> Steven Bosscher wrote: >> Mostafa Hagog <[EMAIL PROTECTED]> wrote: >> This is interesting, so there could be cases were want to copy CC >> register when doing SMS. what happens if we want to move the set >> of a CC to another iteration of the loop ? or the use of the CC ? but >> usually this is couldn't happen in a simple loop, right? the use of CC >> is eventually used in a branch, or there is something that I am missing ? > > IIRC these notes are for CCO, and you have to move the CC setter > and user together.
- unless it can be guaranteed that the particular setter's cc, will be preserved (i.e. not corrupted by successive operations) prior to it's ultimate use; or alternatively regenerating the setter's cc typically by comparing it's previously computed data result with 0 (to regenerate the cc side effect, not necessarily the operation), if the user is moved past potentially corrupting successive operations; it would seem? > Actually I think SMS for CC0 targets is Just Silly to do at all ;-) - with the exception that it should be useful to eliminate otherwise unnecessary explicit comparison operations if an otherwise required operation (with the the desired setter cc side effects) can be more optimally scheduled immediately prior to a user of it's cc side effect (as is often typically the case when a conditional branch is dependant on a previously computed result being compared against 0). (but agree that as cc0 targets tend to be lightly pipelined in-order issue and completion machines, they tend to not be highly sensitive to instruction ordering; with the exception of conditional branching code does typically benefit from ideally scheduled sequences which do not require the re-synthesis of a cc through the use of an explicit comparison (or likely worse, a saved cc register) operation; which a good schedule would tend to likely avoid if possible; I'd guess.)
