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 //===- Dominators.h - Dominator Info Calculation ----------------*- 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 the DominatorTree class, which provides fast and efficient
 // dominance queries.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_IR_DOMINATORS_H
 #define LLVM_IR_DOMINATORS_H
 
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/ADT/ilist_iterator.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/Use.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/CFGDiff.h"
 #include "llvm/Support/CFGUpdate.h"
 #include "llvm/Support/GenericDomTree.h"
 #include <algorithm>
 #include <utility>
 
 namespace llvm {
 
 class Function;
 class Instruction;
 class Module;
 class Value;
 class raw_ostream;
 template <class GraphType> struct GraphTraits;
 
 extern template class DomTreeNodeBase<BasicBlock>;
 extern template class DominatorTreeBase<BasicBlock, false>; // DomTree
 extern template class DominatorTreeBase<BasicBlock, true>; // PostDomTree
 
 extern template class cfg::Update<BasicBlock *>;
 
 namespace DomTreeBuilder {
 using BBDomTree = DomTreeBase<BasicBlock>;
 using BBPostDomTree = PostDomTreeBase<BasicBlock>;
 
 using BBUpdates = ArrayRef<llvm::cfg::Update<BasicBlock *>>;
 
 using BBDomTreeGraphDiff = GraphDiff<BasicBlock *, false>;
 using BBPostDomTreeGraphDiff = GraphDiff<BasicBlock *, true>;
 
 extern template void Calculate<BBDomTree>(BBDomTree &DT);
 extern template void CalculateWithUpdates<BBDomTree>(BBDomTree &DT,
                                                      BBUpdates U);
 
 extern template void Calculate<BBPostDomTree>(BBPostDomTree &DT);
 
 extern template void InsertEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From,
                                            BasicBlock *To);
 extern template void InsertEdge<BBPostDomTree>(BBPostDomTree &DT,
                                                BasicBlock *From,
                                                BasicBlock *To);
 
 extern template void DeleteEdge<BBDomTree>(BBDomTree &DT, BasicBlock *From,
                                            BasicBlock *To);
 extern template void DeleteEdge<BBPostDomTree>(BBPostDomTree &DT,
                                                BasicBlock *From,
                                                BasicBlock *To);
 
 extern template void ApplyUpdates<BBDomTree>(BBDomTree &DT,
                                              BBDomTreeGraphDiff &,
                                              BBDomTreeGraphDiff *);
 extern template void ApplyUpdates<BBPostDomTree>(BBPostDomTree &DT,
                                                  BBPostDomTreeGraphDiff &,
                                                  BBPostDomTreeGraphDiff *);
 
 extern template bool Verify<BBDomTree>(const BBDomTree &DT,
                                        BBDomTree::VerificationLevel VL);
 extern template bool Verify<BBPostDomTree>(const BBPostDomTree &DT,
                                            BBPostDomTree::VerificationLevel VL);
 }  // namespace DomTreeBuilder
 
 using DomTreeNode = DomTreeNodeBase<BasicBlock>;
 
 class BasicBlockEdge {
   const BasicBlock *Start;
   const BasicBlock *End;
 
 public:
   BasicBlockEdge(const BasicBlock *Start_, const BasicBlock *End_) :
     Start(Start_), End(End_) {}
 
   BasicBlockEdge(const std::pair<BasicBlock *, BasicBlock *> &Pair)
       : Start(Pair.first), End(Pair.second) {}
 
   BasicBlockEdge(const std::pair<const BasicBlock *, const BasicBlock *> &Pair)
       : Start(Pair.first), End(Pair.second) {}
 
   const BasicBlock *getStart() const {
     return Start;
   }
 
   const BasicBlock *getEnd() const {
     return End;
   }
 
   /// Check if this is the only edge between Start and End.
   bool isSingleEdge() const;
 };
 
 template <> struct DenseMapInfo<BasicBlockEdge> {
   using BBInfo = DenseMapInfo<const BasicBlock *>;
 
   static unsigned getHashValue(const BasicBlockEdge *V);
 
   static inline BasicBlockEdge getEmptyKey() {
     return BasicBlockEdge(BBInfo::getEmptyKey(), BBInfo::getEmptyKey());
   }
 
   static inline BasicBlockEdge getTombstoneKey() {
     return BasicBlockEdge(BBInfo::getTombstoneKey(), BBInfo::getTombstoneKey());
   }
 
   static unsigned getHashValue(const BasicBlockEdge &Edge) {
     return hash_combine(BBInfo::getHashValue(Edge.getStart()),
                         BBInfo::getHashValue(Edge.getEnd()));
   }
 
   static bool isEqual(const BasicBlockEdge &LHS, const BasicBlockEdge &RHS) {
     return BBInfo::isEqual(LHS.getStart(), RHS.getStart()) &&
            BBInfo::isEqual(LHS.getEnd(), RHS.getEnd());
   }
 };
 
 /// Concrete subclass of DominatorTreeBase that is used to compute a
 /// normal dominator tree.
 ///
 /// Definition: A block is said to be forward statically reachable if there is
 /// a path from the entry of the function to the block.  A statically reachable
 /// block may become statically unreachable during optimization.
 ///
 /// A forward unreachable block may appear in the dominator tree, or it may
 /// not.  If it does, dominance queries will return results as if all reachable
 /// blocks dominate it.  When asking for a Node corresponding to a potentially
 /// unreachable block, calling code must handle the case where the block was
 /// unreachable and the result of getNode() is nullptr.
 ///
 /// Generally, a block known to be unreachable when the dominator tree is
 /// constructed will not be in the tree.  One which becomes unreachable after
 /// the dominator tree is initially constructed may still exist in the tree,
 /// even if the tree is properly updated. Calling code should not rely on the
 /// preceding statements; this is stated only to assist human understanding.
 class DominatorTree : public DominatorTreeBase<BasicBlock, false> {
  public:
   using Base = DominatorTreeBase<BasicBlock, false>;
 
   DominatorTree() = default;
   explicit DominatorTree(Function &F) { recalculate(F); }
   explicit DominatorTree(DominatorTree &DT, DomTreeBuilder::BBUpdates U) {
     recalculate(*DT.Parent, U);
   }
 
   /// Handle invalidation explicitly.
   bool invalidate(Function &F, const PreservedAnalyses &PA,
                   FunctionAnalysisManager::Invalidator &);
 
   // Ensure base-class overloads are visible.
   using Base::dominates;
 
   /// Return true if the (end of the) basic block BB dominates the use U.
   bool dominates(const BasicBlock *BB, const Use &U) const;
 
   /// Return true if value Def dominates use U, in the sense that Def is
   /// available at U, and could be substituted as the used value without
   /// violating the SSA dominance requirement.
   ///
   /// In particular, it is worth noting that:
   ///  * Non-instruction Defs dominate everything.
   ///  * Def does not dominate a use in Def itself (outside of degenerate cases
   ///    like unreachable code or trivial phi cycles).
   ///  * Invoke Defs only dominate uses in their default destination.
   bool dominates(const Value *Def, const Use &U) const;
 
   /// Return true if value Def dominates all possible uses inside instruction
   /// User. Same comments as for the Use-based API apply.
   bool dominates(const Value *Def, const Instruction *User) const;
   bool dominates(const Value *Def, BasicBlock::iterator User) const {
     return dominates(Def, &*User);
   }
 
   /// Returns true if Def would dominate a use in any instruction in BB.
   /// If Def is an instruction in BB, then Def does not dominate BB.
   ///
   /// Does not accept Value to avoid ambiguity with dominance checks between
   /// two basic blocks.
   bool dominates(const Instruction *Def, const BasicBlock *BB) const;
 
   /// Return true if an edge dominates a use.
   ///
   /// If BBE is not a unique edge between start and end of the edge, it can
   /// never dominate the use.
   bool dominates(const BasicBlockEdge &BBE, const Use &U) const;
   bool dominates(const BasicBlockEdge &BBE, const BasicBlock *BB) const;
   /// Returns true if edge \p BBE1 dominates edge \p BBE2.
   bool dominates(const BasicBlockEdge &BBE1, const BasicBlockEdge &BBE2) const;
 
   // Ensure base class overloads are visible.
   using Base::isReachableFromEntry;
 
   /// Provide an overload for a Use.
   bool isReachableFromEntry(const Use &U) const;
 
   // Ensure base class overloads are visible.
   using Base::findNearestCommonDominator;
 
   /// Find the nearest instruction I that dominates both I1 and I2, in the sense
   /// that a result produced before I will be available at both I1 and I2.
   Instruction *findNearestCommonDominator(Instruction *I1,
                                           Instruction *I2) const;
 
   // Pop up a GraphViz/gv window with the Dominator Tree rendered using `dot`.
   void viewGraph(const Twine &Name, const Twine &Title);
   void viewGraph();
 };
 
 //===-------------------------------------
 // DominatorTree GraphTraits specializations so the DominatorTree can be
 // iterable by generic graph iterators.
 
 template <class Node, class ChildIterator> struct DomTreeGraphTraitsBase {
   using NodeRef = Node *;
   using ChildIteratorType = ChildIterator;
   using nodes_iterator = df_iterator<Node *, df_iterator_default_set<Node*>>;
 
   static NodeRef getEntryNode(NodeRef N) { return N; }
   static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
   static ChildIteratorType child_end(NodeRef N) { return N->end(); }
 
   static nodes_iterator nodes_begin(NodeRef N) {
     return df_begin(getEntryNode(N));
   }
 
   static nodes_iterator nodes_end(NodeRef N) { return df_end(getEntryNode(N)); }
 };
 
 template <>
 struct GraphTraits<DomTreeNode *>
     : public DomTreeGraphTraitsBase<DomTreeNode, DomTreeNode::const_iterator> {
 };
 
 template <>
 struct GraphTraits<const DomTreeNode *>
     : public DomTreeGraphTraitsBase<const DomTreeNode,
                                     DomTreeNode::const_iterator> {};
 
 template <> struct GraphTraits<DominatorTree*>
   : public GraphTraits<DomTreeNode*> {
   static NodeRef getEntryNode(DominatorTree *DT) { return DT->getRootNode(); }
 
   static nodes_iterator nodes_begin(DominatorTree *N) {
     return df_begin(getEntryNode(N));
   }
 
   static nodes_iterator nodes_end(DominatorTree *N) {
     return df_end(getEntryNode(N));
   }
 };
 
 /// Analysis pass which computes a \c DominatorTree.
 class DominatorTreeAnalysis : public AnalysisInfoMixin<DominatorTreeAnalysis> {
   friend AnalysisInfoMixin<DominatorTreeAnalysis>;
   static AnalysisKey Key;
 
 public:
   /// Provide the result typedef for this analysis pass.
   using Result = DominatorTree;
 
   /// Run the analysis pass over a function and produce a dominator tree.
   DominatorTree run(Function &F, FunctionAnalysisManager &);
 };
 
 /// Printer pass for the \c DominatorTree.
 class DominatorTreePrinterPass
     : public PassInfoMixin<DominatorTreePrinterPass> {
   raw_ostream &OS;
 
 public:
   explicit DominatorTreePrinterPass(raw_ostream &OS);
 
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 
   static bool isRequired() { return true; }
 };
 
 /// Verifier pass for the \c DominatorTree.
 struct DominatorTreeVerifierPass : PassInfoMixin<DominatorTreeVerifierPass> {
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
   static bool isRequired() { return true; }
 };
 
 /// Enables verification of dominator trees.
 ///
 /// This check is expensive and is disabled by default.  `-verify-dom-info`
 /// allows selectively enabling the check without needing to recompile.
 extern bool VerifyDomInfo;
 
 /// Legacy analysis pass which computes a \c DominatorTree.
 class DominatorTreeWrapperPass : public FunctionPass {
   DominatorTree DT;
 
 public:
   static char ID;
 
   DominatorTreeWrapperPass();
 
   DominatorTree &getDomTree() { return DT; }
   const DominatorTree &getDomTree() const { return DT; }
 
   bool runOnFunction(Function &F) override;
 
   void verifyAnalysis() const override;
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesAll();
   }
 
   void releaseMemory() override { DT.reset(); }
 
   void print(raw_ostream &OS, const Module *M = nullptr) const override;
 };
 } // end namespace llvm
 
 #endif // LLVM_IR_DOMINATORS_H

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