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Re: [PATCH, i386]: Do not emit "cld" instructions

On 12/5/06, Uros Bizjak <ubizjak@gmail.com> wrote:

>>According to the guide, it applies to pentium4.
>>
>>
>
>This is pretty high.  Would be possible for you to rerun the
>test_stringops script on P4 machine after removing the CLD?  If it
>really is 48 cycles, it should show difference in the preffered memcpy
>codegen.
>
>
>
Sure! But I think that this is an error in the optimizing guide.

... NOT.

--cut here--
#define rdtsc(value) \
asm volatile("rdtsc":"=A" (value))

int main(int argc, char ** argv)
{
 unsigned long long a,b;

 rdtsc(a);
 rdtsc(b);
 printf("%lld\n", b-a);

 rdtsc(a);
 asm volatile ("std; cld;");
 rdtsc(b);
 printf("%lld\n", b-a);

 return 0;
}

--cut here--

gcc -O2
./a.out

./a.out
84
172
./a.out
84
172
/a.out
84
188
/a.out
84
188
./a.out
84
172

Uros.

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