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 // 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
createGVExtractionPass(std::vector<GlobalValue * > & GVs,bool deleteFn)157 ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue *> &GVs,
158 bool deleteFn) {
159 return new GVExtractorPass(GVs, deleteFn);
160 }
161