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" 24using namespace llvm; 25 26// Explicitly instantiate methods in LoopInfoImpl.h for MI-level Loops. 27template class llvm::LoopBase<MachineBasicBlock, MachineLoop>; 28template class llvm::LoopInfoBase<MachineBasicBlock, MachineLoop>; 29 30char MachineLoopInfo::ID = 0; 31MachineLoopInfo::MachineLoopInfo() : MachineFunctionPass(ID) { 32 initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry()); 33} 34INITIALIZE_PASS_BEGIN(MachineLoopInfo, "machine-loops", 35 "Machine Natural Loop Construction", true, true) 36INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) 37INITIALIZE_PASS_END(MachineLoopInfo, "machine-loops", 38 "Machine Natural Loop Construction", true, true) 39 40char &llvm::MachineLoopInfoID = MachineLoopInfo::ID; 41 42bool MachineLoopInfo::runOnMachineFunction(MachineFunction &) { 43 calculate(getAnalysis<MachineDominatorTree>()); 44 return false; 45} 46 47void MachineLoopInfo::calculate(MachineDominatorTree &MDT) { 48 releaseMemory(); 49 LI.analyze(MDT.getBase()); 50} 51 52void MachineLoopInfo::getAnalysisUsage(AnalysisUsage &AU) const { 53 AU.setPreservesAll(); 54 AU.addRequired<MachineDominatorTree>(); 55 MachineFunctionPass::getAnalysisUsage(AU); 56} 57 58MachineBasicBlock *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 73MachineBasicBlock *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 88MachineBasicBlock *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 98DebugLoc 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 114MachineBasicBlock * 115MachineLoopInfo::findLoopPreheader(MachineLoop *L, 116 bool SpeculativePreheader) const { 117 if (MachineBasicBlock *PB = L->getLoopPreheader()) 118 return PB; 119 120 if (!SpeculativePreheader) 121 return nullptr; 122 123 MachineBasicBlock *HB = L->getHeader(), *LB = L->getLoopLatch(); 124 if (HB->pred_size() != 2 || HB->hasAddressTaken()) 125 return nullptr; 126 // Find the predecessor of the header that is not the latch block. 127 MachineBasicBlock *Preheader = nullptr; 128 for (MachineBasicBlock *P : HB->predecessors()) { 129 if (P == LB) 130 continue; 131 // Sanity. 132 if (Preheader) 133 return nullptr; 134 Preheader = P; 135 } 136 137 // Check if the preheader candidate is a successor of any other loop 138 // headers. We want to avoid having two loop setups in the same block. 139 for (MachineBasicBlock *S : Preheader->successors()) { 140 if (S == HB) 141 continue; 142 MachineLoop *T = getLoopFor(S); 143 if (T && T->getHeader() == S) 144 return nullptr; 145 } 146 return Preheader; 147} 148 149#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 150LLVM_DUMP_METHOD void MachineLoop::dump() const { 151 print(dbgs()); 152} 153#endif 154