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Re: About the number of DOM's iterations.


On Tue, 2005-04-12 at 14:36 -0400, Kazu Hirata wrote:
> Hi,
> 
> Note that with -O1, we limit the number of iterations of DOM to 1 so
> that we can get resonable compile time performance.  I was wondering
> what happens if we do the same with -O2 now that we have passes like
> copy-prop, VRP, and improved FRE as well as good and old CCP.
[ ... ]
Note that the iteration step is has two purposes.  One is to find more
jump threading opportunities.  Two is to find new redundancy elimination
and const/copy propagation opportnities that were exposed by jump
threading.

The latter is more important and more common than the former.  If you're
going to look at limiting the iteration, you really need to look at both
effects.  [ In fact, the latter effect is what got me looking at jump
threading in the first place! ]


I would also strongly suggest you look at my recent message to Diego
which outlines how I think we can eliminate the iteration step in favor
of a worklist approach which just looks at optimization of statements
that may now be redundant due to the effects of jump threading.

Jeff


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