🚀 go-pugleaf

tremblay@flayout.Eng.Sun.COM (Marc Tremblay) writes:

>In article <1992Nov19.204729.24714@crl.dec.com> payne@crl.dec.com (Andrew Payne) writes:
>>>The last sentence is key here. If branches can be predicted with decent
>>>accuracy then it is hard to obtain benefits from conditional moves
>>>over using conditional branches. 
>>
>>Do you have any data to back up this claim?

>Sure do. If branches can be predicted with 100% accuracy then the
>version with conditional branches may run up to twice as fast. :-)
>Seriously, the silly example above should nonetheless show that if
>there are many instructions to guard, then potentially only half of the 
>functional units will accomplish useful work while running the code
>surrounded with conditional moves. 

If you can predict conditional branches, surely you can predict
conditional moves and other conditional instructions as well, even
using much the same techniques. In general any technique that can be
used to optimize conditional branches can also be used to optimize
other conditional instructions, so I can't see that using conditional
instructions in general can ever be worse than using conditional
branches only. One can then discuss how to reduce the penalty of
having conditions only on branches.

	Torben Mogensen (torbenm@diku.dk)