[llvm-dev] Getting a pointer to a i8 from a global variable that holds a constant string

Lorin Atzberger via llvm-dev llvm-dev at lists.llvm.org
Sat Apr 8 05:18:11 PDT 2017


I'm trying to get the pointer to the first element of a string (so that I
can pass it to a function).
The string itself is a constant kept in a global variable.
My end goal is to generate the IR for something like "puts("Hello World")";
I'm stuck on the parameter part of the call instruction.

So far I have something like this:

const std::string& str = strExpr->value();
llvm::ArrayType* type = llvm::ArrayType::get(llvm::IntegerType::get(m_context,
8), str.size()+1);
llvm::GlobalVariable* var = new llvm::GlobalVariable(m_module, type, true,
llvm::GlobalValue::PrivateLinkage, nullptr, ".str");

llvm::Constant* c = llvm::ConstantDataArray::getString(m_context, str);

The part below is the one I have problems with:

llvm::ConstantInt* const_int32_12 = llvm::ConstantInt::get(m_context,
llvm::APInt(32, llvm::StringRef("0"), 10));
std::vector<llvm::Constant*> const_ptr_14_indices;
return llvm::ConstantExpr::getGetElementPtr(nullptr,c,

I realize that the GlobalVariable should not be declared every time I get
in that function but that's something I'll fix after I get this working.

Any help here would be appreciated.

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