1 //===-- GlobalDCE.h - DCE unreachable internal functions ------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This transform is designed to eliminate unreachable internal globals from the
11 // program.  It uses an aggressive algorithm, searching out globals that are
12 // known to be alive.  After it finds all of the globals which are needed, it
13 // deletes whatever is left over.  This allows it to delete recursive chunks of
14 // the program which are unreachable.
15 //
16 //===----------------------------------------------------------------------===//
17 
18 #ifndef LLVM_TRANSFORMS_IPO_GLOBALDCE_H
19 #define LLVM_TRANSFORMS_IPO_GLOBALDCE_H
20 
21 #include "llvm/IR/Module.h"
22 #include "llvm/IR/PassManager.h"
23 #include <unordered_map>
24 
25 namespace llvm {
26 
27 /// Pass to remove unused function declarations.
28 class GlobalDCEPass : public PassInfoMixin<GlobalDCEPass> {
29 public:
30   PreservedAnalyses run(Module &M, ModuleAnalysisManager &);
31 
32 private:
33   SmallPtrSet<GlobalValue*, 32> AliveGlobals;
34   SmallPtrSet<Constant *, 8> SeenConstants;
35   std::unordered_multimap<Comdat *, GlobalValue *> ComdatMembers;
36 
37   /// Mark the specific global value as needed, and
38   /// recursively mark anything that it uses as also needed.
39   void GlobalIsNeeded(GlobalValue *GV);
40   void MarkUsedGlobalsAsNeeded(Constant *C);
41   bool RemoveUnusedGlobalValue(GlobalValue &GV);
42 };
43 
44 }
45 
46 #endif // LLVM_TRANSFORMS_IPO_GLOBALDCE_H
47