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Subject[PATCH] fix i386 memcpy
Date
This patch shortens non-constant memcpy() by two bytes
and fixes spurious out-of-line constant memcpy().

Patch is run-tested (I run on patched kernel right now).

Benchmark and code generation test program will be mailed as reply.

# size vmlinux.org vmlinux
text data bss dec hex filename
3954591 1553426 236544 5744561 57a7b1 vmlinux.org
3952615 1553426 236544 5742585 579ff9 vmlinux

Example of changes (part of dump_fpu() body):
old.............................................. new......................
8d 83 40 02 00 00 lea 0x240(%ebx),%eax 8d b3 40 02 00 00 lea 0x240(%ebx),%esi
74 31 je c0108b27 <dump_fpu+0x9c> 74 2e je c0108b1d <dump_fpu+0x92>
6a 1c push $0x1c 8b 7d 0c mov 0xc(%ebp),%edi
50 push %eax b9 07 00 00 00 mov $0x7,%ecx
56 push %esi f3 a5 repz movsl %ds:(%esi),%es:(%edi)
e8 49 21 10 00 call c020ac48 <memcpy> 8b 55 0c mov 0xc(%ebp),%edx
83 c4 0c add $0xc,%esp 83 c2 1c add $0x1c,%edx
83 c6 1c add $0x1c,%esi 8d 83 60 02 00 00 lea 0x260(%ebx),%eax
81 c3 60 02 00 00 add $0x260,%ebx b9 07 00 00 00 mov $0x7,%ecx
bf 07 00 00 00 mov $0x7,%edi 89 d7 mov %edx,%edi
6a 0a push $0xa 89 c6 mov %eax,%esi
53 push %ebx a5 movsl %ds:(%esi),%es:(%edi)
56 push %esi a5 movsl %ds:(%esi),%es:(%edi)
e8 2f 21 10 00 call c020ac48 <memcpy> 66 a5 movsw %ds:(%esi),%es:(%edi)
83 c4 0c add $0xc,%esp 83 c2 0a add $0xa,%edx
83 c6 0a add $0xa,%esi 83 c0 10 add $0x10,%eax
83 c3 10 add $0x10,%ebx 49 dec %ecx
4f dec %edi 79 ef jns c0108b0a <dump_fpu+0x7f>
79 eb jns c0108b10 <dump_fpu+0x85> eb 0a jmp c0108b27 <dump_fpu+0x9c>
eb 0c jmp c0108b33 <dump_fpu+0xa8> 8b 7d 0c mov 0xc(%ebp),%edi
6a 6c push $0x6c b9 1b 00 00 00 mov $0x1b,%ecx
50 push %eax f3 a5 repz movsl %ds:(%esi),%es:(%edi)
56 push %esi 8b 45 f0 mov 0xfffffff0(%ebp),%eax
e8 18 21 10 00 call c020ac48 <memcpy> 5a pop %edx
83 c4 0c add $0xc,%esp 5b pop %ebx
8b 45 f0 mov 0xfffffff0(%ebp),%eax
8d 65 f4 lea 0xfffffff4(%ebp),%esp
5b pop %ebx
5e pop %esi
--
vda
--- linux-2.6.11.src/include/asm-i386/string.h.orig Thu Mar 3 09:31:08 2005
+++ linux-2.6.11.src/include/asm-i386/string.h Tue Mar 29 22:05:00 2005
@@ -198,46 +198,75 @@ static inline void * __memcpy(void * to,
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:"
+ "movl %4,%%ecx\n\t"
+ "andl $3,%%ecx\n\t"
+ "jz 1f\n\t" /* pay 2 byte penalty for a chance to skip microcoded rep */
+ "rep ; movsb\n\t"
+ "1:"
: "=&c" (d0), "=&D" (d1), "=&S" (d2)
- :"0" (n/4), "q" (n),"1" ((long) to),"2" ((long) from)
+ : "0" (n/4), "g" (n), "1" ((long) to), "2" ((long) from)
: "memory");
return (to);
}

/*
- * This looks horribly ugly, but the compiler can optimize it totally,
+ * This looks ugly, but the compiler can optimize it totally,
* as the count is constant.
*/
static inline void * __constant_memcpy(void * to, const void * from, size_t n)
{
- if (n <= 128)
- return __builtin_memcpy(to, from, n);
-
-#define COMMON(x) \
-__asm__ __volatile__( \
- "rep ; movsl" \
- x \
- : "=&c" (d0), "=&D" (d1), "=&S" (d2) \
- : "0" (n/4),"1" ((long) to),"2" ((long) from) \
- : "memory");
-{
- int d0, d1, d2;
+#if 1 /* want to do small copies with non-string ops? */
+ switch (n) {
+ case 0: return to;
+ case 1: *(char*)to = *(char*)from; return to;
+ case 2: *(short*)to = *(short*)from; return to;
+ case 4: *(int*)to = *(int*)from; return to;
+#if 1 /* including those doable with two moves? */
+ case 3: *(short*)to = *(short*)from;
+ *((char*)to+2) = *((char*)from+2); return to;
+ case 5: *(int*)to = *(int*)from;
+ *((char*)to+4) = *((char*)from+4); return to;
+ case 6: *(int*)to = *(int*)from;
+ *((short*)to+2) = *((short*)from+2); return to;
+ case 8: *(int*)to = *(int*)from;
+ *((int*)to+1) = *((int*)from+1); return to;
+#endif
+ }
+#else
+ if (!n) return to;
+#endif
+ {
+ /* load esi/edi */
+ int esi, edi;
+ __asm__ __volatile__(
+ ""
+ : "=&D" (edi), "=&S" (esi)
+ : "0" ((long) to),"1" ((long) from)
+ : "memory"
+ );
+ }
+ if (n >= 5*4) {
+ /* large block: use rep prefix */
+ int ecx;
+ __asm__ __volatile__(
+ "rep ; movsl"
+ : "=&c" (ecx)
+ : "0" (n/4)
+ );
+ } else {
+ /* small block: don't clobber ecx + smaller code */
+ if (n >= 4*4) __asm__ __volatile__("movsl");
+ if (n >= 3*4) __asm__ __volatile__("movsl");
+ if (n >= 2*4) __asm__ __volatile__("movsl");
+ if (n >= 1*4) __asm__ __volatile__("movsl");
+ }
switch (n % 4) {
- case 0: COMMON(""); return to;
- case 1: COMMON("\n\tmovsb"); return to;
- case 2: COMMON("\n\tmovsw"); return to;
- default: COMMON("\n\tmovsw\n\tmovsb"); return to;
+ /* tail */
+ case 0: return to;
+ case 1: __asm__ __volatile__("movsb"); return to;
+ case 2: __asm__ __volatile__("movsw"); return to;
+ default: __asm__ __volatile__("movsw\n\tmovsb"); return to;
}
-}
-
-#undef COMMON
}

#define __HAVE_ARCH_MEMCPY
\
 
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