On 6/12/2013, at 8:44 am, shmeel gutl <shmeelg...@shmuelhome.mine.nu> wrote:
> On 05-Dec-13 02:39 AM, Maxim Kuvyrkov wrote: >> Dependency type plays a role for estimating costs and latencies between >> instructions (which affects performance), but using wrong or imprecise >> dependency type does not affect correctness. > On multi-issue architectures it does make a difference. Anti dependence > permits the two instructions to be issued during the same cycle whereas true > dependency and output dependency would forbid this. > > Or am I misinterpreting your comment? On VLIW-flavoured machines without resource conflict checking -- "yes", it is critical not to use anti dependency where an output or true dependency exist. This is the case though, only because these machines do not follow sequential semantics for instruction execution (i.e., effects from previous instructions are not necessarily observed by subsequent instructions on the same/close cycles. On machines with internal resource conflict checking having a wrong type on the dependency should not cause wrong behavior, but "only" suboptimal performance. Thank you, -- Maxim Kuvyrkov www.kugelworks.com
