lib/Transforms/Utils/NameAnonGlobals.cpp

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