1 //===- llvm/Analysis/LoopInfo.h - Natural Loop Calculator -------*- C++ -*-===//
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 natural
12 // loops may actually be several loops that share the same header node.
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 function, the basic blocks the make up the
17 // loop, the nesting depth of the loop, and the successor blocks of the loop.
19 // It can calculate on the fly a variety of different bits of information, such
20 // as whether there is a preheader for the loop, the number of back edges to the
21 // header, and whether or not a particular block branches out of the loop.
23 //===----------------------------------------------------------------------===//
25 #ifndef LLVM_ANALYSIS_LOOP_INFO_H
26 #define LLVM_ANALYSIS_LOOP_INFO_H
28 #include "llvm/Pass.h"
29 #include "Support/GraphTraits.h"
39 //===----------------------------------------------------------------------===//
40 /// Loop class - Instances of this class are used to represent loops that are
41 /// detected in the flow graph
45 std::vector<Loop*> SubLoops; // Loops contained entirely within this one
46 std::vector<BasicBlock*> Blocks; // First entry is the header node
47 unsigned LoopDepth; // Nesting depth of this loop
49 Loop(const Loop &); // DO NOT IMPLEMENT
50 const Loop &operator=(const Loop &); // DO NOT IMPLEMENT
52 /// Loop ctor - This creates an empty loop.
53 Loop() : ParentLoop(0), LoopDepth(0) {
56 for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
60 unsigned getLoopDepth() const { return LoopDepth; }
61 BasicBlock *getHeader() const { return Blocks.front(); }
62 Loop *getParentLoop() const { return ParentLoop; }
64 /// contains - Return true of the specified basic block is in this loop
66 bool contains(const BasicBlock *BB) const;
68 /// iterator/begin/end - Return the loops contained entirely within this loop.
70 typedef std::vector<Loop*>::const_iterator iterator;
71 iterator begin() const { return SubLoops.begin(); }
72 iterator end() const { return SubLoops.end(); }
74 /// getBlocks - Get a list of the basic blocks which make up this loop.
76 const std::vector<BasicBlock*> &getBlocks() const { return Blocks; }
77 typedef std::vector<BasicBlock*>::const_iterator block_iterator;
78 block_iterator block_begin() const { return Blocks.begin(); }
79 block_iterator block_end() const { return Blocks.end(); }
81 /// isLoopExit - True if terminator in the block can branch to another block
82 /// that is outside of the current loop.
84 bool isLoopExit(const BasicBlock *BB) const;
86 /// getNumBackEdges - Calculate the number of back edges to the loop header
88 unsigned getNumBackEdges() const;
90 /// isLoopInvariant - Return true if the specified value is loop invariant
92 bool isLoopInvariant(Value *V) const;
94 //===--------------------------------------------------------------------===//
95 // APIs for simple analysis of the loop.
97 // Note that all of these methods can fail on general loops (ie, there may not
98 // be a preheader, etc). For best success, the loop simplification and
99 // induction variable canonicalization pass should be used to normalize loops
100 // for easy analysis. These methods assume canonical loops.
102 /// getExitBlocks - Return all of the successor blocks of this loop. These
103 /// are the blocks _outside of the current loop_ which are branched to.
105 void getExitBlocks(std::vector<BasicBlock*> &Blocks) const;
107 /// getLoopPreheader - If there is a preheader for this loop, return it. A
108 /// loop has a preheader if there is only one edge to the header of the loop
109 /// from outside of the loop. If this is the case, the block branching to the
110 /// header of the loop is the preheader node.
112 /// This method returns null if there is no preheader for the loop.
114 BasicBlock *getLoopPreheader() const;
116 /// getCanonicalInductionVariable - Check to see if the loop has a canonical
117 /// induction variable: an integer recurrence that starts at 0 and increments
118 /// by one each time through the loop. If so, return the phi node that
119 /// corresponds to it.
121 PHINode *getCanonicalInductionVariable() const;
123 /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
124 /// the canonical induction variable value for the "next" iteration of the
125 /// loop. This always succeeds if getCanonicalInductionVariable succeeds.
127 Instruction *getCanonicalInductionVariableIncrement() const;
129 /// getTripCount - Return a loop-invariant LLVM value indicating the number of
130 /// times the loop will be executed. Note that this means that the backedge
131 /// of the loop executes N-1 times. If the trip-count cannot be determined,
132 /// this returns null.
134 Value *getTripCount() const;
136 //===--------------------------------------------------------------------===//
137 // APIs for updating loop information after changing the CFG
140 /// addBasicBlockToLoop - This method is used by other analyses to update loop
141 /// information. NewBB is set to be a new member of the current loop.
142 /// Because of this, it is added as a member of all parent loops, and is added
143 /// to the specified LoopInfo object as being in the current basic block. It
144 /// is not valid to replace the loop header with this method.
146 void addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI);
148 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
149 /// the OldChild entry in our children list with NewChild, and updates the
150 /// parent pointer of OldChild to be null and the NewChild to be this loop.
151 /// This updates the loop depth of the new child.
152 void replaceChildLoopWith(Loop *OldChild, Loop *NewChild);
154 /// addChildLoop - Add the specified loop to be a child of this loop. This
155 /// updates the loop depth of the new child.
157 void addChildLoop(Loop *NewChild);
159 /// removeChildLoop - This removes the specified child from being a subloop of
160 /// this loop. The loop is not deleted, as it will presumably be inserted
161 /// into another loop.
162 Loop *removeChildLoop(iterator OldChild);
164 /// addBlockEntry - This adds a basic block directly to the basic block list.
165 /// This should only be used by transformations that create new loops. Other
166 /// transformations should use addBasicBlockToLoop.
167 void addBlockEntry(BasicBlock *BB) {
168 Blocks.push_back(BB);
171 /// removeBlockFromLoop - This removes the specified basic block from the
172 /// current loop, updating the Blocks as appropriate. This does not update
173 /// the mapping in the LoopInfo class.
174 void removeBlockFromLoop(BasicBlock *BB);
176 void print(std::ostream &O, unsigned Depth = 0) const;
179 friend class LoopInfo;
180 Loop(BasicBlock *BB) : ParentLoop(0) {
181 Blocks.push_back(BB); LoopDepth = 0;
183 void setLoopDepth(unsigned Level) {
185 for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
186 SubLoops[i]->setLoopDepth(Level+1);
192 //===----------------------------------------------------------------------===//
193 /// LoopInfo - This class builds and contains all of the top level loop
194 /// structures in the specified function.
196 class LoopInfo : public FunctionPass {
197 // BBMap - Mapping of basic blocks to the inner most loop they occur in
198 std::map<BasicBlock*, Loop*> BBMap;
199 std::vector<Loop*> TopLevelLoops;
202 ~LoopInfo() { releaseMemory(); }
204 /// iterator/begin/end - The interface to the top-level loops in the current
207 typedef std::vector<Loop*>::const_iterator iterator;
208 iterator begin() const { return TopLevelLoops.begin(); }
209 iterator end() const { return TopLevelLoops.end(); }
211 /// getLoopFor - Return the inner most loop that BB lives in. If a basic
212 /// block is in no loop (for example the entry node), null is returned.
214 const Loop *getLoopFor(const BasicBlock *BB) const {
215 std::map<BasicBlock *, Loop*>::const_iterator I=BBMap.find((BasicBlock*)BB);
216 return I != BBMap.end() ? I->second : 0;
219 /// operator[] - same as getLoopFor...
221 inline const Loop *operator[](const BasicBlock *BB) const {
222 return getLoopFor(BB);
225 /// getLoopDepth - Return the loop nesting level of the specified block...
227 unsigned getLoopDepth(const BasicBlock *BB) const {
228 const Loop *L = getLoopFor(BB);
229 return L ? L->getLoopDepth() : 0;
232 // isLoopHeader - True if the block is a loop header node
233 bool isLoopHeader(BasicBlock *BB) const {
234 return getLoopFor(BB)->getHeader() == BB;
237 /// runOnFunction - Calculate the natural loop information.
239 virtual bool runOnFunction(Function &F);
241 virtual void releaseMemory();
242 void print(std::ostream &O) const;
244 /// getAnalysisUsage - Requires dominator sets
246 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
248 /// removeLoop - This removes the specified top-level loop from this loop info
249 /// object. The loop is not deleted, as it will presumably be inserted into
251 Loop *removeLoop(iterator I);
253 /// changeLoopFor - Change the top-level loop that contains BB to the
254 /// specified loop. This should be used by transformations that restructure
255 /// the loop hierarchy tree.
256 void changeLoopFor(BasicBlock *BB, Loop *L);
258 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
259 /// list with the indicated loop.
260 void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop);
262 /// removeBlock - This method completely removes BB from all data structures,
263 /// including all of the Loop objects it is nested in and our mapping from
264 /// BasicBlocks to loops.
265 void removeBlock(BasicBlock *BB);
267 static void stub(); // Noop
269 void Calculate(const DominatorSet &DS);
270 Loop *ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS);
271 void MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent);
272 void InsertLoopInto(Loop *L, Loop *Parent);
276 // Make sure that any clients of this file link in LoopInfo.cpp
278 LOOP_INFO_INCLUDE_FILE((void*)&LoopInfo::stub);
280 // Allow clients to walk the list of nested loops...
281 template <> struct GraphTraits<const Loop*> {
282 typedef const Loop NodeType;
283 typedef std::vector<Loop*>::const_iterator ChildIteratorType;
285 static NodeType *getEntryNode(const Loop *L) { return L; }
286 static inline ChildIteratorType child_begin(NodeType *N) {
289 static inline ChildIteratorType child_end(NodeType *N) {
294 template <> struct GraphTraits<Loop*> {
295 typedef Loop NodeType;
296 typedef std::vector<Loop*>::const_iterator ChildIteratorType;
298 static NodeType *getEntryNode(Loop *L) { return L; }
299 static inline ChildIteratorType child_begin(NodeType *N) {
302 static inline ChildIteratorType child_end(NodeType *N) {
307 } // End llvm namespace