On Saturday 18 August 2007 01:34:46 Stephen Hemminger wrote: > Optimize uses of memset with small constant offsets. > This will generate smaller code, and avoid the slow rep/string instructions. > Code copied from i386 with a little cleanup.
Newer gcc should do all this on its own. That is why I intentionally didn't implement it on 64bit. On what compiler version did you see smaller code? -Andi > > Signed-off-by: Stephen Hemminger <[EMAIL PROTECTED]> > > --- a/include/asm-x86_64/string.h 2007-08-17 15:14:32.000000000 -0700 > +++ b/include/asm-x86_64/string.h 2007-08-17 15:36:30.000000000 -0700 > @@ -42,9 +42,51 @@ extern void *__memcpy(void *to, const vo > __ret = __builtin_memcpy((dst),(src),__len); \ > __ret; }) > #endif > - > #define __HAVE_ARCH_MEMSET > -void *memset(void *s, int c, size_t n); > +void *__memset(void *s, int c, size_t n); > + > +/* Optimize for cases of trivial memset's > + * Compiler should optimize away all but the case used. > + */ > +static __always_inline void * > +__constant_c_and_count_memset(void *s, int c, size_t count) > +{ > + unsigned long pattern = 0x01010101UL * (unsigned char) c; > + > + switch (count) { > + case 0: > + return s; > + case 1: > + *(unsigned char *)s = pattern; > + return s; > + case 2: > + *(unsigned short *)s = pattern; > + return s; > + case 3: > + *(unsigned short *)s = pattern; > + *(2+(unsigned char *)s) = pattern; > + return s; > + case 4: > + *(unsigned long *)s = pattern; > + return s; > + case 6: > + *(unsigned long *)s = pattern; > + *(2+(unsigned short *)s) = pattern; > + return s; > + case 8: > + *(unsigned long *)s = pattern; > + *(1+(unsigned long *)s) = pattern; > + return s; > + default: > + return __memset(s, c, count); > + } > +} > +#define memset(s, c, count) \ > + (__builtin_constant_p(c) \ > + ? __constant_c_and_count_memset((s),(c),(count)) \ > + : __memset((s),(c),(count))) > + > + > > #define __HAVE_ARCH_MEMMOVE > void * memmove(void * dest,const void *src,size_t count); > --- a/arch/x86_64/kernel/x8664_ksyms.c 2007-08-17 15:14:32.000000000 > -0700 > +++ b/arch/x86_64/kernel/x8664_ksyms.c 2007-08-17 15:44:58.000000000 > -0700 > @@ -48,10 +48,12 @@ EXPORT_SYMBOL(__read_lock_failed); > #undef memmove > > extern void * memset(void *,int,__kernel_size_t); > +extern void * __memset(void *,int,__kernel_size_t); > extern void * memcpy(void *,const void *,__kernel_size_t); > extern void * __memcpy(void *,const void *,__kernel_size_t); > > EXPORT_SYMBOL(memset); > +EXPORT_SYMBOL(__memset); > EXPORT_SYMBOL(memcpy); > EXPORT_SYMBOL(__memcpy); > > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/