Re: how to generate code-loops

["Brian Budge" <brian dot budge at gmail dot com>]

Hi David -

a)  It looks like a loop to me.
b)  You instructed the compiler to unroll all loops, which is
apparently what it did.

Maybe I'm confused about what you are asking?

 Brian

On 9/30/06, David Livshin <david.livshin@dalsoft.com> wrote:
> Hi,
>
> Is there a way ( command line option ) to instruct the compiler to
> generate code-loops ( when possible ):
>
> Label:
>     <code>
>     conditional jump to 'Label'
>
>
> Compiling
>
> for ( k=0 ; k<n ; k++ )
> {
>     x[k] = y[k+1] - y[k];
> }
>
>
> with the command line options
>
> " -O3 -fomit-frame-pointer -funroll-all-loops -ffast-math
> -march=pentium4 -mfpmath=sse -msse2 -mmmx"
>
> produces
>
> .L1064:
>     movsd as1+32032(,%edx,8), %xmm1
>     subsd as1+32024(,%edx,8), %xmm1
>     movsd %xmm1, as1+24016(,%edx,8)
>     cmpl %ecx, %edx
>     je .L1010
> .L1012:
>     leal 1(%edx), %esi
>     movsd as1+32032(,%esi,8), %xmm0
>     subsd as1+32024(,%esi,8), %xmm0
>     movsd %xmm0, as1+24016(,%esi,8)
>     leal 2(%edx), %ebx
>     movsd as1+32032(,%ebx,8), %xmm7
>     subsd as1+32024(,%ebx,8), %xmm7
>     movsd %xmm7, as1+24016(,%ebx,8)
>     leal 3(%edx), %eax
>     movsd as1+32032(,%eax,8), %xmm6
>     subsd as1+32024(,%eax,8), %xmm6
>     movsd %xmm6, as1+24016(,%eax,8)
>     leal 4(%edx), %esi
>     movsd as1+32032(,%esi,8), %xmm5
>     subsd as1+32024(,%esi,8), %xmm5
>     movsd %xmm5, as1+24016(,%esi,8)
>     leal 5(%edx), %ebx
>     movsd as1+32032(,%ebx,8), %xmm4
>     subsd as1+32024(,%ebx,8), %xmm4
>     movsd %xmm4, as1+24016(,%ebx,8)
>     leal 6(%edx), %eax
>     movsd as1+32032(,%eax,8), %xmm3
>     subsd as1+32024(,%eax,8), %xmm3
>     movsd %xmm3, as1+24016(,%eax,8)
>     leal 7(%edx), %esi
>     movsd as1+32032(,%esi,8), %xmm2
>     subsd as1+32024(,%esi,8), %xmm2
>     movsd %xmm2, as1+24016(,%esi,8)
>     addl $8, %edx
>     jmp .L1064
> .L1010:
>
> which is not a loop; it is difficult to process ( and also runs slower
> then when the code is a loop ).
>
> Thank you in advance,
>
> David
>
> --
> David Livshin
> david.livshin@dalsoft.com
>
> http://www.dalsoft.com