1 //===-- ExtractGV.cpp - Global Value extraction pass ----------------------===//
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
7 //===----------------------------------------------------------------------===//
9 // This pass extracts global values
11 //===----------------------------------------------------------------------===//
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"
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.
25 static void makeVisible(GlobalValue &GV, bool Delete) {
26 bool Local = GV.hasLocalLinkage();
27 if (Local || Delete) {
28 GV.setLinkage(GlobalValue::ExternalLinkage);
30 GV.setVisibility(GlobalValue::HiddenVisibility);
34 if (!GV.hasLinkOnceLinkage()) {
35 assert(!GV.isDiscardableIfUnused());
39 // Map linkonce* to weak* so that llvm doesn't drop this GV.
40 switch(GV.getLinkage()) {
42 llvm_unreachable("Unexpected linkage");
43 case GlobalValue::LinkOnceAnyLinkage:
44 GV.setLinkage(GlobalValue::WeakAnyLinkage);
46 case GlobalValue::LinkOnceODRLinkage:
47 GV.setLinkage(GlobalValue::WeakODRLinkage);
53 /// A pass to extract specific global values and their dependencies.
54 class GVExtractorPass : public ModulePass {
55 SetVector<GlobalValue *> Named;
58 static char ID; // Pass identification, replacement for typeid
60 /// If deleteS is true, this pass deletes the specified global values.
61 /// Otherwise, it deletes as much of the module as possible, except for the
62 /// global values specified.
63 explicit GVExtractorPass(std::vector<GlobalValue*> &GVs,
65 : ModulePass(ID), Named(GVs.begin(), GVs.end()), deleteStuff(deleteS) {}
67 bool runOnModule(Module &M) override {
71 // Visit the global inline asm.
73 M.setModuleInlineAsm("");
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.
82 // Visit the GlobalVariables.
83 for (Module::global_iterator I = M.global_begin(), E = M.global_end();
86 deleteStuff == (bool)Named.count(&*I) && !I->isDeclaration();
88 if (I->hasAvailableExternallyLinkage())
90 if (I->getName() == "llvm.global_ctors")
94 makeVisible(*I, Delete);
97 // Make this a declaration and drop it's comdat.
98 I->setInitializer(nullptr);
99 I->setComdat(nullptr);
103 // Visit the Functions.
104 for (Function &F : M) {
106 deleteStuff == (bool)Named.count(&F) && !F.isDeclaration();
108 if (F.hasAvailableExternallyLinkage())
112 makeVisible(F, Delete);
115 // Make this a declaration and drop it's comdat.
117 F.setComdat(nullptr);
121 // Visit the Aliases.
122 for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
124 Module::alias_iterator CurI = I;
127 bool Delete = deleteStuff == (bool)Named.count(&*CurI);
128 makeVisible(*CurI, Delete);
131 Type *Ty = CurI->getValueType();
133 CurI->removeFromParent();
134 llvm::Value *Declaration;
135 if (FunctionType *FTy = dyn_cast<FunctionType>(Ty)) {
136 Declaration = Function::Create(FTy, GlobalValue::ExternalLinkage,
137 CurI->getAddressSpace(),
138 CurI->getName(), &M);
142 new GlobalVariable(M, Ty, false, GlobalValue::ExternalLinkage,
143 nullptr, CurI->getName());
146 CurI->replaceAllUsesWith(Declaration);
155 char GVExtractorPass::ID = 0;
158 ModulePass *llvm::createGVExtractionPass(std::vector<GlobalValue *> &GVs,
160 return new GVExtractorPass(GVs, deleteFn);