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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 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.
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Pass.h"
#include "llvm/Support/GenericDomTree.h"
#include <utility>
namespace llvm {
class Function;
class Instruction;
class Module;
class raw_ostream;
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 *>>;
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, BBUpdates);
extern template void ApplyUpdates<BBPostDomTree>(BBPostDomTree &DT, BBUpdates);
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;
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()),
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> {
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 Def dominates a use in User.
/// This performs the special checks necessary if Def and User are in the same
/// basic block. Note that Def doesn't dominate a use in Def itself!
bool dominates(const Instruction *Def, const Use &U) const;
bool dominates(const Instruction *Def, const Instruction *User) const;
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;
// Ensure base class overloads are visible.
using Base::isReachableFromEntry;
/// Provide an overload for a Use.
bool isReachableFromEntry(const Use &U) 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::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;
/// 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;
explicit DominatorTreePrinterPass(raw_ostream &OS);
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
/// Verifier pass for the \c DominatorTree.
struct DominatorTreeVerifierPass : PassInfoMixin<DominatorTreeVerifierPass> {
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
/// Legacy analysis pass which computes a \c DominatorTree.
class DominatorTreeWrapperPass : public FunctionPass {
DominatorTree DT;
static char ID;
DominatorTreeWrapperPass() : FunctionPass(ID) {
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 {
void releaseMemory() override { DT.releaseMemory(); }
void print(raw_ostream &OS, const Module *M = nullptr) const override;
} // end namespace llvm