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/ADT/SmallBitVector.h" 17 #include "llvm/CodeGen/Passes.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.reset(new DominatorTreeBase<MachineBasicBlock>(false)); 53 DT->recalculate(F); 54 return false; 55 } 56 57 MachineDominatorTree::MachineDominatorTree() 58 : MachineFunctionPass(ID) { 59 initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry()); 60 } 61 62 void MachineDominatorTree::releaseMemory() { 63 CriticalEdgesToSplit.clear(); 64 DT.reset(nullptr); 65 } 66 67 void MachineDominatorTree::verifyAnalysis() const { 68 if (DT && VerifyMachineDomInfo) 69 verifyDomTree(); 70 } 71 72 void MachineDominatorTree::print(raw_ostream &OS, const Module*) const { 73 if (DT) 74 DT->print(OS); 75 } 76 77 void MachineDominatorTree::applySplitCriticalEdges() const { 78 // Bail out early if there is nothing to do. 79 if (CriticalEdgesToSplit.empty()) 80 return; 81 82 // For each element in CriticalEdgesToSplit, remember whether or not element 83 // is the new immediate domminator of its successor. The mapping is done by 84 // index, i.e., the information for the ith element of CriticalEdgesToSplit is 85 // the ith element of IsNewIDom. 86 SmallBitVector IsNewIDom(CriticalEdgesToSplit.size(), true); 87 size_t Idx = 0; 88 89 // Collect all the dominance properties info, before invalidating 90 // the underlying DT. 91 for (CriticalEdge &Edge : CriticalEdgesToSplit) { 92 // Update dominator information. 93 MachineBasicBlock *Succ = Edge.ToBB; 94 MachineDomTreeNode *SuccDTNode = DT->getNode(Succ); 95 96 for (MachineBasicBlock *PredBB : Succ->predecessors()) { 97 if (PredBB == Edge.NewBB) 98 continue; 99 // If we are in this situation: 100 // FromBB1 FromBB2 101 // + + 102 // + + + + 103 // + + + + 104 // ... Split1 Split2 ... 105 // + + 106 // + + 107 // + 108 // Succ 109 // Instead of checking the domiance property with Split2, we check it with 110 // FromBB2 since Split2 is still unknown of the underlying DT structure. 111 if (NewBBs.count(PredBB)) { 112 assert(PredBB->pred_size() == 1 && "A basic block resulting from a " 113 "critical edge split has more " 114 "than one predecessor!"); 115 PredBB = *PredBB->pred_begin(); 116 } 117 if (!DT->dominates(SuccDTNode, DT->getNode(PredBB))) { 118 IsNewIDom[Idx] = false; 119 break; 120 } 121 } 122 ++Idx; 123 } 124 125 // Now, update DT with the collected dominance properties info. 126 Idx = 0; 127 for (CriticalEdge &Edge : CriticalEdgesToSplit) { 128 // We know FromBB dominates NewBB. 129 MachineDomTreeNode *NewDTNode = DT->addNewBlock(Edge.NewBB, Edge.FromBB); 130 131 // If all the other predecessors of "Succ" are dominated by "Succ" itself 132 // then the new block is the new immediate dominator of "Succ". Otherwise, 133 // the new block doesn't dominate anything. 134 if (IsNewIDom[Idx]) 135 DT->changeImmediateDominator(DT->getNode(Edge.ToBB), NewDTNode); 136 ++Idx; 137 } 138 NewBBs.clear(); 139 CriticalEdgesToSplit.clear(); 140 } 141 142 void MachineDominatorTree::verifyDomTree() const { 143 if (!DT) 144 return; 145 MachineFunction &F = *getRoot()->getParent(); 146 147 DominatorTreeBase<MachineBasicBlock> OtherDT(false); 148 OtherDT.recalculate(F); 149 if (getRootNode()->getBlock() != OtherDT.getRootNode()->getBlock() || 150 DT->compare(OtherDT)) { 151 errs() << "MachineDominatorTree is not up to date!\nComputed:\n"; 152 DT->print(errs()); 153 errs() << "\nActual:\n"; 154 OtherDT.print(errs()); 155 abort(); 156 } 157 } 158