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 //===--------------------------------------------------------------------===// 00151 // APIs for updating loop information after changing the CFG 00152 // 00153 00154 /// addBasicBlockToLoop - This method is used by other analyses to update loop 00155 /// information. NewBB is set to be a new member of the current loop. 00156 /// Because of this, it is added as a member of all parent loops, and is added 00157 /// to the specified LoopInfo object as being in the current basic block. It 00158 /// is not valid to replace the loop header with this method. 00159 /// 00160 void addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI); 00161 00162 /// replaceChildLoopWith - This is used when splitting loops up. It replaces 00163 /// the OldChild entry in our children list with NewChild, and updates the 00164 /// parent pointer of OldChild to be null and the NewChild to be this loop. 00165 /// This updates the loop depth of the new child. 00166 void replaceChildLoopWith(Loop *OldChild, Loop *NewChild); 00167 00168 /// addChildLoop - Add the specified loop to be a child of this loop. This 00169 /// updates the loop depth of the new child. 00170 /// 00171 void addChildLoop(Loop *NewChild); 00172 00173 /// removeChildLoop - This removes the specified child from being a subloop of 00174 /// this loop. The loop is not deleted, as it will presumably be inserted 00175 /// into another loop. 00176 Loop *removeChildLoop(iterator OldChild); 00177 00178 /// addBlockEntry - This adds a basic block directly to the basic block list. 00179 /// This should only be used by transformations that create new loops. Other 00180 /// transformations should use addBasicBlockToLoop. 00181 void addBlockEntry(BasicBlock *BB) { 00182 Blocks.push_back(BB); 00183 } 00184 00185 /// moveToHeader - This method is used to move BB (which must be part of this 00186 /// loop) to be the loop header of the loop (the block that dominates all 00187 /// others). 00188 void moveToHeader(BasicBlock *BB) { 00189 if (Blocks[0] == BB) return; 00190 for (unsigned i = 0; ; ++i) { 00191 assert(i != Blocks.size() && "Loop does not contain BB!"); 00192 if (Blocks[i] == BB) { 00193 Blocks[i] = Blocks[0]; 00194 Blocks[0] = BB; 00195 return; 00196 } 00197 } 00198 } 00199 00200 /// removeBlockFromLoop - This removes the specified basic block from the 00201 /// current loop, updating the Blocks as appropriate. This does not update 00202 /// the mapping in the LoopInfo class. 00203 void removeBlockFromLoop(BasicBlock *BB); 00204 00205 void print(std::ostream &O, unsigned Depth = 0) const; 00206 void dump() const; 00207 private: 00208 friend class LoopInfo; 00209 Loop(BasicBlock *BB) : ParentLoop(0) { 00210 Blocks.push_back(BB); 00211 } 00212 }; 00213 00214 00215 00216 //===----------------------------------------------------------------------===// 00217 /// LoopInfo - This class builds and contains all of the top level loop 00218 /// structures in the specified function. 00219 /// 00220 class LoopInfo : public FunctionPass { 00221 // BBMap - Mapping of basic blocks to the inner most loop they occur in 00222 std::map<BasicBlock*, Loop*> BBMap; 00223 std::vector<Loop*> TopLevelLoops; 00224 friend class Loop; 00225 public: 00226 ~LoopInfo() { releaseMemory(); } 00227 00228 /// iterator/begin/end - The interface to the top-level loops in the current 00229 /// function. 00230 /// 00231 typedef std::vector<Loop*>::const_iterator iterator; 00232 iterator begin() const { return TopLevelLoops.begin(); } 00233 iterator end() const { return TopLevelLoops.end(); } 00234 00235 /// getLoopFor - Return the inner most loop that BB lives in. If a basic 00236 /// block is in no loop (for example the entry node), null is returned. 00237 /// 00238 Loop *getLoopFor(const BasicBlock *BB) const { 00239 std::map<BasicBlock *, Loop*>::const_iterator I= 00240 BBMap.find(const_cast<BasicBlock*>(BB)); 00241 return I != BBMap.end() ? I->second : 0; 00242 } 00243 00244 /// operator[] - same as getLoopFor... 00245 /// 00246 const Loop *operator[](const BasicBlock *BB) const { 00247 return getLoopFor(BB); 00248 } 00249 00250 /// getLoopDepth - Return the loop nesting level of the specified block... 00251 /// 00252 unsigned getLoopDepth(const BasicBlock *BB) const { 00253 const Loop *L = getLoopFor(BB); 00254 return L ? L->getLoopDepth() : 0; 00255 } 00256 00257 // isLoopHeader - True if the block is a loop header node 00258 bool isLoopHeader(BasicBlock *BB) const { 00259 const Loop *L = getLoopFor(BB); 00260 return L && L->getHeader() == BB; 00261 } 00262 00263 /// runOnFunction - Calculate the natural loop information. 00264 /// 00265 virtual bool runOnFunction(Function &F); 00266 00267 virtual void releaseMemory(); 00268 void print(std::ostream &O, const Module* = 0) const; 00269 00270 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 00271 00272 /// removeLoop - This removes the specified top-level loop from this loop info 00273 /// object. The loop is not deleted, as it will presumably be inserted into 00274 /// another loop. 00275 Loop *removeLoop(iterator I); 00276 00277 /// changeLoopFor - Change the top-level loop that contains BB to the 00278 /// specified loop. This should be used by transformations that restructure 00279 /// the loop hierarchy tree. 00280 void changeLoopFor(BasicBlock *BB, Loop *L); 00281 00282 /// changeTopLevelLoop - Replace the specified loop in the top-level loops 00283 /// list with the indicated loop. 00284 void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop); 00285 00286 /// addTopLevelLoop - This adds the specified loop to the collection of 00287 /// top-level loops. 00288 void addTopLevelLoop(Loop *New) { 00289 assert(New->getParentLoop() == 0 && "Loop already in subloop!"); 00290 TopLevelLoops.push_back(New); 00291 } 00292 00293 /// removeBlock - This method completely removes BB from all data structures, 00294 /// including all of the Loop objects it is nested in and our mapping from 00295 /// BasicBlocks to loops. 00296 void removeBlock(BasicBlock *BB); 00297 00298 static void stub(); // Noop 00299 private: 00300 void Calculate(ETForest &EF); 00301 Loop *ConsiderForLoop(BasicBlock *BB, ETForest &EF); 00302 void MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent); 00303 void InsertLoopInto(Loop *L, Loop *Parent); 00304 }; 00305 00306 00307 // Make sure that any clients of this file link in LoopInfo.cpp 00308 static IncludeFile 00309 LOOP_INFO_INCLUDE_FILE((void*)(&LoopInfo::stub)); 00310 00311 // Allow clients to walk the list of nested loops... 00312 template <> struct GraphTraits<const Loop*> { 00313 typedef const Loop NodeType; 00314 typedef std::vector<Loop*>::const_iterator ChildIteratorType; 00315 00316 static NodeType *getEntryNode(const Loop *L) { return L; } 00317 static inline ChildIteratorType child_begin(NodeType *N) { 00318 return N->begin(); 00319 } 00320 static inline ChildIteratorType child_end(NodeType *N) { 00321 return N->end(); 00322 } 00323 }; 00324 00325 template <> struct GraphTraits<Loop*> { 00326 typedef Loop NodeType; 00327 typedef std::vector<Loop*>::const_iterator ChildIteratorType; 00328 00329 static NodeType *getEntryNode(Loop *L) { return L; } 00330 static inline ChildIteratorType child_begin(NodeType *N) { 00331 return N->begin(); 00332 } 00333 static inline ChildIteratorType child_end(NodeType *N) { 00334 return N->end(); 00335 } 00336 }; 00337 00338 } // End llvm namespace 00339 00340 #endif