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 //===- CFGDiff.h - Define a CFG snapshot. -----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines specializations of GraphTraits that allows generic
 // algorithms to see a different snapshot of a CFG.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_CFGDIFF_H
 #define LLVM_SUPPORT_CFGDIFF_H
 
 #include "llvm/ADT/GraphTraits.h"
 #include "llvm/ADT/iterator.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/CFGUpdate.h"
 #include "llvm/Support/type_traits.h"
 #include <cassert>
 #include <cstddef>
 #include <iterator>
 
 // Two booleans are used to define orders in graphs:
 // InverseGraph defines when we need to reverse the whole graph and is as such
 // also equivalent to applying updates in reverse.
 // InverseEdge defines whether we want to change the edges direction. E.g., for
 // a non-inversed graph, the children are naturally the successors when
 // InverseEdge is false and the predecessors when InverseEdge is true.
 
 namespace llvm {
 
 namespace detail {
 template <typename Range>
 auto reverse_if_helper(Range &&R, std::integral_constant<bool, false>) {
   return std::forward<Range>(R);
 }
 
 template <typename Range>
 auto reverse_if_helper(Range &&R, std::integral_constant<bool, true>) {
   return llvm::reverse(std::forward<Range>(R));
 }
 
 template <bool B, typename Range> auto reverse_if(Range &&R) {
   return reverse_if_helper(std::forward<Range>(R),
                            std::integral_constant<bool, B>{});
 }
 } // namespace detail
 
 // GraphDiff defines a CFG snapshot: given a set of Update<NodePtr>, provides
 // a getChildren method to get a Node's children based on the additional updates
 // in the snapshot. The current diff treats the CFG as a graph rather than a
 // multigraph. Added edges are pruned to be unique, and deleted edges will
 // remove all existing edges between two blocks.
 template <typename NodePtr, bool InverseGraph = false> class GraphDiff {
   struct DeletesInserts {
     SmallVector<NodePtr, 2> DI[2];
   };
   using UpdateMapType = SmallDenseMap<NodePtr, DeletesInserts>;
   UpdateMapType Succ;
   UpdateMapType Pred;
 
   // By default, it is assumed that, given a CFG and a set of updates, we wish
   // to apply these updates as given. If UpdatedAreReverseApplied is set, the
   // updates will be applied in reverse: deleted edges are considered re-added
   // and inserted edges are considered deleted when returning children.
   bool UpdatedAreReverseApplied;
 
   // Keep the list of legalized updates for a deterministic order of updates
   // when using a GraphDiff for incremental updates in the DominatorTree.
   // The list is kept in reverse to allow popping from end.
   SmallVector<cfg::Update<NodePtr>, 4> LegalizedUpdates;
 
   void printMap(raw_ostream &OS, const UpdateMapType &M) const {
     StringRef DIText[2] = {"Delete", "Insert"};
     for (auto Pair : M) {
       for (unsigned IsInsert = 0; IsInsert <= 1; ++IsInsert) {
         OS << DIText[IsInsert] << " edges: \n";
         for (auto Child : Pair.second.DI[IsInsert]) {
           OS << "(";
           Pair.first->printAsOperand(OS, false);
           OS << ", ";
           Child->printAsOperand(OS, false);
           OS << ") ";
         }
       }
     }
     OS << "\n";
   }
 
 public:
   GraphDiff() : UpdatedAreReverseApplied(false) {}
   GraphDiff(ArrayRef<cfg::Update<NodePtr>> Updates,
             bool ReverseApplyUpdates = false) {
     cfg::LegalizeUpdates<NodePtr>(Updates, LegalizedUpdates, InverseGraph);
     for (auto U : LegalizedUpdates) {
       unsigned IsInsert =
           (U.getKind() == cfg::UpdateKind::Insert) == !ReverseApplyUpdates;
       Succ[U.getFrom()].DI[IsInsert].push_back(U.getTo());
       Pred[U.getTo()].DI[IsInsert].push_back(U.getFrom());
     }
     UpdatedAreReverseApplied = ReverseApplyUpdates;
   }
 
   auto getLegalizedUpdates() const {
     return make_range(LegalizedUpdates.begin(), LegalizedUpdates.end());
   }
 
   unsigned getNumLegalizedUpdates() const { return LegalizedUpdates.size(); }
 
   cfg::Update<NodePtr> popUpdateForIncrementalUpdates() {
     assert(!LegalizedUpdates.empty() && "No updates to apply!");
     auto U = LegalizedUpdates.pop_back_val();
     unsigned IsInsert =
         (U.getKind() == cfg::UpdateKind::Insert) == !UpdatedAreReverseApplied;
     auto &SuccDIList = Succ[U.getFrom()];
     auto &SuccList = SuccDIList.DI[IsInsert];
     assert(SuccList.back() == U.getTo());
     SuccList.pop_back();
     if (SuccList.empty() && SuccDIList.DI[!IsInsert].empty())
       Succ.erase(U.getFrom());
 
     auto &PredDIList = Pred[U.getTo()];
     auto &PredList = PredDIList.DI[IsInsert];
     assert(PredList.back() == U.getFrom());
     PredList.pop_back();
     if (PredList.empty() && PredDIList.DI[!IsInsert].empty())
       Pred.erase(U.getTo());
     return U;
   }
 
   using VectRet = SmallVector<NodePtr, 8>;
   template <bool InverseEdge> VectRet getChildren(NodePtr N) const {
     using DirectedNodeT =
         std::conditional_t<InverseEdge, Inverse<NodePtr>, NodePtr>;
     auto R = children<DirectedNodeT>(N);
     VectRet Res = VectRet(detail::reverse_if<!InverseEdge>(R));
 
     // Remove nullptr children for clang.
     llvm::erase(Res, nullptr);
 
     auto &Children = (InverseEdge != InverseGraph) ? Pred : Succ;
     auto It = Children.find(N);
     if (It == Children.end())
       return Res;
 
     // Remove children present in the CFG but not in the snapshot.
     for (auto *Child : It->second.DI[0])
       llvm::erase(Res, Child);
 
     // Add children present in the snapshot for not in the real CFG.
     auto &AddedChildren = It->second.DI[1];
     llvm::append_range(Res, AddedChildren);
 
     return Res;
   }
 
   void print(raw_ostream &OS) const {
     OS << "===== GraphDiff: CFG edge changes to create a CFG snapshot. \n"
           "===== (Note: notion of children/inverse_children depends on "
           "the direction of edges and the graph.)\n";
     OS << "Children to delete/insert:\n\t";
     printMap(OS, Succ);
     OS << "Inverse_children to delete/insert:\n\t";
     printMap(OS, Pred);
     OS << "\n";
   }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
   LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
 #endif
 };
 } // end namespace llvm
 
 #endif // LLVM_SUPPORT_CFGDIFF_H

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