For this code LLVM generates code that doesn't use tailcall optimization.

struct token
{
    char const* tok_start;
    char const* tok_end;
    int tok_type;
    unsigned identifier_hash;
};

token f();

token g()
{
  return f();
}

Generated code:

g():                                  # @g()
        pushq   %rbx
        movq    %rdi, %rbx
        callq   f()
        movq    %rbx, %rax
        popq    %rbx
        retq



Expected code:

g():                                  # @g()
        jmpq    f()