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
