(unknown charset) Re: Problems Building 7.0-Beta3 with -Os

Ruslan Ermilov <ru_at_freebsd.org> (from Thu, 6 Dec 2007 10:22:39 wrote:
>> In otherwords:  -O1 < -Os < -O2   (properly)
>>
> I read it differently.  From the manpage:
> : -Os Optimize for size.  -Os enables all -O2 optimizations that do not
> :     typically increase code size.  It also performs further optimiza-
> :     tions designed to reduce code size.
>
> It says that -Os is a subset of -O2 optimizations plus some
> extra optimizations.  Reading further in a manpage, there's
> only one, -mspace.

Yeah, GCC 4.2 now adds a few things to -Os:
  sets optimize = 2, and
  remove from -O1: flag_tree_ch
  remove from -O2: flag_tree_pre
  }
  if (optimize_size)¶ {¶
    align_loops = 1;
    align_jumps = 1;
    align_labels = 1;¶
    align_functions = 1;¶
    flag_reorder_blocks = 0;¶
    flag_reorder_blocks_and_partition = 0;¶
    /* Inlining of very small functions usually reduces total size. */¶
    set_param_value ("max-inline-insns-single", 5);¶
    set_param_value ("max-inline-insns-auto", 5);¶
    flag_inline_functions = 1;  // taken from -O3¶
    /* We want to crossjump as much as possible.  */¶
    set_param_value ("min-crossjump-insns", 1);
  }


On Thu, Dec 06, 2007 at 08:43:42AM +0100, Alexander Leidinger wrote:
> And after the import of the new gcc in 7, a lot of people noticed, that
> the resulting binaries are larger with -Os than with -O2.

    quynh:/usr/src/usr.bin/vi> uname -m
    amd64
    quynh:/usr/src/usr.bin/vi> /bin/ls -l nvi.-O*
    -rwxr-xr-x  1 root  ncvs  366894 Dec  6 08:21 nvi.-O2
    -rwxr-xr-x  1 root  ncvs  313043 Dec  6 08:21 nvi.-Os
    quynh:/usr/src/usr.bin/vi> size nvi.-O*
       text    data     bss     dec     hex filename
     326132    1944    4392  332468   512b4 nvi.-O2
     273759    1944    4392  280095   4461f nvi.-Os

Perhaps you mean *sometimes* larger.
Also -Os goal is run-time foot print, not disk foot print.

--
-- David  (obrien_at_FreeBSD.org)