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/ADT/SetVector.h"
15 #include "llvm/IR/LLVMContext.h"
16 #include "llvm/IR/Module.h"
17 #include "llvm/Pass.h"
18 #include "llvm/Transforms/IPO.h"
19 #include <algorithm>
20 using namespace llvm;
21
22 /// Make sure GV is visible from both modules. Delete is true if it is
23 /// being deleted from this module.
24 /// This also makes sure GV cannot be dropped so that references from
25 /// the split module remain valid.
makeVisible(GlobalValue & GV,bool Delete)26 static void makeVisible(GlobalValue &GV, bool Delete) {
27 bool Local = GV.hasLocalLinkage();
28 if (Local || Delete) {
29 GV.setLinkage(GlobalValue::ExternalLinkage);
30 if (Local)
31 GV.setVisibility(GlobalValue::HiddenVisibility);
32 return;
33 }
34
35 if (!GV.hasLinkOnceLinkage()) {
36 assert(!GV.isDiscardableIfUnused());
37 return;
38 }
39
40 // Map linkonce* to weak* so that llvm doesn't drop this GV.
41 switch(GV.getLinkage()) {
42 default:
43 llvm_unreachable("Unexpected linkage");
44 case GlobalValue::LinkOnceAnyLinkage:
45 GV.setLinkage(GlobalValue::WeakAnyLinkage);
46 return;
47 case GlobalValue::LinkOnceODRLinkage:
48 GV.setLinkage(GlobalValue::WeakODRLinkage);
49 return;
50 }
51 }
52
53 namespace {
54 /// A pass to extract specific global values and their dependencies.
55 class GVExtractorPass : public ModulePass {
56 SetVector<GlobalValue *> Named;
57 bool deleteStuff;
58 public:
59 static char ID; // Pass identification, replacement for typeid
60
61 /// If deleteS is true, this pass deletes the specified global values.
62 /// Otherwise, it deletes as much of the module as possible, except for the
63 /// global values specified.
GVExtractorPass(std::vector<GlobalValue * > & GVs,bool deleteS=true)64 explicit GVExtractorPass(std::vector<GlobalValue*> &GVs,
65 bool deleteS = true)
66 : ModulePass(ID), Named(GVs.begin(), GVs.end()), deleteStuff(deleteS) {}
67
runOnModule(Module & M)68 bool runOnModule(Module &M) override {
69 if (skipModule(M))
70 return false;
71
72 // Visit the global inline asm.
73 if (!deleteStuff)
74 M.setModuleInlineAsm("");
75
76 // For simplicity, just give all GlobalValues ExternalLinkage. A trickier
77 // implementation could figure out which GlobalValues are actually
78 // referenced by the Named set, and which GlobalValues in the rest of
79 // the module are referenced by the NamedSet, and get away with leaving
80 // more internal and private things internal and private. But for now,
81 // be conservative and simple.
82
83 // Visit the GlobalVariables.
84 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
85 I != E; ++I) {
86 bool Delete =
87 deleteStuff == (bool)Named.count(&*I) && !I->isDeclaration();
88 if (!Delete) {
89 if (I->hasAvailableExternallyLinkage())
90 continue;
91 if (I->getName() == "llvm.global_ctors")
92 continue;
93 }
94
95 makeVisible(*I, Delete);
96
97 if (Delete) {
98 // Make this a declaration and drop it's comdat.
99 I->setInitializer(nullptr);
100 I->setComdat(nullptr);
101 }
102 }
103
104 // Visit the Functions.
105 for (Function &F : M) {
106 bool Delete =
107 deleteStuff == (bool)Named.count(&F) && !F.isDeclaration();
108 if (!Delete) {
109 if (F.hasAvailableExternallyLinkage())
110 continue;
111 }
112
113 makeVisible(F, Delete);
114
115 if (Delete) {
116 // Make this a declaration and drop it's comdat.
117 F.deleteBody();
118 F.setComdat(nullptr);
119 }
120 }
121
122 // Visit the Aliases.
123 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
124 I != E;) {
125 Module::alias_iterator CurI = I;
126 ++I;
127
128 bool Delete = deleteStuff == (bool)Named.count(&*CurI);
129 makeVisible(*CurI, Delete);
130
131 if (Delete) {
132 Type *Ty = CurI->getValueType();
133
134 CurI->removeFromParent();
135 llvm::Value *Declaration;
136 if (FunctionType *FTy = dyn_cast<FunctionType>(Ty)) {
137 Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage,
138 CurI->getName(), &M);
139
140 } else {
141 Declaration =
142 new GlobalVariable(M, Ty, false, GlobalValue::ExternalLinkage,
143 nullptr, CurI->getName());
144
145 }
146 CurI->replaceAllUsesWith(Declaration);
147 delete &*CurI;
148 }
149 }
150
151 return true;
152 }
153 };
154
155 char GVExtractorPass::ID = 0;
156 }
157
createGVExtractionPass(std::vector<GlobalValue * > & GVs,bool deleteFn)158 ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue *> &GVs,
159 bool deleteFn) {
160 return new GVExtractorPass(GVs, deleteFn);
161 }
162