Re: [PATCH] Add type_unknown/type_executable/type_pic to output_type

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sun, Aug 23, 2015 at 6:50 AM, Alan Modra <amodra@gmail.com> wrote:
> Hmm, with x86_64 gcc 5.1.1 20150526, the size (as per size utility) of
> an --enable-targets=all ld went from 11546435 to 11537515 bytes with
> your patch.  I wondered where this was coming from, so added
>   unsigned int pad: 1;
> to struct bfd_link_info, after "type".
> That gave me 11546275 bytes.  So some of the improvement from your
> patch is due to better location of other fields.
>

I compared the assembly outputs of elflink.c on x86-64 with GCC 5.2.1
using -O2 -g0:

[hjl@gnu-tools-1 bfd]$ wc -l old.s new.s
 27370 old.s
 27304 new.s

My patch removes 66 lines of assembly codes.  I looked at
the differences and found:

old:

        testb   $8, 100(%rdi)
        movq    16(%rsi), %rbp
        jne     .L631
        movq    0(%rbp), %rax
        xorl    %r13d, %r13d
        movzbl  (%rax), %eax
        movl    %eax, %edx
        andl    $3, %edx
        cmpb    $1, %dl
        jbe     .L863
.L631:
        cmpb    $7, 24(%rbx)
        je      .L864
.L632:
        movl    4(%r12), %r9d
        testl   %r9d, %r9d
        jne     .L865
        testl   %r13d, %r13d
        jne     .L739
.L635:
        movq    8(%rbp), %rax

new

        testb   $8, 100(%rdi)
        movq    16(%rsi), %rbp
        jne     .L628
        movq    0(%rbp), %rax
        xorl    %r13d, %r13d
        movzbl  (%rax), %eax
        testb   $1, %al
        jne     .L862
.L628:
        cmpb    $7, 24(%rbx)
        je      .L863
.L629:
        movl    4(%r12), %eax
        testl   %eax, %eax
        jne     .L864
        testl   %r13d, %r13d
        jne     .L733
.L632:
        movq    8(%rbp), %rax

for

static bfd_boolean
elf_link_output_extsym (struct bfd_hash_entry *bh, void *data)
{
  struct elf_link_hash_entry *h = (struct elf_link_hash_entry *) bh;
  struct elf_outext_info *eoinfo = (struct elf_outext_info *) data;
  struct elf_final_link_info *flinfo = eoinfo->flinfo;
  bfd_boolean strip;
  Elf_Internal_Sym sym;
  asection *input_sec;
  const struct elf_backend_data *bed;
  long indx;
  int ret;
  /* A symbol is bound locally if it is forced local or it is locally
     defined, hidden versioned, not referenced by shared library and
     not exported when linking executable.  */
  bfd_boolean local_bind = (h->forced_local
                            || (bfd_link_executable (flinfo->info)
                                && !flinfo->info->export_dynamic
                                && !h->dynamic
                                && !h->ref_dynamic
                                && h->def_regular
                                && h->versioned == versioned_hidden));

My patch improves the generated code by changing

        movzbl  (%rax), %eax
        movl    %eax, %edx
        andl    $3, %edx
        cmpb    $1, %dl

to

        movzbl  (%rax), %eax
        testb   $1, %al

for bfd_link_executable (flinfo->info).

-- 
H.J.