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Re: Minor CCP improvement and add comments to tree.h
On Wed, 2004-09-22 at 10:25, Jeffrey A Law wrote:
> By recording those constants we can avoid state transitions in CCP
> (ie, we've discovered them in DOM, there's no need to rediscover
> them again and take the state transitions in CCP).
>
OK. If that's the case, it would be better to mark them VARYING right
off the bat. That saves us more propagation work. After all, CCP won't
be able to substitute and fold them.
Now, is this significant to increase the size of tree_ssa_name?
SSA_NAME_VALUE is currently a scratch pad, do we want to make it
persistent?
If we have a persistent value holding slot, then how do we make sure
that its contents are valid from pass to pass? What if CCP is scheduled
before DOM and there's garbage in SSA_NAME_EQUIV? How do we know that
the data in there is good for which pass?
Would it be better to have a sparse data structure to hold
SSA_NAME_EQUIV? A hash table, perhaps? It doesn't seem like it will be
accessed in places other than initialization code.
Diego.