LLVM  10.0.0svn
GlobalDCE.h
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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 
26 namespace llvm {
27 
28 /// Pass to remove unused function declarations.
29 class GlobalDCEPass : public PassInfoMixin<GlobalDCEPass> {
30 public:
32 
33 private:
34  SmallPtrSet<GlobalValue*, 32> AliveGlobals;
35 
36  /// Global -> Global that uses this global.
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
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
This class represents lattice values for constants.
Definition: AllocatorList.h:23
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:66
A templated base class for SmallPtrSet which provides the typesafe interface that is common across al...
Definition: SmallPtrSet.h:343
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:41
A CRTP mix-in to automatically provide informational APIs needed for passes.
Definition: PassManager.h:373
Pass to remove unused function declarations.
Definition: GlobalDCE.h:29
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:154
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:417
Module.h This file contains the declarations for the Module class.
LLVM Value Representation.
Definition: Value.h:74
A container for analyses that lazily runs them and caches their results.
This header defines various interfaces for pass management in LLVM.
Root of the metadata hierarchy.
Definition: Metadata.h:57
PreservedAnalyses run(Module &M, ModuleAnalysisManager &)
Definition: GlobalDCE.cpp:278