On Tue, Jun 07, 2016 at 04:30:59PM -0700, H. Peter Anvin wrote: > From: "H. Peter Anvin" <[email protected]> > > gcc 6+ has the ability to let flags (actually, conditions, which are > specific combinations of flags) to be used directly as asm() outputs. > The syntax for that is "=@cc<cc>" where <cc> is the same set of > letters that would be used in a j<cc> or set<cc> instruction > (e.g. "=@ccz" to test the ZF flag.) > > This patchset by itself reduces the size of the x86-64 kernel by > 0.12%, from a baseline of 4.7-rc2 built with gcc 6.1 (first line is > with the patchset, the second one is without): > > text data bss dec hex filename > > 68245656 41004339 20533248 129783243 7bc55cb o.i386-allconfig/vmlinux > 68355716 41008499 20533248 129897463 7be13f7 o.i386-allconfig/vmlinux > > 127384005 129742359 38150144 295276508 11998fdc o.x86_64-allconfig/vmlinux > 127538765 129742295 38150144 295431204 119bec24 o.x86_64-allconfig/vmlinux
Very nice! Acked-by: Peter Zijlstra (Intel) <[email protected]> Do you happen to know if GCC plans to support other architectures for =@cc ?
