LLVM API Documentation
00001 //===- llvm/Analysis/LoopInfo.h - Natural Loop Calculator -------*- C++ -*-===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // This file defines the LoopInfo class that is used to identify natural loops 00011 // and determine the loop depth of various nodes of the CFG. Note that natural 00012 // loops may actually be several loops that share the same header node. 00013 // 00014 // This analysis calculates the nesting structure of loops in a function. For 00015 // each natural loop identified, this analysis identifies natural loops 00016 // contained entirely within the loop and the basic blocks the make up the loop. 00017 // 00018 // It can calculate on the fly various bits of information, for example: 00019 // 00020 // * whether there is a preheader for the loop 00021 // * the number of back edges to the header 00022 // * whether or not a particular block branches out of the loop 00023 // * the successor blocks of the loop 00024 // * the loop depth 00025 // * the trip count 00026 // * etc... 00027 // 00028 //===----------------------------------------------------------------------===// 00029 00030 #ifndef LLVM_ANALYSIS_LOOP_INFO_H 00031 #define LLVM_ANALYSIS_LOOP_INFO_H 00032 00033 #include "llvm/Pass.h" 00034 #include "llvm/ADT/GraphTraits.h" 00035 00036 namespace llvm { 00037 00038 struct ETForest; 00039 class LoopInfo; 00040 class PHINode; 00041 class Instruction; 00042 00043 //===----------------------------------------------------------------------===// 00044 /// Loop class - Instances of this class are used to represent loops that are 00045 /// detected in the flow graph 00046 /// 00047 class Loop { 00048 Loop *ParentLoop; 00049 std::vector<Loop*> SubLoops; // Loops contained entirely within this one 00050 std::vector<BasicBlock*> Blocks; // First entry is the header node 00051 00052 Loop(const Loop &); // DO NOT IMPLEMENT 00053 const Loop &operator=(const Loop &); // DO NOT IMPLEMENT 00054 public: 00055 /// Loop ctor - This creates an empty loop. 00056 Loop() : ParentLoop(0) {} 00057 ~Loop() { 00058 for (unsigned i = 0, e = SubLoops.size(); i != e; ++i) 00059 delete SubLoops[i]; 00060 } 00061 00062 unsigned getLoopDepth() const { 00063 unsigned D = 0; 00064 for (const Loop *CurLoop = this; CurLoop; CurLoop = CurLoop->ParentLoop) 00065 ++D; 00066 return D; 00067 } 00068 BasicBlock *getHeader() const { return Blocks.front(); } 00069 Loop *getParentLoop() const { return ParentLoop; } 00070 00071 /// contains - Return true of the specified basic block is in this loop 00072 /// 00073 bool contains(const BasicBlock *BB) const; 00074 00075 /// iterator/begin/end - Return the loops contained entirely within this loop. 00076 /// 00077 const std::vector<Loop*> &getSubLoops() const { return SubLoops; } 00078 typedef std::vector<Loop*>::const_iterator iterator; 00079 iterator begin() const { return SubLoops.begin(); } 00080 iterator end() const { return SubLoops.end(); } 00081 00082 /// getBlocks - Get a list of the basic blocks which make up this loop. 00083 /// 00084 const std::vector<BasicBlock*> &getBlocks() const { return Blocks; } 00085 typedef std::vector<BasicBlock*>::const_iterator block_iterator; 00086 block_iterator block_begin() const { return Blocks.begin(); } 00087 block_iterator block_end() const { return Blocks.end(); } 00088 00089 /// isLoopExit - True if terminator in the block can branch to another block 00090 /// that is outside of the current loop. 00091 /// 00092 bool isLoopExit(const BasicBlock *BB) const; 00093 00094 /// getNumBackEdges - Calculate the number of back edges to the loop header 00095 /// 00096 unsigned getNumBackEdges() const; 00097 00098 /// isLoopInvariant - Return true if the specified value is loop invariant 00099 /// 00100 bool isLoopInvariant(Value *V) const; 00101 00102 //===--------------------------------------------------------------------===// 00103 // APIs for simple analysis of the loop. 00104 // 00105 // Note that all of these methods can fail on general loops (ie, there may not 00106 // be a preheader, etc). For best success, the loop simplification and 00107 // induction variable canonicalization pass should be used to normalize loops 00108 // for easy analysis. These methods assume canonical loops. 00109 00110 /// getExitBlocks - Return all of the successor blocks of this loop. These 00111 /// are the blocks _outside of the current loop_ which are branched to. 00112 /// 00113 void getExitBlocks(std::vector<BasicBlock*> &Blocks) const; 00114 00115 /// getLoopPreheader - If there is a preheader for this loop, return it. A 00116 /// loop has a preheader if there is only one edge to the header of the loop 00117 /// from outside of the loop. If this is the case, the block branching to the 00118 /// header of the loop is the preheader node. 00119 /// 00120 /// This method returns null if there is no preheader for the loop. 00121 /// 00122 BasicBlock *getLoopPreheader() const; 00123 00124 /// getLoopLatch - If there is a latch block for this loop, return it. A 00125 /// latch block is the canonical backedge for a loop. A loop header in normal 00126 /// form has two edges into it: one from a preheader and one from a latch 00127 /// block. 00128 BasicBlock *getLoopLatch() const; 00129 00130 /// getCanonicalInductionVariable - Check to see if the loop has a canonical 00131 /// induction variable: an integer recurrence that starts at 0 and increments 00132 /// by one each time through the loop. If so, return the phi node that 00133 /// corresponds to it. 00134 /// 00135 PHINode *getCanonicalInductionVariable() const; 00136 00137 /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds 00138 /// the canonical induction variable value for the "next" iteration of the 00139 /// loop. This always succeeds if getCanonicalInductionVariable succeeds. 00140 /// 00141 Instruction *getCanonicalInductionVariableIncrement() const; 00142 00143 /// getTripCount - Return a loop-invariant LLVM value indicating the number of 00144 /// times the loop will be executed. Note that this means that the backedge 00145 /// of the loop executes N-1 times. If the trip-count cannot be determined, 00146 /// this returns null. 00147 /// 00148 Value *getTripCount() const; 00149 00150 /// isLCSSAForm - Return true if the Loop is in LCSSA form 00151 bool isLCSSAForm() const; 00152 00153 //===--------------------------------------------------------------------===// 00154 // APIs for updating loop information after changing the CFG 00155 // 00156 00157 /// addBasicBlockToLoop - This method is used by other analyses to update loop 00158 /// information. NewBB is set to be a new member of the current loop. 00159 /// Because of this, it is added as a member of all parent loops, and is added 00160 /// to the specified LoopInfo object as being in the current basic block. It 00161 /// is not valid to replace the loop header with this method. 00162 /// 00163 void addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI); 00164 00165 /// replaceChildLoopWith - This is used when splitting loops up. It replaces 00166 /// the OldChild entry in our children list with NewChild, and updates the 00167 /// parent pointer of OldChild to be null and the NewChild to be this loop. 00168 /// This updates the loop depth of the new child. 00169 void replaceChildLoopWith(Loop *OldChild, Loop *NewChild); 00170 00171 /// addChildLoop - Add the specified loop to be a child of this loop. This 00172 /// updates the loop depth of the new child. 00173 /// 00174 void addChildLoop(Loop *NewChild); 00175 00176 /// removeChildLoop - This removes the specified child from being a subloop of 00177 /// this loop. The loop is not deleted, as it will presumably be inserted 00178 /// into another loop. 00179 Loop *removeChildLoop(iterator OldChild); 00180 00181 /// addBlockEntry - This adds a basic block directly to the basic block list. 00182 /// This should only be used by transformations that create new loops. Other 00183 /// transformations should use addBasicBlockToLoop. 00184 void addBlockEntry(BasicBlock *BB) { 00185 Blocks.push_back(BB); 00186 } 00187 00188 /// moveToHeader - This method is used to move BB (which must be part of this 00189 /// loop) to be the loop header of the loop (the block that dominates all 00190 /// others). 00191 void moveToHeader(BasicBlock *BB) { 00192 if (Blocks[0] == BB) return; 00193 for (unsigned i = 0; ; ++i) { 00194 assert(i != Blocks.size() && "Loop does not contain BB!"); 00195 if (Blocks[i] == BB) { 00196 Blocks[i] = Blocks[0]; 00197 Blocks[0] = BB; 00198 return; 00199 } 00200 } 00201 } 00202 00203 /// removeBlockFromLoop - This removes the specified basic block from the 00204 /// current loop, updating the Blocks as appropriate. This does not update 00205 /// the mapping in the LoopInfo class. 00206 void removeBlockFromLoop(BasicBlock *BB); 00207 00208 void print(std::ostream &O, unsigned Depth = 0) const; 00209 void dump() const; 00210 private: 00211 friend class LoopInfo; 00212 Loop(BasicBlock *BB) : ParentLoop(0) { 00213 Blocks.push_back(BB); 00214 } 00215 }; 00216 00217 00218 00219 //===----------------------------------------------------------------------===// 00220 /// LoopInfo - This class builds and contains all of the top level loop 00221 /// structures in the specified function. 00222 /// 00223 class LoopInfo : public FunctionPass { 00224 // BBMap - Mapping of basic blocks to the inner most loop they occur in 00225 std::map<BasicBlock*, Loop*> BBMap; 00226 std::vector<Loop*> TopLevelLoops; 00227 friend class Loop; 00228 public: 00229 ~LoopInfo() { releaseMemory(); } 00230 00231 /// iterator/begin/end - The interface to the top-level loops in the current 00232 /// function. 00233 /// 00234 typedef std::vector<Loop*>::const_iterator iterator; 00235 iterator begin() const { return TopLevelLoops.begin(); } 00236 iterator end() const { return TopLevelLoops.end(); } 00237 00238 /// getLoopFor - Return the inner most loop that BB lives in. If a basic 00239 /// block is in no loop (for example the entry node), null is returned. 00240 /// 00241 Loop *getLoopFor(const BasicBlock *BB) const { 00242 std::map<BasicBlock *, Loop*>::const_iterator I= 00243 BBMap.find(const_cast<BasicBlock*>(BB)); 00244 return I != BBMap.end() ? I->second : 0; 00245 } 00246 00247 /// operator[] - same as getLoopFor... 00248 /// 00249 const Loop *operator[](const BasicBlock *BB) const { 00250 return getLoopFor(BB); 00251 } 00252 00253 /// getLoopDepth - Return the loop nesting level of the specified block... 00254 /// 00255 unsigned getLoopDepth(const BasicBlock *BB) const { 00256 const Loop *L = getLoopFor(BB); 00257 return L ? L->getLoopDepth() : 0; 00258 } 00259 00260 // isLoopHeader - True if the block is a loop header node 00261 bool isLoopHeader(BasicBlock *BB) const { 00262 const Loop *L = getLoopFor(BB); 00263 return L && L->getHeader() == BB; 00264 } 00265 00266 /// runOnFunction - Calculate the natural loop information. 00267 /// 00268 virtual bool runOnFunction(Function &F); 00269 00270 virtual void releaseMemory(); 00271 void print(std::ostream &O, const Module* = 0) const; 00272 00273 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 00274 00275 /// removeLoop - This removes the specified top-level loop from this loop info 00276 /// object. The loop is not deleted, as it will presumably be inserted into 00277 /// another loop. 00278 Loop *removeLoop(iterator I); 00279 00280 /// changeLoopFor - Change the top-level loop that contains BB to the 00281 /// specified loop. This should be used by transformations that restructure 00282 /// the loop hierarchy tree. 00283 void changeLoopFor(BasicBlock *BB, Loop *L); 00284 00285 /// changeTopLevelLoop - Replace the specified loop in the top-level loops 00286 /// list with the indicated loop. 00287 void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop); 00288 00289 /// addTopLevelLoop - This adds the specified loop to the collection of 00290 /// top-level loops. 00291 void addTopLevelLoop(Loop *New) { 00292 assert(New->getParentLoop() == 0 && "Loop already in subloop!"); 00293 TopLevelLoops.push_back(New); 00294 } 00295 00296 /// removeBlock - This method completely removes BB from all data structures, 00297 /// including all of the Loop objects it is nested in and our mapping from 00298 /// BasicBlocks to loops. 00299 void removeBlock(BasicBlock *BB); 00300 00301 private: 00302 void Calculate(ETForest &EF); 00303 Loop *ConsiderForLoop(BasicBlock *BB, ETForest &EF); 00304 void MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent); 00305 void InsertLoopInto(Loop *L, Loop *Parent); 00306 }; 00307 00308 00309 // Allow clients to walk the list of nested loops... 00310 template <> struct GraphTraits<const Loop*> { 00311 typedef const Loop NodeType; 00312 typedef std::vector<Loop*>::const_iterator ChildIteratorType; 00313 00314 static NodeType *getEntryNode(const Loop *L) { return L; } 00315 static inline ChildIteratorType child_begin(NodeType *N) { 00316 return N->begin(); 00317 } 00318 static inline ChildIteratorType child_end(NodeType *N) { 00319 return N->end(); 00320 } 00321 }; 00322 00323 template <> struct GraphTraits<Loop*> { 00324 typedef Loop NodeType; 00325 typedef std::vector<Loop*>::const_iterator ChildIteratorType; 00326 00327 static NodeType *getEntryNode(Loop *L) { return L; } 00328 static inline ChildIteratorType child_begin(NodeType *N) { 00329 return N->begin(); 00330 } 00331 static inline ChildIteratorType child_end(NodeType *N) { 00332 return N->end(); 00333 } 00334 }; 00335 00336 } // End llvm namespace 00337 00338 // Make sure that any clients of this file link in LoopInfo.cpp 00339 FORCE_DEFINING_FILE_TO_BE_LINKED(LoopInfo) 00340 00341 #endif