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Re: A question about redundant PHI expression stmt
On Tue, 2012-02-28 at 11:03 -0600, William J. Schmidt wrote:
> I think this is probably a problem with how cprop_into_successor_phis
> works. It only propagates into immediate successors of a block. In
> this case copies are propagated from bb12 into phis in bb13 and bb14 (of
> which there are none). Seems like it could propagate into phis of all
> dominator children, which would catch bb15. I haven't looked at this
> part of the code in too much detail, but I'm guessing since bb15's
> immediate dominator is bb12, this is the last chance to get the value
> propagated into the phi.
>
> When I get more time, I'll walk through the logic for this test to
> confirm, and post here with the results.
>
> If this is the problem, then I doubt anything will be fixed for this in
> the limited time left for 4.7. You'd want to open a missed-optimization
> PR for it.
No, this isn't right. I see in the dump that the copy is being removed
from the const_and_copies_table after processing block 13 and before
processing block 14. That's presumably a bug. I'll keep looking.
Bill