Re: GCC no longer synthesizing v2sf operations from v4sf operations?

[Uros Bizjak <uros at kss-loka dot si>]

Richard Guenther wrote:

> Oh, so we used to expand to 3dnow?  I see with gcc 3.4 produced:
>
> foo:
>        pushl   %ebp
>        movl    %esp, %ebp
>        pushl   %ebx
>        subl    $84, %esp
>        movl    12(%ebp), %eax
>        movl    16(%ebp), %edx
> [...]
>        movq    -64(%ebp), %mm0
>        movl    %ebx, -72(%ebp)
>        movl    -36(%ebp), %ebx
>        movl    %ebx, -68(%ebp)
>        pfadd   -72(%ebp), %mm0
>        movq    %mm0, -56(%ebp)
>        movl    12(%eax), %eax
> etc.
>
> This doesn't happen anymore with 4.0/4.1.
>  
IIRC, any generic code that produces MMX or 3DNow! instructions is 
disabled ATM, because gcc doesn't know how/when to insert emms/femms 
instruction. You don't want to mix 3dNow insns with x87 insn and use 
shared 3DNow/x87 registers without this insn...

Uros.