[Bug tree-optimization/103168] Value numbering for PRE of pure functions can be improved

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103168

--- Comment #16 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jan Hubicka from comment #13)
> Concerning comment #10, the problem was that the loop walking all accesses
> was missing loads->every_base check.  This is used to represent that we
> track no useful info about loads performed at all.
> 
> Anyway if I read the code correctly, it does nothing useful if the access
> tree contains any access for which we can not construct ref and thus one can
> simply check global_memory_access and do not care about
> every_base/every_ref/every_access since these must be all false.
> 
> I simplified the walk a bit and added code pre-computing number of accesses
> in the tree into the summary.
> 
> What we can also do is, when hitting access for which we can not construct
> ref, or when hitting every_ref/every_acccess, is to construct ref with
> base_alias_set/ref_alias_set as given by the access tree but with base=NULL,
> offset=0 and size=max_size=-1. This should still let the basic TBAA oracle
> to disambiguate.

I don't think we support base = NULL in the oracle (ref = NULL is supported
though).  Can you attach your patch instead of cut&pasting so I can take it
from there?  Thanks.