Re: how to generate code-loops

[David Livshin <david.livshin@xxxxxxxxxxx>]

Brian Budge wrote:
> Hi David -
>
> a)  It looks like a loop to me.
No it is not a loop, at least not a loop I would like to have. Perhaps I 
had to mention this in my message, but the boy of the "loop" should be a 
basic block ( no jump to/from it ) - the code generated is not a such.
> 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@xxxxxxxxxxx> 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@xxxxxxxxxxx
> >
> > http://www.dalsoft.com


--
David Livshin
david.livshin@xxxxxxxxxxx
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