Re: GCC beaten by ICC in stupid trig test!

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

> >The reason why still is that ICC will just unroll the loop to be "r = 
> >doit(a)*100000000.0" so that is the reasons why
> >ICC is better than GCC at doing this stupid trig test (note this is 
> >transformation
> >is only valid if fast-math is on as you loose precision).
> 
> In the meanwhile we have learned that the real reason why Icc performs
> better then mainline gcc is the use of an iterative SSE instruction
> (see Dan Nicolaescu message).
> 
> On the other hand, gcc-lno "appear" to perform as well as Icc because of
> the unrolling trick (just checked that gcc-lno transforms the loop to
> the trivial:
>
>   8048470:       40                      inc    %eax
>   8048471:       d8 c1                   fadd   %st(1),%st
>   8048473:       3d 00 e1 f5 05          cmp    $0x5f5e100,%eax
>   8048478:       75 f6                   jne    8048470 <main+0x20>)
> 
> Now, my question is: why gcc-lno is doing that also when -ffast-math is
> *not* passed???

doing what? I do not see any loop related optimization here.

Zdenek