1 //===- MachineLoopInfo.cpp - Natural Loop Calculator ----------------------===// 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 // the loops identified may actually be several natural loops that share the 12 // same header node... not just a single natural loop. 13 // 14 //===----------------------------------------------------------------------===// 15 16 #include "llvm/CodeGen/MachineLoopInfo.h" 17 #include "llvm/Analysis/LoopInfoImpl.h" 18 #include "llvm/CodeGen/MachineDominators.h" 19 #include "llvm/CodeGen/Passes.h" 20 #include "llvm/Config/llvm-config.h" 21 #include "llvm/Support/Debug.h" 22 #include "llvm/Support/raw_ostream.h" 23 using namespace llvm; 24 25 // Explicitly instantiate methods in LoopInfoImpl.h for MI-level Loops. 26 template class llvm::LoopBase<MachineBasicBlock, MachineLoop>; 27 template class llvm::LoopInfoBase<MachineBasicBlock, MachineLoop>; 28 29 char MachineLoopInfo::ID = 0; 30 INITIALIZE_PASS_BEGIN(MachineLoopInfo, "machine-loops", 31 "Machine Natural Loop Construction", true, true) 32 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) 33 INITIALIZE_PASS_END(MachineLoopInfo, "machine-loops", 34 "Machine Natural Loop Construction", true, true) 35 36 char &llvm::MachineLoopInfoID = MachineLoopInfo::ID; 37 38 bool MachineLoopInfo::runOnMachineFunction(MachineFunction &) { 39 releaseMemory(); 40 LI.analyze(getAnalysis<MachineDominatorTree>().getBase()); 41 return false; 42 } 43 44 void MachineLoopInfo::getAnalysisUsage(AnalysisUsage &AU) const { 45 AU.setPreservesAll(); 46 AU.addRequired<MachineDominatorTree>(); 47 MachineFunctionPass::getAnalysisUsage(AU); 48 } 49 50 MachineBasicBlock *MachineLoop::getTopBlock() { 51 MachineBasicBlock *TopMBB = getHeader(); 52 MachineFunction::iterator Begin = TopMBB->getParent()->begin(); 53 if (TopMBB->getIterator() != Begin) { 54 MachineBasicBlock *PriorMBB = &*std::prev(TopMBB->getIterator()); 55 while (contains(PriorMBB)) { 56 TopMBB = PriorMBB; 57 if (TopMBB->getIterator() == Begin) 58 break; 59 PriorMBB = &*std::prev(TopMBB->getIterator()); 60 } 61 } 62 return TopMBB; 63 } 64 65 MachineBasicBlock *MachineLoop::getBottomBlock() { 66 MachineBasicBlock *BotMBB = getHeader(); 67 MachineFunction::iterator End = BotMBB->getParent()->end(); 68 if (BotMBB->getIterator() != std::prev(End)) { 69 MachineBasicBlock *NextMBB = &*std::next(BotMBB->getIterator()); 70 while (contains(NextMBB)) { 71 BotMBB = NextMBB; 72 if (BotMBB == &*std::next(BotMBB->getIterator())) 73 break; 74 NextMBB = &*std::next(BotMBB->getIterator()); 75 } 76 } 77 return BotMBB; 78 } 79 80 MachineBasicBlock *MachineLoop::findLoopControlBlock() { 81 if (MachineBasicBlock *Latch = getLoopLatch()) { 82 if (isLoopExiting(Latch)) 83 return Latch; 84 else 85 return getExitingBlock(); 86 } 87 return nullptr; 88 } 89 90 DebugLoc MachineLoop::getStartLoc() const { 91 // Try the pre-header first. 92 if (MachineBasicBlock *PHeadMBB = getLoopPreheader()) 93 if (const BasicBlock *PHeadBB = PHeadMBB->getBasicBlock()) 94 if (DebugLoc DL = PHeadBB->getTerminator()->getDebugLoc()) 95 return DL; 96 97 // If we have no pre-header or there are no instructions with debug 98 // info in it, try the header. 99 if (MachineBasicBlock *HeadMBB = getHeader()) 100 if (const BasicBlock *HeadBB = HeadMBB->getBasicBlock()) 101 return HeadBB->getTerminator()->getDebugLoc(); 102 103 return DebugLoc(); 104 } 105 106 MachineBasicBlock * 107 MachineLoopInfo::findLoopPreheader(MachineLoop *L, 108 bool SpeculativePreheader) const { 109 if (MachineBasicBlock *PB = L->getLoopPreheader()) 110 return PB; 111 112 if (!SpeculativePreheader) 113 return nullptr; 114 115 MachineBasicBlock *HB = L->getHeader(), *LB = L->getLoopLatch(); 116 if (HB->pred_size() != 2 || HB->hasAddressTaken()) 117 return nullptr; 118 // Find the predecessor of the header that is not the latch block. 119 MachineBasicBlock *Preheader = nullptr; 120 for (MachineBasicBlock *P : HB->predecessors()) { 121 if (P == LB) 122 continue; 123 // Sanity. 124 if (Preheader) 125 return nullptr; 126 Preheader = P; 127 } 128 129 // Check if the preheader candidate is a successor of any other loop 130 // headers. We want to avoid having two loop setups in the same block. 131 for (MachineBasicBlock *S : Preheader->successors()) { 132 if (S == HB) 133 continue; 134 MachineLoop *T = getLoopFor(S); 135 if (T && T->getHeader() == S) 136 return nullptr; 137 } 138 return Preheader; 139 } 140 141 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 142 LLVM_DUMP_METHOD void MachineLoop::dump() const { 143 print(dbgs()); 144 } 145 #endif 146