1 //===- MachineDominators.cpp - Machine Dominator Calculation --------------===// 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 implements simple dominator construction algorithms for finding 11 // forward dominators on machine functions. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/CodeGen/MachineDominators.h" 16 #include "llvm/CodeGen/Passes.h" 17 #include "llvm/ADT/SmallBitVector.h" 18 #include "llvm/Support/CommandLine.h" 19 20 using namespace llvm; 21 22 // Always verify dominfo if expensive checking is enabled. 23 #ifdef EXPENSIVE_CHECKS 24 static bool VerifyMachineDomInfo = true; 25 #else 26 static bool VerifyMachineDomInfo = false; 27 #endif 28 static cl::opt<bool, true> VerifyMachineDomInfoX( 29 "verify-machine-dom-info", cl::location(VerifyMachineDomInfo), 30 cl::desc("Verify machine dominator info (time consuming)")); 31 32 namespace llvm { 33 template class DomTreeNodeBase<MachineBasicBlock>; 34 template class DominatorTreeBase<MachineBasicBlock>; 35 } 36 37 char MachineDominatorTree::ID = 0; 38 39 INITIALIZE_PASS(MachineDominatorTree, "machinedomtree", 40 "MachineDominator Tree Construction", true, true) 41 42 char &llvm::MachineDominatorsID = MachineDominatorTree::ID; 43 44 void MachineDominatorTree::getAnalysisUsage(AnalysisUsage &AU) const { 45 AU.setPreservesAll(); 46 MachineFunctionPass::getAnalysisUsage(AU); 47 } 48 49 bool MachineDominatorTree::runOnMachineFunction(MachineFunction &F) { 50 CriticalEdgesToSplit.clear(); 51 NewBBs.clear(); 52 DT->recalculate(F); 53 54 return false; 55 } 56 57 MachineDominatorTree::MachineDominatorTree() 58 : MachineFunctionPass(ID) { 59 initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry()); 60 DT = new DominatorTreeBase<MachineBasicBlock>(false); 61 } 62 63 MachineDominatorTree::~MachineDominatorTree() { 64 delete DT; 65 } 66 67 void MachineDominatorTree::releaseMemory() { 68 DT->releaseMemory(); 69 } 70 71 void MachineDominatorTree::verifyAnalysis() const { 72 if (VerifyMachineDomInfo) 73 verifyDomTree(); 74 } 75 76 void MachineDominatorTree::print(raw_ostream &OS, const Module*) const { 77 DT->print(OS); 78 } 79 80 void MachineDominatorTree::applySplitCriticalEdges() const { 81 // Bail out early if there is nothing to do. 82 if (CriticalEdgesToSplit.empty()) 83 return; 84 85 // For each element in CriticalEdgesToSplit, remember whether or not element 86 // is the new immediate domminator of its successor. The mapping is done by 87 // index, i.e., the information for the ith element of CriticalEdgesToSplit is 88 // the ith element of IsNewIDom. 89 SmallBitVector IsNewIDom(CriticalEdgesToSplit.size(), true); 90 size_t Idx = 0; 91 92 // Collect all the dominance properties info, before invalidating 93 // the underlying DT. 94 for (CriticalEdge &Edge : CriticalEdgesToSplit) { 95 // Update dominator information. 96 MachineBasicBlock *Succ = Edge.ToBB; 97 MachineDomTreeNode *SuccDTNode = DT->getNode(Succ); 98 99 for (MachineBasicBlock *PredBB : Succ->predecessors()) { 100 if (PredBB == Edge.NewBB) 101 continue; 102 // If we are in this situation: 103 // FromBB1 FromBB2 104 // + + 105 // + + + + 106 // + + + + 107 // ... Split1 Split2 ... 108 // + + 109 // + + 110 // + 111 // Succ 112 // Instead of checking the domiance property with Split2, we check it with 113 // FromBB2 since Split2 is still unknown of the underlying DT structure. 114 if (NewBBs.count(PredBB)) { 115 assert(PredBB->pred_size() == 1 && "A basic block resulting from a " 116 "critical edge split has more " 117 "than one predecessor!"); 118 PredBB = *PredBB->pred_begin(); 119 } 120 if (!DT->dominates(SuccDTNode, DT->getNode(PredBB))) { 121 IsNewIDom[Idx] = false; 122 break; 123 } 124 } 125 ++Idx; 126 } 127 128 // Now, update DT with the collected dominance properties info. 129 Idx = 0; 130 for (CriticalEdge &Edge : CriticalEdgesToSplit) { 131 // We know FromBB dominates NewBB. 132 MachineDomTreeNode *NewDTNode = DT->addNewBlock(Edge.NewBB, Edge.FromBB); 133 134 // If all the other predecessors of "Succ" are dominated by "Succ" itself 135 // then the new block is the new immediate dominator of "Succ". Otherwise, 136 // the new block doesn't dominate anything. 137 if (IsNewIDom[Idx]) 138 DT->changeImmediateDominator(DT->getNode(Edge.ToBB), NewDTNode); 139 ++Idx; 140 } 141 NewBBs.clear(); 142 CriticalEdgesToSplit.clear(); 143 } 144 145 void MachineDominatorTree::verifyDomTree() const { 146 MachineFunction &F = *getRoot()->getParent(); 147 148 MachineDominatorTree OtherDT; 149 OtherDT.DT->recalculate(F); 150 if (compare(OtherDT)) { 151 errs() << "MachineDominatorTree is not up to date!\nComputed:\n"; 152 print(errs(), nullptr); 153 errs() << "\nActual:\n"; 154 OtherDT.print(errs(), nullptr); 155 abort(); 156 } 157 } 158
