1 //===- MachineDominators.cpp - Machine Dominator Calculation --------------===// 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 implements simple dominator construction algorithms for finding 10 // forward dominators on machine functions. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/CodeGen/MachineDominators.h" 15 #include "llvm/ADT/SmallBitVector.h" 16 #include "llvm/CodeGen/Passes.h" 17 #include "llvm/InitializePasses.h" 18 #include "llvm/Pass.h" 19 #include "llvm/PassRegistry.h" 20 #include "llvm/Support/CommandLine.h" 21 #include "llvm/Support/GenericDomTreeConstruction.h" 22 23 using namespace llvm; 24 25 namespace llvm { 26 // Always verify dominfo if expensive checking is enabled. 27 #ifdef EXPENSIVE_CHECKS 28 bool VerifyMachineDomInfo = true; 29 #else 30 bool VerifyMachineDomInfo = false; 31 #endif 32 } // namespace llvm 33 34 static cl::opt<bool, true> VerifyMachineDomInfoX( 35 "verify-machine-dom-info", cl::location(VerifyMachineDomInfo), cl::Hidden, 36 cl::desc("Verify machine dominator info (time consuming)")); 37 38 namespace llvm { 39 template class DomTreeNodeBase<MachineBasicBlock>; 40 template class DominatorTreeBase<MachineBasicBlock, false>; // DomTreeBase 41 42 namespace DomTreeBuilder { 43 template void Calculate<MBBDomTree>(MBBDomTree &DT); 44 template void CalculateWithUpdates<MBBDomTree>(MBBDomTree &DT, MBBUpdates U); 45 46 template void InsertEdge<MBBDomTree>(MBBDomTree &DT, MachineBasicBlock *From, 47 MachineBasicBlock *To); 48 49 template void DeleteEdge<MBBDomTree>(MBBDomTree &DT, MachineBasicBlock *From, 50 MachineBasicBlock *To); 51 52 template void ApplyUpdates<MBBDomTree>(MBBDomTree &DT, MBBDomTreeGraphDiff &, 53 MBBDomTreeGraphDiff *); 54 55 template bool Verify<MBBDomTree>(const MBBDomTree &DT, 56 MBBDomTree::VerificationLevel VL); 57 } // namespace DomTreeBuilder 58 } 59 60 bool MachineDominatorTree::invalidate( 61 MachineFunction &, const PreservedAnalyses &PA, 62 MachineFunctionAnalysisManager::Invalidator &) { 63 // Check whether the analysis, all analyses on machine functions, or the 64 // machine function's CFG have been preserved. 65 auto PAC = PA.getChecker<MachineDominatorTreeAnalysis>(); 66 return !PAC.preserved() && 67 !PAC.preservedSet<AllAnalysesOn<MachineFunction>>() && 68 !PAC.preservedSet<CFGAnalyses>(); 69 } 70 71 AnalysisKey MachineDominatorTreeAnalysis::Key; 72 73 MachineDominatorTreeAnalysis::Result 74 MachineDominatorTreeAnalysis::run(MachineFunction &MF, 75 MachineFunctionAnalysisManager &) { 76 return MachineDominatorTree(MF); 77 } 78 79 PreservedAnalyses 80 MachineDominatorTreePrinterPass::run(MachineFunction &MF, 81 MachineFunctionAnalysisManager &MFAM) { 82 OS << "MachineDominatorTree for machine function: " << MF.getName() << '\n'; 83 MFAM.getResult<MachineDominatorTreeAnalysis>(MF).print(OS); 84 return PreservedAnalyses::all(); 85 } 86 87 char MachineDominatorTreeWrapperPass::ID = 0; 88 89 INITIALIZE_PASS(MachineDominatorTreeWrapperPass, "machinedomtree", 90 "MachineDominator Tree Construction", true, true) 91 92 MachineDominatorTreeWrapperPass::MachineDominatorTreeWrapperPass() 93 : MachineFunctionPass(ID) { 94 initializeMachineDominatorTreeWrapperPassPass( 95 *PassRegistry::getPassRegistry()); 96 } 97 98 void MachineDominatorTree::calculate(MachineFunction &F) { 99 CriticalEdgesToSplit.clear(); 100 NewBBs.clear(); 101 recalculate(F); 102 } 103 104 char &llvm::MachineDominatorsID = MachineDominatorTreeWrapperPass::ID; 105 106 bool MachineDominatorTreeWrapperPass::runOnMachineFunction(MachineFunction &F) { 107 DT = MachineDominatorTree(F); 108 return false; 109 } 110 111 void MachineDominatorTreeWrapperPass::releaseMemory() { DT.reset(); } 112 113 void MachineDominatorTreeWrapperPass::verifyAnalysis() const { 114 if (VerifyMachineDomInfo && DT) 115 if (!DT->verify(MachineDominatorTree::VerificationLevel::Basic)) 116 report_fatal_error("MachineDominatorTree verification failed!"); 117 } 118 119 void MachineDominatorTreeWrapperPass::print(raw_ostream &OS, 120 const Module *) const { 121 if (DT) 122 DT->print(OS); 123 } 124 125 void MachineDominatorTree::applySplitCriticalEdges() const { 126 // Bail out early if there is nothing to do. 127 if (CriticalEdgesToSplit.empty()) 128 return; 129 130 // For each element in CriticalEdgesToSplit, remember whether or not element 131 // is the new immediate domminator of its successor. The mapping is done by 132 // index, i.e., the information for the ith element of CriticalEdgesToSplit is 133 // the ith element of IsNewIDom. 134 SmallBitVector IsNewIDom(CriticalEdgesToSplit.size(), true); 135 size_t Idx = 0; 136 137 // Collect all the dominance properties info, before invalidating 138 // the underlying DT. 139 for (CriticalEdge &Edge : CriticalEdgesToSplit) { 140 // Update dominator information. 141 MachineBasicBlock *Succ = Edge.ToBB; 142 MachineDomTreeNode *SuccDTNode = Base::getNode(Succ); 143 144 for (MachineBasicBlock *PredBB : Succ->predecessors()) { 145 if (PredBB == Edge.NewBB) 146 continue; 147 // If we are in this situation: 148 // FromBB1 FromBB2 149 // + + 150 // + + + + 151 // + + + + 152 // ... Split1 Split2 ... 153 // + + 154 // + + 155 // + 156 // Succ 157 // Instead of checking the domiance property with Split2, we check it with 158 // FromBB2 since Split2 is still unknown of the underlying DT structure. 159 if (NewBBs.count(PredBB)) { 160 assert(PredBB->pred_size() == 1 && "A basic block resulting from a " 161 "critical edge split has more " 162 "than one predecessor!"); 163 PredBB = *PredBB->pred_begin(); 164 } 165 if (!Base::dominates(SuccDTNode, Base::getNode(PredBB))) { 166 IsNewIDom[Idx] = false; 167 break; 168 } 169 } 170 ++Idx; 171 } 172 173 // Now, update DT with the collected dominance properties info. 174 Idx = 0; 175 for (CriticalEdge &Edge : CriticalEdgesToSplit) { 176 // We know FromBB dominates NewBB. 177 MachineDomTreeNode *NewDTNode = 178 const_cast<MachineDominatorTree *>(this)->Base::addNewBlock( 179 Edge.NewBB, Edge.FromBB); 180 181 // If all the other predecessors of "Succ" are dominated by "Succ" itself 182 // then the new block is the new immediate dominator of "Succ". Otherwise, 183 // the new block doesn't dominate anything. 184 if (IsNewIDom[Idx]) 185 const_cast<MachineDominatorTree *>(this)->Base::changeImmediateDominator( 186 Base::getNode(Edge.ToBB), NewDTNode); 187 ++Idx; 188 } 189 NewBBs.clear(); 190 CriticalEdgesToSplit.clear(); 191 } 192