I was looking at this all evening:
static inline void *
__memcpy(void * to, const void * from, size_t n)
{
int d0, d1, d2;
__asm__ __volatile__(
"rep ; movsl\n\t"
"testb $2,%b4\n\t"
"je 1f\n\t"
"movsw\n"
"1:\ttestb $1,%b4\n\t"
"je 2f\n\t"
"movsb\n"
"2:"
: "=&c" (d0), "=&D" (d1), "=&S" (d2)
:"0" (n/4), "q" (n),"1" ((long) to),"2" ((long) from)
: "memory");
return (to);
}
Something was not okay there... no, not and ugly style,
something else... finally I saw it:
there are two jumps too many! This is how it can be done:
static inline void *
vda_memcpy(void * to, const void * from, size_t n)
{
int d0, d1, d2;
char flag;
__asm__ __volatile__(
" shrl $1, %%ecx\n"
" setc %3\n"
" shrl $1, %%ecx\n"
" rep; movsl\n"
" rcll $1, %%ecx\n"
" rep; movsw\n"
" movb %3, %%cl\n"
" rep; movsb\n"
: "=&c" (d0), "=&D" (d1), "=&S" (d2), "=rb" (flag)
:"0" (n), "1" ((long) to), "2" ((long) from)
: "memory"
);
return (to);
}
But it is still looked not okay...
I think there are 3 intructions too many! Maybe:
static inline void *
vda_memcpy2(void * to, const void * from, size_t n)
{
int d0, d1, d2, d3;
__asm__ __volatile__(
" shrdl $2, %%ecx, %3\n"
" shrl $2, %%ecx\n"
" rep; movsl\n"
" shldl $2, %3, %%ecx\n"
" rep; movsb\n"
: "=&c" (d0), "=&D" (d1), "=&S" (d2), "=r" (d3)
: "0" (n), "1" ((long) to), "2" ((long) from)
: "memory"
);
return (to);
}
Just before mailing this, I thought a bit more...
static inline void *
vda_memcpy3(void * to, const void * from, size_t n)
{
int d0, d1, d2;
__asm__ __volatile__(
" rep; movsl\n"
" movl %4, %%ecx\n"
" rep; movsb\n"
: "=&c" (d0), "=&D" (d1), "=&S" (d2)
: "0" (n/4), "g" (n&3), "1" ((long) to), "2" ((long) from)
: "memory"
);
return (to);
}
# cat test.c
#include <stdlib.h> // for size_t
#include "string.h" // for abm memcpys
void *to, *from; int sz;
void f2() __attribute__ ((section ("ff2")));
void f3() __attribute__ ((section ("ff3")));
void f4() __attribute__ ((section ("ff4")));
void f5() __attribute__ ((section ("ff5")));
void f2() { memcpy(to,from,sz); }
void f3() { vda_memcpy(to,from,sz); }
void f4() { vda_memcpy2(to,from,sz); }
void f5() { vda_memcpy3(to,from,sz); }
# gcc -c -O2 -fomit-frame-pointer test.c
# objdump -D test.o
Disassembly of section ff2:
00000000 <f2>:
0: a1 00 00 00 00 mov 0x0,%eax
5: 57 push %edi
6: 89 c1 mov %eax,%ecx
8: 56 push %esi
9: 8b 3d 00 00 00 00 mov 0x0,%edi
f: 8b 35 00 00 00 00 mov 0x0,%esi
15: c1 e9 02 shr $0x2,%ecx
18: f3 a5 repz movsl %ds:(%esi),%es:(%edi)
1a: a8 02 test $0x2,%al
1c: 74 02 je 20 <f2+0x20>
1e: 66 a5 movsw %ds:(%esi),%es:(%edi)
20: a8 01 test $0x1,%al
22: 74 01 je 25 <f2+0x25>
24: a4 movsb %ds:(%esi),%es:(%edi)
25: 5e pop %esi
26: 5f pop %edi
27: c3 ret
Disassembly of section ff3:
00000000 <f3>:
0: 57 push %edi
1: 56 push %esi
2: 8b 3d 00 00 00 00 mov 0x0,%edi
8: 8b 35 00 00 00 00 mov 0x0,%esi
e: 8b 0d 00 00 00 00 mov 0x0,%ecx
14: d1 e9 shr %ecx
16: 0f 92 c0 setb %al
19: d1 e9 shr %ecx
1b: f3 a5 repz movsl %ds:(%esi),%es:(%edi)
1d: d1 d1 rcl %ecx
1f: f3 66 a5 repz movsw %ds:(%esi),%es:(%edi)
22: 88 c1 mov %al,%cl
24: f3 a4 repz movsb %ds:(%esi),%es:(%edi)
26: 5e pop %esi
27: 5f pop %edi
28: c3 ret
Disassembly of section ff4:
00000000 <f4>:
0: 57 push %edi
1: 56 push %esi
2: 8b 3d 00 00 00 00 mov 0x0,%edi
8: 8b 35 00 00 00 00 mov 0x0,%esi
e: 8b 0d 00 00 00 00 mov 0x0,%ecx
14: 0f ac c8 02 shrd $0x2,%ecx,%eax
18: c1 e9 02 shr $0x2,%ecx
1b: f3 a5 repz movsl %ds:(%esi),%es:(%edi)
1d: 0f a4 c1 02 shld $0x2,%eax,%ecx
21: f3 a4 repz movsb %ds:(%esi),%es:(%edi)
23: 5e pop %esi
24: 5f pop %edi
25: c3 ret
Disassembly of section ff5:
00000000 <f5>:
0: 8b 0d 00 00 00 00 mov 0x0,%ecx
6: 57 push %edi
7: 89 c8 mov %ecx,%eax
9: 56 push %esi
a: 8b 3d 00 00 00 00 mov 0x0,%edi
10: 8b 35 00 00 00 00 mov 0x0,%esi
16: 83 e0 03 and $0x3,%eax
19: c1 e9 02 shr $0x2,%ecx
1c: f3 a5 repz movsl %ds:(%esi),%es:(%edi)
1e: 89 c1 mov %eax,%ecx
20: f3 a4 repz movsb %ds:(%esi),%es:(%edi)
22: 5e pop %esi
23: 5f pop %edi
24: c3 ret
I think I shall not look there for a while ;)
Please somebody stop me... ;) ;)
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This archive was generated by hypermail 2b29 : Thu Nov 07 2002 - 22:00:32 EST