Function LLVMGetIntrinsicDeclaration 

pub unsafe extern "C" fn LLVMGetIntrinsicDeclaration(
    Mod: LLVMModuleRef,
    ID: c_uint,
    ParamTypes: *mut LLVMTypeRef,
    ParamCount: usize,
) -> LLVMValueRef

Get or insert the declaration of an intrinsic. For overloaded intrinsics, parameter types must be provided to uniquely identify an overload.

@see llvm::Intrinsic::getOrInsertDeclaration()