bool Linker::linkInMetadata(Module &Src,
DenseMap<unsigned, MDNode *> *ValIDToTempMDMap) {
SetVector<GlobalValue *> ValuesToLink;
if (Mover.move(
Src, ValuesToLink.getArrayRef(),
[this](GlobalValue &GV, IRMover::ValueAdder Add) { assert(false); },
ValIDToTempMDMap, true))
return true;
return false;
}
// If a linkonce global is present in the MustPreserveSymbols, we need to make
// sure we honor this. To force the compiler to not drop it, we add it to the
// "llvm.compiler.used" global.
void LTOCodeGenerator::preserveDiscardableGVs(
Module &TheModule,
llvm::function_ref<bool(const GlobalValue &)> mustPreserveGV) {
SetVector<Constant *> UsedValuesSet;
if (GlobalVariable *LLVMUsed =
TheModule.getGlobalVariable("llvm.compiler.used")) {
ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
for (auto &V : Inits->operands())
UsedValuesSet.insert(cast<Constant>(&V));
LLVMUsed->eraseFromParent();
}
llvm::Type *i8PTy = llvm::Type::getInt8PtrTy(TheModule.getContext());
auto mayPreserveGlobal = [&](GlobalValue &GV) {
if (!GV.isDiscardableIfUnused() || GV.isDeclaration())
return;
if (!mustPreserveGV(GV))
return;
if (GV.hasAvailableExternallyLinkage()) {
emitWarning(
(Twine("Linker asked to preserve available_externally global: '") +
GV.getName() + "'").str());
return;
}
if (GV.hasInternalLinkage()) {
emitWarning((Twine("Linker asked to preserve internal global: '") +
GV.getName() + "'").str());
return;
}
UsedValuesSet.insert(ConstantExpr::getBitCast(&GV, i8PTy));
};
for (auto &GV : TheModule)
mayPreserveGlobal(GV);
for (auto &GV : TheModule.globals())
mayPreserveGlobal(GV);
for (auto &GV : TheModule.aliases())
mayPreserveGlobal(GV);
if (UsedValuesSet.empty())
return;
llvm::ArrayType *ATy = llvm::ArrayType::get(i8PTy, UsedValuesSet.size());
auto *LLVMUsed = new llvm::GlobalVariable(
TheModule, ATy, false, llvm::GlobalValue::AppendingLinkage,
llvm::ConstantArray::get(ATy, UsedValuesSet.getArrayRef()),
"llvm.compiler.used");
LLVMUsed->setSection("llvm.metadata");
}
