1//===- NameAnonGlobals.cpp - ThinLTO Support: Name Unnamed Globals --------===//
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 file implements naming anonymous globals to make sure they can be
10// referred to by ThinLTO.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Transforms/Utils/NameAnonGlobals.h"
15#include "llvm/ADT/SmallString.h"
16#include "llvm/IR/Module.h"
17#include "llvm/InitializePasses.h"
18#include "llvm/Support/MD5.h"
19#include "llvm/Transforms/Utils/ModuleUtils.h"
20
21using namespace llvm;
22
23namespace {
24// Compute a "unique" hash for the module based on the name of the public
25// globals.
26class ModuleHasher {
27  Module &TheModule;
28  std::string TheHash;
29
30public:
31  ModuleHasher(Module &M) : TheModule(M) {}
32
33  /// Return the lazily computed hash.
34  std::string &get() {
35    if (!TheHash.empty())
36      // Cache hit :)
37      return TheHash;
38
39    MD5 Hasher;
40    for (auto &F : TheModule) {
41      if (F.isDeclaration() || F.hasLocalLinkage() || !F.hasName())
42        continue;
43      auto Name = F.getName();
44      Hasher.update(Name);
45    }
46    for (auto &GV : TheModule.globals()) {
47      if (GV.isDeclaration() || GV.hasLocalLinkage() || !GV.hasName())
48        continue;
49      auto Name = GV.getName();
50      Hasher.update(Name);
51    }
52
53    // Now return the result.
54    MD5::MD5Result Hash;
55    Hasher.final(Hash);
56    SmallString<32> Result;
57    MD5::stringifyResult(Hash, Result);
58    TheHash = Result.str();
59    return TheHash;
60  }
61};
62} // end anonymous namespace
63
64// Rename all the anon globals in the module
65bool llvm::nameUnamedGlobals(Module &M) {
66  bool Changed = false;
67  ModuleHasher ModuleHash(M);
68  int count = 0;
69  auto RenameIfNeed = [&](GlobalValue &GV) {
70    if (GV.hasName())
71      return;
72    GV.setName(Twine("anon.") + ModuleHash.get() + "." + Twine(count++));
73    Changed = true;
74  };
75  for (auto &GO : M.global_objects())
76    RenameIfNeed(GO);
77  for (auto &GA : M.aliases())
78    RenameIfNeed(GA);
79
80  return Changed;
81}
82
83namespace {
84
85// Legacy pass that provides a name to every anon globals.
86class NameAnonGlobalLegacyPass : public ModulePass {
87
88public:
89  /// Pass identification, replacement for typeid
90  static char ID;
91
92  /// Specify pass name for debug output
93  StringRef getPassName() const override { return "Name Anon Globals"; }
94
95  explicit NameAnonGlobalLegacyPass() : ModulePass(ID) {}
96
97  bool runOnModule(Module &M) override { return nameUnamedGlobals(M); }
98};
99char NameAnonGlobalLegacyPass::ID = 0;
100
101} // anonymous namespace
102
103PreservedAnalyses NameAnonGlobalPass::run(Module &M,
104                                          ModuleAnalysisManager &AM) {
105  if (!nameUnamedGlobals(M))
106    return PreservedAnalyses::all();
107
108  return PreservedAnalyses::none();
109}
110
111INITIALIZE_PASS_BEGIN(NameAnonGlobalLegacyPass, "name-anon-globals",
112                      "Provide a name to nameless globals", false, false)
113INITIALIZE_PASS_END(NameAnonGlobalLegacyPass, "name-anon-globals",
114                    "Provide a name to nameless globals", false, false)
115
116namespace llvm {
117ModulePass *createNameAnonGlobalPass() {
118  return new NameAnonGlobalLegacyPass();
119}
120}
121