On Tue, Jul 29, 2008 at 7:26 AM, Agner Fog <[EMAIL PROTECTED]> wrote: > Michael Matz wrote: >> >> You must be doing something wrong. If the compiler decides to inline the >> string ops it either knows the size or you told it to do it anyway >> (-minline-all-stringops or -minline-stringops-dynamically). In both cases >> will it use wider than byte moves when possible. >> > > g++ (v. 4.2.3) without any options converts memcpy with unknown size to rep > movsb
Make sure to use -D__NO_STRING_INLINES to not get glibcs inline implementation. Richard. > g++ with option -fno-builtin calls memcpy in libc > > The rep movs, stos, scas, cmps instructions are slower than function calls > except in rare cases. The compiler should never use the string instructions. > It is OK to use mov instructions if the size is known, but not string > instructions. >
