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>
22 using 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.
makeVisible(GlobalValue & GV,bool Delete)28 static 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
55 namespace {
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 ///
GVExtractorPass(std::vector<GlobalValue * > & GVs,bool deleteS=true)67 explicit GVExtractorPass(std::vector<GlobalValue*>& GVs, bool deleteS = true)
68 : ModulePass(ID), Named(GVs.begin(), GVs.end()), deleteStuff(deleteS) {}
69
runOnModule(Module & M)70 bool runOnModule(Module &M) override {
71 if (skipModule(M))
72 return false;
73
74 // Visit the global inline asm.
75 if (!deleteStuff)
76 M.setModuleInlineAsm("");
77
78 // For simplicity, just give all GlobalValues ExternalLinkage. A trickier
79 // implementation could figure out which GlobalValues are actually
80 // referenced by the Named set, and which GlobalValues in the rest of
81 // the module are referenced by the NamedSet, and get away with leaving
82 // more internal and private things internal and private. But for now,
83 // be conservative and simple.
84
85 // Visit the GlobalVariables.
86 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
87 I != E; ++I) {
88 bool Delete =
89 deleteStuff == (bool)Named.count(&*I) && !I->isDeclaration();
90 if (!Delete) {
91 if (I->hasAvailableExternallyLinkage())
92 continue;
93 if (I->getName() == "llvm.global_ctors")
94 continue;
95 }
96
97 makeVisible(*I, Delete);
98
99 if (Delete) {
100 // Make this a declaration and drop it's comdat.
101 I->setInitializer(nullptr);
102 I->setComdat(nullptr);
103 }
104 }
105
106 // Visit the Functions.
107 for (Function &F : M) {
108 bool Delete =
109 deleteStuff == (bool)Named.count(&F) && !F.isDeclaration();
110 if (!Delete) {
111 if (F.hasAvailableExternallyLinkage())
112 continue;
113 }
114
115 makeVisible(F, Delete);
116
117 if (Delete) {
118 // Make this a declaration and drop it's comdat.
119 F.deleteBody();
120 F.setComdat(nullptr);
121 }
122 }
123
124 // Visit the Aliases.
125 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
126 I != E;) {
127 Module::alias_iterator CurI = I;
128 ++I;
129
130 bool Delete = deleteStuff == (bool)Named.count(&*CurI);
131 makeVisible(*CurI, Delete);
132
133 if (Delete) {
134 Type *Ty = CurI->getValueType();
135
136 CurI->removeFromParent();
137 llvm::Value *Declaration;
138 if (FunctionType *FTy = dyn_cast<FunctionType>(Ty)) {
139 Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage,
140 CurI->getName(), &M);
141
142 } else {
143 Declaration =
144 new GlobalVariable(M, Ty, false, GlobalValue::ExternalLinkage,
145 nullptr, CurI->getName());
146
147 }
148 CurI->replaceAllUsesWith(Declaration);
149 delete &*CurI;
150 }
151 }
152
153 return true;
154 }
155 };
156
157 char GVExtractorPass::ID = 0;
158 }
159
createGVExtractionPass(std::vector<GlobalValue * > & GVs,bool deleteFn)160 ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue *> &GVs,
161 bool deleteFn) {
162 return new GVExtractorPass(GVs, deleteFn);
163 }
164