...
455 const LoopT *operator[](const BlockT *BB) const {
456 return getLoopFor(BB);
459 /// getLoopDepth - Return the loop nesting level of the specified block. A
460 /// depth of 0 means the block is not inside any loop.
462 unsigned getLoopDepth(const BlockT *BB) const {
463 const LoopT *L = getLoopFor(BB);
464 return L ? L->getLoopDepth() : 0;
467 // isLoopHeader - True if the block is a loop header node
468 bool isLoopHeader(BlockT *BB) const {
469 const LoopT *L = getLoopFor(BB);
470 return L && L->getHeader() == BB;
473 /// removeLoop - This removes the specified top-level loop from this loop info
474 /// object. The loop is not deleted, as it will presumably be inserted into
476 LoopT *removeLoop(iterator I) {
477 assert(I != end() && "Cannot remove end iterator!");
479 assert(L->getParentLoop() == 0 && "Not a top-level loop!");
480 TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin()));
484 /// changeLoopFor - Change the top-level loop that contains BB to the
485 /// specified loop. This should be used by transformations that restructure
486 /// the loop hierarchy tree.
487 void changeLoopFor(BlockT *BB, LoopT *L) {
495 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
496 /// list with the indicated loop.
497 void changeTopLevelLoop(LoopT *OldLoop,
499 typename std::vector<LoopT *>::iterator I =
500 std::find(TopLevelLoops.begin(), TopLevelLoops.end(), OldLoop);
501 assert(I != TopLevelLoops.end() && "Old loop not at top level!");
503 assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 &&
504 "Loops already embedded into a subloop!");
507 /// addTopLevelLoop - This adds the specified loop to the collection of
509 void addTopLevelLoop(LoopT *New) {
510 assert(New->getParentLoop() == 0 && "Loop already in subloop!");
511 TopLevelLoops.push_back(New);
514 /// removeBlock - This method completely removes BB from all data structures,
515 /// including all of the Loop objects it is nested in and our mapping from
516 /// BasicBlocks to loops.
517 void removeBlock(BlockT *BB) {
518 typename DenseMap<BlockT *, LoopT *>::iterator I = BBMap.find(BB);
519 if (I != BBMap.end()) {
520 for (LoopT *L = I->second; L; L = L->getParentLoop())
521 L->removeBlockFromLoop(BB);
529 static bool isNotAlreadyContainedIn(const LoopT *SubLoop,
530 const LoopT *ParentLoop) {
531 if (SubLoop == 0) return true;
532 if (SubLoop == ParentLoop) return false;
533 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
536 /// Create the loop forest using a stable algorithm.
537 void Analyze(DominatorTreeBase<BlockT> &DomTree);
541 void print(raw_ostream &OS) const;
544 // Implementation in LoopInfoImpl.h
546 __extension__ extern template class LoopInfoBase<BasicBlock, Loop>;
549 class LoopInfo : public FunctionPass {
550 LoopInfoBase<BasicBlock, Loop> LI;
551 friend class LoopBase<BasicBlock, Loop>;
553 void operator=(const LoopInfo &); // do not implement
554 LoopInfo(const LoopInfo &); // do not implement
556 static char ID; // Pass identification, replacement for typeid
558 LoopInfo() : FunctionPass(ID) {
559 initializeLoopInfoPass(*PassRegistry::getPassRegistry());
562 LoopInfoBase<BasicBlock, Loop>& getBase() { return LI; }
564 /// iterator/begin/end - The interface to the top-level loops in the current
567 typedef LoopInfoBase<BasicBlock, Loop>::iterator iterator;
568 typedef LoopInfoBase<BasicBlock, Loop>::reverse_iterator reverse_iterator;
569 inline iterator begin() const { return LI.begin(); }
570 inline iterator end() const { return LI.end(); }
571 inline reverse_iterator rbegin() const { return LI.rbegin(); }
572 inline reverse_iterator rend() const { return LI.rend(); }
573 bool empty() const { return LI.empty(); }
575 /// getLoopFor - Return the inner most loop that BB lives in. If a basic
576 /// block is in no loop (for example the entry node), null is returned.
578 inline Loop *getLoopFor(const BasicBlock *BB) const {
579 return LI.getLoopFor(BB);
582 /// operator[] - same as getLoopFor...
584 inline const Loop *operator[](const BasicBlock *BB) const {
585 return LI.getLoopFor(BB);
588 /// getLoopDepth - Return the loop nesting level of the specified block. A
589 /// depth of 0 means the block is not inside any loop.
591 inline unsigned getLoopDepth(const BasicBlock *BB) const {
592 return LI.getLoopDepth(BB);
595 // isLoopHeader - True if the block is a loop header node
596 inline bool isLoopHeader(BasicBlock *BB) const {
597 return LI.isLoopHeader(BB);
600 /// runOnFunction - Calculate the natural loop information.
602 virtual bool runOnFunction(Function &F);
604 virtual void verifyAnalysis() const;
606 virtual void releaseMemory() { LI.releaseMemory(); }
608 virtual void print(raw_ostream &O, const Module* M = 0) const;
610 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
612 /// removeLoop - This removes the specified top-level loop from this loop info
613 /// object. The loop is not deleted, as it will presumably be inserted into
615 inline Loop *removeLoop(iterator I) { return LI.removeLoop(I); }
617 /// changeLoopFor - Change the top-level loop that contains BB to the
618 /// specified loop. This should be used by transformations that restructure
619 /// the loop hierarchy tree.
620 inline void changeLoopFor(BasicBlock *BB, Loop *L) {
621 LI.changeLoopFor(BB, L);
624 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
625 /// list with the indicated loop.
626 inline void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) {
627 LI.changeTopLevelLoop(OldLoop, NewLoop);
630 /// addTopLevelLoop - This adds the specified loop to the collection of
632 inline void addTopLevelLoop(Loop *New) {
633 LI.addTopLevelLoop(New);
636 /// removeBlock - This method completely removes BB from all data structures,
637 /// including all of the Loop objects it is nested in and our mapping from
638 /// BasicBlocks to loops.
639 void removeBlock(BasicBlock *BB) {
643 /// updateUnloop - Update LoopInfo after removing the last backedge from a
644 /// loop--now the "unloop". This updates the loop forest and parent loops for
645 /// each block so that Unloop is no longer referenced, but the caller must
646 /// actually delete the Unloop object.
647 void updateUnloop(Loop *Unloop);
649 /// replacementPreservesLCSSAForm - Returns true if replacing From with To
650 /// everywhere is guaranteed to preserve LCSSA form.
651 bool replacementPreservesLCSSAForm(Instruction *From, Value *To) {
652 // Preserving LCSSA form is only problematic if the replacing value is an
654 Instruction *I = dyn_cast<Instruction>(To);
656 // If both instructions are defined in the same basic block then replacement
657 // cannot break LCSSA form.
658 if (I->getParent() == From->getParent())
660 // If the instruction is not defined in a loop then it can safely replace
662 Loop *ToLoop = getLoopFor(I->getParent());
663 if (!ToLoop) return true;
664 // If the replacing instruction is defined in the same loop as the original
665 // instruction, or in a loop that contains it as an inner loop, then using
666 // it as a replacement will not break LCSSA form.
667 return ToLoop->contains(getLoopFor(From->getParent()));
672 // Allow clients to walk the list of nested loops...
673 template <> struct GraphTraits<const Loop*> {
674 typedef const Loop NodeType;
675 typedef LoopInfo::iterator ChildIteratorType;
677 static NodeType *getEntryNode(const Loop *L) { return L; }
678 static inline ChildIteratorType child_begin(NodeType *N) {
681 static inline ChildIteratorType child_end(NodeType *N) {
686 template <> struct GraphTraits<Loop*> {
687 typedef Loop NodeType;
688 typedef LoopInfo::iterator ChildIteratorType;
690 static NodeType *getEntryNode(Loop *L) { return L; }
691 static inline ChildIteratorType child_begin(NodeType *N) {
694 static inline ChildIteratorType child_end(NodeType *N) {
699 } // End llvm namespace