lib/VMCore/Dominators.cpp

   1 //===- Dominators.cpp - 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.  Postdominators are available in libanalysis, but are not
  12 // included in libvmcore, because it's not needed.  Forward dominators are
  13 // needed to support the Verifier pass.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #include "llvm/Analysis/Dominators.h"
  18 #include "llvm/Support/CFG.h"
  19 #include "llvm/Support/Compiler.h"
  20 #include "llvm/Support/Debug.h"
  21 #include "llvm/ADT/DepthFirstIterator.h"
  22 #include "llvm/ADT/SetOperations.h"
  23 #include "llvm/ADT/SmallPtrSet.h"
  24 #include "llvm/ADT/SmallVector.h"
  25 #include "llvm/Analysis/DominatorInternals.h"
  26 #include "llvm/Instructions.h"
  27 #include "llvm/Support/raw_ostream.h"
  28 #include "llvm/Support/CommandLine.h"
  29 #include <algorithm>
  30 using namespace llvm;
  31
  32 // Always verify dominfo if expensive checking is enabled.
  33 #ifdef XDEBUG
  34 static bool VerifyDomInfo = true;
  35 #else
  36 static bool VerifyDomInfo = false;
  37 #endif
  38 static cl::opt<bool,true>
  39 VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo),
  40                cl::desc("Verify dominator info (time consuming)"));
  41
  42 //===----------------------------------------------------------------------===//
  43 //  DominatorTree Implementation
  44 //===----------------------------------------------------------------------===//
  45 //
  46 // Provide public access to DominatorTree information.  Implementation details
  47 // can be found in DominatorCalculation.h.
  48 //
  49 //===----------------------------------------------------------------------===//
  50
  51 TEMPLATE_INSTANTIATION(class llvm::DomTreeNodeBase<BasicBlock>);
  52 TEMPLATE_INSTANTIATION(class llvm::DominatorTreeBase<BasicBlock>);
  53
  54 char DominatorTree::ID = 0;
  55 INITIALIZE_PASS(DominatorTree, "domtree",
  56                 "Dominator Tree Construction", true, true)
  57
  58 bool DominatorTree::runOnFunction(Function &F) {
  59   DT->recalculate(F);
  60   return false;
  61 }
  62
  63 void DominatorTree::verifyAnalysis() const {
  64   if (!VerifyDomInfo) return;
  65
  66   Function &F = *getRoot()->getParent();
  67
  68   DominatorTree OtherDT;
  69   OtherDT.getBase().recalculate(F);
  70   assert(!compare(OtherDT) && "Invalid DominatorTree info!");
  71 }
  72
  73 void DominatorTree::print(raw_ostream &OS, const Module *) const {
  74   DT->print(OS);
  75 }
  76
  77 // dominates - Return true if A dominates a use in B. This performs the
  78 // special checks necessary if A and B are in the same basic block.
  79 bool DominatorTree::dominates(const Instruction *A, const Instruction *B) const{
  80   const BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
  81
  82   // If A is an invoke instruction, its value is only available in this normal
  83   // successor block.
  84   if (const InvokeInst *II = dyn_cast<InvokeInst>(A))
  85     BBA = II->getNormalDest();
  86
  87   if (BBA != BBB) return dominates(BBA, BBB);
  88
  89   // It is not possible to determine dominance between two PHI nodes
  90   // based on their ordering.
  91   if (isa<PHINode>(A) && isa<PHINode>(B))
  92     return false;
  93
  94   // Loop through the basic block until we find A or B.
  95   BasicBlock::const_iterator I = BBA->begin();
  96   for (; &*I != A && &*I != B; ++I)
  97     /*empty*/;
  98
  99   return &*I == A;
 100 }
 101
 102
 103
 104 //===----------------------------------------------------------------------===//
 105 //  DominanceFrontier Implementation
 106 //===----------------------------------------------------------------------===//
 107
 108 char DominanceFrontier::ID = 0;
 109 INITIALIZE_PASS_BEGIN(DominanceFrontier, "domfrontier",
 110                 "Dominance Frontier Construction", true, true)
 111 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
 112 INITIALIZE_PASS_END(DominanceFrontier, "domfrontier",
 113                 "Dominance Frontier Construction", true, true)
 114
 115 void DominanceFrontier::verifyAnalysis() const {
 116   if (!VerifyDomInfo) return;
 117
 118   DominatorTree &DT = getAnalysis<DominatorTree>();
 119
 120   DominanceFrontier OtherDF;
 121   const std::vector<BasicBlock*> &DTRoots = DT.getRoots();
 122   OtherDF.calculate(DT, DT.getNode(DTRoots[0]));
 123   assert(!compare(OtherDF) && "Invalid DominanceFrontier info!");
 124 }
 125
 126 // NewBB is split and now it has one successor. Update dominance frontier to
 127 // reflect this change.
 128 void DominanceFrontier::splitBlock(BasicBlock *NewBB) {
 129   assert(NewBB->getTerminator()->getNumSuccessors() == 1 &&
 130          "NewBB should have a single successor!");
 131   BasicBlock *NewBBSucc = NewBB->getTerminator()->getSuccessor(0);
 132
 133   // NewBBSucc inherits original NewBB frontier.
 134   DominanceFrontier::iterator NewBBI = find(NewBB);
 135   if (NewBBI != end())
 136     addBasicBlock(NewBBSucc, NewBBI->second);
 137
 138   // If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
 139   // DF(NewBBSucc) without the stuff that the new block does not dominate
 140   // a predecessor of.
 141   DominatorTree &DT = getAnalysis<DominatorTree>();
 142   DomTreeNode *NewBBNode = DT.getNode(NewBB);
 143   DomTreeNode *NewBBSuccNode = DT.getNode(NewBBSucc);
 144   if (DT.dominates(NewBBNode, NewBBSuccNode)) {
 145     DominanceFrontier::iterator DFI = find(NewBBSucc);
 146     if (DFI != end()) {
 147       DominanceFrontier::DomSetType Set = DFI->second;
 148       // Filter out stuff in Set that we do not dominate a predecessor of.
 149       for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
 150              E = Set.end(); SetI != E;) {
 151         bool DominatesPred = false;
 152         for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
 153              PI != E; ++PI)
 154           if (DT.dominates(NewBBNode, DT.getNode(*PI))) {
 155             DominatesPred = true;
 156             break;
 157           }
 158         if (!DominatesPred)
 159           Set.erase(SetI++);
 160         else
 161           ++SetI;
 162       }
 163
 164       if (NewBBI != end()) {
 165         for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
 166                E = Set.end(); SetI != E; ++SetI) {
 167           BasicBlock *SB = *SetI;
 168           addToFrontier(NewBBI, SB);
 169         }
 170       } else
 171         addBasicBlock(NewBB, Set);
 172     }
 173
 174   } else {
 175     // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
 176     // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
 177     // NewBBSucc)).  NewBBSucc is the single successor of NewBB.
 178     DominanceFrontier::DomSetType NewDFSet;
 179     NewDFSet.insert(NewBBSucc);
 180     addBasicBlock(NewBB, NewDFSet);
 181   }
 182
 183   // Now update dominance frontiers which either used to contain NewBBSucc
 184   // or which now need to include NewBB.
 185
 186   // Collect the set of blocks which dominate a predecessor of NewBB or
 187   // NewSuccBB and which don't dominate both. This is an initial
 188   // approximation of the blocks whose dominance frontiers will need updates.
 189   SmallVector<DomTreeNode *, 16> AllPredDoms;
 190
 191   // Compute the block which dominates both NewBBSucc and NewBB. This is
 192   // the immediate dominator of NewBBSucc unless NewBB dominates NewBBSucc.
 193   // The code below which climbs dominator trees will stop at this point,
 194   // because from this point up, dominance frontiers are unaffected.
 195   DomTreeNode *DominatesBoth = 0;
 196   if (NewBBSuccNode) {
 197     DominatesBoth = NewBBSuccNode->getIDom();
 198     if (DominatesBoth == NewBBNode)
 199       DominatesBoth = NewBBNode->getIDom();
 200   }
 201
 202   // Collect the set of all blocks which dominate a predecessor of NewBB.
 203   SmallPtrSet<DomTreeNode *, 8> NewBBPredDoms;
 204   for (pred_iterator PI = pred_begin(NewBB), E = pred_end(NewBB); PI != E; ++PI)
 205     for (DomTreeNode *DTN = DT.getNode(*PI); DTN; DTN = DTN->getIDom()) {
 206       if (DTN == DominatesBoth)
 207         break;
 208       if (!NewBBPredDoms.insert(DTN))
 209         break;
 210       AllPredDoms.push_back(DTN);
 211     }
 212
 213   // Collect the set of all blocks which dominate a predecessor of NewSuccBB.
 214   SmallPtrSet<DomTreeNode *, 8> NewBBSuccPredDoms;
 215   for (pred_iterator PI = pred_begin(NewBBSucc),
 216        E = pred_end(NewBBSucc); PI != E; ++PI)
 217     for (DomTreeNode *DTN = DT.getNode(*PI); DTN; DTN = DTN->getIDom()) {
 218       if (DTN == DominatesBoth)
 219         break;
 220       if (!NewBBSuccPredDoms.insert(DTN))
 221         break;
 222       if (!NewBBPredDoms.count(DTN))
 223         AllPredDoms.push_back(DTN);
 224     }
 225
 226   // Visit all relevant dominance frontiers and make any needed updates.
 227   for (SmallVectorImpl<DomTreeNode *>::const_iterator I = AllPredDoms.begin(),
 228        E = AllPredDoms.end(); I != E; ++I) {
 229     DomTreeNode *DTN = *I;
 230     iterator DFI = find((*I)->getBlock());
 231
 232     // Only consider nodes that have NewBBSucc in their dominator frontier.
 233     if (DFI == end() || !DFI->second.count(NewBBSucc)) continue;
 234
 235     // If the block dominates a predecessor of NewBB but does not properly
 236     // dominate NewBB itself, add NewBB to its dominance frontier.
 237     if (NewBBPredDoms.count(DTN) &&
 238         !DT.properlyDominates(DTN, NewBBNode))
 239       addToFrontier(DFI, NewBB);
 240
 241     // If the block does not dominate a predecessor of NewBBSucc or
 242     // properly dominates NewBBSucc itself, remove NewBBSucc from its
 243     // dominance frontier.
 244     if (!NewBBSuccPredDoms.count(DTN) ||
 245         DT.properlyDominates(DTN, NewBBSuccNode))
 246       removeFromFrontier(DFI, NewBBSucc);
 247   }
 248 }
 249
 250 namespace {
 251   class DFCalculateWorkObject {
 252   public:
 253     DFCalculateWorkObject(BasicBlock *B, BasicBlock *P,
 254                           const DomTreeNode *N,
 255                           const DomTreeNode *PN)
 256     : currentBB(B), parentBB(P), Node(N), parentNode(PN) {}
 257     BasicBlock *currentBB;
 258     BasicBlock *parentBB;
 259     const DomTreeNode *Node;
 260     const DomTreeNode *parentNode;
 261   };
 262 }
 263
 264 const DominanceFrontier::DomSetType &
 265 DominanceFrontier::calculate(const DominatorTree &DT,
 266                              const DomTreeNode *Node) {
 267   BasicBlock *BB = Node->getBlock();
 268   DomSetType *Result = NULL;
 269
 270   std::vector<DFCalculateWorkObject> workList;
 271   SmallPtrSet<BasicBlock *, 32> visited;
 272
 273   workList.push_back(DFCalculateWorkObject(BB, NULL, Node, NULL));
 274   do {
 275     DFCalculateWorkObject *currentW = &workList.back();
 276     assert (currentW && "Missing work object.");
 277
 278     BasicBlock *currentBB = currentW->currentBB;
 279     BasicBlock *parentBB = currentW->parentBB;
 280     const DomTreeNode *currentNode = currentW->Node;
 281     const DomTreeNode *parentNode = currentW->parentNode;
 282     assert (currentBB && "Invalid work object. Missing current Basic Block");
 283     assert (currentNode && "Invalid work object. Missing current Node");
 284     DomSetType &S = Frontiers[currentBB];
 285
 286     // Visit each block only once.
 287     if (visited.count(currentBB) == 0) {
 288       visited.insert(currentBB);
 289
 290       // Loop over CFG successors to calculate DFlocal[currentNode]
 291       for (succ_iterator SI = succ_begin(currentBB), SE = succ_end(currentBB);
 292            SI != SE; ++SI) {
 293         // Does Node immediately dominate this successor?
 294         if (DT[*SI]->getIDom() != currentNode)
 295           S.insert(*SI);
 296       }
 297     }
 298
 299     // At this point, S is DFlocal.  Now we union in DFup's of our children...
 300     // Loop through and visit the nodes that Node immediately dominates (Node's
 301     // children in the IDomTree)
 302     bool visitChild = false;
 303     for (DomTreeNode::const_iterator NI = currentNode->begin(),
 304            NE = currentNode->end(); NI != NE; ++NI) {
 305       DomTreeNode *IDominee = *NI;
 306       BasicBlock *childBB = IDominee->getBlock();
 307       if (visited.count(childBB) == 0) {
 308         workList.push_back(DFCalculateWorkObject(childBB, currentBB,
 309                                                  IDominee, currentNode));
 310         visitChild = true;
 311       }
 312     }
 313
 314     // If all children are visited or there is any child then pop this block
 315     // from the workList.
 316     if (!visitChild) {
 317
 318       if (!parentBB) {
 319         Result = &S;
 320         break;
 321       }
 322
 323       DomSetType::const_iterator CDFI = S.begin(), CDFE = S.end();
 324       DomSetType &parentSet = Frontiers[parentBB];
 325       for (; CDFI != CDFE; ++CDFI) {
 326         if (!DT.properlyDominates(parentNode, DT[*CDFI]))
 327           parentSet.insert(*CDFI);
 328       }
 329       workList.pop_back();
 330     }
 331
 332   } while (!workList.empty());
 333
 334   return *Result;
 335 }
 336
 337 void DominanceFrontierBase::print(raw_ostream &OS, const Module* ) const {
 338   for (const_iterator I = begin(), E = end(); I != E; ++I) {
 339     OS << "  DomFrontier for BB ";
 340     if (I->first)
 341       WriteAsOperand(OS, I->first, false);
 342     else
 343       OS << " <<exit node>>";
 344     OS << " is:\t";
 345
 346     const std::set<BasicBlock*> &BBs = I->second;
 347
 348     for (std::set<BasicBlock*>::const_iterator I = BBs.begin(), E = BBs.end();
 349          I != E; ++I) {
 350       OS << ' ';
 351       if (*I)
 352         WriteAsOperand(OS, *I, false);
 353       else
 354         OS << "<<exit node>>";
 355     }
 356     OS << "\n";
 357   }
 358 }
 359
 360 void DominanceFrontierBase::dump() const {
 361   print(dbgs());
 362 }
 363