Il 03/08/2012 17:08, Richard Henderson ha scritto: > On 2012-08-03 08:01, Uros Bizjak wrote: >> On Fri, Aug 3, 2012 at 4:40 PM, Richard Henderson <r...@redhat.com> wrote: >>> On 2012-08-03 01:51, Uros Bizjak wrote: >>>> The same reasoning goes for dynamic negation: for neg %eax,%eax value >>>> 0x80000000 stays the same, but we have changed (x)sub to an (x)add in >>>> the code stream. >>> >>> So? Did you think the xadd will trap? >> >> No, but can we ignore the fact that we changed xsub -0x80000000, mem >> to xadd -0x080000000, mem? > > Yes, since it'll have the same effect on the bits.
In fact we can even use this trick for "xxor"... Paolo