Hi, [ replaced stable@ and greg@ by netdev@ as my question below is not relevant to stable ]
On Mon, Jan 29, 2018 at 02:48:54AM +0100, Daniel Borkmann wrote: > From: Eric Dumazet <eduma...@google.com> > > [ upstream commit 84ccac6e7854ebbfb56d2fc6d5bef9be49bb304c ] > > Saves 4 bytes replacing following instructions : > > lea rax, [rsi + rdx * 8 + offsetof(...)] > mov rax, qword ptr [rax] > cmp rax, 0 > > by : > > mov rax, [rsi + rdx * 8 + offsetof(...)] > test rax, rax I've just noticed this on stable@. If these 4 bytes matter, why not use cmpq with an immediate value instead, which saves 2 extra bytes ? : - the mov above is 11 bytes total : 0: 48 8b 84 d6 78 56 34 mov 0x12345678(%rsi,%rdx,8),%rax 7: 12 8: 48 85 c0 test %rax,%rax - the equivalent cmp is only 9 bytes : 0: 48 83 bc d6 78 56 34 cmpq $0x0,0x12345678(%rsi,%rdx,8) 7: 12 00 And as a bonus, it doesn't even clobber rax. Just my two cents, Willy
