x86/asm/bitops: Force inlining of test_and_set_bit and friends

x86/asm/bitops: Force inlining of test_and_set_bit and friends

Sometimes GCC mysteriously doesn't inline very small functions
we expect to be inlined, see:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66122

Arguably, GCC should do better, but GCC people aren't willing
to invest time into it and are asking to use __always_inline
instead.

With this .config:

  http://busybox.net/~vda/kernel_config_OPTIMIZE_INLINING_and_Os

here's an example of functions getting deinlined many times:

  test_and_set_bit (166 copies, ~1260 calls)
         55                      push   %rbp
         48 89 e5                mov    %rsp,%rbp
         f0 48 0f ab 3e          lock bts %rdi,(%rsi)
         72 04                   jb     <test_and_set_bit+0xf>
         31 c0                   xor    %eax,%eax
         eb 05                   jmp    <test_and_set_bit+0x14>
         b8 01 00 00 00          mov    $0x1,%eax
         5d                      pop    %rbp
         c3                      retq

  test_and_clear_bit (124 copies, ~1000 calls)
         55                      push   %rbp
         48 89 e5                mov    %rsp,%rbp
         f0 48 0f b3 3e          lock btr %rdi,(%rsi)
         72 04                   jb     <test_and_clear_bit+0xf>
         31 c0                   xor    %eax,%eax
         eb 05                   jmp    <test_and_clear_bit+0x14>
         b8 01 00 00 00          mov    $0x1,%eax
         5d                      pop    %rbp
         c3                      retq

  change_bit (3 copies, 8 calls)
         55                      push   %rbp
         48 89 e5                mov    %rsp,%rbp
         f0 48 0f bb 3e          lock btc %rdi,(%rsi)
         5d                      pop    %rbp
         c3                      retq

  clear_bit_unlock (2 copies, 11 calls)
         55                      push   %rbp
         48 89 e5                mov    %rsp,%rbp
         f0 48 0f b3 3e          lock btr %rdi,(%rsi)
         5d                      pop    %rbp
         c3                      retq

This patch works it around via s/inline/__always_inline/.

Code size decrease by ~13.5k after the patch:

      text     data      bss       dec    filename
  92110727 20826144 36417536 149354407    vmlinux.before
  92097234 20826176 36417536 149340946    vmlinux.after

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Graf <tgraf@suug.ch>
Link: http://lkml.kernel.org/r/1454881887-1367-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>