1//===-- GlobalDCE.h - DCE unreachable internal functions ------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This transform is designed to eliminate unreachable internal globals from the
10// program.  It uses an aggressive algorithm, searching out globals that are
11// known to be alive.  After it finds all of the globals which are needed, it
12// deletes whatever is left over.  This allows it to delete recursive chunks of
13// the program which are unreachable.
14//
15//===----------------------------------------------------------------------===//
16
17#ifndef LLVM_TRANSFORMS_IPO_GLOBALDCE_H
18#define LLVM_TRANSFORMS_IPO_GLOBALDCE_H
19
20#include "llvm/ADT/DenseMap.h"
21#include "llvm/ADT/SmallSet.h"
22#include "llvm/IR/Module.h"
23#include "llvm/IR/PassManager.h"
24#include <unordered_map>
25
26namespace llvm {
27
28/// Pass to remove unused function declarations.
29class GlobalDCEPass : public PassInfoMixin<GlobalDCEPass> {
30public:
31  PreservedAnalyses run(Module &M, ModuleAnalysisManager &);
32
33private:
34  SmallPtrSet<GlobalValue*, 32> AliveGlobals;
35
36  /// Global -> Global that uses this global.
37  DenseMap<GlobalValue *, SmallPtrSet<GlobalValue *, 4>> GVDependencies;
38
39  /// Constant -> Globals that use this global cache.
40  std::unordered_map<Constant *, SmallPtrSet<GlobalValue *, 8>>
41      ConstantDependenciesCache;
42
43  /// Comdat -> Globals in that Comdat section.
44  std::unordered_multimap<Comdat *, GlobalValue *> ComdatMembers;
45
46  /// !type metadata -> set of (vtable, offset) pairs
47  DenseMap<Metadata *, SmallSet<std::pair<GlobalVariable *, uint64_t>, 4>>
48      TypeIdMap;
49
50  // Global variables which are vtables, and which we have enough information
51  // about to safely do dead virtual function elimination.
52  SmallPtrSet<GlobalValue *, 32> VFESafeVTables;
53
54  void UpdateGVDependencies(GlobalValue &GV);
55  void MarkLive(GlobalValue &GV,
56                SmallVectorImpl<GlobalValue *> *Updates = nullptr);
57  bool RemoveUnusedGlobalValue(GlobalValue &GV);
58
59  // Dead virtual function elimination.
60  void AddVirtualFunctionDependencies(Module &M);
61  void ScanVTables(Module &M);
62  void ScanTypeCheckedLoadIntrinsics(Module &M);
63  void ScanVTableLoad(Function *Caller, Metadata *TypeId, uint64_t CallOffset);
64
65  void ComputeDependencies(Value *V, SmallPtrSetImpl<GlobalValue *> &U);
66};
67
68}
69
70#endif // LLVM_TRANSFORMS_IPO_GLOBALDCE_H
71