Re: [boost] Ann: Floating Point Utilities Review starts today

From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2008-02-26 17:18:58

On Tue, Feb 26, 2008 at 4:59 PM, Sebastian Redl
<sebastian.redl_at_[hidden]> wrote:
> Giovanni Piero Deretta wrote:
>  >    _Z9get_bits3f:
>  >         movss   %xmm0, -4(%rsp)
>  >         movl    -4(%rsp), %eax
>  >         ret
>  >
>  > Which should be optimal (IIRC you can't move from an xmms register to
>  > an integer register without passing through memory).
>  >
>  SSE2:
>  movd %xmm0, %eax
>

Right, it was the old x87 register stack that doesn't support
fp-register/general-purpose-register moves.
Anyways, after reading some documentation, it seems that the generated
assembly is probably still optimal for K8 and pentium4 which have
high latency and very high latency (respectively) xmm
register/register moves. My gcc version isn't specifically capable
of optimizing for core2, which shouldn't have this limitation.

-- 
gpd