disabling loop unrolling in GCC

[Aviv Greenberg]

This is what i get if i set i to be volatile in gcc 4.3.1 with -O3:

 0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   83 ec 10                sub    $0x10,%esp
   6:   c7 45 fc 00 00 00 00    movl   $0x0,-0x4(%ebp)
   d:   8b 45 fc                mov    -0x4(%ebp),%eax
  10:   83 f8 07                cmp    $0x7,%eax
  13:   7f 1e                   jg     33 <func+0x33>
  15:   8d 76 00                lea    0x0(%esi),%esi
  18:   c7 05 00 00 00 00 00    movl   $0x0,0x0
  1f:   00 00 00
  22:   8b 45 fc                mov    -0x4(%ebp),%eax
  25:   83 c0 01                add    $0x1,%eax
  28:   89 45 fc                mov    %eax,-0x4(%ebp)
  2b:   8b 45 fc                mov    -0x4(%ebp),%eax
  2e:   83 f8 07                cmp    $0x7,%eax
  31:   7e e5                   jle    18 <func+0x18>
  33:   c9                      leave
  34:   c3                      ret

looks like i was right!

On Mon, Dec 21, 2009 at 15:54, Shachar Shemesh <shachar at shemesh.biz> wrote:
> Aviv Greenberg wrote:
>
> Just out of curiousity: why do you care about the resulting assembly?
> It's a strong indication that you are doing something wrong :)
>
>
> First, we have found several bugs in GCC as a result of "caring about the
> assembly". Lets agree that it's an indication that someone is doing
> something wrong.
>
> The reason I'm trying to disable this optimization is because it causes the
> code to be too big to fit onto the available ROM on which the code needs to
> be flashed. The X86 version I gave here shows the problem, but is no the
> platform on which the problem was diagnosed.
>
> Shachar
>
> --
> Shachar Shemesh
> Lingnu Open Source Consulting Ltd.
> http://www.lingnu.com
>



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