On Wed, 2008-07-09 at 14:50 +0200, Christian Franke wrote: > Overall size from inline asm would only be smaller if there is any > benefit from additional optimizations.
Correct. Function calls use fixed registers for everything, but macros don't have to. > Result with the test script from my last mail: > > Debian gcc 4.1.2-7: > inline (portable)=357, inline (asm)=126, function=104 > > Cygwin gcc 3.4.4: > inline (portable)=340, inline (asm)=124, function=96 > > Function call is still better. The only candidate for inline is probably > grub_swap_bytes16(). But we are getting closer! > > .... And if written properly, it could work with any of > > the registers that allow access to the lower two bytes (%eax, %ebx, > > %ecx and %edx), thus giving more flexibility to the optimizer. > > > > This would require support to access the Rl and Rh parts of eRx for each > R in [a-d]. Something like: > > asm ( > "xchg %0:l,%0:h\n" > "roll $0x10,%0\n" > "xchg %0:l,%0:h\n" > : "=r"(_y) : "0"(_x) \ > ); > > Do gcc or gas provide a syntax to do this? Yes. That's %b0 and %h0. Use "=q" for all registers with "upper halves" (%ah-%dh). Also, please be consistent and use width suffixes everywhere. xchg should be xchgb. -- Regards, Pavel Roskin _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org http://lists.gnu.org/mailman/listinfo/grub-devel
