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 iterator begin() const { return SubLoops.begin(); }
131 iterator end() const { return SubLoops.end(); }
132 bool empty() const { return SubLoops.empty(); }
134 /// getBlocks - Get a list of the basic blocks which make up this loop.
136 const std::vector<BlockT*> &getBlocks() const { return Blocks; }
137 std::vector<BlockT*> &getBlocksVector() { return Blocks; }
138 typedef typename std::vector<BlockT*>::const_iterator block_iterator;
139 block_iterator block_begin() const { return Blocks.begin(); }
140 block_iterator block_end() const { return Blocks.end(); }
142 /// getNumBlocks - Get the number of blocks in this loop in constant time.
143 unsigned getNumBlocks() const {
144 return Blocks.size();
147 /// isLoopExiting - True if terminator in the block can branch to another
148 /// block that is outside of the current loop.
150 bool isLoopExiting(const BlockT *BB) const {
151 typedef GraphTraits<BlockT*> BlockTraits;
152 for (typename BlockTraits::ChildIteratorType SI =
153 BlockTraits::child_begin(const_cast<BlockT*>(BB)),
154 SE = BlockTraits::child_end(const_cast<BlockT*>(BB)); SI != SE; ++SI) {
161 /// getNumBackEdges - Calculate the number of back edges to the loop header
163 unsigned getNumBackEdges() const {
164 unsigned NumBackEdges = 0;
165 BlockT *H = getHeader();
167 typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
168 for (typename InvBlockTraits::ChildIteratorType I =
169 InvBlockTraits::child_begin(const_cast<BlockT*>(H)),
170 E = InvBlockTraits::child_end(const_cast<BlockT*>(H)); I != E; ++I)
177 //===--------------------------------------------------------------------===//
178 // APIs for simple analysis of the loop.
180 // Note that all of these methods can fail on general loops (ie, there may not
181 // be a preheader, etc). For best success, the loop simplification and
182 // induction variable canonicalization pass should be used to normalize loops
183 // for easy analysis. These methods assume canonical loops.
185 /// getExitingBlocks - Return all blocks inside the loop that have successors
186 /// outside of the loop. These are the blocks _inside of the current loop_
187 /// which branch out. The returned list is always unique.
189 void getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const;
191 /// getExitingBlock - If getExitingBlocks would return exactly one block,
192 /// return that block. Otherwise return null.
193 BlockT *getExitingBlock() const;
195 /// getExitBlocks - Return all of the successor blocks of this loop. These
196 /// are the blocks _outside of the current loop_ which are branched to.
198 void getExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const;
200 /// getExitBlock - If getExitBlocks would return exactly one block,
201 /// return that block. Otherwise return null.
202 BlockT *getExitBlock() const;
205 typedef std::pair<const BlockT*, const BlockT*> Edge;
207 /// getExitEdges - Return all pairs of (_inside_block_,_outside_block_).
208 void getExitEdges(SmallVectorImpl<Edge> &ExitEdges) const;
210 /// getLoopPreheader - If there is a preheader for this loop, return it. A
211 /// loop has a preheader if there is only one edge to the header of the loop
212 /// from outside of the loop. If this is the case, the block branching to the
213 /// header of the loop is the preheader node.
215 /// This method returns null if there is no preheader for the loop.
217 BlockT *getLoopPreheader() const;
219 /// getLoopPredecessor - If the given loop's header has exactly one unique
220 /// predecessor outside the loop, return it. Otherwise return null.
221 /// This is less strict that the loop "preheader" concept, which requires
222 /// the predecessor to have exactly one successor.
224 BlockT *getLoopPredecessor() const;
226 /// getLoopLatch - If there is a single latch block for this loop, return it.
227 /// A latch block is a block that contains a branch back to the header.
228 BlockT *getLoopLatch() const;
230 //===--------------------------------------------------------------------===//
231 // APIs for updating loop information after changing the CFG
234 /// addBasicBlockToLoop - This method is used by other analyses to update loop
235 /// information. NewBB is set to be a new member of the current loop.
236 /// Because of this, it is added as a member of all parent loops, and is added
237 /// to the specified LoopInfo object as being in the current basic block. It
238 /// is not valid to replace the loop header with this method.
240 void addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LI);
242 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
243 /// the OldChild entry in our children list with NewChild, and updates the
244 /// parent pointer of OldChild to be null and the NewChild to be this loop.
245 /// This updates the loop depth of the new child.
246 void replaceChildLoopWith(LoopT *OldChild, LoopT *NewChild);
248 /// addChildLoop - Add the specified loop to be a child of this loop. This
249 /// updates the loop depth of the new child.
251 void addChildLoop(LoopT *NewChild) {
252 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
253 NewChild->ParentLoop = static_cast<LoopT *>(this);
254 SubLoops.push_back(NewChild);
257 /// removeChildLoop - This removes the specified child from being a subloop of
258 /// this loop. The loop is not deleted, as it will presumably be inserted
259 /// into another loop.
260 LoopT *removeChildLoop(iterator I) {
261 assert(I != SubLoops.end() && "Cannot remove end iterator!");
263 assert(Child->ParentLoop == this && "Child is not a child of this loop!");
264 SubLoops.erase(SubLoops.begin()+(I-begin()));
265 Child->ParentLoop = 0;
269 /// addBlockEntry - This adds a basic block directly to the basic block list.
270 /// This should only be used by transformations that create new loops. Other
271 /// transformations should use addBasicBlockToLoop.
272 void addBlockEntry(BlockT *BB) {
273 Blocks.push_back(BB);
276 /// moveToHeader - This method is used to move BB (which must be part of this
277 /// loop) to be the loop header of the loop (the block that dominates all
279 void moveToHeader(BlockT *BB) {
280 if (Blocks[0] == BB) return;
281 for (unsigned i = 0; ; ++i) {
282 assert(i != Blocks.size() && "Loop does not contain BB!");
283 if (Blocks[i] == BB) {
284 Blocks[i] = Blocks[0];
291 /// removeBlockFromLoop - This removes the specified basic block from the
292 /// current loop, updating the Blocks as appropriate. This does not update
293 /// the mapping in the LoopInfo class.
294 void removeBlockFromLoop(BlockT *BB) {
295 RemoveFromVector(Blocks, BB);
298 /// verifyLoop - Verify loop structure
299 void verifyLoop() const;
301 /// verifyLoop - Verify loop structure of this loop and all nested loops.
302 void verifyLoopNest(DenseSet<const LoopT*> *Loops) const;
304 void print(raw_ostream &OS, unsigned Depth = 0) const;
307 friend class LoopInfoBase<BlockT, LoopT>;
308 explicit LoopBase(BlockT *BB) : ParentLoop(0) {
309 Blocks.push_back(BB);
313 template<class BlockT, class LoopT>
314 raw_ostream& operator<<(raw_ostream &OS, const LoopBase<BlockT, LoopT> &Loop) {
319 class Loop : public LoopBase<BasicBlock, Loop> {
323 /// isLoopInvariant - Return true if the specified value is loop invariant
325 bool isLoopInvariant(Value *V) const;
327 /// hasLoopInvariantOperands - Return true if all the operands of the
328 /// specified instruction are loop invariant.
329 bool hasLoopInvariantOperands(Instruction *I) const;
331 /// makeLoopInvariant - If the given value is an instruction inside of the
332 /// loop and it can be hoisted, do so to make it trivially loop-invariant.
333 /// Return true if the value after any hoisting is loop invariant. This
334 /// function can be used as a slightly more aggressive replacement for
337 /// If InsertPt is specified, it is the point to hoist instructions to.
338 /// If null, the terminator of the loop preheader is used.
340 bool makeLoopInvariant(Value *V, bool &Changed,
341 Instruction *InsertPt = 0) const;
343 /// makeLoopInvariant - If the given instruction is inside of the
344 /// loop and it can be hoisted, do so to make it trivially loop-invariant.
345 /// Return true if the instruction after any hoisting is loop invariant. This
346 /// function can be used as a slightly more aggressive replacement for
349 /// If InsertPt is specified, it is the point to hoist instructions to.
350 /// If null, the terminator of the loop preheader is used.
352 bool makeLoopInvariant(Instruction *I, bool &Changed,
353 Instruction *InsertPt = 0) const;
355 /// getCanonicalInductionVariable - Check to see if the loop has a canonical
356 /// induction variable: an integer recurrence that starts at 0 and increments
357 /// by one each time through the loop. If so, return the phi node that
358 /// corresponds to it.
360 /// The IndVarSimplify pass transforms loops to have a canonical induction
363 PHINode *getCanonicalInductionVariable() const;
365 /// isLCSSAForm - Return true if the Loop is in LCSSA form
366 bool isLCSSAForm(DominatorTree &DT) const;
368 /// isLoopSimplifyForm - Return true if the Loop is in the form that
369 /// the LoopSimplify form transforms loops to, which is sometimes called
371 bool isLoopSimplifyForm() const;
373 /// isSafeToClone - Return true if the loop body is safe to clone in practice.
374 bool isSafeToClone() const;
376 /// hasDedicatedExits - Return true if no exit block for the loop
377 /// has a predecessor that is outside the loop.
378 bool hasDedicatedExits() const;
380 /// getUniqueExitBlocks - Return all unique successor blocks of this loop.
381 /// These are the blocks _outside of the current loop_ which are branched to.
382 /// This assumes that loop exits are in canonical form.
384 void getUniqueExitBlocks(SmallVectorImpl<BasicBlock *> &ExitBlocks) const;
386 /// getUniqueExitBlock - If getUniqueExitBlocks would return exactly one
387 /// block, return that block. Otherwise return null.
388 BasicBlock *getUniqueExitBlock() const;
393 friend class LoopInfoBase<BasicBlock, Loop>;
394 explicit Loop(BasicBlock *BB) : LoopBase<BasicBlock, Loop>(BB) {}
397 //===----------------------------------------------------------------------===//
398 /// LoopInfo - This class builds and contains all of the top level loop
399 /// structures in the specified function.
402 template<class BlockT, class LoopT>
404 // BBMap - Mapping of basic blocks to the inner most loop they occur in
405 DenseMap<BlockT *, LoopT *> BBMap;
406 std::vector<LoopT *> TopLevelLoops;
407 friend class LoopBase<BlockT, LoopT>;
408 friend class LoopInfo;
410 void operator=(const LoopInfoBase &); // do not implement
411 LoopInfoBase(const LoopInfo &); // do not implement
414 ~LoopInfoBase() { releaseMemory(); }
416 void releaseMemory() {
417 for (typename std::vector<LoopT *>::iterator I =
418 TopLevelLoops.begin(), E = TopLevelLoops.end(); I != E; ++I)
419 delete *I; // Delete all of the loops...
421 BBMap.clear(); // Reset internal state of analysis
422 TopLevelLoops.clear();
425 /// iterator/begin/end - The interface to the top-level loops in the current
428 typedef typename std::vector<LoopT *>::const_iterator iterator;
429 iterator begin() const { return TopLevelLoops.begin(); }
430 iterator end() const { return TopLevelLoops.end(); }
431 bool empty() const { return TopLevelLoops.empty(); }
433 /// getLoopFor - Return the inner most loop that BB lives in. If a basic
434 /// block is in no loop (for example the entry node), null is returned.
436 LoopT *getLoopFor(const BlockT *BB) const {
437 return BBMap.lookup(const_cast<BlockT*>(BB));
440 /// operator[] - same as getLoopFor...
442 const LoopT *operator[](const BlockT *BB) const {
443 return getLoopFor(BB);
446 /// getLoopDepth - Return the loop nesting level of the specified block. A
447 /// depth of 0 means the block is not inside any loop.
449 unsigned getLoopDepth(const BlockT *BB) const {
450 const LoopT *L = getLoopFor(BB);
451 return L ? L->getLoopDepth() : 0;
454 // isLoopHeader - True if the block is a loop header node
455 bool isLoopHeader(BlockT *BB) const {
456 const LoopT *L = getLoopFor(BB);
457 return L && L->getHeader() == BB;
460 /// removeLoop - This removes the specified top-level loop from this loop info
461 /// object. The loop is not deleted, as it will presumably be inserted into
463 LoopT *removeLoop(iterator I) {
464 assert(I != end() && "Cannot remove end iterator!");
466 assert(L->getParentLoop() == 0 && "Not a top-level loop!");
467 TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin()));
471 /// changeLoopFor - Change the top-level loop that contains BB to the
472 /// specified loop. This should be used by transformations that restructure
473 /// the loop hierarchy tree.
474 void changeLoopFor(BlockT *BB, LoopT *L) {
482 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
483 /// list with the indicated loop.
484 void changeTopLevelLoop(LoopT *OldLoop,
486 typename std::vector<LoopT *>::iterator I =
487 std::find(TopLevelLoops.begin(), TopLevelLoops.end(), OldLoop);
488 assert(I != TopLevelLoops.end() && "Old loop not at top level!");
490 assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 &&
491 "Loops already embedded into a subloop!");
494 /// addTopLevelLoop - This adds the specified loop to the collection of
496 void addTopLevelLoop(LoopT *New) {
497 assert(New->getParentLoop() == 0 && "Loop already in subloop!");
498 TopLevelLoops.push_back(New);
501 /// removeBlock - This method completely removes BB from all data structures,
502 /// including all of the Loop objects it is nested in and our mapping from
503 /// BasicBlocks to loops.
504 void removeBlock(BlockT *BB) {
505 typename DenseMap<BlockT *, LoopT *>::iterator I = BBMap.find(BB);
506 if (I != BBMap.end()) {
507 for (LoopT *L = I->second; L; L = L->getParentLoop())
508 L->removeBlockFromLoop(BB);
516 static bool isNotAlreadyContainedIn(const LoopT *SubLoop,
517 const LoopT *ParentLoop) {
518 if (SubLoop == 0) return true;
519 if (SubLoop == ParentLoop) return false;
520 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
523 void Calculate(DominatorTreeBase<BlockT> &DT);
525 LoopT *ConsiderForLoop(BlockT *BB, DominatorTreeBase<BlockT> &DT);
527 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside
528 /// of the NewParent Loop, instead of being a sibling of it.
529 void MoveSiblingLoopInto(LoopT *NewChild, LoopT *NewParent);
531 /// InsertLoopInto - This inserts loop L into the specified parent loop. If
532 /// the parent loop contains a loop which should contain L, the loop gets
533 /// inserted into L instead.
534 void InsertLoopInto(LoopT *L, LoopT *Parent);
536 /// Create the loop forest using a stable algorithm.
537 void Analyze(DominatorTreeBase<BlockT> &DomTree);
541 void print(raw_ostream &OS) const;
544 class LoopInfo : public FunctionPass {
545 LoopInfoBase<BasicBlock, Loop> LI;
546 friend class LoopBase<BasicBlock, Loop>;
548 void operator=(const LoopInfo &); // do not implement
549 LoopInfo(const LoopInfo &); // do not implement
551 static char ID; // Pass identification, replacement for typeid
553 LoopInfo() : FunctionPass(ID) {
554 initializeLoopInfoPass(*PassRegistry::getPassRegistry());
557 LoopInfoBase<BasicBlock, Loop>& getBase() { return LI; }
559 /// iterator/begin/end - The interface to the top-level loops in the current
562 typedef LoopInfoBase<BasicBlock, Loop>::iterator iterator;
563 inline iterator begin() const { return LI.begin(); }
564 inline iterator end() const { return LI.end(); }
565 bool empty() const { return LI.empty(); }
567 /// getLoopFor - Return the inner most loop that BB lives in. If a basic
568 /// block is in no loop (for example the entry node), null is returned.
570 inline Loop *getLoopFor(const BasicBlock *BB) const {
571 return LI.getLoopFor(BB);
574 /// operator[] - same as getLoopFor...
576 inline const Loop *operator[](const BasicBlock *BB) const {
577 return LI.getLoopFor(BB);
580 /// getLoopDepth - Return the loop nesting level of the specified block. A
581 /// depth of 0 means the block is not inside any loop.
583 inline unsigned getLoopDepth(const BasicBlock *BB) const {
584 return LI.getLoopDepth(BB);
587 // isLoopHeader - True if the block is a loop header node
588 inline bool isLoopHeader(BasicBlock *BB) const {
589 return LI.isLoopHeader(BB);
592 /// runOnFunction - Calculate the natural loop information.
594 virtual bool runOnFunction(Function &F);
596 virtual void verifyAnalysis() const;
598 virtual void releaseMemory() { LI.releaseMemory(); }
600 virtual void print(raw_ostream &O, const Module* M = 0) const;
602 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
604 /// removeLoop - This removes the specified top-level loop from this loop info
605 /// object. The loop is not deleted, as it will presumably be inserted into
607 inline Loop *removeLoop(iterator I) { return LI.removeLoop(I); }
609 /// changeLoopFor - Change the top-level loop that contains BB to the
610 /// specified loop. This should be used by transformations that restructure
611 /// the loop hierarchy tree.
612 inline void changeLoopFor(BasicBlock *BB, Loop *L) {
613 LI.changeLoopFor(BB, L);
616 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
617 /// list with the indicated loop.
618 inline void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) {
619 LI.changeTopLevelLoop(OldLoop, NewLoop);
622 /// addTopLevelLoop - This adds the specified loop to the collection of
624 inline void addTopLevelLoop(Loop *New) {
625 LI.addTopLevelLoop(New);
628 /// removeBlock - This method completely removes BB from all data structures,
629 /// including all of the Loop objects it is nested in and our mapping from
630 /// BasicBlocks to loops.
631 void removeBlock(BasicBlock *BB) {
635 /// updateUnloop - Update LoopInfo after removing the last backedge from a
636 /// loop--now the "unloop". This updates the loop forest and parent loops for
637 /// each block so that Unloop is no longer referenced, but the caller must
638 /// actually delete the Unloop object.
639 void updateUnloop(Loop *Unloop);
641 /// replacementPreservesLCSSAForm - Returns true if replacing From with To
642 /// everywhere is guaranteed to preserve LCSSA form.
643 bool replacementPreservesLCSSAForm(Instruction *From, Value *To) {
644 // Preserving LCSSA form is only problematic if the replacing value is an
646 Instruction *I = dyn_cast<Instruction>(To);
648 // If both instructions are defined in the same basic block then replacement
649 // cannot break LCSSA form.
650 if (I->getParent() == From->getParent())
652 // If the instruction is not defined in a loop then it can safely replace
654 Loop *ToLoop = getLoopFor(I->getParent());
655 if (!ToLoop) return true;
656 // If the replacing instruction is defined in the same loop as the original
657 // instruction, or in a loop that contains it as an inner loop, then using
658 // it as a replacement will not break LCSSA form.
659 return ToLoop->contains(getLoopFor(From->getParent()));
664 // Allow clients to walk the list of nested loops...
665 template <> struct GraphTraits<const Loop*> {
666 typedef const Loop NodeType;
667 typedef LoopInfo::iterator ChildIteratorType;
669 static NodeType *getEntryNode(const Loop *L) { return L; }
670 static inline ChildIteratorType child_begin(NodeType *N) {
673 static inline ChildIteratorType child_end(NodeType *N) {
678 template <> struct GraphTraits<Loop*> {
679 typedef Loop NodeType;
680 typedef LoopInfo::iterator ChildIteratorType;
682 static NodeType *getEntryNode(Loop *L) { return L; }
683 static inline ChildIteratorType child_begin(NodeType *N) {
686 static inline ChildIteratorType child_end(NodeType *N) {
691 } // End llvm namespace