1 //===- llvm/CodeGen/MachineLoopInfo.h - Natural Loop Calculator -*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file defines the MachineLoopInfo class that is used to identify natural 10 // loops and determine the loop depth of various nodes of the CFG. Note that 11 // natural loops may actually be several loops that share the same header node. 12 // 13 // This analysis calculates the nesting structure of loops in a function. For 14 // each natural loop identified, this analysis identifies natural loops 15 // contained entirely within the loop and the basic blocks the make up the loop. 16 // 17 // It can calculate on the fly various bits of information, for example: 18 // 19 // * whether there is a preheader for the loop 20 // * the number of back edges to the header 21 // * whether or not a particular block branches out of the loop 22 // * the successor blocks of the loop 23 // * the loop depth 24 // * the trip count 25 // * etc... 26 // 27 //===----------------------------------------------------------------------===// 28 29 #ifndef LLVM_CODEGEN_MACHINELOOPINFO_H 30 #define LLVM_CODEGEN_MACHINELOOPINFO_H 31 32 #include "llvm/Analysis/LoopInfo.h" 33 #include "llvm/CodeGen/MachineBasicBlock.h" 34 #include "llvm/CodeGen/MachineFunctionPass.h" 35 #include "llvm/IR/DebugLoc.h" 36 #include "llvm/Pass.h" 37 38 namespace llvm { 39 40 class MachineDominatorTree; 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 /// 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 MachineLoop(MachineBasicBlock * MBB)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(); MachineLoopInfo(MachineDominatorTree & MDT)93 explicit MachineLoopInfo(MachineDominatorTree &MDT) 94 : MachineFunctionPass(ID) { 95 calculate(MDT); 96 } 97 MachineLoopInfo(const MachineLoopInfo &) = delete; 98 MachineLoopInfo &operator=(const MachineLoopInfo &) = delete; 99 getBase()100 LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; } 101 102 /// Find the block that either is the loop preheader, or could 103 /// speculatively be used as the preheader. This is e.g. useful to place 104 /// loop setup code. Code that cannot be speculated should not be placed 105 /// here. SpeculativePreheader is controlling whether it also tries to 106 /// find the speculative preheader if the regular preheader is not present. 107 MachineBasicBlock *findLoopPreheader(MachineLoop *L, 108 bool SpeculativePreheader = false) const; 109 110 /// The iterator interface to the top-level loops in the current function. 111 using iterator = LoopInfoBase<MachineBasicBlock, MachineLoop>::iterator; begin()112 inline iterator begin() const { return LI.begin(); } end()113 inline iterator end() const { return LI.end(); } empty()114 bool empty() const { return LI.empty(); } 115 116 /// Return the innermost loop that BB lives in. If a basic block is in no loop 117 /// (for example the entry node), null is returned. getLoopFor(const MachineBasicBlock * BB)118 inline MachineLoop *getLoopFor(const MachineBasicBlock *BB) const { 119 return LI.getLoopFor(BB); 120 } 121 122 /// Same as getLoopFor. 123 inline const MachineLoop *operator[](const MachineBasicBlock *BB) const { 124 return LI.getLoopFor(BB); 125 } 126 127 /// Return the loop nesting level of the specified block. getLoopDepth(const MachineBasicBlock * BB)128 inline unsigned getLoopDepth(const MachineBasicBlock *BB) const { 129 return LI.getLoopDepth(BB); 130 } 131 132 /// True if the block is a loop header node. isLoopHeader(const MachineBasicBlock * BB)133 inline bool isLoopHeader(const MachineBasicBlock *BB) const { 134 return LI.isLoopHeader(BB); 135 } 136 137 /// Calculate the natural loop information. 138 bool runOnMachineFunction(MachineFunction &F) override; 139 void calculate(MachineDominatorTree &MDT); 140 releaseMemory()141 void releaseMemory() override { LI.releaseMemory(); } 142 143 void getAnalysisUsage(AnalysisUsage &AU) const override; 144 145 /// This removes the specified top-level loop from this loop info object. The 146 /// loop is not deleted, as it will presumably be inserted into another loop. removeLoop(iterator I)147 inline MachineLoop *removeLoop(iterator I) { return LI.removeLoop(I); } 148 149 /// Change the top-level loop that contains BB to the specified loop. This 150 /// should be used by transformations that restructure the loop hierarchy 151 /// tree. changeLoopFor(MachineBasicBlock * BB,MachineLoop * L)152 inline void changeLoopFor(MachineBasicBlock *BB, MachineLoop *L) { 153 LI.changeLoopFor(BB, L); 154 } 155 156 /// Replace the specified loop in the top-level loops list with the indicated 157 /// loop. changeTopLevelLoop(MachineLoop * OldLoop,MachineLoop * NewLoop)158 inline void changeTopLevelLoop(MachineLoop *OldLoop, MachineLoop *NewLoop) { 159 LI.changeTopLevelLoop(OldLoop, NewLoop); 160 } 161 162 /// This adds the specified loop to the collection of top-level loops. addTopLevelLoop(MachineLoop * New)163 inline void addTopLevelLoop(MachineLoop *New) { 164 LI.addTopLevelLoop(New); 165 } 166 167 /// This method completely removes BB from all data structures, including all 168 /// of the Loop objects it is nested in and our mapping from 169 /// MachineBasicBlocks to loops. removeBlock(MachineBasicBlock * BB)170 void removeBlock(MachineBasicBlock *BB) { 171 LI.removeBlock(BB); 172 } 173 }; 174 175 // Allow clients to walk the list of nested loops... 176 template <> struct GraphTraits<const MachineLoop*> { 177 using NodeRef = const MachineLoop *; 178 using ChildIteratorType = MachineLoopInfo::iterator; 179 180 static NodeRef getEntryNode(const MachineLoop *L) { return L; } 181 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); } 182 static ChildIteratorType child_end(NodeRef N) { return N->end(); } 183 }; 184 185 template <> struct GraphTraits<MachineLoop*> { 186 using NodeRef = MachineLoop *; 187 using ChildIteratorType = MachineLoopInfo::iterator; 188 189 static NodeRef getEntryNode(MachineLoop *L) { return L; } 190 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); } 191 static ChildIteratorType child_end(NodeRef N) { return N->end(); } 192 }; 193 194 } // end namespace llvm 195 196 #endif // LLVM_CODEGEN_MACHINELOOPINFO_H 197