$ cat a.c a.s
__thread int n__thread;
_Thread_local int n_Thread_local;

int main(void)
{
  ++n__thread;
  --n_Thread_local;
  n__thread += n_Thread_local;
  n_Thread_local += n__thread;
}
    .file   "a.c"
    .globl  n__thread
    .section    .tbss,"awT",@nobits
    .align 4
    .type   n__thread, @object
    .size   n__thread, 4
n__thread:
    .zero   4
    .globl  n_Thread_local
    .align 4
    .type   n_Thread_local, @object
    .size   n_Thread_local, 4
n_Thread_local:
    .zero   4
    .text
    .globl  main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    pushl   %ebp
    .cfi_def_cfa_offset 8
    .cfi_offset 5, -8
    movl    %esp, %ebp
    .cfi_def_cfa_register 5
    movl    %gs:n__thread@ntpoff, %eax
    addl    $1, %eax
    movl    %eax, %gs:n__thread@ntpoff
    movl    %gs:n_Thread_local@ntpoff, %eax
    subl    $1, %eax
    movl    %eax, %gs:n_Thread_local@ntpoff
    movl    %gs:n__thread@ntpoff, %edx
    movl    %gs:n_Thread_local@ntpoff, %eax
    addl    %edx, %eax
    movl    %eax, %gs:n__thread@ntpoff
    movl    %gs:n_Thread_local@ntpoff, %edx
    movl    %gs:n__thread@ntpoff, %eax
    addl    %edx, %eax
    movl    %eax, %gs:n_Thread_local@ntpoff
    popl    %ebp
    .cfi_restore 5
    .cfi_def_cfa 4, 4
    ret
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (Ubuntu 4.9.2-10ubuntu13) 4.9.2"
    .section    .note.GNU-stack,"",@progbits