LLVM IR C++ API create anonymous global variable - c++

Question

How can I create an anonymous global variable in LLVM IR C++ API?
I can create a named global variable as follows:
GlobalVariable *createGlobalVariable(
Module *module,
Type *type,
std::string name
) {
module->getOrInsertGlobal(name, type);
return module->getNamedGlobal(name);
}
For example:
auto context = new LLVMContext();
auto module = new Module("Module", *context);
auto type = IntegerType::getInt32Ty(*context);
auto globalVariable = createGlobalVariable(
module,
type,
"globalVariableName"
);
auto constantInt = ConstantInt::getIntegerValue(
type,
APInt(32, 42)
);
globalVariable->setInitializer(constantInt);
module->dump();
It will generate:
; ModuleID = 'Module'
source_filename = "Module"
#globalVariableName = global i32 42
How can I create an anonymous global variable?
I would like to generate somethings like:
; ModuleID = 'Module'
source_filename = "Module"
#0 = global i32 42
#0 is a unique identifiers

Answer 1

In comment, #IlCapitano said that Pass "" as name
I try
auto context = new LLVMContext();
auto module = new Module("Module", *context);
auto type = IntegerType::getInt32Ty(*context);
auto constant = module->getOrInsertGlobal("", type);
module->dump();
It generates:
; ModuleID = 'Module'
source_filename = "Module"
#0 = external global i32
But if I set initializer, will be Segmentation fault
auto constant = module->getOrInsertGlobal("", type);
auto anonymousGlobalVariable = module->getNamedGlobal(constant->getName());
anonymousGlobalVariable->setInitializer(constantInt);
// -> Segmentation fault
The correct way is creating GlobalVariable by using constructor:
auto context = new LLVMContext();
auto module = new Module("Module", *context);
auto type = IntegerType::getInt32Ty(*context);
auto constantInt = ConstantInt::getIntegerValue(type, APInt(32, 42));
auto anonymousGlobalVariable = new GlobalVariable(
*module,
type,
false,
GlobalValue::CommonLinkage,
constantInt,
""
);
module->dump();
Nice
; ModuleID = 'Module'
source_filename = "Module"
#0 = common global i32 42

Answer 2

I'm kinda new to the llvm c++ api, but using the llvm toolchain, we can determine how c++ static global variables are represented in llvm ir (assuming your intention is to generate unique identifiers among multiple translation units (i.e. fix name collisions when linking multiple llvm ir files together)).
Given non-static.cpp:
int x = 0;
clang -S -emit-llvm non-static.cpp emits this for our global x:
[...]
#x = dso_local global i32 0, align 4
[...]
Given static.cpp:
static int x = 0;
int main() {
return x; // refer to `x` so llvm doesn't optimize it away
}
clang -S -emit-llvm static.cpp emits this for our global x:
[...]
#_ZL1x = internal global i32 0, align 4
[...]
Note the presence of the internal linkage type.
To set this modifier using the llvm c++ api, you have to call one of GlobalVariable's constructors and pass llvm::GlobalValue::LinkageTypes::InternalLinkage to the Linkage parameter.