1 //===- MachineLoopInfo.cpp - Natural Loop Calculator ----------------------===// 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 // the loops identified may actually be several natural loops that share the 13 // same header node... not just a single natural loop. 14 // 15 //===----------------------------------------------------------------------===// 16 17 #include "llvm/CodeGen/MachineLoopInfo.h" 18 #include "llvm/Analysis/LoopInfoImpl.h" 19 #include "llvm/CodeGen/MachineDominators.h" 20 #include "llvm/CodeGen/Passes.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 MachineBasicBlock * 91 MachineLoopInfo::findLoopPreheader(MachineLoop *L, 92 bool SpeculativePreheader) const { 93 if (MachineBasicBlock *PB = L->getLoopPreheader()) 94 return PB; 95 96 if (!SpeculativePreheader) 97 return nullptr; 98 99 MachineBasicBlock *HB = L->getHeader(), *LB = L->getLoopLatch(); 100 if (HB->pred_size() != 2 || HB->hasAddressTaken()) 101 return nullptr; 102 // Find the predecessor of the header that is not the latch block. 103 MachineBasicBlock *Preheader = nullptr; 104 for (MachineBasicBlock *P : HB->predecessors()) { 105 if (P == LB) 106 continue; 107 // Sanity. 108 if (Preheader) 109 return nullptr; 110 Preheader = P; 111 } 112 113 // Check if the preheader candidate is a successor of any other loop 114 // headers. We want to avoid having two loop setups in the same block. 115 for (MachineBasicBlock *S : Preheader->successors()) { 116 if (S == HB) 117 continue; 118 MachineLoop *T = getLoopFor(S); 119 if (T && T->getHeader() == S) 120 return nullptr; 121 } 122 return Preheader; 123 } 124 125 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 126 LLVM_DUMP_METHOD void MachineLoop::dump() const { 127 print(dbgs()); 128 } 129 #endif 130