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