C++ DomTreeNode类代码示例

void TempScopInfo::buildCondition(BasicBlock *BB, BasicBlock *RegionEntry) {
  BBCond Cond;

  DomTreeNode *BBNode = DT->getNode(BB), *EntryNode = DT->getNode(RegionEntry);
  assert(BBNode && EntryNode && "Get null node while building condition!");

  // Walk up the dominance tree until reaching the entry node. Add all
  // conditions on the path to BB except if BB postdominates the block
  // containing the condition.
  while (BBNode != EntryNode) {
    BasicBlock *CurBB = BBNode->getBlock();
    BBNode = BBNode->getIDom();
    assert(BBNode && "BBNode should not reach the root node!");

    if (PDT->dominates(CurBB, BBNode->getBlock()))
      continue;

    BranchInst *Br = dyn_cast<BranchInst>(BBNode->getBlock()->getTerminator());
    assert(Br && "A Valid Scop should only contain branch instruction");

    if (Br->isUnconditional())
      continue;

    // Is BB on the ELSE side of the branch?
    bool inverted = DT->dominates(Br->getSuccessor(1), BB);

    Comparison *Cmp;
    buildAffineCondition(*(Br->getCondition()), inverted, &Cmp);
    Cond.push_back(*Cmp);
  }

  if (!Cond.empty())
    BBConds[BB] = Cond;
}

/*update the dominator tree when a new block is created*/
void updateDT(BasicBlock *oldB, BasicBlock *newB, DominatorTree *DT) {
  errs() << "\n -----------------------" << oldB->getName()
         << "\n  dominated by  \n"
         << newB->getName() << "\n";

  DomTreeNode *OldNode = DT->getNode(oldB);
  if (OldNode) {
    std::vector<DomTreeNode *> Children;
    for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end(); I != E;
         ++I)
      Children.push_back(*I);

    DomTreeNode *inDT = DT->getNode(newB);
    DomTreeNode *NewNode;

    if (inDT == 0)
      NewNode = DT->addNewBlock(newB, oldB);
    else
      NewNode = DT->getNode(newB);

    for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
                                              E = Children.end();
         I != E; ++I)
      DT->changeImmediateDominator(*I, NewNode);
  }
}

SILValue
StackAllocationPromoter::getLiveOutValue(BlockSet &PhiBlocks,
                                         SILBasicBlock *StartBB) {
  DEBUG(llvm::dbgs() << "*** Searching for a value definition.\n");
  // Walk the Dom tree in search of a defining value:
  for (DomTreeNode *Node = DT->getNode(StartBB); Node; Node = Node->getIDom()) {
    SILBasicBlock *BB = Node->getBlock();

    // If there is a store (that must come after the phi), use its value.
    BlockToInstMap::iterator it = LastStoreInBlock.find(BB);
    if (it != LastStoreInBlock.end())
      if (auto *St = dyn_cast_or_null<StoreInst>(it->second)) {
        DEBUG(llvm::dbgs() << "*** Found Store def " << *St->getSrc());
        return St->getSrc();
      }

    // If there is a Phi definition in this block:
    if (PhiBlocks.count(BB)) {
      // Return the dummy instruction that represents the new value that we will
      // add to the basic block.
      SILValue Phi = BB->getArgument(BB->getNumArguments() - 1);
      DEBUG(llvm::dbgs() << "*** Found a dummy Phi def " << *Phi);
      return Phi;
    }

    // Move to the next dominating block.
    DEBUG(llvm::dbgs() << "*** Walking up the iDOM.\n");
  }
  DEBUG(llvm::dbgs() << "*** Could not find a Def. Using Undef.\n");
  return SILUndef::get(ASI->getElementType(), ASI->getModule());
}

/// SinkInstruction - Determine whether it is safe to sink the specified machine
/// instruction out of its current block into a successor.
bool Sinking::SinkInstruction(Instruction *Inst,
                              SmallPtrSetImpl<Instruction *> &Stores) {

  // Don't sink static alloca instructions.  CodeGen assumes allocas outside the
  // entry block are dynamically sized stack objects.
  if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
    if (AI->isStaticAlloca())
      return false;

  // Check if it's safe to move the instruction.
  if (!isSafeToMove(Inst, AA, Stores))
    return false;

  // FIXME: This should include support for sinking instructions within the
  // block they are currently in to shorten the live ranges.  We often get
  // instructions sunk into the top of a large block, but it would be better to
  // also sink them down before their first use in the block.  This xform has to
  // be careful not to *increase* register pressure though, e.g. sinking
  // "x = y + z" down if it kills y and z would increase the live ranges of y
  // and z and only shrink the live range of x.

  // SuccToSinkTo - This is the successor to sink this instruction to, once we
  // decide.
  BasicBlock *SuccToSinkTo = nullptr;

  // Instructions can only be sunk if all their uses are in blocks
  // dominated by one of the successors.
  // Look at all the postdominators and see if we can sink it in one.
  DomTreeNode *DTN = DT->getNode(Inst->getParent());
  for (DomTreeNode::iterator I = DTN->begin(), E = DTN->end();
      I != E && SuccToSinkTo == nullptr; ++I) {
    BasicBlock *Candidate = (*I)->getBlock();
    if ((*I)->getIDom()->getBlock() == Inst->getParent() &&
        IsAcceptableTarget(Inst, Candidate))
      SuccToSinkTo = Candidate;
  }

  // If no suitable postdominator was found, look at all the successors and
  // decide which one we should sink to, if any.
  for (succ_iterator I = succ_begin(Inst->getParent()),
      E = succ_end(Inst->getParent()); I != E && !SuccToSinkTo; ++I) {
    if (IsAcceptableTarget(Inst, *I))
      SuccToSinkTo = *I;
  }

  // If we couldn't find a block to sink to, ignore this instruction.
  if (!SuccToSinkTo)
    return false;

  DEBUG(dbgs() << "Sink" << *Inst << " (";
        Inst->getParent()->printAsOperand(dbgs(), false);
        dbgs() << " -> ";
        SuccToSinkTo->printAsOperand(dbgs(), false);
        dbgs() << ")\n");

  // Move the instruction.
  Inst->moveBefore(SuccToSinkTo->getFirstInsertionPt());
  return true;
}

bool OrderedInstructions::dfsBefore(const Instruction *InstA,
                                    const Instruction *InstB) const {
  // Use ordered basic block in case the 2 instructions are in the same basic
  // block.
  if (InstA->getParent() == InstB->getParent())
    return localDominates(InstA, InstB);

  DomTreeNode *DA = DT->getNode(InstA->getParent());
  DomTreeNode *DB = DT->getNode(InstB->getParent());
  return DA->getDFSNumIn() < DB->getDFSNumIn();
}

/// Optimize placement of initializer calls given a list of calls to the
/// same initializer. All original initialization points must be dominated by
/// the final initialization calls.
///
/// The current heuristic hoists all initialization points within a function to
/// a single dominating call in the outer loop preheader.
void SILGlobalOpt::placeInitializers(SILFunction *InitF,
                                     ArrayRef<ApplyInst *> Calls) {
  LLVM_DEBUG(llvm::dbgs() << "GlobalOpt: calls to "
             << Demangle::demangleSymbolAsString(InitF->getName())
             << " : " << Calls.size() << "\n");
  // Map each initializer-containing function to its final initializer call.
  llvm::DenseMap<SILFunction *, ApplyInst *> ParentFuncs;
  for (auto *AI : Calls) {
    assert(AI->getNumArguments() == 0 && "ill-formed global init call");
    assert(cast<FunctionRefInst>(AI->getCallee())->getReferencedFunction()
           == InitF && "wrong init call");
    SILFunction *ParentF = AI->getFunction();
    DominanceInfo *DT = DA->get(ParentF);
    ApplyInst *HoistAI =
        getHoistedApplyForInitializer(AI, DT, InitF, ParentF, ParentFuncs);

    // If we were unable to find anything, just go onto the next apply.
    if (!HoistAI) {
      continue;
    }

    // Otherwise, move this call to the outermost loop preheader.
    SILBasicBlock *BB = HoistAI->getParent();
    typedef llvm::DomTreeNodeBase<SILBasicBlock> DomTreeNode;
    DomTreeNode *Node = DT->getNode(BB);
    while (Node) {
      SILBasicBlock *DomParentBB = Node->getBlock();
      if (isAvailabilityCheck(DomParentBB)) {
        LLVM_DEBUG(llvm::dbgs() << "  don't hoist above availability check "
                                   "at bb"
                                << DomParentBB->getDebugID() << "\n");
        break;
      }
      BB = DomParentBB;
      if (!isInLoop(BB))
        break;
      Node = Node->getIDom();
    }

    if (BB == HoistAI->getParent()) {
      // BB is either unreachable or not in a loop.
      LLVM_DEBUG(llvm::dbgs() << "  skipping (not in a loop): " << *HoistAI
                              << "  in " << HoistAI->getFunction()->getName()
                              << "\n");
      continue;
    }

    LLVM_DEBUG(llvm::dbgs() << "  hoisting: " << *HoistAI << "  in "
                       << HoistAI->getFunction()->getName() << "\n");
    HoistAI->moveBefore(&*BB->begin());
    placeFuncRef(HoistAI, DT);
    HasChanged = true;
  }
}

/**
 * removeUndefBranches -- remove branches with undef condition
 *
 * These are irrelevant to the code, so may be removed completely with their
 * bodies.
 */
void FunctionStaticSlicer::removeUndefBranches(ModulePass *MP, Function &F) {
#ifdef DEBUG_SLICE
  errs() << __func__ << " ============ Removing unused branches\n";
#endif
  PostDominatorTree &PDT = MP->getAnalysis<PostDominatorTree>(F);
  typedef llvm::SmallVector<const BasicBlock *, 10> Unsafe;
  Unsafe unsafe;

  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
    BasicBlock &bb = *I;
    if (std::distance(succ_begin(&bb), succ_end(&bb)) <= 1)
      continue;
    Instruction &back = bb.back();
    if (back.getOpcode() != Instruction::Br &&
        back.getOpcode() != Instruction::Switch)
      continue;
    const Value *cond = back.getOperand(0);
    if (cond->getValueID() != Value::UndefValueVal)
      continue;
    DomTreeNode *node = PDT.getNode(&bb);
    if (!node) /* this bb is unreachable */
      continue;
    DomTreeNode *idom = node->getIDom();
    assert(idom);
/*    if (!idom)
      continue;*/
    BasicBlock *dest = idom->getBlock();
    if (!dest) /* TODO when there are nodes with noreturn calls */
      continue;
#ifdef DEBUG_SLICE
    errs() << "  considering branch: " << bb.getName() << '\n';
    errs() << "  dest=" << dest->getName() << "\n";
#endif
    if (PHINode *PHI = dyn_cast<PHINode>(&dest->front()))
      if (PHI->getBasicBlockIndex(&bb) == -1) {
        /* TODO this is unsafe! */
        unsafe.push_back(&bb);
        PHI->addIncoming(Constant::getNullValue(PHI->getType()), &bb);
    }
    BasicBlock::iterator ii(back);
    Instruction *newI = BranchInst::Create(dest);
    ReplaceInstWithInst(bb.getInstList(), ii, newI);
  }
  for (Unsafe::const_iterator I = unsafe.begin(), E = unsafe.end();
       I != E; ++I) {
    const BasicBlock *bb = *I;
    if (std::distance(pred_begin(bb), pred_end(bb)) > 1)
      errs() << "WARNING: PHI node with added value which is zero\n";
  }
#ifdef DEBUG_SLICE
  errs() << __func__ << " ============ END\n";
#endif
}

/// Compute the dominator tree levels for DT.
static void computeDomTreeLevels(DominanceInfo *DT,
                                 DomTreeLevelMap &DomTreeLevels) {
  // TODO: This should happen once per function.
  SmallVector<DomTreeNode *, 32> Worklist;
  DomTreeNode *Root = DT->getRootNode();
  DomTreeLevels[Root] = 0;
  Worklist.push_back(Root);
  while (!Worklist.empty()) {
    DomTreeNode *Node = Worklist.pop_back_val();
    unsigned ChildLevel = DomTreeLevels[Node] + 1;
    for (auto CI = Node->begin(), CE = Node->end(); CI != CE; ++CI) {
      DomTreeLevels[*CI] = ChildLevel;
      Worklist.push_back(*CI);
    }
  }
}

void CodeExtractor::splitReturnBlocks() {
  for (BasicBlock *Block : Blocks)
    if (ReturnInst *RI = dyn_cast<ReturnInst>(Block->getTerminator())) {
      BasicBlock *New =
          Block->splitBasicBlock(RI->getIterator(), Block->getName() + ".ret");
      if (DT) {
        // Old dominates New. New node dominates all other nodes dominated
        // by Old.
        DomTreeNode *OldNode = DT->getNode(Block);
        SmallVector<DomTreeNode *, 8> Children(OldNode->begin(),
                                               OldNode->end());

        DomTreeNode *NewNode = DT->addNewBlock(New, Block);

        for (DomTreeNode *I : Children)
          DT->changeImmediateDominator(I, NewNode);
      }
    }
}

void ControlDependenceGraphBase::computeDependencies(Function &F, PostDominatorTree &pdt) {
  root = new ControlDependenceNode();
  nodes.insert(root);

  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
    ControlDependenceNode *bn = new ControlDependenceNode(BB);
    nodes.insert(bn);
    bbMap[BB] = bn;
  }

  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
    BasicBlock *A = BB;
    ControlDependenceNode *AN = bbMap[A];

    for (succ_iterator succ = succ_begin(A), end = succ_end(A); succ != end; ++succ) {
      BasicBlock *B = *succ;
      assert(A && B);
      if (A == B || !pdt.dominates(B,A)) {
	BasicBlock *L = pdt.findNearestCommonDominator(A,B);
	ControlDependenceNode::EdgeType type = ControlDependenceGraphBase::getEdgeType(A,B);
	if (A == L) {
	  switch (type) {
	  case ControlDependenceNode::TRUE:
	    AN->addTrue(AN); break;
	  case ControlDependenceNode::FALSE:
	    AN->addFalse(AN); break;
	  case ControlDependenceNode::OTHER:
	    AN->addOther(AN); break;
	  }
	  AN->addParent(AN);
	}
	for (DomTreeNode *cur = pdt[B]; cur && cur != pdt[L]; cur = cur->getIDom()) {
	  ControlDependenceNode *CN = bbMap[cur->getBlock()];
	  switch (type) {
	  case ControlDependenceNode::TRUE:
	    AN->addTrue(CN); break;
	  case ControlDependenceNode::FALSE:
	    AN->addFalse(CN); break;
	  case ControlDependenceNode::OTHER:
	    AN->addOther(CN); break;
	  }
	  assert(CN);
	  CN->addParent(AN);
	}
      }
    }
  }

  // ENTRY -> START
  for (DomTreeNode *cur = pdt[&F.getEntryBlock()]; cur; cur = cur->getIDom()) {
    if (cur->getBlock()) {
      ControlDependenceNode *CN = bbMap[cur->getBlock()];
      assert(CN);
      root->addOther(CN); CN->addParent(root);
    }
  }
}

void GCPtrTracker::gatherDominatingDefs(const BasicBlock *BB,
                                        AvailableValueSet &Result,
                                        const DominatorTree &DT) {
  DomTreeNode *DTN = DT[const_cast<BasicBlock *>(BB)];

  while (DTN->getIDom()) {
    DTN = DTN->getIDom();
    const auto &Defs = BlockMap[DTN->getBlock()]->Contribution;
    Result.insert(Defs.begin(), Defs.end());
    // If this block is 'Cleared', then nothing LiveIn to this block can be
    // available after this block completes.  Note: This turns out to be
    // really important for reducing memory consuption of the initial available
    // sets and thus peak memory usage by this verifier.
    if (BlockMap[DTN->getBlock()]->Cleared)
      return;
  }

  for (const Argument &A : BB->getParent()->args())
    if (containsGCPtrType(A.getType()))
      Result.insert(&A);
}

/// \return true if the given block is dominated by a _slowPath branch hint.
///
/// Cache all blocks visited to avoid introducing quadratic behavior.
bool ColdBlockInfo::isCold(const SILBasicBlock *BB, int recursionDepth) {
  auto I = ColdBlockMap.find(BB);
  if (I != ColdBlockMap.end())
    return I->second;

  typedef llvm::DomTreeNodeBase<SILBasicBlock> DomTreeNode;
  DominanceInfo *DT = DA->get(const_cast<SILFunction*>(BB->getParent()));
  DomTreeNode *Node = DT->getNode(const_cast<SILBasicBlock*>(BB));
  // Always consider unreachable code cold.
  if (!Node)
    return true;

  std::vector<const SILBasicBlock*> DomChain;
  DomChain.push_back(BB);
  bool IsCold = false;
  Node = Node->getIDom();
  while (Node) {
    if (isSlowPath(Node->getBlock(), DomChain.back(), recursionDepth)) {
      IsCold = true;
      break;
    }
    auto I = ColdBlockMap.find(Node->getBlock());
    if (I != ColdBlockMap.end()) {
      IsCold = I->second;
      break;
    }
    DomChain.push_back(Node->getBlock());
    Node = Node->getIDom();
  }
  for (auto *ChainBB : DomChain)
    ColdBlockMap[ChainBB] = IsCold;
  return IsCold;
}

void RegionInfo::findRegionsWithEntry(BasicBlock *entry, BBtoBBMap *ShortCut) {
  assert(entry);

  DomTreeNode *N = PDT->getNode(entry);

  if (!N)
    return;

  Region *lastRegion= 0;
  BasicBlock *lastExit = entry;

  // As only a BasicBlock that postdominates entry can finish a region, walk the
  // post dominance tree upwards.
  while ((N = getNextPostDom(N, ShortCut))) {
    BasicBlock *exit = N->getBlock();

    if (!exit)
      break;

    if (isRegion(entry, exit)) {
      Region *newRegion = createRegion(entry, exit);

      if (lastRegion)
        newRegion->addSubRegion(lastRegion);

      lastRegion = newRegion;
      lastExit = exit;
    }

    // This can never be a region, so stop the search.
    if (!DT->dominates(entry, exit))
      break;
  }

  // Tried to create regions from entry to lastExit.  Next time take a
  // shortcut from entry to lastExit.
  if (lastExit != entry)
    insertShortCut(entry, lastExit, ShortCut);
}

void RegionExtractor::splitReturnBlocks() {
  for (SetVector<BasicBlock *>::iterator I = Blocks.begin(), E = Blocks.end();
       I != E; ++I)
    if (ReturnInst *RI = dyn_cast<ReturnInst>((*I)->getTerminator())) {
      BasicBlock *New = (*I)->splitBasicBlock(RI, (*I)->getName()+".ret");
      if (DT) {
        // Old dominates New. New node dominates all other nodes dominated
        // by Old.
        DomTreeNode *OldNode = DT->getNode(*I);
        SmallVector<DomTreeNode*, 8> Children;
        for (DomTreeNode::iterator DI = OldNode->begin(), DE = OldNode->end();
             DI != DE; ++DI)
          Children.push_back(*DI);

        DomTreeNode *NewNode = DT->addNewBlock(New, *I);
#if LLVM_VERSION_MINOR == 5
        for (SmallVectorImpl<DomTreeNode *>::iterator I = Children.begin(),
#else
        for (SmallVector<DomTreeNode *, 8>::iterator I = Children.begin(),
#endif
               E = Children.end(); I != E; ++I)
          DT->changeImmediateDominator(*I, NewNode);
      }
    }

const DominanceFrontier::DomSetType &
PostDominanceFrontier::calculate(const PostDominatorTree &DT,
                                 const DomTreeNode *Node) {
  // Loop over CFG successors to calculate DFlocal[Node]
  BasicBlock *BB = Node->getBlock();
  DomSetType &S = Frontiers[BB];       // The new set to fill in...
  if (getRoots().empty()) return S;

  if (BB)
    for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB);
         SI != SE; ++SI) {
      BasicBlock *P = *SI;
      // Does Node immediately dominate this predecessor?
      DomTreeNode *SINode = DT[P];
      if (SINode && SINode->getIDom() != Node)
        S.insert(P);
    }

  // At this point, S is DFlocal.  Now we union in DFup's of our children...
  // Loop through and visit the nodes that Node immediately dominates (Node's
  // children in the IDomTree)
  //
  for (DomTreeNode::const_iterator
         NI = Node->begin(), NE = Node->end(); NI != NE; ++NI) {
    DomTreeNode *IDominee = *NI;
    const DomSetType &ChildDF = calculate(DT, IDominee);

    DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
    for (; CDFI != CDFE; ++CDFI) {
      if (!DT.properlyDominates(Node, DT[*CDFI]))
        S.insert(*CDFI);
    }
  }

  return S;
}