contrib/llvm/lib/CodeGen/MachineDominators.cpp

   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 }