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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/103168] Value numbering for PRE of pure
 functions can be improved
Date: Mon, 22 Nov 2021 23:07:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103168

--- Comment #13 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
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 t=
ree
contains any access for which we can not construct ref and thus one can sim=
ply
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=3DNU=
LL,
offset=3D0 and size=3Dmax_size=3D-1. This should still let the basic TBAA o=
racle to
disambiguate.=