[patch] Lno branch merge part 12 -- induction variable optimizations

[Andrew Pinski]

On Aug 30, 2004, at 9:14 AM, Jeffrey A Law wrote:

> So far I've "solved" those problems by punting and waiting for
> DCE to clean things up.  That's been pretty consistent with the
> design decisions we've made regarding isolation of optimizations.
>
> Is there some reason why that model is not appropriate?  For example,
> does leaving these dead statements in the IL until the next DCE
> pass actually inhibit optimizations or cause correctness issues?
>
>
> [ While I sometimes lean towards having dead code automatically go
>   away when the last use of the statement's LHS goes away, I'm
>   very leery of going that direction because of our past experiences
>   of doing this kind of thing at the RTL level. ]

In my loops to memset optimization, I do punt almost everything to
DCE except for the memory access which I transform to the memset
call.  So I remove the memory store as it is not removed by DCE.
Also we don't remove loops on later passes which hurt performance.

Can anyone say when we are going to remove empty loops even without
-funroll-loops?


Thanks,
Andrew Pinski