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Date: Thu, 04 Mar 2004 15:14:33 +1000
From: Peter Grehan <grehan@freebsd.org>
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Subject: Re: User-space context switch and floating-point
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 > how do you generate code that does:
> 
>   double x, y;
> 
>   ...
>   x = y * 1.5 * sqrt(2.25) - 3.15 + pthread_mutex_lock(&m) + 1.25;

  Substitute integers for float and it's exactly the same problem
and handled in the same way: the caller saves registers it is using
for intermediate results prior to the mutex_lock and restores them
on return according to the calling convention.

> I don't know anything about PPC...

  It's generic RISC, similar to Alpha in terms of register usage.
That's what made me wonder about not saving FP state in the Alpha
code, but I now think that's a requirement if there are 2 or more
threads using FP. That will be a big performance hit as per my
routine comments so I'll do some experiments to see how severe
it is and whether it can be alleviated.

later,

Peter.