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