llvm/lib/Transforms/Utils/NameAnonGlobals.cpp

   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/Support/MD5.h"
  18 #include "llvm/Transforms/Utils/ModuleUtils.h"
  19
  20 using namespace llvm;
  21
  22 namespace {
  23 // Compute a "unique" hash for the module based on the name of the public
  24 // globals.
  25 class ModuleHasher {
  26   Module &TheModule;
  27   std::string TheHash;
  28
  29 public:
  30   ModuleHasher(Module &M) : TheModule(M) {}
  31
  32   /// Return the lazily computed hash.
  33   std::string &get() {
  34     if (!TheHash.empty())
  35       // Cache hit :)
  36       return TheHash;
  37
  38     MD5 Hasher;
  39     for (auto &F : TheModule) {
  40       if (F.isDeclaration() || F.hasLocalLinkage() || !F.hasName())
  41         continue;
  42       auto Name = F.getName();
  43       Hasher.update(Name);
  44     }
  45     for (auto &GV : TheModule.globals()) {
  46       if (GV.isDeclaration() || GV.hasLocalLinkage() || !GV.hasName())
  47         continue;
  48       auto Name = GV.getName();
  49       Hasher.update(Name);
  50     }
  51
  52     // Now return the result.
  53     MD5::MD5Result Hash;
  54     Hasher.final(Hash);
  55     SmallString<32> Result;
  56     MD5::stringifyResult(Hash, Result);
  57     TheHash = std::string(Result);
  58     return TheHash;
  59   }
  60 };
  61 } // end anonymous namespace
  62
  63 // Rename all the anon globals in the module
  64 bool llvm::nameUnamedGlobals(Module &M) {
  65   bool Changed = false;
  66   ModuleHasher ModuleHash(M);
  67   int count = 0;
  68   auto RenameIfNeed = [&](GlobalValue &GV) {
  69     if (GV.hasName())
  70       return;
  71     GV.setName(Twine("anon.") + ModuleHash.get() + "." + Twine(count++));
  72     Changed = true;
  73   };
  74   for (auto &GO : M.global_objects())
  75     RenameIfNeed(GO);
  76   for (auto &GA : M.aliases())
  77     RenameIfNeed(GA);
  78
  79   return Changed;
  80 }
  81
  82 PreservedAnalyses NameAnonGlobalPass::run(Module &M,
  83                                           ModuleAnalysisManager &AM) {
  84   if (!nameUnamedGlobals(M))
  85     return PreservedAnalyses::all();
  86
  87   return PreservedAnalyses::none();
  88 }