C++ DominanceInfo::getNode方法代码示例

/// \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;
}

/// 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;
  }
}

/// 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) {
  DEBUG(llvm::dbgs() << "GlobalOpt: calls to "
        << demangle_wrappers::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);
    auto PFI = ParentFuncs.find(ParentF);
    ApplyInst *HoistAI = nullptr;
    if (PFI != ParentFuncs.end()) {
      // Found a replacement for this init call.
      // Ensure the replacement dominates the original call site.
      ApplyInst *CommonAI = PFI->second;
      assert(cast<FunctionRefInst>(CommonAI->getCallee())
             ->getReferencedFunction() == InitF &&
             "ill-formed global init call");
      SILBasicBlock *DomBB =
        DT->findNearestCommonDominator(AI->getParent(), CommonAI->getParent());
      
      // We must not move initializers around availability-checks.
      if (!isAvailabilityCheckOnDomPath(DomBB, CommonAI->getParent(), DT)) {
        if (DomBB != CommonAI->getParent()) {
          CommonAI->moveBefore(&*DomBB->begin());
          placeFuncRef(CommonAI, DT);
          
          // Try to hoist the existing AI again if we move it to another block,
          // e.g. from a loop exit into the loop.
          HoistAI = CommonAI;
        }
        AI->replaceAllUsesWith(CommonAI);
        AI->eraseFromParent();
        HasChanged = true;
      }
    } else {
      ParentFuncs[ParentF] = AI;
      
      // It's the first time we found a call to InitF in this function, so we
      // try to hoist it out of any loop.
      HoistAI = AI;
    }
    if (HoistAI) {
      // 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)) {
          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.
        DEBUG(llvm::dbgs() << "  skipping (not in a loop): " << *HoistAI
              << "  in " << HoistAI->getFunction()->getName() << "\n");
      }
      else {
        DEBUG(llvm::dbgs() << "  hoisting: " << *HoistAI
              << "  in " << HoistAI->getFunction()->getName() << "\n");
        HoistAI->moveBefore(&*BB->begin());
        placeFuncRef(HoistAI, DT);
        HasChanged = true;
      }
    }
  }
}

bool RCIdentityFunctionInfo::
findDominatingNonPayloadedEdge(SILBasicBlock *IncomingEdgeBB,
                               SILValue RCIdentity) {
  // First grab the NonPayloadedEnumBB and RCIdentityBB. If we cannot find
  // either of them, return false.
  SILBasicBlock *RCIdentityBB = RCIdentity->getParentBlock();
  if (!RCIdentityBB)
    return false;

  // Make sure that the incoming edge bb is not the RCIdentityBB. We are not
  // trying to handle this case here, so simplify by just bailing if we detect
  // it.
  //
  // I think the only way this can happen is if we have a switch_enum of some
  // sort with multiple incoming values going into the destination BB. We are
  // not interested in handling that case anyways.
  //
  // FIXME: If we ever split all critical edges, this should be relooked at.
  if (IncomingEdgeBB == RCIdentityBB)
    return false;

  // Now we know that RCIdentityBB and IncomingEdgeBB are different. Prove that
  // RCIdentityBB dominates IncomingEdgeBB.
  SILFunction *F = RCIdentityBB->getParent();

  // First make sure that IncomingEdgeBB dominates NonPayloadedEnumBB. If not,
  // return false.
  DominanceInfo *DI = DA->get(F);
  if (!DI->dominates(RCIdentityBB, IncomingEdgeBB))
    return false;

  // Now walk up the dominator tree from IncomingEdgeBB to RCIdentityBB and see
  // if we can find a use of RCIdentity that dominates IncomingEdgeBB and
  // enables us to know that RCIdentity must be a no-payload enum along
  // IncomingEdge. We don't care if the case or enum of RCIdentity match the
  // case or enum along RCIdentityBB since a pairing of retain, release of two
  // non-payloaded enums can always be eliminated (since we can always eliminate
  // ref count operations on non-payloaded enums).

  // RCIdentityBB must have a valid dominator tree node.
  auto *EndDomNode = DI->getNode(RCIdentityBB);
  if (!EndDomNode)
    return false;

  for (auto *Node = DI->getNode(IncomingEdgeBB); Node; Node = Node->getIDom()) {
    // Search for uses of RCIdentity in Node->getBlock() that will enable us to
    // know that it has a non-payloaded enum case.
    SILBasicBlock *DominatingBB = Node->getBlock();
    llvm::Optional<bool> Result =
        proveNonPayloadedEnumCase(DominatingBB, RCIdentity);

    // If we found either a signal of a payloaded or a non-payloaded enum,
    // return that value.
    if (Result.hasValue())
      return Result.getValue();

    // If we didn't reach RCIdentityBB, keep processing up the DomTree.
    if (DominatingBB != RCIdentityBB)
      continue;

    // Otherwise, we failed to find any interesting information, return false.
    return false;
  }

  return false;
}