• Arjan van de Ven's avatar
    x86: Use __builtin_memset and __builtin_memcpy for memset/memcpy · ff60fab7
    Arjan van de Ven authored
    GCC provides reasonable memset/memcpy functions itself, with __builtin_memset
    and __builtin_memcpy. For the "unknown" cases, it'll fall back to our
    current existing functions, but for fixed size versions it'll inline
    something smart. Quite often that will be the same as we have now,
    but sometimes it can do something smarter (for example, if the code
    then sets the first member of a struct, it can do a shorter memset).
    
    In addition, and this is more important, gcc knows which registers and
    such are not clobbered (while for our asm version it pretty much
    acts like a compiler barrier), so for various cases it can avoid reloading
    values.
    
    The effect on codesize is shown below on my typical laptop .config:
    
       text	   data	    bss	    dec	    hex	filename
    5605675	2041100	6525148	14171923	 d83f13	vmlinux.before
    5595849	2041668	6525148	14162665	 d81ae9	vmlinux.after
    
    Due to some not-so-good behavior in the gcc 3.x series, this change
    is only done for GCC 4.x and above.
    Signed-off-by: default avatarArjan van de Ven <arjan@linux.intel.com>
    LKML-Reference: <20090928142122.6fc57e9c@infradead.org>
    Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
    ff60fab7
string_32.h 7.66 KB