GlobalDCE.h

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//===-- GlobalDCE.h - DCE unreachable internal functions ------------------===//
//
// 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 transform is designed to eliminate unreachable internal globals from the
// program.  It uses an aggressive algorithm, searching out globals that are
// known to be alive.  After it finds all of the globals which are needed, it
// deletes whatever is left over.  This allows it to delete recursive chunks of
// the program which are unreachable.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_TRANSFORMS_IPO_GLOBALDCE_H
#define LLVM_TRANSFORMS_IPO_GLOBALDCE_H
 
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Support/Compiler.h"
#include <unordered_map>
 
namespace llvm {
class Comdat;
class Constant;
class Function;
class GlobalVariable;
class Metadata;
class Module;
class Value;
class ModulePass;
 
/// Pass to remove unused function declarations.
class GlobalDCEPass : public OptionalPassInfoMixin<GlobalDCEPass> {
public:
  GlobalDCEPass(bool InLTOPostLink = false) : InLTOPostLink(InLTOPostLink) {}
 
  LLVM_ABI PreservedAnalyses run(Module &M, ModuleAnalysisManager &);
 
  LLVM_ABI void
  printPipeline(raw_ostream &OS,
                function_ref<StringRef(StringRef)> MapClassName2PassName);
 
private:
  bool InLTOPostLink = false;
 
  SmallPtrSet<GlobalValue*, 32> AliveGlobals;
 
  /// Global -> Global that uses this global.
  DenseMap<GlobalValue *, SmallPtrSet<GlobalValue *, 4>> GVDependencies;
 
  /// Function -> (vtable, virtual function) pairs. Maps a function to the
  /// virtual functions that it may call and their vtables. This is used to only
  /// mark a virtual function as live when both the caller and the vtable are
  /// live.
  DenseMap<Function *,
           SmallSetVector<std::pair<GlobalVariable *, Function *>, 4>>
      VFuncDependencies;
 
  /// Vtable -> virtual functions that are live once the vtable is live.
  /// If the vtable never becomes live, the virtual function is not kept
  /// alive by this entry.
  DenseMap<GlobalVariable *, SmallVector<Function *>> PendingVFuncs;
 
  /// Constant -> Globals that use this global cache.
  DenseMap<Constant *, SmallPtrSet<GlobalValue *, 8>> ConstantDependenciesCache;
 
  /// Comdat -> Globals in that Comdat section.
  std::unordered_multimap<Comdat *, GlobalValue *> ComdatMembers;
 
  /// !type metadata -> set of (vtable, offset) pairs
  DenseMap<Metadata *, SmallSet<std::pair<GlobalVariable *, uint64_t>, 4>>
      TypeIdMap;
 
  // Global variables which are vtables, and which we have enough information
  // about to safely do dead virtual function elimination.
  SmallPtrSet<GlobalValue *, 32> VFESafeVTables;
 
  void UpdateGVDependencies(GlobalValue &GV);
  void MarkLive(GlobalValue &GV,
                SmallVectorImpl<GlobalValue *> *Updates = nullptr);
 
  // Dead virtual function elimination.
  void AddVirtualFunctionDependencies(Module &M);
  void ScanVTables(Module &M);
  void ScanTypeCheckedLoadIntrinsics(Module &M);
  void ScanVTableLoad(Function *Caller, Metadata *TypeId, uint64_t CallOffset);
 
  void ComputeDependencies(Value *V, SmallPtrSetImpl<GlobalValue *> &U);
};
 
LLVM_ABI ModulePass *createGlobalDCEPass();
}
 
#endif // LLVM_TRANSFORMS_IPO_GLOBALDCE_H