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 // 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 I->setInitializer(nullptr);
98 }
99
100 // Visit the Functions.
101 for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
102 bool Delete =
103 deleteStuff == (bool)Named.count(I) && !I->isDeclaration();
104 if (!Delete) {
105 if (I->hasAvailableExternallyLinkage())
106 continue;
107 }
108
109 makeVisible(*I, Delete);
110
111 if (Delete)
112 I->deleteBody();
113 }
114
115 // Visit the Aliases.
116 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
117 I != E;) {
118 Module::alias_iterator CurI = I;
119 ++I;
120
121 bool Delete = deleteStuff == (bool)Named.count(CurI);
122 makeVisible(*CurI, Delete);
123
124 if (Delete) {
125 Type *Ty = CurI->getType()->getElementType();
126
127 CurI->removeFromParent();
128 llvm::Value *Declaration;
129 if (FunctionType *FTy = dyn_cast<FunctionType>(Ty)) {
130 Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage,
131 CurI->getName(), &M);
132
133 } else {
134 Declaration =
135 new GlobalVariable(M, Ty, false, GlobalValue::ExternalLinkage,
136 nullptr, CurI->getName());
137
138 }
139 CurI->replaceAllUsesWith(Declaration);
140 delete CurI;
141 }
142 }
143
144 return true;
145 }
146 };
147
148 char GVExtractorPass::ID = 0;
149 }
150
createGVExtractionPass(std::vector<GlobalValue * > & GVs,bool deleteFn)151 ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue *> &GVs,
152 bool deleteFn) {
153 return new GVExtractorPass(GVs, deleteFn);
154 }
155