DominanceFrontier.h

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//===- llvm/Analysis/DominanceFrontier.h - Dominator Frontiers --*- 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 DominanceFrontier class, which calculate and holds the
// dominance frontier for a function.
//
// CAUTION: For SSA-construction-like problems there are more efficient ways to
// do that, take a look at GenericIteratedDominanceFrontier.h/SSAUpdater.h. Also
// note that that this analysis computes dominance frontiers for *every* block
// which inherently increases complexity. Unless you do need *all* of them and
// *without* any modifications to the DomTree/CFG in between queries there
// should be better alternatives.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_ANALYSIS_DOMINANCEFRONTIER_H
#define LLVM_ANALYSIS_DOMINANCEFRONTIER_H
 
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Pass.h"
#include "llvm/Support/GenericDomTree.h"
#include <cassert>
 
namespace llvm {
 
class BasicBlock;
class Function;
class raw_ostream;
 
//===----------------------------------------------------------------------===//
/// DominanceFrontierBase - Common base class for computing forward and inverse
/// dominance frontiers for a function.
///
template <class BlockT, bool IsPostDom>
class DominanceFrontierBase {
public:
  // Dom set for a bb. Use SetVector to make iterating dom frontiers of a bb
  // deterministic.
  using DomSetType = SetVector<BlockT *>;
  using DomSetMapType = DenseMap<BlockT *, DomSetType>; // Dom set map
  using DomTreeT = DominatorTreeBase<BlockT, IsPostDom>;
  using DomTreeNodeT = DomTreeNodeBase<BlockT>;
 
protected:
  using GraphTy = std::conditional_t<IsPostDom, Inverse<BlockT *>, BlockT *>;
  using BlockTraits = GraphTraits<GraphTy>;
 
  DomSetMapType Frontiers;
  // Postdominators can have multiple roots.
  SmallVector<BlockT *, IsPostDom ? 4 : 1> Roots;
  static constexpr bool IsPostDominators = IsPostDom;
 
public:
  DominanceFrontierBase() = default;
 
  /// getRoots - Return the root blocks of the current CFG.  This may include
  /// multiple blocks if we are computing post dominators.  For forward
  /// dominators, this will always be a single block (the entry node).
  const SmallVectorImpl<BlockT *> &getRoots() const { return Roots; }
 
  BlockT *getRoot() const {
    assert(Roots.size() == 1 && "Should always have entry node!");
    return Roots[0];
  }
 
  /// isPostDominator - Returns true if analysis based of postdoms
  bool isPostDominator() const {
    return IsPostDominators;
  }
 
  void releaseMemory() {
    Frontiers.clear();
  }
 
  // Accessor interface:
  using iterator = typename DomSetMapType::iterator;
  using const_iterator = typename DomSetMapType::const_iterator;
 
  iterator begin() { return Frontiers.begin(); }
  const_iterator begin() const { return Frontiers.begin(); }
  iterator end() { return Frontiers.end(); }
  const_iterator end() const { return Frontiers.end(); }
  iterator find(BlockT *B) { return Frontiers.find(B); }
  const_iterator find(BlockT *B) const { return Frontiers.find(B); }
 
  /// print - Convert to human readable form
  ///
  void print(raw_ostream &OS) const;
 
  /// dump - Dump the dominance frontier to dbgs().
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
  void dump() const;
#endif
 
  void analyze(DomTreeT &DT) {
    assert((IsPostDom || DT.root_size() == 1) &&
           "Only one entry block for forward domfronts!");
    assert(DT.root_size() == 1 &&
           "Support for post-dom frontiers with multiple roots hasn't been "
           "implemented yet!");
    this->Roots = {DT.getRoot()};
    calculate(DT, DT[this->Roots[0]]);
  }
 
  void calculate(const DomTreeT &DT, const DomTreeNodeT *Node);
};
 
class DominanceFrontier : public DominanceFrontierBase<BasicBlock, false> {
public:
  using DomTreeT = DomTreeBase<BasicBlock>;
  using DomTreeNodeT = DomTreeNodeBase<BasicBlock>;
  using DomSetType = DominanceFrontier::DomSetType;
  using iterator = DominanceFrontier::iterator;
  using const_iterator = DominanceFrontier::const_iterator;
 
  /// Handle invalidation explicitly.
  bool invalidate(Function &F, const PreservedAnalyses &PA,
                  FunctionAnalysisManager::Invalidator &);
};
 
class DominanceFrontierWrapperPass : public FunctionPass {
  DominanceFrontier DF;
 
public:
  static char ID; // Pass ID, replacement for typeid
 
  DominanceFrontierWrapperPass();
 
  DominanceFrontier &getDominanceFrontier() { return DF; }
  const DominanceFrontier &getDominanceFrontier() const { return DF;  }
 
  void releaseMemory() override;
 
  bool runOnFunction(Function &) override;
 
  void getAnalysisUsage(AnalysisUsage &AU) const override;
 
  void print(raw_ostream &OS, const Module * = nullptr) const override;
 
  void dump() const;
};
 
extern template class DominanceFrontierBase<BasicBlock, false>;
extern template class DominanceFrontierBase<BasicBlock, true>;
 
/// Analysis pass which computes a \c DominanceFrontier.
class DominanceFrontierAnalysis
    : public AnalysisInfoMixin<DominanceFrontierAnalysis> {
  friend AnalysisInfoMixin<DominanceFrontierAnalysis>;
 
  static AnalysisKey Key;
 
public:
  /// Provide the result type for this analysis pass.
  using Result = DominanceFrontier;
 
  /// Run the analysis pass over a function and produce a dominator tree.
  DominanceFrontier run(Function &F, FunctionAnalysisManager &AM);
};
 
/// Printer pass for the \c DominanceFrontier.
class DominanceFrontierPrinterPass
    : public PassInfoMixin<DominanceFrontierPrinterPass> {
  raw_ostream &OS;
 
public:
  explicit DominanceFrontierPrinterPass(raw_ostream &OS);
 
  PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 
  static bool isRequired() { return true; }
};
 
} // end namespace llvm
 
#endif // LLVM_ANALYSIS_DOMINANCEFRONTIER_H