1//===-- ExtractGV.cpp - Global Value extraction pass ----------------------===//
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 pass extracts global values
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Transforms/IPO.h"
15#include "llvm/ADT/SetVector.h"
16#include "llvm/IR/Constants.h"
17#include "llvm/IR/Instructions.h"
18#include "llvm/IR/LLVMContext.h"
19#include "llvm/IR/Module.h"
20#include "llvm/Pass.h"
21#include <algorithm>
22using namespace llvm;
23
24/// Make sure GV is visible from both modules. Delete is true if it is
25/// being deleted from this module.
26/// This also makes sure GV cannot be dropped so that references from
27/// the split module remain valid.
28static void makeVisible(GlobalValue &GV, bool Delete) {
29  bool Local = GV.hasLocalLinkage();
30  if (Local || Delete) {
31    GV.setLinkage(GlobalValue::ExternalLinkage);
32    if (Local)
33      GV.setVisibility(GlobalValue::HiddenVisibility);
34    return;
35  }
36
37  if (!GV.hasLinkOnceLinkage()) {
38    assert(!GV.isDiscardableIfUnused());
39    return;
40  }
41
42  // Map linkonce* to weak* so that llvm doesn't drop this GV.
43  switch(GV.getLinkage()) {
44  default:
45    llvm_unreachable("Unexpected linkage");
46  case GlobalValue::LinkOnceAnyLinkage:
47    GV.setLinkage(GlobalValue::WeakAnyLinkage);
48    return;
49  case GlobalValue::LinkOnceODRLinkage:
50    GV.setLinkage(GlobalValue::WeakODRLinkage);
51    return;
52  }
53}
54
55namespace {
56  /// @brief A pass to extract specific functions and their dependencies.
57  class GVExtractorPass : public ModulePass {
58    SetVector<GlobalValue *> Named;
59    bool deleteStuff;
60  public:
61    static char ID; // Pass identification, replacement for typeid
62
63    /// FunctionExtractorPass - If deleteFn is true, this pass deletes as the
64    /// specified function. Otherwise, it deletes as much of the module as
65    /// possible, except for the function specified.
66    ///
67    explicit GVExtractorPass(std::vector<GlobalValue*>& GVs, bool deleteS = true)
68      : ModulePass(ID), Named(GVs.begin(), GVs.end()), deleteStuff(deleteS) {}
69
70    bool runOnModule(Module &M) override {
71      // Visit the global inline asm.
72      if (!deleteStuff)
73        M.setModuleInlineAsm("");
74
75      // For simplicity, just give all GlobalValues ExternalLinkage. A trickier
76      // implementation could figure out which GlobalValues are actually
77      // referenced by the Named set, and which GlobalValues in the rest of
78      // the module are referenced by the NamedSet, and get away with leaving
79      // more internal and private things internal and private. But for now,
80      // be conservative and simple.
81
82      // Visit the GlobalVariables.
83      for (Module::global_iterator I = M.global_begin(), E = M.global_end();
84           I != E; ++I) {
85        bool Delete =
86            deleteStuff == (bool)Named.count(&*I) && !I->isDeclaration();
87        if (!Delete) {
88          if (I->hasAvailableExternallyLinkage())
89            continue;
90          if (I->getName() == "llvm.global_ctors")
91            continue;
92        }
93
94        makeVisible(*I, Delete);
95
96        if (Delete) {
97          // Make this a declaration and drop it's comdat.
98          I->setInitializer(nullptr);
99          I->setComdat(nullptr);
100        }
101      }
102
103      // Visit the Functions.
104      for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
105        bool Delete =
106            deleteStuff == (bool)Named.count(&*I) && !I->isDeclaration();
107        if (!Delete) {
108          if (I->hasAvailableExternallyLinkage())
109            continue;
110        }
111
112        makeVisible(*I, Delete);
113
114        if (Delete) {
115          // Make this a declaration and drop it's comdat.
116          I->deleteBody();
117          I->setComdat(nullptr);
118        }
119      }
120
121      // Visit the Aliases.
122      for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
123           I != E;) {
124        Module::alias_iterator CurI = I;
125        ++I;
126
127        bool Delete = deleteStuff == (bool)Named.count(&*CurI);
128        makeVisible(*CurI, Delete);
129
130        if (Delete) {
131          Type *Ty =  CurI->getType()->getElementType();
132
133          CurI->removeFromParent();
134          llvm::Value *Declaration;
135          if (FunctionType *FTy = dyn_cast<FunctionType>(Ty)) {
136            Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage,
137                                           CurI->getName(), &M);
138
139          } else {
140            Declaration =
141              new GlobalVariable(M, Ty, false, GlobalValue::ExternalLinkage,
142                                 nullptr, CurI->getName());
143
144          }
145          CurI->replaceAllUsesWith(Declaration);
146          delete &*CurI;
147        }
148      }
149
150      return true;
151    }
152  };
153
154  char GVExtractorPass::ID = 0;
155}
156
157ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue *> &GVs,
158                                         bool deleteFn) {
159  return new GVExtractorPass(GVs, deleteFn);
160}
161