* Denys Vlasenko <dvlas...@redhat.com> wrote:
> 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
>
> With this .config:
> http://busybox.net/~vda/kernel_config_OPTIMIZE_INLINING_and_Os,
> the following functions get deinlined many times.
> Examples of disassembly:
>
> <get_unaligned_be16> (12 copies, 51 calls):
> 66 8b 07 mov (%rdi),%ax
> 55 push %rbp
> 48 89 e5 mov %rsp,%rbp
> 86 e0 xchg %ah,%al
> 5d pop %rbp
> c3 retq
>
> <get_unaligned_be32> (12 copies, 135 calls):
> 8b 07 mov (%rdi),%eax
> 55 push %rbp
> 48 89 e5 mov %rsp,%rbp
> 0f c8 bswap %eax
> 5d pop %rbp
> c3 retq
>
> <get_unaligned_be64> (2 copies, 20 calls):
> 48 8b 07 mov (%rdi),%rax
> 55 push %rbp
> 48 89 e5 mov %rsp,%rbp
> 48 0f c8 bswap %rax
> 5d pop %rbp
> c3 retq
>
> <__swab16p> (16 copies, 146 calls):
> 55 push %rbp
> 89 f8 mov %edi,%eax
> 86 e0 xchg %ah,%al
> 48 89 e5 mov %rsp,%rbp
> 5d pop %rbp
> c3 retq
>
> <__swab32p> (43 copies, ~560 calls):
> 55 push %rbp
> 89 f8 mov %edi,%eax
> 0f c8 bswap %eax
> 48 89 e5 mov %rsp,%rbp
> 5d pop %rbp
> c3 retq
>
> <__swab64p> (21 copies, 119 calls):
> 55 push %rbp
> 48 89 f8 mov %rdi,%rax
> 48 0f c8 bswap %rax
> 48 89 e5 mov %rsp,%rbp
> 5d pop %rbp
> c3 retq
>
> <__swab32s> (6 copies, 47 calls):
> 8b 07 mov (%rdi),%eax
> 55 push %rbp
> 48 89 e5 mov %rsp,%rbp
> 0f c8 bswap %eax
> 89 07 mov %eax,(%rdi)
> 5d pop %rbp
> c3 retq
>
> This patch fixes this via s/inline/__always_inline/.
> Code size decrease after the patch is ~4.5k:
>
> text data bss dec hex filename
> 92202377 20826112 36417536 149446025 8e85d89 vmlinux
> 92197848 20826112 36417536 149441496 8e84bd8 vmlinux5_swap_after
Acked-by: Ingo Molnar <mi...@kernel.org>
Thanks,
Ingo
