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 #include "llvm/IR/DebugLoc.h" 37 #include "llvm/Pass.h" 38 39 namespace llvm { 40 41 // Implementation in LoopInfoImpl.h 42 class MachineLoop; 43 extern template class LoopBase<MachineBasicBlock, MachineLoop>; 44 45 class MachineLoop : public LoopBase<MachineBasicBlock, MachineLoop> { 46 public: 47 /// Return the "top" block in the loop, which is the first block in the linear 48 /// layout, ignoring any parts of the loop not contiguous with the part that 49 /// contains the header. 50 MachineBasicBlock *getTopBlock(); 51 52 /// Return the "bottom" block in the loop, which is the last block in the 53 /// linear layout, ignoring any parts of the loop not contiguous with the part 54 /// that contains the header. 55 MachineBasicBlock *getBottomBlock(); 56 57 /// \brief Find the block that contains the loop control variable and the 58 /// loop test. This will return the latch block if it's one of the exiting 59 /// blocks. Otherwise, return the exiting block. Return 'null' when 60 /// multiple exiting blocks are present. 61 MachineBasicBlock *findLoopControlBlock(); 62 63 /// Return the debug location of the start of this loop. 64 /// This looks for a BB terminating instruction with a known debug 65 /// location by looking at the preheader and header blocks. If it 66 /// cannot find a terminating instruction with location information, 67 /// it returns an unknown location. 68 DebugLoc getStartLoc() const; 69 70 void dump() const; 71 72 private: 73 friend class LoopInfoBase<MachineBasicBlock, MachineLoop>; 74 75 explicit MachineLoop(MachineBasicBlock *MBB) 76 : LoopBase<MachineBasicBlock, MachineLoop>(MBB) {} 77 78 MachineLoop() = default; 79 }; 80 81 // Implementation in LoopInfoImpl.h 82 extern template class LoopInfoBase<MachineBasicBlock, MachineLoop>; 83 84 class MachineLoopInfo : public MachineFunctionPass { 85 friend class LoopBase<MachineBasicBlock, MachineLoop>; 86 87 LoopInfoBase<MachineBasicBlock, MachineLoop> LI; 88 89 public: 90 static char ID; // Pass identification, replacement for typeid 91 92 MachineLoopInfo() : MachineFunctionPass(ID) { 93 initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry()); 94 } 95 MachineLoopInfo(const MachineLoopInfo &) = delete; 96 MachineLoopInfo &operator=(const MachineLoopInfo &) = delete; 97 98 LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; } 99 100 /// \brief Find the block that either is the loop preheader, or could 101 /// speculatively be used as the preheader. This is e.g. useful to place 102 /// loop setup code. Code that cannot be speculated should not be placed 103 /// here. SpeculativePreheader is controlling whether it also tries to 104 /// find the speculative preheader if the regular preheader is not present. 105 MachineBasicBlock *findLoopPreheader(MachineLoop *L, 106 bool SpeculativePreheader = false) const; 107 108 /// The iterator interface to the top-level loops in the current function. 109 using iterator = LoopInfoBase<MachineBasicBlock, MachineLoop>::iterator; 110 inline iterator begin() const { return LI.begin(); } 111 inline iterator end() const { return LI.end(); } 112 bool empty() const { return LI.empty(); } 113 114 /// Return the innermost loop that BB lives in. If a basic block is in no loop 115 /// (for example the entry node), null is returned. 116 inline MachineLoop *getLoopFor(const MachineBasicBlock *BB) const { 117 return LI.getLoopFor(BB); 118 } 119 120 /// Same as getLoopFor. 121 inline const MachineLoop *operator[](const MachineBasicBlock *BB) const { 122 return LI.getLoopFor(BB); 123 } 124 125 /// Return the loop nesting level of the specified block. 126 inline unsigned getLoopDepth(const MachineBasicBlock *BB) const { 127 return LI.getLoopDepth(BB); 128 } 129 130 /// True if the block is a loop header node. 131 inline bool isLoopHeader(const MachineBasicBlock *BB) const { 132 return LI.isLoopHeader(BB); 133 } 134 135 /// Calculate the natural loop information. 136 bool runOnMachineFunction(MachineFunction &F) override; 137 138 void releaseMemory() override { LI.releaseMemory(); } 139 140 void getAnalysisUsage(AnalysisUsage &AU) const override; 141 142 /// This removes the specified top-level loop from this loop info object. The 143 /// loop is not deleted, as it will presumably be inserted into another loop. 144 inline MachineLoop *removeLoop(iterator I) { return LI.removeLoop(I); } 145 146 /// Change the top-level loop that contains BB to the specified loop. This 147 /// should be used by transformations that restructure the loop hierarchy 148 /// tree. 149 inline void changeLoopFor(MachineBasicBlock *BB, MachineLoop *L) { 150 LI.changeLoopFor(BB, L); 151 } 152 153 /// Replace the specified loop in the top-level loops list with the indicated 154 /// loop. 155 inline void changeTopLevelLoop(MachineLoop *OldLoop, MachineLoop *NewLoop) { 156 LI.changeTopLevelLoop(OldLoop, NewLoop); 157 } 158 159 /// This adds the specified loop to the collection of top-level loops. 160 inline void addTopLevelLoop(MachineLoop *New) { 161 LI.addTopLevelLoop(New); 162 } 163 164 /// This method completely removes BB from all data structures, including all 165 /// of the Loop objects it is nested in and our mapping from 166 /// MachineBasicBlocks to loops. 167 void removeBlock(MachineBasicBlock *BB) { 168 LI.removeBlock(BB); 169 } 170 }; 171 172 // Allow clients to walk the list of nested loops... 173 template <> struct GraphTraits<const MachineLoop*> { 174 using NodeRef = const MachineLoop *; 175 using ChildIteratorType = MachineLoopInfo::iterator; 176 177 static NodeRef getEntryNode(const MachineLoop *L) { return L; } 178 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); } 179 static ChildIteratorType child_end(NodeRef N) { return N->end(); } 180 }; 181 182 template <> struct GraphTraits<MachineLoop*> { 183 using NodeRef = MachineLoop *; 184 using ChildIteratorType = MachineLoopInfo::iterator; 185 186 static NodeRef getEntryNode(MachineLoop *L) { return L; } 187 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); } 188 static ChildIteratorType child_end(NodeRef N) { return N->end(); } 189 }; 190 191 } // end namespace llvm 192 193 #endif // LLVM_CODEGEN_MACHINELOOPINFO_H 194
