LoopInfo.h revision 21c276d2fa99914d5ed958ac0aec7d78e3dd87cf
1//===- llvm/Analysis/LoopInfo.h - Natural Loop Calculator -------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
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.
7//
8//===----------------------------------------------------------------------===//
9//
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 natural
12// loops may actually be several loops that share the same header node.
13//
14// This analysis calculates the nesting structure of loops in a function.  For
15// each natural loop identified, this analysis identifies natural loops
16// contained entirely within the loop and the basic blocks the make up the loop.
17//
18// It can calculate on the fly various bits of information, for example:
19//
20//  * whether there is a preheader for the loop
21//  * the number of back edges to the header
22//  * whether or not a particular block branches out of the loop
23//  * the successor blocks of the loop
24//  * the loop depth
25//  * the trip count
26//  * etc...
27//
28//===----------------------------------------------------------------------===//
29
30#ifndef LLVM_ANALYSIS_LOOP_INFO_H
31#define LLVM_ANALYSIS_LOOP_INFO_H
32
33#include "llvm/Pass.h"
34#include "llvm/ADT/GraphTraits.h"
35#include "llvm/ADT/SmallVector.h"
36
37namespace llvm {
38
39class DominatorTree;
40class LoopInfo;
41class PHINode;
42class Instruction;
43
44//===----------------------------------------------------------------------===//
45/// Loop class - Instances of this class are used to represent loops that are
46/// detected in the flow graph
47///
48class Loop {
49  Loop *ParentLoop;
50  std::vector<Loop*> SubLoops;       // Loops contained entirely within this one
51  std::vector<BasicBlock*> Blocks;   // First entry is the header node
52
53  Loop(const Loop &);                  // DO NOT IMPLEMENT
54  const Loop &operator=(const Loop &); // DO NOT IMPLEMENT
55public:
56  /// Loop ctor - This creates an empty loop.
57  Loop() : ParentLoop(0) {}
58  ~Loop() {
59    for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
60      delete SubLoops[i];
61  }
62
63  unsigned getLoopDepth() const {
64    unsigned D = 0;
65    for (const Loop *CurLoop = this; CurLoop; CurLoop = CurLoop->ParentLoop)
66      ++D;
67    return D;
68  }
69  BasicBlock *getHeader() const { return Blocks.front(); }
70  Loop *getParentLoop() const { return ParentLoop; }
71
72  /// contains - Return true of the specified basic block is in this loop
73  ///
74  bool contains(const BasicBlock *BB) const;
75
76  /// iterator/begin/end - Return the loops contained entirely within this loop.
77  ///
78  const std::vector<Loop*> &getSubLoops() const { return SubLoops; }
79  typedef std::vector<Loop*>::const_iterator iterator;
80  iterator begin() const { return SubLoops.begin(); }
81  iterator end() const { return SubLoops.end(); }
82  bool empty() const { return SubLoops.empty(); }
83
84  /// getBlocks - Get a list of the basic blocks which make up this loop.
85  ///
86  const std::vector<BasicBlock*> &getBlocks() const { return Blocks; }
87  typedef std::vector<BasicBlock*>::const_iterator block_iterator;
88  block_iterator block_begin() const { return Blocks.begin(); }
89  block_iterator block_end() const { return Blocks.end(); }
90
91  /// isLoopExit - True if terminator in the block can branch to another block
92  /// that is outside of the current loop.
93  ///
94  bool isLoopExit(const BasicBlock *BB) const;
95
96  /// getNumBackEdges - Calculate the number of back edges to the loop header
97  ///
98  unsigned getNumBackEdges() const;
99
100  /// isLoopInvariant - Return true if the specified value is loop invariant
101  ///
102  bool isLoopInvariant(Value *V) const;
103
104  //===--------------------------------------------------------------------===//
105  // APIs for simple analysis of the loop.
106  //
107  // Note that all of these methods can fail on general loops (ie, there may not
108  // be a preheader, etc).  For best success, the loop simplification and
109  // induction variable canonicalization pass should be used to normalize loops
110  // for easy analysis.  These methods assume canonical loops.
111
112  /// getExitingBlocks - Return all blocks inside the loop that have successors
113  /// outside of the loop.  These are the blocks _inside of the current loop_
114  /// which branch out.  The returned list is always unique.
115  ///
116  void getExitingBlocks(SmallVectorImpl<BasicBlock *> &Blocks) const;
117
118  /// getExitBlocks - Return all of the successor blocks of this loop.  These
119  /// are the blocks _outside of the current loop_ which are branched to.
120  ///
121  void getExitBlocks(SmallVectorImpl<BasicBlock* > &Blocks) const;
122
123  /// getUniqueExitBlocks - Return all unique successor blocks of this loop.
124  /// These are the blocks _outside of the current loop_ which are branched to.
125  /// This assumes that loop is in canonical form.
126  ///
127  void getUniqueExitBlocks(SmallVectorImpl<BasicBlock*> &ExitBlocks) const;
128
129  /// getLoopPreheader - If there is a preheader for this loop, return it.  A
130  /// loop has a preheader if there is only one edge to the header of the loop
131  /// from outside of the loop.  If this is the case, the block branching to the
132  /// header of the loop is the preheader node.
133  ///
134  /// This method returns null if there is no preheader for the loop.
135  ///
136  BasicBlock *getLoopPreheader() const;
137
138  /// getLoopLatch - If there is a latch block for this loop, return it.  A
139  /// latch block is the canonical backedge for a loop.  A loop header in normal
140  /// form has two edges into it: one from a preheader and one from a latch
141  /// block.
142  BasicBlock *getLoopLatch() const;
143
144  /// getCanonicalInductionVariable - Check to see if the loop has a canonical
145  /// induction variable: an integer recurrence that starts at 0 and increments
146  /// by one each time through the loop.  If so, return the phi node that
147  /// corresponds to it.
148  ///
149  PHINode *getCanonicalInductionVariable() const;
150
151  /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
152  /// the canonical induction variable value for the "next" iteration of the
153  /// loop.  This always succeeds if getCanonicalInductionVariable succeeds.
154  ///
155  Instruction *getCanonicalInductionVariableIncrement() const;
156
157  /// getTripCount - Return a loop-invariant LLVM value indicating the number of
158  /// times the loop will be executed.  Note that this means that the backedge
159  /// of the loop executes N-1 times.  If the trip-count cannot be determined,
160  /// this returns null.
161  ///
162  Value *getTripCount() const;
163
164  /// isLCSSAForm - Return true if the Loop is in LCSSA form
165  bool isLCSSAForm() const;
166
167  //===--------------------------------------------------------------------===//
168  // APIs for updating loop information after changing the CFG
169  //
170
171  /// addBasicBlockToLoop - This method is used by other analyses to update loop
172  /// information.  NewBB is set to be a new member of the current loop.
173  /// Because of this, it is added as a member of all parent loops, and is added
174  /// to the specified LoopInfo object as being in the current basic block.  It
175  /// is not valid to replace the loop header with this method.
176  ///
177  void addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI);
178
179  /// replaceChildLoopWith - This is used when splitting loops up.  It replaces
180  /// the OldChild entry in our children list with NewChild, and updates the
181  /// parent pointer of OldChild to be null and the NewChild to be this loop.
182  /// This updates the loop depth of the new child.
183  void replaceChildLoopWith(Loop *OldChild, Loop *NewChild);
184
185  /// addChildLoop - Add the specified loop to be a child of this loop.  This
186  /// updates the loop depth of the new child.
187  ///
188  void addChildLoop(Loop *NewChild);
189
190  /// removeChildLoop - This removes the specified child from being a subloop of
191  /// this loop.  The loop is not deleted, as it will presumably be inserted
192  /// into another loop.
193  Loop *removeChildLoop(iterator OldChild);
194
195  /// addBlockEntry - This adds a basic block directly to the basic block list.
196  /// This should only be used by transformations that create new loops.  Other
197  /// transformations should use addBasicBlockToLoop.
198  void addBlockEntry(BasicBlock *BB) {
199    Blocks.push_back(BB);
200  }
201
202  /// moveToHeader - This method is used to move BB (which must be part of this
203  /// loop) to be the loop header of the loop (the block that dominates all
204  /// others).
205  void moveToHeader(BasicBlock *BB) {
206    if (Blocks[0] == BB) return;
207    for (unsigned i = 0; ; ++i) {
208      assert(i != Blocks.size() && "Loop does not contain BB!");
209      if (Blocks[i] == BB) {
210        Blocks[i] = Blocks[0];
211        Blocks[0] = BB;
212        return;
213      }
214    }
215  }
216
217  /// removeBlockFromLoop - This removes the specified basic block from the
218  /// current loop, updating the Blocks as appropriate.  This does not update
219  /// the mapping in the LoopInfo class.
220  void removeBlockFromLoop(BasicBlock *BB);
221
222  /// verifyLoop - Verify loop structure
223  void verifyLoop() const;
224
225  void print(std::ostream &O, unsigned Depth = 0) const;
226  void print(std::ostream *O, unsigned Depth = 0) const {
227    if (O) print(*O, Depth);
228  }
229  void dump() const;
230private:
231  friend class LoopInfo;
232  Loop(BasicBlock *BB) : ParentLoop(0) {
233    Blocks.push_back(BB);
234  }
235};
236
237
238
239//===----------------------------------------------------------------------===//
240/// LoopInfo - This class builds and contains all of the top level loop
241/// structures in the specified function.
242///
243class LoopInfo : public FunctionPass {
244  // BBMap - Mapping of basic blocks to the inner most loop they occur in
245  std::map<BasicBlock*, Loop*> BBMap;
246  std::vector<Loop*> TopLevelLoops;
247  friend class Loop;
248public:
249  static char ID; // Pass identification, replacement for typeid
250
251  LoopInfo() : FunctionPass(intptr_t(&ID)) {}
252  ~LoopInfo() { releaseMemory(); }
253
254  /// iterator/begin/end - The interface to the top-level loops in the current
255  /// function.
256  ///
257  typedef std::vector<Loop*>::const_iterator iterator;
258  iterator begin() const { return TopLevelLoops.begin(); }
259  iterator end() const { return TopLevelLoops.end(); }
260
261  /// getLoopFor - Return the inner most loop that BB lives in.  If a basic
262  /// block is in no loop (for example the entry node), null is returned.
263  ///
264  Loop *getLoopFor(const BasicBlock *BB) const {
265    std::map<BasicBlock *, Loop*>::const_iterator I=
266      BBMap.find(const_cast<BasicBlock*>(BB));
267    return I != BBMap.end() ? I->second : 0;
268  }
269
270  /// operator[] - same as getLoopFor...
271  ///
272  const Loop *operator[](const BasicBlock *BB) const {
273    return getLoopFor(BB);
274  }
275
276  /// getLoopDepth - Return the loop nesting level of the specified block...
277  ///
278  unsigned getLoopDepth(const BasicBlock *BB) const {
279    const Loop *L = getLoopFor(BB);
280    return L ? L->getLoopDepth() : 0;
281  }
282
283  // isLoopHeader - True if the block is a loop header node
284  bool isLoopHeader(BasicBlock *BB) const {
285    const Loop *L = getLoopFor(BB);
286    return L && L->getHeader() == BB;
287  }
288
289  /// runOnFunction - Calculate the natural loop information.
290  ///
291  virtual bool runOnFunction(Function &F);
292
293  virtual void releaseMemory();
294
295  void print(std::ostream &O, const Module* = 0) const;
296  void print(std::ostream *O, const Module* M = 0) const {
297    if (O) print(*O, M);
298  }
299
300  virtual void getAnalysisUsage(AnalysisUsage &AU) const;
301
302  /// removeLoop - This removes the specified top-level loop from this loop info
303  /// object.  The loop is not deleted, as it will presumably be inserted into
304  /// another loop.
305  Loop *removeLoop(iterator I);
306
307  /// changeLoopFor - Change the top-level loop that contains BB to the
308  /// specified loop.  This should be used by transformations that restructure
309  /// the loop hierarchy tree.
310  void changeLoopFor(BasicBlock *BB, Loop *L);
311
312  /// changeTopLevelLoop - Replace the specified loop in the top-level loops
313  /// list with the indicated loop.
314  void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop);
315
316  /// addTopLevelLoop - This adds the specified loop to the collection of
317  /// top-level loops.
318  void addTopLevelLoop(Loop *New) {
319    assert(New->getParentLoop() == 0 && "Loop already in subloop!");
320    TopLevelLoops.push_back(New);
321  }
322
323  /// removeBlock - This method completely removes BB from all data structures,
324  /// including all of the Loop objects it is nested in and our mapping from
325  /// BasicBlocks to loops.
326  void removeBlock(BasicBlock *BB);
327
328private:
329  void Calculate(DominatorTree &DT);
330  Loop *ConsiderForLoop(BasicBlock *BB, DominatorTree &DT);
331  void MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent);
332  void InsertLoopInto(Loop *L, Loop *Parent);
333};
334
335
336// Allow clients to walk the list of nested loops...
337template <> struct GraphTraits<const Loop*> {
338  typedef const Loop NodeType;
339  typedef std::vector<Loop*>::const_iterator ChildIteratorType;
340
341  static NodeType *getEntryNode(const Loop *L) { return L; }
342  static inline ChildIteratorType child_begin(NodeType *N) {
343    return N->begin();
344  }
345  static inline ChildIteratorType child_end(NodeType *N) {
346    return N->end();
347  }
348};
349
350template <> struct GraphTraits<Loop*> {
351  typedef Loop NodeType;
352  typedef std::vector<Loop*>::const_iterator ChildIteratorType;
353
354  static NodeType *getEntryNode(Loop *L) { return L; }
355  static inline ChildIteratorType child_begin(NodeType *N) {
356    return N->begin();
357  }
358  static inline ChildIteratorType child_end(NodeType *N) {
359    return N->end();
360  }
361};
362
363} // End llvm namespace
364
365// Make sure that any clients of this file link in LoopInfo.cpp
366FORCE_DEFINING_FILE_TO_BE_LINKED(LoopInfo)
367
368#endif
369