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/InitializePasses.h" 22 #include "llvm/Support/Debug.h" 23 #include "llvm/Support/raw_ostream.h" 24 using namespace llvm; 25 26 // Explicitly instantiate methods in LoopInfoImpl.h for MI-level Loops. 27 template class llvm::LoopBase<MachineBasicBlock, MachineLoop>; 28 template class llvm::LoopInfoBase<MachineBasicBlock, MachineLoop>; 29 30 char MachineLoopInfo::ID = 0; 31 MachineLoopInfo::MachineLoopInfo() : MachineFunctionPass(ID) { 32 initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry()); 33 } 34 INITIALIZE_PASS_BEGIN(MachineLoopInfo, "machine-loops", 35 "Machine Natural Loop Construction", true, true) 36 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) 37 INITIALIZE_PASS_END(MachineLoopInfo, "machine-loops", 38 "Machine Natural Loop Construction", true, true) 39 40 char &llvm::MachineLoopInfoID = MachineLoopInfo::ID; 41 42 bool MachineLoopInfo::runOnMachineFunction(MachineFunction &) { 43 calculate(getAnalysis<MachineDominatorTree>()); 44 return false; 45 } 46 47 void MachineLoopInfo::calculate(MachineDominatorTree &MDT) { 48 releaseMemory(); 49 LI.analyze(MDT.getBase()); 50 } 51 52 void MachineLoopInfo::getAnalysisUsage(AnalysisUsage &AU) const { 53 AU.setPreservesAll(); 54 AU.addRequired<MachineDominatorTree>(); 55 MachineFunctionPass::getAnalysisUsage(AU); 56 } 57 58 MachineBasicBlock *MachineLoop::getTopBlock() { 59 MachineBasicBlock *TopMBB = getHeader(); 60 MachineFunction::iterator Begin = TopMBB->getParent()->begin(); 61 if (TopMBB->getIterator() != Begin) { 62 MachineBasicBlock *PriorMBB = &*std::prev(TopMBB->getIterator()); 63 while (contains(PriorMBB)) { 64 TopMBB = PriorMBB; 65 if (TopMBB->getIterator() == Begin) 66 break; 67 PriorMBB = &*std::prev(TopMBB->getIterator()); 68 } 69 } 70 return TopMBB; 71 } 72 73 MachineBasicBlock *MachineLoop::getBottomBlock() { 74 MachineBasicBlock *BotMBB = getHeader(); 75 MachineFunction::iterator End = BotMBB->getParent()->end(); 76 if (BotMBB->getIterator() != std::prev(End)) { 77 MachineBasicBlock *NextMBB = &*std::next(BotMBB->getIterator()); 78 while (contains(NextMBB)) { 79 BotMBB = NextMBB; 80 if (BotMBB == &*std::next(BotMBB->getIterator())) 81 break; 82 NextMBB = &*std::next(BotMBB->getIterator()); 83 } 84 } 85 return BotMBB; 86 } 87 88 MachineBasicBlock *MachineLoop::findLoopControlBlock() { 89 if (MachineBasicBlock *Latch = getLoopLatch()) { 90 if (isLoopExiting(Latch)) 91 return Latch; 92 else 93 return getExitingBlock(); 94 } 95 return nullptr; 96 } 97 98 DebugLoc MachineLoop::getStartLoc() const { 99 // Try the pre-header first. 100 if (MachineBasicBlock *PHeadMBB = getLoopPreheader()) 101 if (const BasicBlock *PHeadBB = PHeadMBB->getBasicBlock()) 102 if (DebugLoc DL = PHeadBB->getTerminator()->getDebugLoc()) 103 return DL; 104 105 // If we have no pre-header or there are no instructions with debug 106 // info in it, try the header. 107 if (MachineBasicBlock *HeadMBB = getHeader()) 108 if (const BasicBlock *HeadBB = HeadMBB->getBasicBlock()) 109 return HeadBB->getTerminator()->getDebugLoc(); 110 111 return DebugLoc(); 112 } 113 114 bool MachineLoop::hasStaticProfInfo() const { 115 return llvm::any_of(blocks(), [](const MachineBasicBlock *MBB){ 116 const BasicBlock *BB = MBB->getBasicBlock(); 117 return BB && BB->getTerminator()->hasMetadata(LLVMContext::MD_prof); 118 }); 119 } 120 121 MachineBasicBlock * 122 MachineLoopInfo::findLoopPreheader(MachineLoop *L, 123 bool SpeculativePreheader) const { 124 if (MachineBasicBlock *PB = L->getLoopPreheader()) 125 return PB; 126 127 if (!SpeculativePreheader) 128 return nullptr; 129 130 MachineBasicBlock *HB = L->getHeader(), *LB = L->getLoopLatch(); 131 if (HB->pred_size() != 2 || HB->hasAddressTaken()) 132 return nullptr; 133 // Find the predecessor of the header that is not the latch block. 134 MachineBasicBlock *Preheader = nullptr; 135 for (MachineBasicBlock *P : HB->predecessors()) { 136 if (P == LB) 137 continue; 138 // Sanity. 139 if (Preheader) 140 return nullptr; 141 Preheader = P; 142 } 143 144 // Check if the preheader candidate is a successor of any other loop 145 // headers. We want to avoid having two loop setups in the same block. 146 for (MachineBasicBlock *S : Preheader->successors()) { 147 if (S == HB) 148 continue; 149 MachineLoop *T = getLoopFor(S); 150 if (T && T->getHeader() == S) 151 return nullptr; 152 } 153 return Preheader; 154 } 155 156 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 157 LLVM_DUMP_METHOD void MachineLoop::dump() const { 158 print(dbgs()); 159 } 160 #endif 161