LLVM API Documentation

Main Page | Namespace List | Class Hierarchy | Alphabetical List | Class List | Directories | File List | Namespace Members | Class Members | File Members | Related Pages

LoopInfo.h

Go to the documentation of this file.
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 DominatorSet;
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   typedef std::vector<Loop*>::const_iterator iterator;
00078   iterator begin() const { return SubLoops.begin(); }
00079   iterator end() const { return SubLoops.end(); }
00080 
00081   /// getBlocks - Get a list of the basic blocks which make up this loop.
00082   ///
00083   const std::vector<BasicBlock*> &getBlocks() const { return Blocks; }
00084   typedef std::vector<BasicBlock*>::const_iterator block_iterator;
00085   block_iterator block_begin() const { return Blocks.begin(); }
00086   block_iterator block_end() const { return Blocks.end(); }
00087 
00088   /// isLoopExit - True if terminator in the block can branch to another block
00089   /// that is outside of the current loop.
00090   ///
00091   bool isLoopExit(const BasicBlock *BB) const;
00092 
00093   /// getNumBackEdges - Calculate the number of back edges to the loop header
00094   ///
00095   unsigned getNumBackEdges() const;
00096 
00097   /// isLoopInvariant - Return true if the specified value is loop invariant
00098   ///
00099   bool isLoopInvariant(Value *V) const;
00100 
00101   //===--------------------------------------------------------------------===//
00102   // APIs for simple analysis of the loop.
00103   //
00104   // Note that all of these methods can fail on general loops (ie, there may not
00105   // be a preheader, etc).  For best success, the loop simplification and
00106   // induction variable canonicalization pass should be used to normalize loops
00107   // for easy analysis.  These methods assume canonical loops.
00108 
00109   /// getExitBlocks - Return all of the successor blocks of this loop.  These
00110   /// are the blocks _outside of the current loop_ which are branched to.
00111   ///
00112   void getExitBlocks(std::vector<BasicBlock*> &Blocks) const;
00113 
00114   /// getLoopPreheader - If there is a preheader for this loop, return it.  A
00115   /// loop has a preheader if there is only one edge to the header of the loop
00116   /// from outside of the loop.  If this is the case, the block branching to the
00117   /// header of the loop is the preheader node.
00118   ///
00119   /// This method returns null if there is no preheader for the loop.
00120   ///
00121   BasicBlock *getLoopPreheader() const;
00122 
00123   /// getCanonicalInductionVariable - Check to see if the loop has a canonical
00124   /// induction variable: an integer recurrence that starts at 0 and increments
00125   /// by one each time through the loop.  If so, return the phi node that
00126   /// corresponds to it.
00127   ///
00128   PHINode *getCanonicalInductionVariable() const;
00129 
00130   /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
00131   /// the canonical induction variable value for the "next" iteration of the
00132   /// loop.  This always succeeds if getCanonicalInductionVariable succeeds.
00133   ///
00134   Instruction *getCanonicalInductionVariableIncrement() const;
00135 
00136   /// getTripCount - Return a loop-invariant LLVM value indicating the number of
00137   /// times the loop will be executed.  Note that this means that the backedge
00138   /// of the loop executes N-1 times.  If the trip-count cannot be determined,
00139   /// this returns null.
00140   ///
00141   Value *getTripCount() const;
00142 
00143   //===--------------------------------------------------------------------===//
00144   // APIs for updating loop information after changing the CFG
00145   //
00146 
00147   /// addBasicBlockToLoop - This method is used by other analyses to update loop
00148   /// information.  NewBB is set to be a new member of the current loop.
00149   /// Because of this, it is added as a member of all parent loops, and is added
00150   /// to the specified LoopInfo object as being in the current basic block.  It
00151   /// is not valid to replace the loop header with this method.
00152   ///
00153   void addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI);
00154 
00155   /// replaceChildLoopWith - This is used when splitting loops up.  It replaces
00156   /// the OldChild entry in our children list with NewChild, and updates the
00157   /// parent pointer of OldChild to be null and the NewChild to be this loop.
00158   /// This updates the loop depth of the new child.
00159   void replaceChildLoopWith(Loop *OldChild, Loop *NewChild);
00160 
00161   /// addChildLoop - Add the specified loop to be a child of this loop.  This
00162   /// updates the loop depth of the new child.
00163   ///
00164   void addChildLoop(Loop *NewChild);
00165 
00166   /// removeChildLoop - This removes the specified child from being a subloop of
00167   /// this loop.  The loop is not deleted, as it will presumably be inserted
00168   /// into another loop.
00169   Loop *removeChildLoop(iterator OldChild);
00170 
00171   /// addBlockEntry - This adds a basic block directly to the basic block list.
00172   /// This should only be used by transformations that create new loops.  Other
00173   /// transformations should use addBasicBlockToLoop.
00174   void addBlockEntry(BasicBlock *BB) {
00175     Blocks.push_back(BB);
00176   }
00177 
00178   /// removeBlockFromLoop - This removes the specified basic block from the
00179   /// current loop, updating the Blocks as appropriate.  This does not update
00180   /// the mapping in the LoopInfo class.
00181   void removeBlockFromLoop(BasicBlock *BB);
00182 
00183   void print(std::ostream &O, unsigned Depth = 0) const;
00184   void dump() const;
00185 private:
00186   friend class LoopInfo;
00187   Loop(BasicBlock *BB) : ParentLoop(0) {
00188     Blocks.push_back(BB);
00189   }
00190 };
00191 
00192 
00193 
00194 //===----------------------------------------------------------------------===//
00195 /// LoopInfo - This class builds and contains all of the top level loop
00196 /// structures in the specified function.
00197 ///
00198 class LoopInfo : public FunctionPass {
00199   // BBMap - Mapping of basic blocks to the inner most loop they occur in
00200   std::map<BasicBlock*, Loop*> BBMap;
00201   std::vector<Loop*> TopLevelLoops;
00202   friend class Loop;
00203 public:
00204   ~LoopInfo() { releaseMemory(); }
00205 
00206   /// iterator/begin/end - The interface to the top-level loops in the current
00207   /// function.
00208   ///
00209   typedef std::vector<Loop*>::const_iterator iterator;
00210   iterator begin() const { return TopLevelLoops.begin(); }
00211   iterator end() const { return TopLevelLoops.end(); }
00212 
00213   /// getLoopFor - Return the inner most loop that BB lives in.  If a basic
00214   /// block is in no loop (for example the entry node), null is returned.
00215   ///
00216   Loop *getLoopFor(const BasicBlock *BB) const {
00217     std::map<BasicBlock *, Loop*>::const_iterator I=BBMap.find((BasicBlock*)BB);
00218     return I != BBMap.end() ? I->second : 0;
00219   }
00220 
00221   /// operator[] - same as getLoopFor...
00222   ///
00223   const Loop *operator[](const BasicBlock *BB) const {
00224     return getLoopFor(BB);
00225   }
00226 
00227   /// getLoopDepth - Return the loop nesting level of the specified block...
00228   ///
00229   unsigned getLoopDepth(const BasicBlock *BB) const {
00230     const Loop *L = getLoopFor(BB);
00231     return L ? L->getLoopDepth() : 0;
00232   }
00233 
00234   // isLoopHeader - True if the block is a loop header node
00235   bool isLoopHeader(BasicBlock *BB) const {
00236     return getLoopFor(BB)->getHeader() == BB;
00237   }
00238 
00239   /// runOnFunction - Calculate the natural loop information.
00240   ///
00241   virtual bool runOnFunction(Function &F);
00242 
00243   virtual void releaseMemory();
00244   void print(std::ostream &O) const;
00245 
00246   /// getAnalysisUsage - Requires dominator sets
00247   ///
00248   virtual void getAnalysisUsage(AnalysisUsage &AU) const;
00249 
00250   /// removeLoop - This removes the specified top-level loop from this loop info
00251   /// object.  The loop is not deleted, as it will presumably be inserted into
00252   /// another loop.
00253   Loop *removeLoop(iterator I);
00254 
00255   /// changeLoopFor - Change the top-level loop that contains BB to the
00256   /// specified loop.  This should be used by transformations that restructure
00257   /// the loop hierarchy tree.
00258   void changeLoopFor(BasicBlock *BB, Loop *L);
00259 
00260   /// changeTopLevelLoop - Replace the specified loop in the top-level loops
00261   /// list with the indicated loop.
00262   void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop);
00263 
00264   /// addTopLevelLoop - This adds the specified loop to the collection of
00265   /// top-level loops.
00266   void addTopLevelLoop(Loop *New) {
00267     assert(New->getParentLoop() == 0 && "Loop already in subloop!");
00268     TopLevelLoops.push_back(New);
00269   }
00270 
00271   /// removeBlock - This method completely removes BB from all data structures,
00272   /// including all of the Loop objects it is nested in and our mapping from
00273   /// BasicBlocks to loops.
00274   void removeBlock(BasicBlock *BB);
00275 
00276   static void stub();  // Noop
00277 private:
00278   void Calculate(const DominatorSet &DS);
00279   Loop *ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS);
00280   void MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent);
00281   void InsertLoopInto(Loop *L, Loop *Parent);
00282 };
00283 
00284 
00285 // Make sure that any clients of this file link in LoopInfo.cpp
00286 static IncludeFile
00287 LOOP_INFO_INCLUDE_FILE((void*)&LoopInfo::stub);
00288 
00289 // Allow clients to walk the list of nested loops...
00290 template <> struct GraphTraits<const Loop*> {
00291   typedef const Loop NodeType;
00292   typedef std::vector<Loop*>::const_iterator ChildIteratorType;
00293 
00294   static NodeType *getEntryNode(const Loop *L) { return L; }
00295   static inline ChildIteratorType child_begin(NodeType *N) { 
00296     return N->begin();
00297   }
00298   static inline ChildIteratorType child_end(NodeType *N) { 
00299     return N->end();
00300   }
00301 };
00302 
00303 template <> struct GraphTraits<Loop*> {
00304   typedef Loop NodeType;
00305   typedef std::vector<Loop*>::const_iterator ChildIteratorType;
00306 
00307   static NodeType *getEntryNode(Loop *L) { return L; }
00308   static inline ChildIteratorType child_begin(NodeType *N) { 
00309     return N->begin();
00310   }
00311   static inline ChildIteratorType child_end(NodeType *N) { 
00312     return N->end();
00313   }
00314 };
00315 
00316 } // End llvm namespace
00317 
00318 #endif