Hi Eric, On Mon, Jan 29, 2018 at 06:04:30AM -0800, Eric Dumazet wrote: > > 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, > > > Hi Willy > > Please look more closely at following instructions. > > We need the value later, not only testing it being zero :)
Ah OK that makes total sense then ;-) Thanks, willy
