1 //===-- ExtractGV.cpp - Global Value extraction pass ----------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This pass extracts global values
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "llvm/ADT/SetVector.h"
14 #include "llvm/IR/LLVMContext.h"
15 #include "llvm/IR/Module.h"
16 #include "llvm/Pass.h"
17 #include "llvm/Transforms/IPO.h"
18 #include <algorithm>
19 using namespace llvm;
20
21 /// Make sure GV is visible from both modules. Delete is true if it is
22 /// being deleted from this module.
23 /// This also makes sure GV cannot be dropped so that references from
24 /// the split module remain valid.
makeVisible(GlobalValue & GV,bool Delete)25 static void makeVisible(GlobalValue &GV, bool Delete) {
26 bool Local = GV.hasLocalLinkage();
27 if (Local || Delete) {
28 GV.setLinkage(GlobalValue::ExternalLinkage);
29 if (Local)
30 GV.setVisibility(GlobalValue::HiddenVisibility);
31 return;
32 }
33
34 if (!GV.hasLinkOnceLinkage()) {
35 assert(!GV.isDiscardableIfUnused());
36 return;
37 }
38
39 // Map linkonce* to weak* so that llvm doesn't drop this GV.
40 switch(GV.getLinkage()) {
41 default:
42 llvm_unreachable("Unexpected linkage");
43 case GlobalValue::LinkOnceAnyLinkage:
44 GV.setLinkage(GlobalValue::WeakAnyLinkage);
45 return;
46 case GlobalValue::LinkOnceODRLinkage:
47 GV.setLinkage(GlobalValue::WeakODRLinkage);
48 return;
49 }
50 }
51
52 namespace {
53 /// A pass to extract specific global values and their dependencies.
54 class GVExtractorPass : public ModulePass {
55 SetVector<GlobalValue *> Named;
56 bool deleteStuff;
57 bool keepConstInit;
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,bool keepConstInit=false)64 explicit GVExtractorPass(std::vector<GlobalValue*> &GVs,
65 bool deleteS = true, bool keepConstInit = false)
66 : ModulePass(ID), Named(GVs.begin(), GVs.end()), deleteStuff(deleteS),
67 keepConstInit(keepConstInit) {}
68
runOnModule(Module & M)69 bool runOnModule(Module &M) override {
70 if (skipModule(M))
71 return false;
72
73 // Visit the global inline asm.
74 if (!deleteStuff)
75 M.setModuleInlineAsm("");
76
77 // For simplicity, just give all GlobalValues ExternalLinkage. A trickier
78 // implementation could figure out which GlobalValues are actually
79 // referenced by the Named set, and which GlobalValues in the rest of
80 // the module are referenced by the NamedSet, and get away with leaving
81 // more internal and private things internal and private. But for now,
82 // be conservative and simple.
83
84 // Visit the GlobalVariables.
85 for (GlobalVariable &GV : M.globals()) {
86 bool Delete = deleteStuff == (bool)Named.count(&GV) &&
87 !GV.isDeclaration() &&
88 (!GV.isConstant() || !keepConstInit);
89 if (!Delete) {
90 if (GV.hasAvailableExternallyLinkage())
91 continue;
92 if (GV.getName() == "llvm.global_ctors")
93 continue;
94 }
95
96 makeVisible(GV, Delete);
97
98 if (Delete) {
99 // Make this a declaration and drop it's comdat.
100 GV.setInitializer(nullptr);
101 GV.setComdat(nullptr);
102 }
103 }
104
105 // Visit the Functions.
106 for (Function &F : M) {
107 bool Delete =
108 deleteStuff == (bool)Named.count(&F) && !F.isDeclaration();
109 if (!Delete) {
110 if (F.hasAvailableExternallyLinkage())
111 continue;
112 }
113
114 makeVisible(F, Delete);
115
116 if (Delete) {
117 // Make this a declaration and drop it's comdat.
118 F.deleteBody();
119 F.setComdat(nullptr);
120 }
121 }
122
123 // Visit the Aliases.
124 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
125 I != E;) {
126 Module::alias_iterator CurI = I;
127 ++I;
128
129 bool Delete = deleteStuff == (bool)Named.count(&*CurI);
130 makeVisible(*CurI, Delete);
131
132 if (Delete) {
133 Type *Ty = CurI->getValueType();
134
135 CurI->removeFromParent();
136 llvm::Value *Declaration;
137 if (FunctionType *FTy = dyn_cast<FunctionType>(Ty)) {
138 Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage,
139 CurI->getAddressSpace(),
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,bool keepConstInit)160 ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue *> &GVs,
161 bool deleteFn, bool keepConstInit) {
162 return new GVExtractorPass(GVs, deleteFn, keepConstInit);
163 }
164