Date: Wed, 14 Nov 2001 15:26:58 -0800 From: Mark Peek <mark@peek.org> To: Greg Lehey <grog@FreeBSD.org> Cc: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/powerpc/powerpc machdep.c Message-ID: <p05101008b818a9b71348@[207.76.207.129]> In-Reply-To: <20011115093118.G40270@monorchid.lemis.com> References: <200111130044.fAD0iL972345@freefall.freebsd.org> <20011115093118.G40270@monorchid.lemis.com>
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At 9:31 AM +1030 11/15/01, Greg Lehey wrote:
>On Monday, 12 November 2001 at 16:44:21 -0800, Mark Peek wrote:
>> mp 2001/11/12 16:44:21 PST
>>
>> Modified files:
>> sys/powerpc/powerpc machdep.c
>> Log:
>> Don't enable FP in the kernel. It is not needed when -msoft-float is used.
>
>Why is FP needed at all?
Without -msoft-float, gcc uses the FP registers for code optimization
like 8 byte structure copies. For instance, this contrived example:
struct foo {
char c[8];
} a, b;
bar()
{
a = b;
}
produces this:
...
bar:
lis 9,a@ha
la 9,a@l(9)
lis 11,b@ha
la 11,b@l(11)
lfd 0,0(11) <====
stfd 0,0(9) <====
blr
...
and with -msoft-float:
...
bar:
lis 9,a@ha
la 9,a@l(9)
lis 11,b@ha
la 11,b@l(11)
lwz 12,4(11)
lwz 11,0(11)
stw 11,0(9)
stw 12,4(9)
blr
...
Mark
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