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      1 //===- llvm/CodeGen/MachineLoopInfo.h - Natural Loop Calculator -*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file defines the MachineLoopInfo class that is used to identify natural
     11 // loops and determine the loop depth of various nodes of the CFG.  Note that
     12 // natural 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_CODEGEN_MACHINE_LOOP_INFO_H
     31 #define LLVM_CODEGEN_MACHINE_LOOP_INFO_H
     32 
     33 #include "llvm/CodeGen/MachineFunctionPass.h"
     34 #include "llvm/Analysis/LoopInfo.h"
     35 
     36 namespace llvm {
     37 
     38 // Implementation in LoopInfoImpl.h
     39 #ifdef __GNUC__
     40 class MachineLoop;
     41 __extension__ extern template class LoopBase<MachineBasicBlock, MachineLoop>;
     42 #endif
     43 
     44 class MachineLoop : public LoopBase<MachineBasicBlock, MachineLoop> {
     45 public:
     46   MachineLoop();
     47 
     48   /// getTopBlock - Return the "top" block in the loop, which is the first
     49   /// block in the linear layout, ignoring any parts of the loop not
     50   /// contiguous with the part the contains the header.
     51   MachineBasicBlock *getTopBlock();
     52 
     53   /// getBottomBlock - Return the "bottom" block in the loop, which is the last
     54   /// block in the linear layout, ignoring any parts of the loop not
     55   /// contiguous with the part the contains the header.
     56   MachineBasicBlock *getBottomBlock();
     57 
     58   void dump() const;
     59 
     60 private:
     61   friend class LoopInfoBase<MachineBasicBlock, MachineLoop>;
     62   explicit MachineLoop(MachineBasicBlock *MBB)
     63     : LoopBase<MachineBasicBlock, MachineLoop>(MBB) {}
     64 };
     65 
     66 // Implementation in LoopInfoImpl.h
     67 #ifdef __GNUC__
     68 __extension__ extern template
     69 class LoopInfoBase<MachineBasicBlock, MachineLoop>;
     70 #endif
     71 
     72 class MachineLoopInfo : public MachineFunctionPass {
     73   LoopInfoBase<MachineBasicBlock, MachineLoop> LI;
     74   friend class LoopBase<MachineBasicBlock, MachineLoop>;
     75 
     76   void operator=(const MachineLoopInfo &);  // do not implement
     77   MachineLoopInfo(const MachineLoopInfo &); // do not implement
     78 
     79 public:
     80   static char ID; // Pass identification, replacement for typeid
     81 
     82   MachineLoopInfo() : MachineFunctionPass(ID) {
     83     initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
     84   }
     85 
     86   LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
     87 
     88   /// iterator/begin/end - The interface to the top-level loops in the current
     89   /// function.
     90   ///
     91   typedef LoopInfoBase<MachineBasicBlock, MachineLoop>::iterator iterator;
     92   inline iterator begin() const { return LI.begin(); }
     93   inline iterator end() const { return LI.end(); }
     94   bool empty() const { return LI.empty(); }
     95 
     96   /// getLoopFor - Return the inner most loop that BB lives in.  If a basic
     97   /// block is in no loop (for example the entry node), null is returned.
     98   ///
     99   inline MachineLoop *getLoopFor(const MachineBasicBlock *BB) const {
    100     return LI.getLoopFor(BB);
    101   }
    102 
    103   /// operator[] - same as getLoopFor...
    104   ///
    105   inline const MachineLoop *operator[](const MachineBasicBlock *BB) const {
    106     return LI.getLoopFor(BB);
    107   }
    108 
    109   /// getLoopDepth - Return the loop nesting level of the specified block...
    110   ///
    111   inline unsigned getLoopDepth(const MachineBasicBlock *BB) const {
    112     return LI.getLoopDepth(BB);
    113   }
    114 
    115   // isLoopHeader - True if the block is a loop header node
    116   inline bool isLoopHeader(MachineBasicBlock *BB) const {
    117     return LI.isLoopHeader(BB);
    118   }
    119 
    120   /// runOnFunction - Calculate the natural loop information.
    121   ///
    122   virtual bool runOnMachineFunction(MachineFunction &F);
    123 
    124   virtual void releaseMemory() { LI.releaseMemory(); }
    125 
    126   virtual void getAnalysisUsage(AnalysisUsage &AU) const;
    127 
    128   /// removeLoop - This removes the specified top-level loop from this loop info
    129   /// object.  The loop is not deleted, as it will presumably be inserted into
    130   /// another loop.
    131   inline MachineLoop *removeLoop(iterator I) { return LI.removeLoop(I); }
    132 
    133   /// changeLoopFor - Change the top-level loop that contains BB to the
    134   /// specified loop.  This should be used by transformations that restructure
    135   /// the loop hierarchy tree.
    136   inline void changeLoopFor(MachineBasicBlock *BB, MachineLoop *L) {
    137     LI.changeLoopFor(BB, L);
    138   }
    139 
    140   /// changeTopLevelLoop - Replace the specified loop in the top-level loops
    141   /// list with the indicated loop.
    142   inline void changeTopLevelLoop(MachineLoop *OldLoop, MachineLoop *NewLoop) {
    143     LI.changeTopLevelLoop(OldLoop, NewLoop);
    144   }
    145 
    146   /// addTopLevelLoop - This adds the specified loop to the collection of
    147   /// top-level loops.
    148   inline void addTopLevelLoop(MachineLoop *New) {
    149     LI.addTopLevelLoop(New);
    150   }
    151 
    152   /// removeBlock - This method completely removes BB from all data structures,
    153   /// including all of the Loop objects it is nested in and our mapping from
    154   /// MachineBasicBlocks to loops.
    155   void removeBlock(MachineBasicBlock *BB) {
    156     LI.removeBlock(BB);
    157   }
    158 };
    159 
    160 
    161 // Allow clients to walk the list of nested loops...
    162 template <> struct GraphTraits<const MachineLoop*> {
    163   typedef const MachineLoop NodeType;
    164   typedef MachineLoopInfo::iterator ChildIteratorType;
    165 
    166   static NodeType *getEntryNode(const MachineLoop *L) { return L; }
    167   static inline ChildIteratorType child_begin(NodeType *N) {
    168     return N->begin();
    169   }
    170   static inline ChildIteratorType child_end(NodeType *N) {
    171     return N->end();
    172   }
    173 };
    174 
    175 template <> struct GraphTraits<MachineLoop*> {
    176   typedef MachineLoop NodeType;
    177   typedef MachineLoopInfo::iterator ChildIteratorType;
    178 
    179   static NodeType *getEntryNode(MachineLoop *L) { return L; }
    180   static inline ChildIteratorType child_begin(NodeType *N) {
    181     return N->begin();
    182   }
    183   static inline ChildIteratorType child_end(NodeType *N) {
    184     return N->end();
    185   }
    186 };
    187 
    188 } // End llvm namespace
    189 
    190 #endif
    191